diff --git a/CHANGELOG.md b/CHANGELOG.md
index dbace593..2acd739a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -54,6 +54,16 @@ accepts both, but the store flags the old spelling as deprecated
   - Backups record `src.__version__`.
   - Removed: `BackgroundDataService`'s `queue_size` stat and `clear_completed_requests()`.
 
+- Web API fixes:
+  - A plugin save drops repeated entries in lists whose schema says `uniqueItems`, instead of failing validation.
+  - `/api/v3/health` reports the real plugin count.
+  - A malformed `vegas_plugin_order` or `vegas_excluded_plugins` is refused with a 400 and nothing is saved. It used to wipe the saved list.
+  - The per-plugin health and metrics routes return the display service's latest state.
+  - Resetting a plugin's config takes a backup first and reports a failed save.
+  - System metrics that can't be read are `null` everywhere: `cpu_temp` off a Pi, and every metric without psutil, where `/system/status` now answers 200 instead of 503.
+  - `/plugins/store/refresh` no longer claims a commit-metadata refresh it doesn't do.
+  - The plugin-config list repair code is in one place, `src/web_interface/config_arrays.py`.
+
 - The web service (`ledmatrix-web`) logs through `src.logging_config` like the
   display service, so `journalctl -p err -u ledmatrix-web` works. Successful
   GET/HEAD/OPTIONS requests (the UI's polling) are logged at DEBUG instead of
diff --git a/src/web_interface/config_arrays.py b/src/web_interface/config_arrays.py
new file mode 100644
index 00000000..9dd5c32e
--- /dev/null
+++ b/src/web_interface/config_arrays.py
@@ -0,0 +1,60 @@
+"""Putting a submitted plugin config's lists back into list shape.
+
+A list reaches a plugin-config save keyed by position more often than as a
+list. The settings form posts one field per element (``feeds.custom_feeds.0.name``),
+which ``_set_nested_value`` stores as ``{"0": {"name": ...}}``, and the JSON
+path's dotToNested() in the browser builds the same dict. Validation expects
+an array there, so the save converts them first.
+"""
+from typing import Any, Dict
+
+
+def _is_index_dict(value: Any) -> bool:
+    """True for a dict keyed only by list positions ("0", "1", ...), or empty."""
+    return isinstance(value, dict) and all(str(k).isdigit() for k in value)
+
+
+def coerce_array_shapes(config: Dict[str, Any], schema_props: Dict[str, Any],
+                        short_lists_take_default: bool = False) -> None:
+    """Turn position-keyed dicts into lists wherever the schema has an array.
+
+    Walks ``config`` alongside the schema's ``properties``, in place: into
+    nested objects, and into the objects of an array's items. An empty dict
+    where an array belongs becomes ``[]``.
+
+    ``short_lists_take_default`` is for form posts. A form draws a fixed-length
+    list (an RGB colour, say) as one input per element, and a blanked input
+    drops out of the parsed list; the schema default then stands in, as long as
+    it is itself long enough, instead of the save failing on ``minItems``.
+
+    Element types are left alone: normalization after this converts numeric
+    strings to the numbers the schema asks for.
+    """
+    if not isinstance(config, dict):
+        return
+    for key, prop_schema in schema_props.items():
+        if key not in config or not isinstance(prop_schema, dict):
+            continue
+        prop_type = prop_schema.get('type')
+        value = config[key]
+
+        if prop_type == 'array':
+            if _is_index_dict(value):
+                value = config[key] = [value[k] for k in sorted(value, key=lambda k: int(str(k)))]
+            if not isinstance(value, list):
+                continue
+            min_items = prop_schema.get('minItems')
+            default = prop_schema.get('default')
+            if (short_lists_take_default and min_items is not None
+                    and len(value) < min_items
+                    and isinstance(default, list) and len(default) >= min_items):
+                value = config[key] = list(default)
+            items_schema = prop_schema.get('items')
+            if (isinstance(items_schema, dict) and items_schema.get('type') == 'object'
+                    and 'properties' in items_schema):
+                for element in value:
+                    coerce_array_shapes(element, items_schema['properties'],
+                                        short_lists_take_default)
+
+        elif prop_type == 'object' and 'properties' in prop_schema:
+            coerce_array_shapes(value, prop_schema['properties'], short_lists_take_default)
diff --git a/test/test_api_v3_health.py b/test/test_api_v3_health.py
new file mode 100644
index 00000000..d4921c67
--- /dev/null
+++ b/test/test_api_v3_health.py
@@ -0,0 +1,90 @@
+"""GET /api/v3/health: the plugin count is real, and a failed check is logged.
+
+The plugin check counted ``plugin_manager.get_available_plugins()``, which
+PluginManager does not have; a hasattr guard turned that into a permanent 0.
+Each check that fails answers "see logs for details", so it has to log.
+"""
+
+import logging
+import sys
+from pathlib import Path
+from types import SimpleNamespace
+
+import pytest
+
+sys.path.insert(0, str(Path(__file__).parent.parent))
+
+from test._api_v3_test_helpers import api_v3_client, api_v3_module  # noqa: F401,E402
+
+URL = "/api/v3/health"
+
+
+@pytest.fixture(autouse=True)
+def _no_systemctl(monkeypatch):
+    monkeypatch.setattr("web_interface.blueprints.api_v3.misc._get_display_service_status",
+                        lambda: {"active": True})
+
+
+def _checks(client):
+    response = client.get(URL)
+    assert response.status_code == 200, response.get_json()
+    return response.get_json()["data"]["checks"]
+
+
+def test_plugin_count_is_the_number_of_discovered_plugins(api_v3_client, api_v3_module):
+    api_v3_module.api_v3.plugin_manager.plugin_manifests = {
+        "clock": {"id": "clock"}, "weather": {"id": "weather"}, "stocks": {"id": "stocks"},
+    }
+
+    check = _checks(api_v3_client)["plugin_system"]
+
+    assert check == {"status": "operational", "plugin_count": 3}
+
+
+def test_plugin_count_discovers_when_nothing_is_discovered_yet(api_v3_client, api_v3_module):
+    pm = api_v3_module.api_v3.plugin_manager
+    pm.plugin_manifests = {}
+
+    def discover():
+        pm.plugin_manifests = {"clock": {"id": "clock"}}
+    pm.discover_plugins.side_effect = discover
+
+    assert _checks(api_v3_client)["plugin_system"]["plugin_count"] == 1
+
+
+def test_a_failed_config_check_is_logged(api_v3_client, api_v3_module, caplog):
+    api_v3_module.api_v3.config_manager.load_config.side_effect = OSError("disk gone")
+
+    with caplog.at_level(logging.WARNING):
+        check = _checks(api_v3_client)["config_file"]
+
+    assert check["error"] == "see logs for details"
+    logged = [r for r in caplog.records if "config file" in r.getMessage()]
+    assert logged and logged[0].exc_info and "disk gone" in str(logged[0].exc_info[1])
+
+
+def test_a_failed_plugin_check_is_logged(api_v3_client, api_v3_module, caplog, monkeypatch):
+    def boom():
+        raise RuntimeError("manifests unreadable")
+    monkeypatch.setattr("web_interface.blueprints.api_v3.misc._discovered_plugin_manifests", boom)
+
+    with caplog.at_level(logging.WARNING):
+        check = _checks(api_v3_client)["plugin_system"]
+
+    assert check["status"] == "error"
+    logged = [r for r in caplog.records if "count plugins" in r.getMessage()]
+    assert logged and logged[0].exc_info
+
+
+def test_a_failed_hardware_check_is_logged(api_v3_client, api_v3_module, caplog, monkeypatch):
+    def getmtime(_path):
+        raise PermissionError("denied")
+    fake_os = SimpleNamespace(path=SimpleNamespace(exists=lambda _p: True, getmtime=getmtime))
+    monkeypatch.setattr("web_interface.blueprints.api_v3.misc.os", fake_os)
+
+    with caplog.at_level(logging.WARNING):
+        check = _checks(api_v3_client)["hardware"]
+
+    assert check["status"] == "unknown"
+    logged = [r for r in caplog.records if "snapshot" in r.getMessage()]
+    assert logged and logged[0].exc_info
diff --git a/test/test_api_v3_plugin_health_single.py b/test/test_api_v3_plugin_health_single.py
new file mode 100644
index 00000000..455914ea
--- /dev/null
+++ b/test/test_api_v3_plugin_health_single.py
@@ -0,0 +1,68 @@
+"""GET /plugins/health/<id> and /plugins/metrics/<id> read the display
+service's latest state, not the web process's first snapshot.
+
+The display service writes health and metrics to the shared cache; the web
+process only reads them. Its tracker and monitor keep what they read first in
+memory, so without ``force_reload`` the per-plugin routes kept answering with
+that first read while the list routes (which pass it) moved on.
+"""
+
+import sys
+from pathlib import Path
+
+import pytest
+
+sys.path.insert(0, str(Path(__file__).parent.parent))
+
+from src.plugin_system.plugin_health import PluginHealthTracker  # noqa: E402
+from src.plugin_system.resource_monitor import PluginResourceMonitor  # noqa: E402
+from test._api_v3_test_helpers import api_v3_client, api_v3_module  # noqa: F401,E402
+
+
+class SharedCache:
+    """The on-disk cache both processes see, reduced to a dict."""
+
+    def __init__(self):
+        self.entries = {}
+
+    def get(self, key, max_age=None, memory_ttl=None):
+        return self.entries.get(key)
+
+    def set(self, key, value, *args, **kwargs):
+        self.entries[key] = value
+
+
+@pytest.fixture
+def shared_cache(api_v3_module):
+    cache = SharedCache()
+    pm = api_v3_module.api_v3.plugin_manager
+    pm.health_tracker = PluginHealthTracker(cache)
+    pm.resource_monitor = PluginResourceMonitor(cache)
+    return cache
+
+
+def test_health_reflects_failures_recorded_after_the_first_read(api_v3_client, shared_cache):
+    first = api_v3_client.get("/api/v3/plugins/health/weather").get_json()["data"]
+    assert first["total_failures"] == 0
+
+    display_side = PluginHealthTracker(shared_cache)
+    display_side.record_failure("weather", RuntimeError("api down"))
+    display_side.record_failure("weather", RuntimeError("api down"))
+
+    later = api_v3_client.get("/api/v3/plugins/health/weather").get_json()["data"]
+    assert later["total_failures"] == 2
+
+
+def test_metrics_reflect_calls_recorded_after_the_first_read(api_v3_client, shared_cache):
+    first = api_v3_client.get("/api/v3/plugins/metrics/weather").get_json()["data"]
+    assert first["call_count"] == 0
+
+    shared_cache.set("plugin_metrics:weather", {
+        "memory_mb": 12.5, "cpu_percent": 3.0, "execution_time": 0.2,
+        "call_count": 40, "total_execution_time": 8.0,
+        "max_execution_time": 0.5, "min_execution_time": 0.1,
+        "last_update_time": 1000.0,
+    })
+
+    later = api_v3_client.get("/api/v3/plugins/metrics/weather").get_json()["data"]
+    assert later["call_count"] == 40
diff --git a/test/test_api_v3_registry_endpoints.py b/test/test_api_v3_registry_endpoints.py
index 85f4b377..b4e6dd1f 100644
--- a/test/test_api_v3_registry_endpoints.py
+++ b/test/test_api_v3_registry_endpoints.py
@@ -66,12 +66,16 @@ class TestRefreshPluginStore:
         assert response.status_code == 200
 
     @pytest.mark.parametrize("key", ["fetch_commit_info", "fetch_latest_versions"])
-    def test_either_commit_info_key_extends_the_message(
+    def test_commit_info_flag_claims_no_refresh_it_does_not_do(
             self, api_v3_client, api_v3_module, key):
-        # fetch_latest_versions is the older spelling; both must work.
-        api_v3_module.api_v3.plugin_store_manager.fetch_registry.return_value = {"plugins": []}
+        # The route only re-downloads the registry. It used to append "(with
+        # refreshed commit metadata from GitHub)" for either flag without
+        # fetching any.
+        store = api_v3_module.api_v3.plugin_store_manager
+        store.fetch_registry.return_value = {"plugins": [{"id": "a"}]}
         response = api_v3_client.post(self.URL, json={key: True})
-        assert "commit metadata" in response.get_json()["message"]
+        assert response.get_json()["message"] == "Plugin store refreshed"
+        store.fetch_registry.assert_called_once_with(force_refresh=True)
 
     def test_message_stays_plain_without_the_flag(self, api_v3_client, api_v3_module):
         api_v3_module.api_v3.plugin_store_manager.fetch_registry.return_value = {"plugins": []}
diff --git a/test/test_api_v3_vegas_plugin_lists.py b/test/test_api_v3_vegas_plugin_lists.py
new file mode 100644
index 00000000..e5dd709c
--- /dev/null
+++ b/test/test_api_v3_vegas_plugin_lists.py
@@ -0,0 +1,55 @@
+"""POST /config/main refuses a malformed Vegas plugin order or exclusion list.
+
+Both were parsed with ``except JSONDecodeError: ... = []``, so a bad value
+cleared the saved list and answered 200. They now fail the save with a 400,
+as plugin_rotation_order already did.
+"""
+
+import sys
+from pathlib import Path
+
+import pytest
+
+sys.path.insert(0, str(Path(__file__).parent.parent))
+
+from test._api_v3_test_helpers import api_v3_client, api_v3_module  # noqa: F401,E402
+
+URL = "/api/v3/config/main"
+
+
+@pytest.fixture
+def saved(api_v3_module):
+    config = {"display": {"vegas_scroll": {"plugin_order": ["clock", "weather"],
+                                            "excluded_plugins": ["stocks"]}}}
+    cm = api_v3_module.api_v3.config_manager
+    cm.load_config.return_value = config
+    cm.save_config_atomic.return_value.status.value = 'success'
+    return cm
+
+
+@pytest.mark.parametrize("field", ["vegas_plugin_order", "vegas_excluded_plugins"])
+@pytest.mark.parametrize("value", ["[not json", '{"a": 1}', "[1, 2]", 7])
+def test_malformed_list_is_refused_and_nothing_is_saved(api_v3_client, saved, field, value):
+    response = api_v3_client.post(URL, json={field: value})
+
+    assert response.status_code == 400, response.get_json()
+    assert field in response.get_json()["message"]
+    saved.save_config_atomic.assert_not_called()
+    saved.save_config.assert_not_called()
+
+
+@pytest.mark.parametrize("value", ['["weather", "clock"]', ["weather", "clock"]])
+def test_json_text_or_array_is_stored(api_v3_client, saved, value):
+    response = api_v3_client.post(URL, json={"vegas_plugin_order": value})
+
+    assert response.status_code == 200, response.get_json()
+    stored = saved.save_config_atomic.call_args.args[0]
+    assert stored["display"]["vegas_scroll"]["plugin_order"] == ["weather", "clock"]
+    assert stored["display"]["vegas_scroll"]["excluded_plugins"] == ["stocks"]
+
+
+def test_rotation_order_keeps_its_messages(api_v3_client, saved):
+    response = api_v3_client.post(URL, json={"plugin_rotation_order": "[oops"})
+
+    assert response.status_code == 400
+    assert response.get_json()["message"] == "plugin_rotation_order must be valid JSON"
diff --git a/test/test_display_preview.py b/test/test_display_preview.py
new file mode 100644
index 00000000..aaaebfe0
--- /dev/null
+++ b/test/test_display_preview.py
@@ -0,0 +1,79 @@
+"""GET /api/v3/display/current passes the snapshot PNG through untouched.
+
+It used to PIL-decode the snapshot and re-encode it, which cost CPU on the Pi
+for no change in the picture, and it swallowed any read failure with
+``except Exception: pass``. It now sends the file's own bytes, the payload the
+/stream/display SSE stream sends, and logs a failed read.
+"""
+
+import base64
+import io
+import logging
+import sys
+from pathlib import Path
+from unittest.mock import MagicMock
+
+import pytest
+from flask import Flask
+from PIL import Image, PngImagePlugin
+
+sys.path.insert(0, str(Path(__file__).parent.parent))
+
+from web_interface import display_preview  # noqa: E402
+
+
+@pytest.fixture
+def client(monkeypatch):
+    from web_interface.blueprints.api_v3 import api_v3
+    monkeypatch.setattr(api_v3, 'config_manager', MagicMock(), raising=False)
+    api_v3.config_manager.load_config.return_value = {}
+    app = Flask(__name__)
+    app.config['TESTING'] = True
+    app.register_blueprint(api_v3, url_prefix='/api/v3')
+    with app.test_client() as test_client:
+        yield test_client
+
+
+@pytest.fixture
+def snapshot(tmp_path, monkeypatch):
+    """A snapshot PNG carrying a text chunk, which a PIL re-encode drops."""
+    info = PngImagePlugin.PngInfo()
+    info.add_text('written-by', 'display_manager')
+    buffer = io.BytesIO()
+    Image.new('RGB', (4, 2), (255, 0, 0)).save(buffer, format='PNG', pnginfo=info)
+    path = tmp_path / 'led_matrix_preview.png'
+    path.write_bytes(buffer.getvalue())
+    monkeypatch.setattr(display_preview, 'SNAPSHOT_PATH', str(path))
+    return path
+
+
+def _image(client):
+    response = client.get('/api/v3/display/current')
+    assert response.status_code == 200
+    return response.get_json()['data']
+
+
+def test_the_snapshot_bytes_are_sent_as_they_are(client, snapshot):
+    data = _image(client)
+    assert base64.b64decode(data['image']) == snapshot.read_bytes()
+
+
+def test_route_and_stream_send_the_same_payload_keys(client, snapshot):
+    data = _image(client)
+    assert set(data) == set(display_preview.preview_payload(1, 1, None))
+
+
+def test_no_snapshot_is_a_null_image_without_a_warning(client, tmp_path, monkeypatch, caplog):
+    monkeypatch.setattr(display_preview, 'SNAPSHOT_PATH', str(tmp_path / 'missing.png'))
+    with caplog.at_level(logging.WARNING):
+        assert _image(client)['image'] is None
+    assert not [r for r in caplog.records if 'snapshot' in r.getMessage()]
+
+
+def test_an_unreadable_snapshot_is_logged(client, snapshot, monkeypatch, caplog):
+    def denied(_path=None):
+        raise PermissionError('denied')
+    monkeypatch.setattr(display_preview, 'read_snapshot_base64', denied)
+    with caplog.at_level(logging.WARNING):
+        assert _image(client)['image'] is None
+    assert [r for r in caplog.records if 'snapshot' in r.getMessage() and r.exc_info]
diff --git a/test/test_live_status_fields.py b/test/test_live_status_fields.py
index 571683de..8f94f20f 100644
--- a/test/test_live_status_fields.py
+++ b/test/test_live_status_fields.py
@@ -31,8 +31,12 @@ import pytest
 PROJECT_ROOT = Path(__file__).parent.parent
 sys.path.insert(0, str(PROJECT_ROOT))
 
+from web_interface import system_metrics  # noqa: E402
 from web_interface.system_metrics import collect_system_metrics  # noqa: E402
 
+MB = 1024 * 1024
+GB = 1024 * MB
+
 
 @pytest.fixture
 def metrics(monkeypatch):
@@ -45,10 +49,11 @@ def metrics(monkeypatch):
                                 lambda _p: (_ for _ in ()).throw(OSError("no such mount")))
         else:
             monkeypatch.setattr(psutil, "disk_usage",
-                                lambda _p: SimpleNamespace(percent=disk_percent))
+                                lambda _p: SimpleNamespace(percent=disk_percent,
+                                                           total=32 * GB, used=4 * GB))
         monkeypatch.setattr(psutil, "virtual_memory",
-                            lambda: SimpleNamespace(percent=used_percent,
-                                                    available=available_bytes))
+                            lambda: SimpleNamespace(percent=used_percent, total=1024 * MB,
+                                                    used=600 * MB, available=available_bytes))
         return collect_system_metrics()
     return _collect
 
@@ -101,3 +106,18 @@ class TestEveryPredictiveFieldIsPresent:
                       "memory_available_mb", "disk_used_percent"):
             assert field in m
         assert m["disk_used_percent"] is None
+        assert all(m[key] is None for key in m if key != "cpu_temp")
+
+
+class TestUnavailableIsNull:
+    """One answer for "could not be read": None, never 0."""
+
+    def test_unreadable_temperature_is_null_not_zero_degrees(self, metrics, monkeypatch):
+        monkeypatch.setattr(system_metrics, "_THERMAL_ZONE", "/nonexistent/thermal/temp")
+        assert metrics()["cpu_temp"] is None
+
+    def test_readable_temperature_is_degrees_c(self, metrics, monkeypatch, tmp_path):
+        zone = tmp_path / "temp"
+        zone.write_text("48312\n")
+        monkeypatch.setattr(system_metrics, "_THERMAL_ZONE", str(zone))
+        assert metrics()["cpu_temp"] == 48.3
diff --git a/test/test_pages_v3_partials.py b/test/test_pages_v3_partials.py
new file mode 100644
index 00000000..83fcf2ab
--- /dev/null
+++ b/test/test_pages_v3_partials.py
@@ -0,0 +1,65 @@
+"""/partials/<name> dispatch and the plugin web_ui page's directory lookup."""
+
+import logging
+import sys
+from pathlib import Path
+from unittest.mock import MagicMock
+
+import pytest
+from flask import Flask
+
+sys.path.insert(0, str(Path(__file__).parent.parent))
+
+from web_interface.blueprints import pages_v3 as module  # noqa: E402
+
+
+@pytest.fixture
+def client(tmp_path, monkeypatch):
+    plugin_manager = MagicMock()
+    plugin_manager.plugins_dir = tmp_path
+    monkeypatch.setattr(module.pages_v3, "plugin_manager", plugin_manager, raising=False)
+    monkeypatch.setattr(module.pages_v3, "config_manager",
+                        MagicMock(load_config=lambda: {}), raising=False)
+    app = Flask(__name__, template_folder=str(
+        Path(module.__file__).resolve().parents[1] / "templates"))
+    app.register_blueprint(module.pages_v3)
+    return app.test_client()
+
+
+def test_every_tab_the_old_if_chain_served_is_still_served():
+    assert set(module._PARTIAL_LOADERS) == {
+        "overview", "general", "display", "durations", "schedule", "plugins",
+        "fonts", "logs", "raw-json", "backup-restore", "wifi", "cache",
+        "operation-history", "tools",
+    }
+
+
+def test_an_unknown_partial_is_a_404(client):
+    response = client.get("/partials/nope")
+    assert response.status_code == 404
+
+
+def test_a_failing_loader_is_one_500_that_names_the_partial(client, monkeypatch, caplog):
+    def boom():
+        raise RuntimeError("template exploded")
+    monkeypatch.setitem(module._PARTIAL_LOADERS, "logs", boom)
+
+    with caplog.at_level(logging.ERROR):
+        response = client.get("/partials/logs")
+
+    assert response.status_code == 500
+    assert response.get_data(as_text=True) == "Error loading partial"
+    errors = [r for r in caplog.records if r.levelno >= logging.ERROR]
+    assert len(errors) == 1
+    assert errors[0].getMessage() == "Error loading partial logs"
+
+
+def test_web_ui_page_uses_the_ledmatrix_prefix_fallback(client, tmp_path):
+    web_ui = tmp_path / "ledmatrix-radar" / "web_ui"
+    web_ui.mkdir(parents=True)
+    (web_ui / "panel.html").write_text("<p>radar panel</p>", encoding="utf-8")
+
+    response = client.get("/plugin-ui/radar/web-ui/panel.html")
+
+    assert response.status_code == 200
+    assert "radar panel" in response.get_data(as_text=True)
diff --git a/test/test_system_status_available_memory.py b/test/test_system_status_available_memory.py
index c08bde22..0113ea67 100644
--- a/test/test_system_status_available_memory.py
+++ b/test/test_system_status_available_memory.py
@@ -51,7 +51,7 @@ def _memory(total_mb, used_mb, available_mb):
 
 def _get_status(client, memory):
     # The endpoint caches for 10s; bypass so each case is measured fresh.
-    with patch("web_interface.cache.get_cached", return_value=None), \
+    with patch("web_interface.blueprints.api_v3.system.get_cached", return_value=None), \
          patch("psutil.virtual_memory", return_value=memory), \
          patch("psutil.cpu_percent", return_value=5.0), \
          patch("psutil.boot_time", return_value=0.0):
@@ -90,3 +90,24 @@ def test_a_nearly_exhausted_board_reports_a_small_number(client):
     # to fork. The readout has to surface that rather than round it away.
     data = _get_status(client, _memory(total_mb=905, used_mb=800, available_mb=73))
     assert data["memory_available_mb"] == pytest.approx(73, abs=0.5)
+
+
+def test_status_and_live_stream_give_the_same_answer(client, monkeypatch):
+    """/system/status is built on collect_system_metrics(), so a metric has one
+    value, and "could not be read" is null in both."""
+    from web_interface import system_metrics
+    monkeypatch.setattr(system_metrics, "_THERMAL_ZONE", "/nonexistent/thermal/temp")
+    memory = _memory(total_mb=905, used_mb=620, available_mb=284)
+    with patch("psutil.virtual_memory", return_value=memory), \
+         patch("psutil.cpu_percent", return_value=5.0), \
+         patch("psutil.boot_time", return_value=0.0), \
+         patch("psutil.disk_usage", side_effect=OSError("no such mount")):
+        streamed = system_metrics.collect_system_metrics()
+        with patch("web_interface.blueprints.api_v3.system.get_cached", return_value=None):
+            status = json.loads(client.get("/api/v3/system/status").data)["data"]
+
+    assert status["cpu_temp"] is None
+    assert status["disk_used_percent"] is None
+    for key in system_metrics.METRIC_KEYS:
+        if key != "uptime_seconds":  # the two reads are a moment apart
+            assert status[key] == streamed[key], key
diff --git a/test/web_interface/test_api_v3_plugin_config_save.py b/test/web_interface/test_api_v3_plugin_config_save.py
new file mode 100644
index 00000000..c0de008c
--- /dev/null
+++ b/test/web_interface/test_api_v3_plugin_config_save.py
@@ -0,0 +1,210 @@
+"""POST /plugins/config and POST /plugins/config/reset over a real
+ConfigManager and SchemaManager.
+
+The save path reshapes what the browser posts before validating it, and these
+tests pin the reshaping that validation depends on: repeats in a uniqueItems
+list are dropped, and a list the form posted as numbered fields becomes a list
+again.
+"""
+
+import json
+import sys
+from pathlib import Path
+from unittest.mock import MagicMock
+
+import pytest
+
+sys.path.insert(0, str(Path(__file__).parent.parent.parent))
+
+from src.config_manager import ConfigManager  # noqa: E402
+from src.plugin_system.schema_manager import SchemaManager  # noqa: E402
+from test._api_v3_test_helpers import api_v3_module, build_app  # noqa: E402,F401
+
+PLUGIN_ID = "stocks"
+
+SCHEMA = {
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "type": "object",
+    "properties": {
+        "enabled": {"type": "boolean", "default": True},
+        "stock_symbols": {
+            "type": "array",
+            "uniqueItems": True,
+            "items": {"type": "string"},
+            "default": ["AAPL"],
+        },
+        "refresh_seconds": {"type": "integer", "default": 60},
+        "api_key": {"type": "string", "x-secret": True, "default": ""},
+    },
+}
+
+# The shape of the news plugin's schema: a list of objects nested one level
+# down. A form posts it as feeds.custom_feeds.0.name, feeds.custom_feeds.0.url,
+# which lands as a dict keyed "0", "1", ...
+NEWS_ID = "news"
+NEWS_SCHEMA = {
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "type": "object",
+    "properties": {
+        "enabled": {"type": "boolean", "default": True},
+        "feeds": {
+            "type": "object",
+            "properties": {
+                "enabled_feeds": {
+                    "type": "array", "items": {"type": "string"}, "default": [],
+                },
+                "custom_feeds": {
+                    "type": "array",
+                    "default": [],
+                    "items": {
+                        "type": "object",
+                        "properties": {
+                            "name": {"type": "string"},
+                            "url": {"type": "string"},
+                            "enabled": {"type": "boolean", "default": True},
+                        },
+                    },
+                },
+            },
+        },
+    },
+}
+
+
+@pytest.fixture
+def env(tmp_path, api_v3_module):
+    """Real config and schema managers under tmp_path, on the blueprint."""
+    plugins_dir = tmp_path / "plugins"
+    for plugin_id, schema in ((PLUGIN_ID, SCHEMA), (NEWS_ID, NEWS_SCHEMA)):
+        plugin_dir = plugins_dir / plugin_id
+        plugin_dir.mkdir(parents=True)
+        (plugin_dir / "config_schema.json").write_text(json.dumps(schema))
+        (plugin_dir / "manifest.json").write_text(json.dumps(
+            {"id": plugin_id, "name": plugin_id, "version": "1.0.0"}))
+
+    config_file = tmp_path / "config.json"
+    config_file.write_text(json.dumps(
+        {PLUGIN_ID: {"enabled": True, "stock_symbols": ["AAPL", "FNMA"]}}))
+    config_manager = ConfigManager(
+        config_path=str(config_file),
+        secrets_path=str(tmp_path / "config_secrets.json"))
+    config_manager.template_path = str(tmp_path / "no-template.json")
+
+    api = api_v3_module.api_v3
+    api.config_manager = config_manager
+    api.schema_manager = SchemaManager(plugins_dir=plugins_dir, project_root=tmp_path)
+    api.plugin_manager.plugin_manifests = {PLUGIN_ID: {"id": PLUGIN_ID},
+                                           NEWS_ID: {"id": NEWS_ID}}
+    api.plugin_manager.get_plugin.return_value = None
+
+    class Env:
+        client = build_app(api).test_client()
+        plugin_manager = api.plugin_manager
+
+        @staticmethod
+        def stored(plugin_id=PLUGIN_ID):
+            return json.loads(config_file.read_text())[plugin_id]
+
+    Env.config_manager = config_manager
+    return Env
+
+
+class TestUniqueItemsRepeats:
+    """A repeat in a uniqueItems list is dropped, not a failed save."""
+
+    def test_form_post_repeating_a_saved_symbol_saves(self, env):
+        response = env.client.post(
+            f"/api/v3/plugins/config?plugin_id={PLUGIN_ID}",
+            data={"stock_symbols": "AAPL, FNMA, FNMA"})
+
+        assert response.status_code == 200, response.get_json()
+        assert env.stored()["stock_symbols"] == ["AAPL", "FNMA"]
+
+    def test_json_post_keeps_first_occurrence_order(self, env):
+        response = env.client.post("/api/v3/plugins/config", json={
+            "plugin_id": PLUGIN_ID,
+            "config": {"stock_symbols": ["TSLA", "AAPL", "TSLA", "FNMA"]},
+        })
+
+        assert response.status_code == 200, response.get_json()
+        assert env.stored()["stock_symbols"] == ["TSLA", "AAPL", "FNMA"]
+
+
+class TestNumberedFieldsBecomeLists:
+    """The news plugin's custom feeds, posted one field per row."""
+
+    FEEDS = [{"name": "Local", "url": "https://example.com/local.xml", "enabled": True},
+             {"name": "Tech", "url": "https://example.com/tech.xml", "enabled": False}]
+
+    def test_form_post(self, env):
+        response = env.client.post(f"/api/v3/plugins/config?plugin_id={NEWS_ID}", data={
+            "feeds.custom_feeds.0.name": "Local",
+            "feeds.custom_feeds.0.url": "https://example.com/local.xml",
+            "feeds.custom_feeds.0.enabled": "on",
+            "feeds.custom_feeds.1.name": "Tech",
+            "feeds.custom_feeds.1.url": "https://example.com/tech.xml",
+        })
+
+        assert response.status_code == 200, response.get_json()
+        assert env.stored(NEWS_ID)["feeds"]["custom_feeds"] == self.FEEDS
+
+    def test_json_post(self, env):
+        response = env.client.post("/api/v3/plugins/config", json={
+            "plugin_id": NEWS_ID,
+            "config": {"feeds": {"custom_feeds": {"1": self.FEEDS[1], "0": self.FEEDS[0]}}},
+        })
+
+        assert response.status_code == 200, response.get_json()
+        assert env.stored(NEWS_ID)["feeds"]["custom_feeds"] == self.FEEDS
+
+
+class TestReset:
+    """POST /plugins/config/reset saves the way every other plugin save does."""
+
+    def test_reset_saves_atomically_with_a_backup(self, env, monkeypatch):
+        cm = env.config_manager
+        calls = []
+        real_atomic = cm.save_config_atomic
+
+        def spy(config, create_backup=True, **kwargs):
+            calls.append(create_backup)
+            return real_atomic(config, create_backup=create_backup, **kwargs)
+
+        def no_plain_save(_config):
+            raise AssertionError("reset bypassed the atomic save")
+
+        monkeypatch.setattr(cm, "save_config_atomic", spy)
+        monkeypatch.setattr(cm, "save_config", no_plain_save)
+
+        response = env.client.post("/api/v3/plugins/config/reset",
+                                   json={"plugin_id": PLUGIN_ID})
+
+        assert response.status_code == 200, response.get_json()
+        assert calls == [True]
+        assert env.stored()["stock_symbols"] == ["AAPL"]
+
+    def test_reset_notifies_the_plugin_with_its_prepared_config(self, env):
+        plugin = MagicMock()
+        env.plugin_manager.get_plugin.return_value = plugin
+        env.plugin_manager.prepare_plugin_config.side_effect = (
+            lambda _pid, raw: {**raw, "prepared": True})
+
+        response = env.client.post("/api/v3/plugins/config/reset",
+                                   json={"plugin_id": PLUGIN_ID})
+
+        assert response.status_code == 200, response.get_json()
+        handed_over = plugin.on_config_change.call_args.args[0]
+        assert handed_over["prepared"] is True
+        assert handed_over["stock_symbols"] == ["AAPL"]
+
+    def test_a_failed_save_is_reported(self, env, monkeypatch):
+        failed = MagicMock(message="disk full")
+        failed.status.value = "failed"
+        monkeypatch.setattr(env.config_manager, "save_config_atomic",
+                            MagicMock(return_value=failed))
+
+        response = env.client.post("/api/v3/plugins/config/reset",
+                                   json={"plugin_id": PLUGIN_ID})
+
+        assert response.status_code == 500
+        assert "disk full" in response.get_json()["message"]
diff --git a/test/web_interface/test_config_arrays.py b/test/web_interface/test_config_arrays.py
new file mode 100644
index 00000000..dd617695
--- /dev/null
+++ b/test/web_interface/test_config_arrays.py
@@ -0,0 +1,58 @@
+"""coerce_array_shapes: position-keyed dicts back into lists before validation."""
+
+from src.web_interface.config_arrays import coerce_array_shapes
+
+COLOR = {"type": "array", "items": {"type": "integer"},
+         "minItems": 3, "maxItems": 3, "default": [255, 255, 255]}
+
+
+def test_position_keys_become_a_list_in_numeric_order():
+    config = {"tags": {"10": "k", "2": "c", "0": "a"}}
+    coerce_array_shapes(config, {"tags": {"type": "array"}})
+    assert config["tags"] == ["a", "c", "k"]
+
+
+def test_an_empty_dict_becomes_an_empty_list():
+    config = {"tags": {}}
+    coerce_array_shapes(config, {"tags": {"type": "array"}})
+    assert config["tags"] == []
+
+
+def test_a_dict_with_other_keys_is_left_for_validation_to_report():
+    config = {"tags": {"0": "a", "name": "b"}}
+    coerce_array_shapes(config, {"tags": {"type": "array"}})
+    assert config["tags"] == {"0": "a", "name": "b"}
+
+
+def test_element_types_are_left_to_normalization():
+    config = {"color": {"0": "1", "1": "2", "2": "3"}}
+    coerce_array_shapes(config, {"color": COLOR})
+    assert config["color"] == ["1", "2", "3"]
+
+
+def test_nested_objects_and_array_items_are_walked():
+    schema = {"feeds": {"type": "object", "properties": {
+        "custom_feeds": {"type": "array", "items": {"type": "object", "properties": {
+            "tags": {"type": "array"},
+        }}},
+    }}}
+    config = {"feeds": {"custom_feeds": {"0": {"tags": {"0": "news"}}}}}
+    coerce_array_shapes(config, schema)
+    assert config == {"feeds": {"custom_feeds": [{"tags": ["news"]}]}}
+
+
+def test_a_short_form_list_takes_the_default_only_when_asked():
+    config = {"color": ["10", "20"]}
+    coerce_array_shapes(config, {"color": COLOR})
+    assert config["color"] == ["10", "20"]
+
+    coerce_array_shapes(config, {"color": COLOR}, short_lists_take_default=True)
+    assert config["color"] == [255, 255, 255]
+    assert config["color"] is not COLOR["default"]
+
+
+def test_a_default_too_short_itself_is_not_used():
+    schema = {"color": dict(COLOR, default=[0])}
+    config = {"color": ["10"]}
+    coerce_array_shapes(config, schema, short_lists_take_default=True)
+    assert config["color"] == ["10"]
diff --git a/test/web_interface/test_dedup_unique_arrays.py b/test/web_interface/test_dedup_unique_arrays.py
index 170f776c..787b4f2f 100644
--- a/test/web_interface/test_dedup_unique_arrays.py
+++ b/test/web_interface/test_dedup_unique_arrays.py
@@ -1,11 +1,9 @@
-"""Tests for dedup_unique_arrays used by save_plugin_config.
+"""Tests for dedup_unique_arrays, which the plugin-config save path
+(_prepare_plugin_config_for_save in api_v3/plugins.py) runs before validation.
 
-Validates that arrays with uniqueItems: true in the JSON schema have
-duplicates removed before validation, preventing spurious validation
-failures when form merging introduces duplicate entries.
-
-Tests import the production function from src.web_interface.validators
-to ensure they exercise the real code path.
+Arrays with uniqueItems: true in the JSON schema lose their duplicates, so a
+repeat introduced by form merging does not fail validation.
+test_api_v3_plugin_config_save.py checks the same through the endpoint.
 """
 
 
diff --git a/web_interface/app.py b/web_interface/app.py
index 2a8822fa..535b055d 100644
--- a/web_interface/app.py
+++ b/web_interface/app.py
@@ -46,6 +46,7 @@ _JOURNALCTL = shutil.which('journalctl')
 _SYSTEMCTL = shutil.which('systemctl')
 _VCGENCMD = shutil.which('vcgencmd')
 
+from web_interface import display_preview
 from web_interface.system_metrics import collect_system_metrics
 
 # Create Flask app
@@ -53,14 +54,10 @@ app = Flask(__name__)
 app.secret_key = os.urandom(24)
 config_manager = ConfigManager()
 
-# CSRF protection disabled for local-only application
-# CSRF is designed for internet-facing web apps to prevent cross-site request forgery.
-# For a local-only Raspberry Pi application, the threat model is different:
-# - If an attacker has network access to perform CSRF, they have other attack vectors
-# - All API endpoints are programmatic (HTMX/fetch) and don't include CSRF tokens
-# - Forms use HTMX which doesn't automatically include CSRF tokens
-# If you need CSRF protection (e.g., exposing to internet), properly implement CSRF tokens in HTMX forms
-csrf = None
+# No CSRF protection: the UI is meant for the local network, where anyone who
+# can forge a request can also send it directly, and neither the HTMX forms
+# nor the fetch() calls carry a token. Exposing the UI beyond the LAN needs
+# CSRF tokens added to both first.
 
 # Initialize rate limiting (prevent accidental abuse, not security)
 try:
@@ -93,8 +90,6 @@ except ImportError:
         "'pip install flask-compress'."
     )
 
-# Import cache functions from separate module to avoid circular imports
-
 # Initialize plugin managers - read plugins directory from config
 config = config_manager.load_config()
 plugin_system_config = config.get('plugin_system', {})
@@ -237,7 +232,6 @@ def serve_plugin_asset(plugin_id, filename):
         if assets_dir is None:
             return jsonify({'status': 'error', 'message': 'Invalid asset path'}), 403
 
-        # Security check: ensure the assets directory exists and is within project_root
         if not assets_dir.exists() or not assets_dir.is_dir():
             return jsonify({'status': 'error', 'message': 'Asset directory not found'}), 404
 
@@ -694,7 +688,7 @@ def system_status_generator():
                 'power': _get_power_status()
             }
             yield status
-        except Exception as e:
+        except Exception:
             app.logger.error("SSE generator error", exc_info=True)
             yield {'error': 'An error occurred; see server logs'}
         time.sleep(10)  # Update every 10 seconds (reduced frequency for better performance)
@@ -702,9 +696,7 @@ def system_status_generator():
 # Display preview generator for SSE
 def display_preview_generator():
     """Generate display preview updates from snapshot file"""
-    import base64
-
-    snapshot_path = "/tmp/led_matrix_preview.png"  # nosec B108 - fixed path matches display_manager; only read here
+    snapshot_path = display_preview.SNAPSHOT_PATH
     # Viewer marker: this generator only runs while the broadcaster has
     # subscribers (it exits with no clients), so touching the marker each
     # loop tells the DISPLAY service a browser is actually watching — it
@@ -739,20 +731,8 @@ def display_preview_generator():
                 # Only read if file is new or has been updated
                 if last_modified is None or current_modified > last_modified:
                     try:
-                        # The snapshot is already a PNG, written atomically by
-                        # the display service (tmp + os.replace in
-                        # display_manager), so pass the raw bytes straight
-                        # through instead of PIL-decoding and re-encoding —
-                        # identical payload, much less CPU on the Pi.
-                        with open(snapshot_path, 'rb') as f:
-                            img_str = base64.b64encode(f.read()).decode('utf-8')
-
-                        preview_data = {
-                            'timestamp': time.time(),
-                            'width': width,
-                            'height': height,
-                            'image': img_str
-                        }
+                        preview_data = display_preview.preview_payload(
+                            width, height, display_preview.read_snapshot_base64(snapshot_path))
                         last_modified = current_modified
                         yield preview_data
                     except OSError:
@@ -760,27 +740,20 @@ def display_preview_generator():
                         # between mtime check and read); skip this update.
                         app.logger.debug("Preview snapshot read failed; skipping frame", exc_info=True)
             else:
-                # No snapshot available
-                yield {
-                    'timestamp': time.time(),
-                    'width': width,
-                    'height': height,
-                    'image': None
-                }
+                yield display_preview.preview_payload(width, height, None)
                 
-        except Exception as e:
+        except Exception:
             app.logger.error("SSE generator error", exc_info=True)
             yield {'error': 'An error occurred; see server logs'}
         
-        time.sleep(1.0)  # Check once per second — halves PIL encode overhead vs 0.5s
+        time.sleep(1.0)  # the snapshot is re-read only when its mtime changes
 
 # Logs generator for SSE
 def logs_generator():
     """Generate log updates from journalctl"""
     while True:
         try:
-            # Get recent logs from journalctl (simplified version)
-            # Note: User should be in systemd-journal group to read logs without sudo
+            # Reading the journal without sudo needs the systemd-journal group.
             try:
                 if not _JOURNALCTL:
                     yield {'timestamp': time.time(), 'logs': 'journalctl not found; cannot read logs'}
@@ -877,29 +850,19 @@ def stream_display():
 def stream_logs():
     return _sse_stream(_logs_broadcaster)
 
-# Exempt SSE streams from CSRF and apply a generous rate limit.
-# SSE connections are long-lived HTTP requests, not repeated API calls, so the
-# tight "20 per minute" default would be exhausted quickly on reconnects.
-if csrf:
-    csrf.exempt(stream_stats)
-    csrf.exempt(stream_display)
-    csrf.exempt(stream_logs)
-    # Note: api_v3 blueprint is exempted above after registration
-
+# Each SSE stream is one long-lived request, so only a (re)connect counts
+# against a limit. The streams get their own 200 per minute, tighter than the
+# 1000 per minute default, which bounds a client stuck reconnecting.
 if limiter:
     limiter.limit("200 per minute")(stream_stats)
     limiter.limit("200 per minute")(stream_display)
     limiter.limit("200 per minute")(stream_logs)
 
-# The pages blueprint's index now serves '/' directly (see the un-prefixed
-# blueprint registration above), so no redirect route is needed here.
-
 @app.route('/favicon.ico')
 def favicon():
     """Return 204 No Content for favicon to avoid 404 errors"""
     return '', 204
 
-_reconciliation_done = False
 _reconciliation_started = False
 import threading as _threading
 _reconciliation_lock = _threading.Lock()
@@ -907,18 +870,13 @@ _reconciliation_lock = _threading.Lock()
 def _run_startup_reconciliation() -> None:
     """Run state reconciliation in background to auto-repair missing plugins.
 
-    Reconciliation runs exactly once per process lifetime, regardless of
-    whether every inconsistency could be auto-fixed. Previously, a failed
-    auto-repair (e.g. a config entry referencing a plugin that no longer
-    exists in the registry) would reset ``_reconciliation_started`` to False,
-    causing the ``@app.before_request`` hook to re-trigger reconciliation on
-    every single HTTP request — an infinite install-retry loop that pegged
-    the CPU and flooded the log. Unresolved issues are now left in place for
-    the user to address via the UI; the reconciler itself also caches
-    per-plugin unrecoverable failures internally so repeated reconcile calls
-    stay cheap.
+    Runs once per process, whether or not every inconsistency could be fixed:
+    ``_reconciliation_started`` is never reset. Resetting it after a failed
+    repair (a config entry naming a plugin the registry no longer has) made
+    the ``before_request`` hook rerun reconciliation on every request, an
+    install-retry loop that pegged the CPU and flooded the log. Unresolved
+    issues are left for the user to address in the UI.
     """
-    global _reconciliation_done
     from src.logging_config import get_logger
     _logger = get_logger('reconciliation')
 
@@ -980,11 +938,6 @@ def _run_startup_reconciliation() -> None:
                     pass
     except Exception as e:
         _logger.error("[Reconciliation] Error: %s", e, exc_info=True)
-    finally:
-        # Always mark done — we do not want an unhandled exception (or an
-        # unresolved inconsistency) to cause the @before_request hook to
-        # retrigger reconciliation on every subsequent request.
-        _reconciliation_done = True
 
 # Run reconciliation in the background on first request
 @app.before_request
diff --git a/web_interface/blueprints/api_v3/__init__.py b/web_interface/blueprints/api_v3/__init__.py
index 4e5815df..46eade4f 100644
--- a/web_interface/blueprints/api_v3/__init__.py
+++ b/web_interface/blueprints/api_v3/__init__.py
@@ -49,7 +49,6 @@ from src.plugin_system.operation_types import OperationType
 from src.web_interface.validators import (
     validate_file_upload
 )
-from src.error_aggregator import get_error_aggregator
 from src.common.permission_utils import install_requirements_file
 from src.common.path_safety import resolve_under
 from src.device_location import DeviceLocationResolver, apply_device_location
@@ -95,13 +94,11 @@ def _scrub_git_remote_url(url: str) -> str:
 # `config_manager` used to resolve to a None that was never assigned, which
 # silently disabled the /health checks and made /display/current fall back
 # to a hardcoded 128x64.
-# Get project root directory (web_interface/../..)
-# web_interface/blueprints/api_v3/_common.py -> up four to the project root.
-# This was three levels when everything lived in web_interface/blueprints/api_v3.py;
-# the split moved the file one directory deeper and silently pointed PROJECT_ROOT
-# at web_interface/ instead. Nothing failed at import -- it surfaced as routes
-# 404ing and "installation script not found", because every path built from it
-# was wrong. Asserted in test_api_v3_url_map.py so the next move cannot repeat it.
+# The project root, three directories above this package. The split from a
+# single api_v3.py moved this file one directory deeper, and a count left at
+# the old depth pointed PROJECT_ROOT at web_interface/ without failing at
+# import: routes 404ed and reported "installation script not found".
+# test_api_v3_url_map.py asserts it so the next move cannot repeat that.
 PROJECT_ROOT = Path(__file__).resolve().parents[3]
 # System fonts that cannot be deleted (used by catalog API and delete endpoint)
 SYSTEM_FONTS = frozenset([
@@ -415,9 +412,9 @@ def resolve_pull_command(project_dir):
     is: first_time_install.sh chmods five scripts that git tracked as 644, so
     every machine that ran the installer carries five permanent mode changes
     and the update button reports "cannot pull with rebase: You have unstaged
-    changes". Those modes are corrected in this commit, but a user cannot pull
-    the correction while the pull is what is blocked, and any other local edit
-    would reproduce it anyway. Autostash reapplies the changes afterwards.
+    changes". The repository now tracks those modes, but a user cannot pull
+    that correction while the pull is what is blocked, and any other local
+    edit would reproduce it anyway. Autostash reapplies the changes afterwards.
 
     Returns ``(args, note, error)``. When ``origin/<branch>`` exists the pull
     is made explicit against it, so the update proceeds and the branch is
@@ -594,12 +591,7 @@ def _installed_plugin_ids():
     enumerate the installed plugins and read each one's persisted summary by ID
     instead of relying on the tracker's in-memory `get_all_*` view.
     """
-    manifests = _discovered_plugin_manifests()
-    try:
-        return list(manifests.keys()) if manifests else []
-    except Exception:
-        logger.debug('listing plugin_manifests failed while building plugin ids', exc_info=True)
-        return []
+    return list(_discovered_plugin_manifests())
 def _discovered_plugin_manifests(plugin_id=None, rescan=False):
     """The plugin manager's manifests, discovering plugins first if needed.
 
@@ -741,8 +733,6 @@ def _parse_form_value(value):
     Parse a form value into the appropriate Python type.
     Handles booleans, numbers, JSON arrays/objects, and strings.
     """
-    import json
-
     if value is None:
         return None
 
@@ -892,8 +882,6 @@ def _parse_form_value_with_schema(value, key_path, schema):
     Returns:
         Parsed value with correct type, or _SKIP_FIELD to indicate the field should not be set
     """
-    import json
-
     # Get the schema property for this field
     prop = _get_schema_property(schema, key_path)
 
@@ -1394,16 +1382,24 @@ def _prune_credential_backups(plugin_dir: Path) -> None:
 # calendarList.list pages at 250 entries maximum. Ten pages is far past any
 # real account and exists only so a malformed nextPageToken cannot spin here.
 _CALENDAR_LIST_MAX_PAGES = 10
+def _plugin_directory(plugin_id: str) -> Optional[Path]:
+    """An installed plugin's directory, or None when it has none on disk.
+
+    Only the plugin manager is asked, so no plugin manager means None. There
+    is no fallback to the legacy plugins/ directory: the loader never scans
+    it, so a plugin found only there is one that never runs.
+    """
+    if not api_v3.plugin_manager:
+        return None
+    plugin_dir = api_v3.plugin_manager.get_plugin_directory(plugin_id)
+    if not plugin_dir or not Path(plugin_dir).exists():
+        return None
+    return Path(plugin_dir)
+
+
 def _calendar_plugin_dir() -> Optional[Path]:
     """Where the calendar plugin is installed, or None if it is not."""
-    if api_v3.plugin_manager:
-        plugin_dir = api_v3.plugin_manager.get_plugin_directory('calendar')
-    else:
-        plugin_dir = PROJECT_ROOT / 'plugins' / 'calendar'
-    if not plugin_dir:
-        return None
-    plugin_dir = Path(plugin_dir)
-    return plugin_dir if plugin_dir.exists() else None
+    return _plugin_directory('calendar')
 def _run_calendar_registration(plugin_dir: Path, stdin_payload: str):
     """Run the plugin's OAuth script and return the JSON object it prints.
 
@@ -1901,8 +1897,6 @@ def _write_starlark_manifest(manifest: Dict[str, Any]) -> bool:
         return False
 def _install_star_file(app_id: str, star_file_path: str, metadata: Dict[str, Any], assets_dir: Optional[str] = None) -> bool:
     """Install a .star file and update the manifest (standalone, no plugin needed)."""
-    import shutil
-    import json
     app_dir, path_error = _validate_starlark_app_path(app_id)
     if path_error:
         logger.warning("Refusing to install %r: %s", app_id, path_error)
diff --git a/web_interface/blueprints/api_v3/backup.py b/web_interface/blueprints/api_v3/backup.py
index f15220ea..edc53865 100644
--- a/web_interface/blueprints/api_v3/backup.py
+++ b/web_interface/blueprints/api_v3/backup.py
@@ -1,7 +1,7 @@
 """Backup creation, listing and restore.
 
-Routes decorate the shared `api_v3` Blueprint from ._common, so their
-endpoint names are unchanged by living here.
+Routes decorate the shared `api_v3` Blueprint from the package `__init__`,
+so their endpoint names are unchanged by living here.
 """
 from web_interface.blueprints.api_v3 import (
     PROJECT_ROOT, Path, _coerce_to_bool, _safe_backup_path, api_v3,
diff --git a/web_interface/blueprints/api_v3/config.py b/web_interface/blueprints/api_v3/config.py
index 4cff4e51..00355af1 100644
--- a/web_interface/blueprints/api_v3/config.py
+++ b/web_interface/blueprints/api_v3/config.py
@@ -1,20 +1,20 @@
 """Reading and writing configuration, including schedules.
 
-Routes decorate the shared `api_v3` Blueprint from ._common, so their
-endpoint names are unchanged by living here.
+Routes decorate the shared `api_v3` Blueprint from the package `__init__`,
+so their endpoint names are unchanged by living here.
 """
 from web_interface.blueprints.api_v3 import (
-    ErrorCode, Optional, PROJECT_ROOT, Path, _coerce_to_bool,
+    ErrorCode, Optional, _coerce_to_bool,
     _redact_credentials, _validate_time_format, api_v3, deep_merge,
-    describe_exception, error_response, find_secret_fields, json, jsonify,
-    logger, logging, mask_all_secret_values, merge_secrets, os,
-    remove_empty_secrets, request, separate_secrets, strip_masked_values,
-    success_response,
+    describe_exception, error_response, json, jsonify,
+    logger, mask_all_secret_values, merge_secrets,
+    request, strip_masked_values, success_response,
 )
 from src.common.path_safety import resolve_under
 from src.display_geometry import ORIENTATION_ROTATE_DEGREES
 from src.matrix_support import INT_SETTING_LIMITS, describe_range, library_refusals, refusal_message
 from src.pi5_matrix_support import is_raspberry_pi_5
+from web_interface.cache import invalidate_cache
 import web_interface.blueprints.api_v3 as _pkg
 
 # Read through the module rather than bound by value: tests patch these
@@ -27,6 +27,33 @@ import web_interface.blueprints.api_v3 as _pkg
 #: that a missing checkbox was unchecked, not merely left out of an API call.
 FORM_SECTION_FIELD = '__form_section'
 
+#: Fields of the General tab. Any one of them in a /config/main post means the
+#: General form was submitted, so its unchecked checkboxes read as False.
+GENERAL_FIELDS = ('timezone', 'city', 'state', 'country', 'web_display_autostart',
+                  'plugins_directory', 'auto_update_enabled')
+
+#: Top-level fields save_main_config stores somewhere of its own (location,
+#: plugin_system, ...), never as a config key of the same name.
+_MAPPED_TOP_LEVEL_FIELDS = GENERAL_FIELDS + (
+    'auto_discover', 'auto_load_enabled', 'development_mode', 'target_fps')
+
+
+def _plugin_id_list(raw, field_name):
+    """``(ids, None)`` for a list of plugin ids, or ``(None, message)``.
+
+    The settings forms post these lists as JSON text in a hidden input; a JSON
+    client may send the array itself. Anything else is refused rather than
+    coerced: storing ``[]`` for a malformed value clears the saved order or
+    exclusions without a word.
+    """
+    try:
+        parsed = json.loads(raw) if isinstance(raw, str) else raw
+    except (json.JSONDecodeError, TypeError, ValueError):
+        return None, f'{field_name} must be valid JSON'
+    if not isinstance(parsed, list) or not all(isinstance(p, str) for p in parsed):
+        return None, f'{field_name} must be a list of plugin-id strings'
+    return parsed, None
+
 
 def _day_setting(data, day, flat_key, nested_key):
     """(present, value) of one per-day schedule setting in a POST body.
@@ -203,16 +230,10 @@ def save_schedule_config():
                 status_code=500
             )
 
-        # Invalidate cache on config change
-        try:
-            from web_interface.cache import invalidate_cache
-            invalidate_cache()
-        except ImportError:
-            pass
+        invalidate_cache()
 
         return success_response(message='Schedule configuration saved successfully')
     except Exception as e:
-        import logging
         logger.error("Error saving schedule config", exc_info=True)
         return error_response(
             ErrorCode.CONFIG_SAVE_FAILED,
@@ -223,11 +244,8 @@ def save_schedule_config():
 @api_v3.route('/config/dim-schedule', methods=['GET'])
 def get_dim_schedule_config():
     """Get current dim schedule configuration"""
-    import logging
-    import json
-
     if not api_v3.config_manager:
-        logging.error("[DIM SCHEDULE] Config manager not initialized")
+        logger.error("[DIM SCHEDULE] Config manager not initialized")
         return error_response(
             ErrorCode.CONFIG_LOAD_FAILED,
             'Config manager not initialized',
@@ -247,28 +265,28 @@ def get_dim_schedule_config():
 
         return success_response(data=dim_schedule_config)
     except FileNotFoundError as e:
-        logging.error(f"[DIM SCHEDULE] Config file not found: {e}", exc_info=True)
+        logger.error(f"[DIM SCHEDULE] Config file not found: {e}", exc_info=True)
         return error_response(
             ErrorCode.CONFIG_LOAD_FAILED,
             "Configuration file not found",
             status_code=500
         )
     except json.JSONDecodeError as e:
-        logging.error(f"[DIM SCHEDULE] Invalid JSON in config file: {e}", exc_info=True)
+        logger.error(f"[DIM SCHEDULE] Invalid JSON in config file: {e}", exc_info=True)
         return error_response(
             ErrorCode.CONFIG_LOAD_FAILED,
             "Configuration file contains invalid JSON",
             status_code=500
         )
     except (IOError, OSError) as e:
-        logging.error(f"[DIM SCHEDULE] Error reading config file: {e}", exc_info=True)
+        logger.error(f"[DIM SCHEDULE] Error reading config file: {e}", exc_info=True)
         return error_response(
             ErrorCode.CONFIG_LOAD_FAILED,
             "An error occurred; see logs for details",
             status_code=500, details=describe_exception(e)
         )
     except Exception as e:
-        logging.error(f"[DIM SCHEDULE] Unexpected error loading config: {e}", exc_info=True)
+        logger.error(f"[DIM SCHEDULE] Unexpected error loading config: {e}", exc_info=True)
         return error_response(
             ErrorCode.CONFIG_LOAD_FAILED,
             "An error occurred; see logs for details",
@@ -420,16 +438,10 @@ def save_dim_schedule_config():
                 status_code=500
             )
 
-        # Invalidate cache on config change
-        try:
-            from web_interface.cache import invalidate_cache
-            invalidate_cache()
-        except ImportError:
-            pass
+        invalidate_cache()
 
         return success_response(message='Dim schedule configuration saved successfully')
     except Exception as e:
-        import logging
         logger.error("Error saving dim schedule config", exc_info=True)
         return error_response(
             ErrorCode.CONFIG_SAVE_FAILED,
@@ -490,11 +502,7 @@ def save_main_config():
         current_config = api_v3.config_manager.load_config()
         was_auto_update_enabled = bool((current_config.get('auto_update') or {}).get('enabled'))
 
-        # Handle general settings
-        # Note: Checkboxes don't send data when unchecked, so we need to check if we're updating general settings
-        # If any general setting is present, we're updating the general tab
-        is_general_update = any(k in data for k in ['timezone', 'city', 'state', 'country', 'web_display_autostart',
-                                                     'plugins_directory', 'auto_update_enabled'])
+        is_general_update = any(k in data for k in GENERAL_FIELDS)
 
         if is_general_update:
             # For checkbox: if not present in data during a general *form*
@@ -872,28 +880,13 @@ def save_main_config():
                         }), 400
                     vegas_config[config_key] = int_value
 
-            # Handle plugin order and exclusions (JSON arrays)
-            if 'vegas_plugin_order' in data:
-                try:
-                    if isinstance(data['vegas_plugin_order'], str):
-                        parsed = json.loads(data['vegas_plugin_order'])
-                    else:
-                        parsed = data['vegas_plugin_order']
-                    # Ensure result is a list
-                    vegas_config['plugin_order'] = list(parsed) if isinstance(parsed, (list, tuple)) else []
-                except (json.JSONDecodeError, TypeError, ValueError):
-                    vegas_config['plugin_order'] = []
-
-            if 'vegas_excluded_plugins' in data:
-                try:
-                    if isinstance(data['vegas_excluded_plugins'], str):
-                        parsed = json.loads(data['vegas_excluded_plugins'])
-                    else:
-                        parsed = data['vegas_excluded_plugins']
-                    # Ensure result is a list
-                    vegas_config['excluded_plugins'] = list(parsed) if isinstance(parsed, (list, tuple)) else []
-                except (json.JSONDecodeError, TypeError, ValueError):
-                    vegas_config['excluded_plugins'] = []
+            for field_name, config_key in (('vegas_plugin_order', 'plugin_order'),
+                                           ('vegas_excluded_plugins', 'excluded_plugins')):
+                if field_name in data:
+                    ids, id_error = _plugin_id_list(data[field_name], field_name)
+                    if id_error:
+                        return jsonify({'status': 'error', 'message': id_error}), 400
+                    vegas_config[config_key] = ids
 
         # Handle multi-display sync settings
         sync_fields = ["sync_role", "sync_port", "sync_follower_position"]
@@ -921,19 +914,11 @@ def save_main_config():
                     return jsonify({"status": "error", "message": "sync_follower_position must be left or right"}), 400
                 current_config["sync"]["follower_position"] = pos_val
 
-        # Handle primary rotation order: must be a JSON array of plugin-id
-        # strings. Reject anything else with a 400 rather than silently
-        # coercing, so a buggy client can't clear or corrupt the saved order.
         if 'plugin_rotation_order' in data:
-            raw_order = data.pop('plugin_rotation_order')
-            try:
-                parsed = json.loads(raw_order) if isinstance(raw_order, str) else raw_order
-            except (json.JSONDecodeError, TypeError, ValueError):
-                return jsonify({'status': 'error',
-                                'message': 'plugin_rotation_order must be valid JSON'}), 400
-            if not isinstance(parsed, list) or not all(isinstance(p, str) for p in parsed):
-                return jsonify({'status': 'error',
-                                'message': 'plugin_rotation_order must be a list of plugin-id strings'}), 400
+            parsed, id_error = _plugin_id_list(data.pop('plugin_rotation_order'),
+                                               'plugin_rotation_order')
+            if id_error:
+                return jsonify({'status': 'error', 'message': id_error}), 400
             if 'display' not in current_config:
                 current_config['display'] = {}
             current_config['display']['plugin_rotation_order'] = parsed
@@ -1084,27 +1069,15 @@ def save_main_config():
         for key in plugin_keys_to_remove:
             del data[key]
 
-        # Handle any remaining config keys
-        # System settings (timezone, city, etc.) are already handled above
-        # Plugin configs should use /api/v3/plugins/config endpoint, but we'll handle them here too for flexibility
+        # Whatever no section above claimed is stored as a top-level key, a
+        # dict merged onto the stored one. Plugin sections were handled and
+        # removed above. Form field names the sections above already stored
+        # elsewhere are skipped, or each would land as a top-level key too.
+        mapped_fields = set(_MAPPED_TOP_LEVEL_FIELDS).union(
+            display_fields, sync_fields, vegas_fields, double_sided_fields)
         for key in data:
-            # Skip system settings that are already handled above
-            if key in ['timezone', 'city', 'state', 'country',
-                       'web_display_autostart', 'auto_discover',
-                       'auto_load_enabled', 'development_mode',
-                       'plugins_directory', 'target_fps', 'auto_update_enabled']:
+            if key in mapped_fields:
                 continue
-            # Skip fields that are already handled above in their own named sections.
-            # Without this, every form field name lands as a top-level config key too.
-            if key in display_fields:
-                continue
-            if key in sync_fields:
-                continue
-            if key in vegas_fields:
-                continue
-            if key in double_sided_fields:
-                continue
-            # For any remaining keys (including plugin keys), use deep merge to preserve existing settings
             if key in current_config and isinstance(current_config[key], dict) and isinstance(data[key], dict):
                 # Deep merge to preserve existing settings
                 current_config[key] = deep_merge(current_config[key], data[key])
@@ -1120,12 +1093,7 @@ def save_main_config():
                 status_code=500
             )
 
-        # Invalidate cache on config change
-        try:
-            from web_interface.cache import invalidate_cache
-            invalidate_cache()
-        except ImportError:
-            pass
+        invalidate_cache()
 
         # Notify saved plugins of their new config (with secrets merged), now
         # that it is on disk.
diff --git a/web_interface/blueprints/api_v3/display.py b/web_interface/blueprints/api_v3/display.py
index 68a0ab0d..0d99c0df 100644
--- a/web_interface/blueprints/api_v3/display.py
+++ b/web_interface/blueprints/api_v3/display.py
@@ -1,13 +1,14 @@
 """Display control, on-demand playback and preview.
 
-Routes decorate the shared `api_v3` Blueprint from ._common, so their
-endpoint names are unchanged by living here.
+Routes decorate the shared `api_v3` Blueprint from the package `__init__`,
+so their endpoint names are unchanged by living here.
 """
 from web_interface.blueprints.api_v3 import (
     _ensure_display_service_running,
     _get_display_service_status, _stop_display_service, api_v3,
-    jsonify, logger, os, request, uuid,
+    jsonify, logger, request, uuid,
 )
+from web_interface import display_preview
 import web_interface.blueprints.api_v3 as _pkg
 # Read through the module rather than bound by value: tests patch these
 # as module attributes, and a value binding would not see the patch.
@@ -30,13 +31,11 @@ def _cache_manager():
 
 @api_v3.route('/display/current', methods=['GET'])
 def get_display_current():
-    """Get current display state"""
-    import base64
-    from PIL import Image
-    import io
-
-    snapshot_path = "/tmp/led_matrix_preview.png"
+    """The latest display preview, as the /stream/display SSE stream sends it.
 
+    ``data`` is ``{timestamp, width, height, image}``; ``image`` is the
+    snapshot PNG base64-encoded, or null when there is none to show.
+    """
     # Get display dimensions from config: the logical size DisplayManager
     # renders at, so double-sided setups preview one screen
     from src.display_geometry import logical_size
@@ -46,26 +45,16 @@ def get_display_current():
     except Exception:
         width, height = logical_size({})
 
-    # Try to read snapshot file
-    image_data = None
-    if os.path.exists(snapshot_path):
-        try:
-            with Image.open(snapshot_path) as img:
-                # Convert to PNG and encode as base64
-                buffer = io.BytesIO()
-                img.save(buffer, format='PNG')
-                image_data = base64.b64encode(buffer.getvalue()).decode('utf-8')
-        except Exception as img_err:
-            # File might be being written or corrupted, return None
-            pass
+    try:
+        image = display_preview.read_snapshot_base64()
+    except FileNotFoundError:
+        image = None  # the display service has not written one yet
+    except OSError:
+        logger.warning("Could not read the display preview snapshot", exc_info=True)
+        image = None
 
-    display_data = {
-        'timestamp': _pkg.time.time(),
-        'width': width,
-        'height': height,
-        'image': image_data  # Base64 encoded image data or None if unavailable
-    }
-    return jsonify({'status': 'success', 'data': display_data})
+    return jsonify({'status': 'success',
+                    'data': display_preview.preview_payload(width, height, image)})
 @api_v3.route('/display/modes', methods=['GET'])
 def get_display_modes():
     """Every display mode that can be requested on-demand, with its plugin.
diff --git a/web_interface/blueprints/api_v3/fonts.py b/web_interface/blueprints/api_v3/fonts.py
index ff52c744..2eb28a8a 100644
--- a/web_interface/blueprints/api_v3/fonts.py
+++ b/web_interface/blueprints/api_v3/fonts.py
@@ -1,12 +1,13 @@
 """Font catalogue, upload, preview and deletion.
 
-Routes decorate the shared `api_v3` Blueprint from ._common, so their
-endpoint names are unchanged by living here.
+Routes decorate the shared `api_v3` Blueprint from the package `__init__`,
+so their endpoint names are unchanged by living here.
 """
 from web_interface.blueprints.api_v3 import (
     PROJECT_ROOT, Path, Response, SYSTEM_FONTS, api_v3,
     jsonify, logger, os, re, request, validate_file_upload,
 )
+from web_interface.cache import delete_cached, get_cached, set_cached
 
 
 def _catalog_response(catalog):
@@ -52,16 +53,9 @@ def _catalog_response(catalog):
 @api_v3.route('/fonts/catalog', methods=['GET'])
 def get_fonts_catalog():
     """Get fonts catalog"""
-    # Check cache first (5 minute TTL)
-    try:
-        from web_interface.cache import get_cached, set_cached
-        cached_result = get_cached('fonts_catalog', ttl_seconds=300)
-        if cached_result is not None:
-            return _catalog_response(cached_result)
-    except ImportError:
-        # Cache not available, continue without caching
-        get_cached = None
-        set_cached = None
+    cached_result = get_cached('fonts_catalog', ttl_seconds=300)
+    if cached_result is not None:
+        return _catalog_response(cached_result)
 
     # Try to import freetype, but continue without it if unavailable
     try:
@@ -148,12 +142,7 @@ def get_fonts_catalog():
                     'metadata': metadata if metadata else None
                 }
 
-    # Cache the result (5 minute TTL) if available
-    if set_cached:
-        try:
-            set_cached('fonts_catalog', catalog, ttl_seconds=300)
-        except Exception:
-            logger.error("[FontCatalog] Failed to cache fonts_catalog", exc_info=True)
+    set_cached('fonts_catalog', catalog, ttl_seconds=300)
 
     return _catalog_response(catalog)
 @api_v3.route('/fonts/tokens', methods=['GET'])
@@ -229,14 +218,7 @@ def upload_font():
     # Save the file
     font_file.save(str(filepath))
 
-    # Clear font catalog cache
-    try:
-        from web_interface.cache import delete_cached
-        delete_cached('fonts_catalog')
-    except ImportError as e:
-        logger.warning("[FontUpload] Cache module not available: %s", e)
-    except Exception:
-        logger.error("[FontUpload] Failed to clear fonts_catalog cache", exc_info=True)
+    delete_cached('fonts_catalog')
 
     return jsonify({
         'status': 'success',
@@ -453,14 +435,7 @@ def delete_font(font_family: str) -> tuple[Response, int] | Response:
     if not deleted:
         return jsonify({'status': 'error', 'message': f'Font not found: {font_family}'}), 404
 
-    # Clear font catalog cache
-    try:
-        from web_interface.cache import delete_cached
-        delete_cached('fonts_catalog')
-    except ImportError as e:
-        logger.warning("[FontDelete] Cache module not available: %s", e)
-    except Exception:
-        logger.error("[FontDelete] Failed to clear fonts_catalog cache", exc_info=True)
+    delete_cached('fonts_catalog')
 
     return jsonify({
         'status': 'success',
diff --git a/web_interface/blueprints/api_v3/misc.py b/web_interface/blueprints/api_v3/misc.py
index 0f4df30e..e1fd7af4 100644
--- a/web_interface/blueprints/api_v3/misc.py
+++ b/web_interface/blueprints/api_v3/misc.py
@@ -1,12 +1,12 @@
 """Routes with no larger group of their own: errors, integrations,
 cache, sync, logs, health and hardware.
 
-Routes decorate the shared `api_v3` Blueprint from ._common, so their
-endpoint names are unchanged by living here.
+Routes decorate the shared `api_v3` Blueprint from the package `__init__`,
+so their endpoint names are unchanged by living here.
 """
 from web_interface.blueprints.api_v3 import (
-    _coerce_to_bool,
-    ErrorCode, Path, _JOURNALCTL, _MQTT_BRIDGE_CONFIG, _MQTT_BRIDGE_DEFAULTS,
+    _coerce_to_bool, _discovered_plugin_manifests,
+    ErrorCode, _JOURNALCTL, _MQTT_BRIDGE_CONFIG, _MQTT_BRIDGE_DEFAULTS,
     _MQTT_BRIDGE_DIR, _SUDO, _coerce_mqtt_bridge_value,
     _get_display_service_status, _mqtt_bridge_service_state,
     _read_mqtt_bridge_config, api_v3, contextlib, describe_exception,
@@ -16,6 +16,7 @@ from web_interface.blueprints.api_v3 import (
 from src.common.path_safety import safe_path_component
 from src.common import sync_manager as _sync
 from src import error_aggregator as _errors
+from web_interface import display_preview
 import web_interface.blueprints.api_v3 as _pkg
 # Read through the module rather than bound by value: tests patch these
 # as module attributes, and a value binding would not see the patch.
@@ -34,11 +35,9 @@ def get_health():
             'checks': {}
         }
 
-        # Check web interface service
-        # Stamp the start _pkg.time before measuring against it -- reading it with a
-        # fallback of _pkg.time.time() and only assigning afterwards made the very
-        # first call subtract two separate clock reads, reporting a small
-        # negative uptime.
+        # Stamp the start time before measuring against it: reading it with a
+        # fallback of time.time() and assigning it afterwards made the first
+        # call subtract two separate clock reads, a small negative uptime.
         if not hasattr(get_health, '_start_time'):
             get_health._start_time = _pkg.time.time()
         health_status['services']['web_interface'] = {
@@ -56,7 +55,7 @@ def get_health():
         # Check config file accessibility
         try:
             if api_v3.config_manager:
-                test_config = api_v3.config_manager.load_config()
+                api_v3.config_manager.load_config()
                 health_status['checks']['config_file'] = {
                     'status': 'accessible',
                     'readable': True
@@ -66,7 +65,8 @@ def get_health():
                     'status': 'unknown',
                     'readable': False
                 }
-        except Exception as e:
+        except Exception:
+            logger.warning("Health check could not read the config file", exc_info=True)
             health_status['checks']['config_file'] = {
                 'status': 'error',
                 'readable': False,
@@ -76,8 +76,7 @@ def get_health():
         # Check plugin system
         try:
             if api_v3.plugin_manager:
-                # Try to discover plugins (lightweight check)
-                plugin_count = len(api_v3.plugin_manager.get_available_plugins()) if hasattr(api_v3.plugin_manager, 'get_available_plugins') else 0
+                plugin_count = len(_discovered_plugin_manifests())
                 health_status['checks']['plugin_system'] = {
                     'status': 'operational',
                     'plugin_count': plugin_count
@@ -86,7 +85,8 @@ def get_health():
                 health_status['checks']['plugin_system'] = {
                     'status': 'not_initialized'
                 }
-        except Exception as e:
+        except Exception:
+            logger.warning("Health check could not count plugins", exc_info=True)
             health_status['checks']['plugin_system'] = {
                 'status': 'error',
                 'error': 'see logs for details'
@@ -94,7 +94,7 @@ def get_health():
 
         # Check hardware connectivity (if display manager available)
         try:
-            snapshot_path = "/tmp/led_matrix_preview.png"
+            snapshot_path = display_preview.SNAPSHOT_PATH
             if os.path.exists(snapshot_path):
                 # Check if snapshot is recent (updated in last 60 seconds)
                 mtime = os.path.getmtime(snapshot_path)
@@ -108,7 +108,8 @@ def get_health():
                     'status': 'no_snapshot',
                     'note': 'Display service may not be running'
                 }
-        except Exception as e:
+        except Exception:
+            logger.warning("Health check could not read the preview snapshot", exc_info=True)
             health_status['checks']['hardware'] = {
                 'status': 'unknown',
                 'error': 'see logs for details'
diff --git a/web_interface/blueprints/api_v3/plugins.py b/web_interface/blueprints/api_v3/plugins.py
index 24ecc362..a5ebefbf 100644
--- a/web_interface/blueprints/api_v3/plugins.py
+++ b/web_interface/blueprints/api_v3/plugins.py
@@ -1,7 +1,7 @@
 """Plugin install, update, enable/disable, config and store routes.
 
-Routes decorate the shared `api_v3` Blueprint from ._common, so their
-endpoint names are unchanged by living here.
+Routes decorate the shared `api_v3` Blueprint from the package `__init__`,
+so their endpoint names are unchanged by living here.
 """
 from web_interface.blueprints.api_v3 import (
     ErrorCode, OperationType, PROJECT_ROOT, Path, Response,
@@ -9,13 +9,14 @@ from web_interface.blueprints.api_v3 import (
     _do_transactional_uninstall, _enhance_schema_with_core_properties,
     _filter_config_by_schema, _get_plugin_version, _get_schema_property,
     _hidden_array_item_property, _installed_plugin_ids, _is_plugin_update_available,
+    _plugin_directory,
     _parse_form_value_with_schema, _prune_credential_backups,
     _run_calendar_registration, _schema_allows_null, _schema_type_is,
     _set_missing_booleans_to_false,
     _set_nested_value, _starlark_virtual_plugins, _toggle_starlark_app,
     api_v3, datetime, deep_merge, describe_exception, error_response,
     exception_error_response,
-    find_secret_fields, hashlib, json, jsonify, logger, logging,
+    find_secret_fields, hashlib, json, jsonify, logger,
     merge_secrets, os, redact_text, remove_empty_secrets, request,
     separate_secrets, shutil, stat, subprocess, success_response,
     tempfile, uuid, validate_request_json,
@@ -23,6 +24,8 @@ from web_interface.blueprints.api_v3 import (
 from src.common.path_safety import (
     resolve_under, safe_path_component, safe_relative_parts,
 )
+from src.web_interface.config_arrays import coerce_array_shapes
+from src.web_interface.validators import dedup_unique_arrays
 import web_interface.blueprints.api_v3 as _pkg
 # Read through the module rather than bound by value: tests patch these
 # as module attributes, and a value binding would not see the patch.
@@ -36,9 +39,6 @@ def get_installed_plugins():
     if not api_v3.plugin_manager or not api_v3.plugin_store_manager:
         return jsonify({'status': 'error', 'message': 'Plugin managers not initialized'}), 500
 
-    import json
-    from pathlib import Path
-
     # Re-discover plugins to ensure we have the latest list
     # This handles cases where plugins are added/removed after app startup
     api_v3.plugin_manager.discover_plugins()
@@ -180,8 +180,7 @@ def get_plugin_health():
     if not api_v3.plugin_manager:
         return jsonify({'status': 'error', 'message': 'Plugin manager not initialized'}), 500
 
-    # Check if health tracker is available
-    if not hasattr(api_v3.plugin_manager, 'health_tracker') or not api_v3.plugin_manager.health_tracker:
+    if not api_v3.plugin_manager.health_tracker:
         return jsonify({
             'status': 'success',
             'data': {},
@@ -216,15 +215,15 @@ def get_plugin_health_single(plugin_id):
     if not api_v3.plugin_manager:
         return jsonify({'status': 'error', 'message': 'Plugin manager not initialized'}), 500
 
-    # Check if health tracker is available
-    if not hasattr(api_v3.plugin_manager, 'health_tracker') or not api_v3.plugin_manager.health_tracker:
+    if not api_v3.plugin_manager.health_tracker:
         return jsonify({
             'status': 'error',
             'message': 'Health tracking not available'
         }), 503
 
-    # Get health summary for specific plugin
-    health_summary = api_v3.plugin_manager.health_tracker.get_health_summary(plugin_id)
+    # force_reload for the same reason as the list route above.
+    health_summary = api_v3.plugin_manager.health_tracker.get_health_summary(
+        plugin_id, force_reload=True)
 
     return jsonify({
         'status': 'success',
@@ -236,8 +235,7 @@ def reset_plugin_health(plugin_id):
     if not api_v3.plugin_manager:
         return jsonify({'status': 'error', 'message': 'Plugin manager not initialized'}), 500
 
-    # Check if health tracker is available
-    if not hasattr(api_v3.plugin_manager, 'health_tracker') or not api_v3.plugin_manager.health_tracker:
+    if not api_v3.plugin_manager.health_tracker:
         return jsonify({
             'status': 'error',
             'message': 'Health tracking not available'
@@ -256,8 +254,7 @@ def get_plugin_metrics():
     if not api_v3.plugin_manager:
         return jsonify({'status': 'error', 'message': 'Plugin manager not initialized'}), 500
 
-    # Check if resource monitor is available
-    if not hasattr(api_v3.plugin_manager, 'resource_monitor') or not api_v3.plugin_manager.resource_monitor:
+    if not api_v3.plugin_manager.resource_monitor:
         return jsonify({
             'status': 'success',
             'data': {},
@@ -291,15 +288,15 @@ def get_plugin_metrics_single(plugin_id):
     if not api_v3.plugin_manager:
         return jsonify({'status': 'error', 'message': 'Plugin manager not initialized'}), 500
 
-    # Check if resource monitor is available
-    if not hasattr(api_v3.plugin_manager, 'resource_monitor') or not api_v3.plugin_manager.resource_monitor:
+    if not api_v3.plugin_manager.resource_monitor:
         return jsonify({
             'status': 'error',
             'message': 'Resource monitoring not available'
         }), 503
 
-    # Get metrics summary for specific plugin
-    metrics_summary = api_v3.plugin_manager.resource_monitor.get_metrics_summary(plugin_id)
+    # force_reload for the same reason as the list route above.
+    metrics_summary = api_v3.plugin_manager.resource_monitor.get_metrics_summary(
+        plugin_id, force_reload=True)
 
     return jsonify({
         'status': 'success',
@@ -311,8 +308,7 @@ def reset_plugin_metrics(plugin_id):
     if not api_v3.plugin_manager:
         return jsonify({'status': 'error', 'message': 'Plugin manager not initialized'}), 500
 
-    # Check if resource monitor is available
-    if not hasattr(api_v3.plugin_manager, 'resource_monitor') or not api_v3.plugin_manager.resource_monitor:
+    if not api_v3.plugin_manager.resource_monitor:
         return jsonify({
             'status': 'error',
             'message': 'Resource monitoring not available'
@@ -331,8 +327,7 @@ def manage_plugin_limits(plugin_id):
     if not api_v3.plugin_manager:
         return jsonify({'status': 'error', 'message': 'Plugin manager not initialized'}), 500
 
-    # Check if resource monitor is available
-    if not hasattr(api_v3.plugin_manager, 'resource_monitor') or not api_v3.plugin_manager.resource_monitor:
+    if not api_v3.plugin_manager.resource_monitor:
         return jsonify({
             'status': 'error',
             'message': 'Resource monitoring not available'
@@ -433,17 +428,13 @@ def toggle_plugin():
             config[plugin_id] = {}
         config[plugin_id]['enabled'] = enabled
 
-        # Use atomic save if available
-        if hasattr(api_v3.config_manager, 'save_config_atomic'):
-            result = api_v3.config_manager.save_config_atomic(config, create_backup=True)
-            if result.status.value != 'success':
-                return error_response(
-                    ErrorCode.CONFIG_SAVE_FAILED,
-                    f"Failed to save configuration: {result.message}",
-                    status_code=500
-                )
-        else:
-            api_v3.config_manager.save_config(config)
+        success, error_msg = _pkg._save_config_atomic(api_v3.config_manager, config, create_backup=True)
+        if not success:
+            return error_response(
+                ErrorCode.CONFIG_SAVE_FAILED,
+                f"Failed to save configuration: {error_msg}",
+                status_code=500
+            )
 
         # Update state manager if available
         if api_v3.plugin_state_manager:
@@ -470,8 +461,7 @@ def toggle_plugin():
                         plugin.on_disable()
             except Exception as lifecycle_error:
                 # Log the error but don't fail the toggle - config is already saved
-                import logging
-                logging.warning(f"Lifecycle method error for {plugin_id}: {lifecycle_error}", exc_info=True)
+                logger.warning("Lifecycle method error for %s: %s", plugin_id, lifecycle_error, exc_info=True)
 
         return success_response(
             message=f"Plugin {plugin_id} {'enabled' if enabled else 'disabled'} successfully"
@@ -748,25 +738,16 @@ def get_plugin_config():
                     plugin_config, schema_mgr.load_schema(plugin_id, use_cache=True), defaults)
             except Exception as e:
                 # Log but don't fail - defaults merge is best effort
-                import logging
-                logging.warning(f"Could not merge defaults for {plugin_id}: {e}")
+                logger.warning("Could not merge defaults for %s: %s", plugin_id, e)
 
         # Special handling for of-the-day plugin: populate uploaded_files and categories from disk
         if plugin_id == 'of-the-day' or plugin_id == 'ledmatrix-of-the-day':
-            # Get plugin directory - plugin_id in manifest is 'of-the-day', but directory is 'ledmatrix-of-the-day'
-            plugin_dir_name = 'ledmatrix-of-the-day'
-            if api_v3.plugin_manager:
-                plugin_dir = api_v3.plugin_manager.get_plugin_directory(plugin_dir_name)
-                # If not found, try with the plugin_id
-                if not plugin_dir or not Path(plugin_dir).exists():
-                    plugin_dir = api_v3.plugin_manager.get_plugin_directory(plugin_id)
-            else:
-                plugin_dir = PROJECT_ROOT / 'plugins' / plugin_dir_name
-                if not plugin_dir.exists():
-                    plugin_dir = PROJECT_ROOT / 'plugins' / plugin_id
-
-            if plugin_dir and Path(plugin_dir).exists():
-                data_dir = Path(plugin_dir) / 'of_the_day'
+            # The manifest id is 'of-the-day'; the directory is usually
+            # 'ledmatrix-of-the-day'.
+            plugin_dir = (_plugin_directory('ledmatrix-of-the-day')
+                          or _plugin_directory(plugin_id))
+            if plugin_dir:
+                data_dir = plugin_dir / 'of_the_day'
                 if data_dir.exists():
                     # Scan for JSON files
                     uploaded_files = []
@@ -934,7 +915,6 @@ def update_plugin():
 
         if manifest_path.exists():
             try:
-                import json
                 with open(manifest_path, 'r', encoding='utf-8') as f:
                     manifest = json.load(f)
                     current_last_updated = manifest.get('last_updated')
@@ -983,7 +963,6 @@ def update_plugin():
             updated_version = current_version
             try:
                 if manifest_path.exists():
-                    import json
                     with open(manifest_path, 'r', encoding='utf-8') as f:
                         manifest = json.load(f)
                         updated_last_updated = manifest.get('last_updated', current_last_updated)
@@ -1224,10 +1203,7 @@ def install_plugin():
         return jsonify({'status': 'error',
                         'message': f"{plugin_id} is a {registry_entry.get('type')!r} entry, not a plugin"}), 400
 
-    # Install the plugin
-    # Log the plugins directory being used for debugging
     plugins_dir = api_v3.plugin_store_manager.plugins_dir
-    branch_info = f" (branch: {branch})" if branch else ""
     logger.info("Installing plugin to directory: %s", plugins_dir)
 
     # Use operation queue if available
@@ -1590,24 +1566,21 @@ def get_github_auth_status():
         })
 @api_v3.route('/plugins/store/refresh', methods=['POST'])
 def refresh_plugin_store():
-    """Refresh plugin store repository"""
+    """Re-download the plugin registry, bypassing its cache.
+
+    Takes no body. Answers ``{status, message, plugin_count}``, the count
+    being the registry's entries. Commit metadata is not refreshed here: the
+    store list fetches it per plugin when it is shown.
+    """
     if not api_v3.plugin_store_manager:
         return jsonify({'status': 'error', 'message': 'Plugin store manager not initialized'}), 500
 
-    data = request.get_json(silent=True) or {}
-    fetch_commit_info = data.get('fetch_commit_info', data.get('fetch_latest_versions', False))
-
-    # Force refresh the registry
     registry = api_v3.plugin_store_manager.fetch_registry(force_refresh=True)
     plugin_count = len(registry.get('plugins', []))
 
-    message = 'Plugin store refreshed'
-    if fetch_commit_info:
-        message += ' (with refreshed commit metadata from GitHub)'
-
     return jsonify({
         'status': 'success',
-        'message': message,
+        'message': 'Plugin store refreshed',
         'plugin_count': plugin_count
     })
 @api_v3.route('/plugins/config', methods=['POST'])
@@ -1699,7 +1672,6 @@ def save_plugin_config():
             
             # Process bracket notation fields and set directly in plugin_config
             # Use JSON encoding instead of comma-join to handle values containing commas
-            import json
             for base_path, values in bracket_array_fields.items():
                 # Get schema property to verify it's an array
                 base_prop = _get_schema_property(schema, base_path)
@@ -1797,254 +1769,11 @@ def save_plugin_config():
                         if parsed_value is not _SKIP_FIELD:
                             _set_nested_value(plugin_config, key, parsed_value)
             
-            # Post-process: Fix array fields that might have been incorrectly structured
-            # This handles cases where array fields are stored as dicts (e.g., from indexed form fields)
-            def fix_array_structures(config_dict, schema_props, prefix=''):
-                """Recursively fix array structures (convert dicts with numeric keys to arrays, fix length issues)"""
-                for prop_key, prop_schema in schema_props.items():
-                    prop_type = prop_schema.get('type')
-
-                    if prop_type == 'array':
-                        # Navigate to the field location
-                        if prefix:
-                            parent_parts = prefix.split('.')
-                            parent = config_dict
-                            for part in parent_parts:
-                                if isinstance(parent, dict) and part in parent:
-                                    parent = parent[part]
-                                else:
-                                    parent = None
-                                    break
-
-                            if parent is not None and isinstance(parent, dict) and prop_key in parent:
-                                current_value = parent[prop_key]
-                                # If it's a dict with numeric string keys, convert to array
-                                if isinstance(current_value, dict) and not isinstance(current_value, list):
-                                    try:
-                                        # Check if all keys are numeric strings (array indices)
-                                        keys = [k for k in current_value.keys()]
-                                        if all(k.isdigit() for k in keys):
-                                            # Convert to sorted array by index
-                                            sorted_keys = sorted(keys, key=int)
-                                            array_value = [current_value[k] for k in sorted_keys]
-                                            # Convert array elements to correct types based on schema
-                                            items_schema = prop_schema.get('items', {})
-                                            item_type = items_schema.get('type')
-                                            if item_type in ('number', 'integer'):
-                                                converted_array = []
-                                                for v in array_value:
-                                                    if isinstance(v, str):
-                                                        try:
-                                                            if item_type == 'integer':
-                                                                converted_array.append(int(v))
-                                                            else:
-                                                                converted_array.append(float(v))
-                                                        except (ValueError, TypeError, OverflowError):
-                                                            converted_array.append(v)
-                                                    else:
-                                                        converted_array.append(v)
-                                                array_value = converted_array
-                                            parent[prop_key] = array_value
-                                            current_value = array_value  # Update for length check below
-                                    except (ValueError, KeyError, TypeError):
-                                        # Conversion failed, check if we should use default
-                                        pass
-
-                                # If it's an array, ensure correct types and check minItems
-                                if isinstance(current_value, list):
-                                    # First, ensure array elements are correct types
-                                    items_schema = prop_schema.get('items', {})
-                                    item_type = items_schema.get('type')
-                                    if item_type in ('number', 'integer'):
-                                        converted_array = []
-                                        for v in current_value:
-                                            if isinstance(v, str):
-                                                try:
-                                                    if item_type == 'integer':
-                                                        converted_array.append(int(v))
-                                                    else:
-                                                        converted_array.append(float(v))
-                                                except (ValueError, TypeError, OverflowError):
-                                                    converted_array.append(v)
-                                            else:
-                                                converted_array.append(v)
-                                        parent[prop_key] = converted_array
-                                        current_value = converted_array
-
-                                    # Then check minItems
-                                    min_items = prop_schema.get('minItems')
-                                    if min_items is not None and len(current_value) < min_items:
-                                        # Use default if available, otherwise keep as-is (validation will catch it)
-                                        default = prop_schema.get('default')
-                                        if default and isinstance(default, list) and len(default) >= min_items:
-                                            parent[prop_key] = default
-                        else:
-                            # Top-level field
-                            if prop_key in config_dict:
-                                current_value = config_dict[prop_key]
-                                # If it's a dict with numeric string keys, convert to array
-                                if isinstance(current_value, dict) and not isinstance(current_value, list):
-                                    try:
-                                        keys = list(current_value.keys())
-                                        if keys and all(str(k).isdigit() for k in keys):
-                                            sorted_keys = sorted(keys, key=lambda x: int(str(x)))
-                                            array_value = [current_value[k] for k in sorted_keys]
-                                            # Convert array elements to correct types based on schema
-                                            items_schema = prop_schema.get('items', {})
-                                            item_type = items_schema.get('type')
-                                            if item_type in ('number', 'integer'):
-                                                converted_array = []
-                                                for v in array_value:
-                                                    if isinstance(v, str):
-                                                        try:
-                                                            if item_type == 'integer':
-                                                                converted_array.append(int(v))
-                                                            else:
-                                                                converted_array.append(float(v))
-                                                        except (ValueError, TypeError, OverflowError):
-                                                            converted_array.append(v)
-                                                    else:
-                                                        converted_array.append(v)
-                                                array_value = converted_array
-                                            config_dict[prop_key] = array_value
-                                            current_value = array_value  # Update for length check below
-                                    except (ValueError, KeyError, TypeError) as e:
-                                        logger.debug(f"Failed to convert {prop_key} to array: {e}")
-
-                                # If it's an array, ensure correct types and check minItems
-                                if isinstance(current_value, list):
-                                    # First, ensure array elements are correct types
-                                    items_schema = prop_schema.get('items', {})
-                                    item_type = items_schema.get('type')
-                                    if item_type in ('number', 'integer'):
-                                        converted_array = []
-                                        for v in current_value:
-                                            if isinstance(v, str):
-                                                try:
-                                                    if item_type == 'integer':
-                                                        converted_array.append(int(v))
-                                                    else:
-                                                        converted_array.append(float(v))
-                                                except (ValueError, TypeError, OverflowError):
-                                                    converted_array.append(v)
-                                            else:
-                                                converted_array.append(v)
-                                        config_dict[prop_key] = converted_array
-                                        current_value = converted_array
-
-                                    # Then check minItems
-                                    min_items = prop_schema.get('minItems')
-                                    if min_items is not None and len(current_value) < min_items:
-                                        default = prop_schema.get('default')
-                                        if default and isinstance(default, list) and len(default) >= min_items:
-                                            config_dict[prop_key] = default
-
-                    # Recurse into nested objects
-                    elif prop_type == 'object' and 'properties' in prop_schema:
-                        nested_prefix = f"{prefix}.{prop_key}" if prefix else prop_key
-                        if prefix:
-                            parent_parts = prefix.split('.')
-                            parent = config_dict
-                            for part in parent_parts:
-                                if isinstance(parent, dict) and part in parent:
-                                    parent = parent[part]
-                                else:
-                                    parent = None
-                                    break
-                            nested_dict = parent.get(prop_key) if parent is not None and isinstance(parent, dict) else None
-                        else:
-                            nested_dict = config_dict.get(prop_key)
-
-                        if isinstance(nested_dict, dict):
-                            # Pass no prefix: config_dict is already the navigated sub-dict,
-                            # so path segments from the parent would mis-navigate it.
-                            fix_array_structures(nested_dict, prop_schema['properties'])
-
-            # Also ensure array fields that are None get converted to empty arrays
-            def ensure_array_defaults(config_dict, schema_props, prefix=''):
-                """Recursively ensure array fields have defaults if None"""
-                for prop_key, prop_schema in schema_props.items():
-                    prop_type = prop_schema.get('type')
-
-                    if prop_type == 'array':
-                        if prefix:
-                            parent_parts = prefix.split('.')
-                            parent = config_dict
-                            for part in parent_parts:
-                                if isinstance(parent, dict) and part in parent:
-                                    parent = parent[part]
-                                else:
-                                    parent = None
-                                    break
-
-                            if parent is not None and isinstance(parent, dict):
-                                if prop_key not in parent or parent[prop_key] is None:
-                                    default = prop_schema.get('default', [])
-                                    parent[prop_key] = default if default else []
-                        else:
-                            if prop_key not in config_dict or config_dict[prop_key] is None:
-                                default = prop_schema.get('default', [])
-                                config_dict[prop_key] = default if default else []
-
-                    elif prop_type == 'object' and 'properties' in prop_schema:
-                        nested_prefix = f"{prefix}.{prop_key}" if prefix else prop_key
-                        if prefix:
-                            parent_parts = prefix.split('.')
-                            parent = config_dict
-                            for part in parent_parts:
-                                if isinstance(parent, dict) and part in parent:
-                                    parent = parent[part]
-                                else:
-                                    parent = None
-                                    break
-                            nested_dict = parent.get(prop_key) if parent is not None and isinstance(parent, dict) else None
-                        else:
-                            nested_dict = config_dict.get(prop_key)
-
-                        if nested_dict is None:
-                            if prefix:
-                                parent_parts = prefix.split('.')
-                                parent = config_dict
-                                for part in parent_parts:
-                                    if part not in parent:
-                                        parent[part] = {}
-                                    parent = parent[part]
-                                if prop_key not in parent:
-                                    parent[prop_key] = {}
-                                nested_dict = parent[prop_key]
-                            else:
-                                if prop_key not in config_dict:
-                                    config_dict[prop_key] = {}
-                                nested_dict = config_dict[prop_key]
-
-                        if isinstance(nested_dict, dict):
-                            # Pass no prefix: config_dict is already navigated.
-                            ensure_array_defaults(nested_dict, prop_schema['properties'])
-
+            # Before the booleans below: that walk replaces anything it
+            # expects to be a list and finds is not one.
             if schema and 'properties' in schema:
-                # First, fix any dict structures that should be arrays
-                # This must be called BEFORE validation to convert dicts with numeric keys to arrays
-                fix_array_structures(plugin_config, schema['properties'])
-                # Then, ensure None arrays get defaults
-                ensure_array_defaults(plugin_config, schema['properties'])
-                
-                # Debug: Log the structure after fixing
-                if 'feeds' in plugin_config and 'custom_feeds' in plugin_config.get('feeds', {}):
-                    custom_feeds = plugin_config['feeds']['custom_feeds']
-                    logger.debug(f"After fix_array_structures: custom_feeds type={type(custom_feeds)}, value={custom_feeds}")
-                
-                # Force fix for feeds.custom_feeds if it's still a dict (fallback)
-                if 'feeds' in plugin_config:
-                    feeds_config = plugin_config.get('feeds') or {}
-                    if feeds_config and 'custom_feeds' in feeds_config and isinstance(feeds_config['custom_feeds'], dict):
-                        custom_feeds_dict = feeds_config['custom_feeds']
-                        # Check if all keys are numeric
-                        keys = list(custom_feeds_dict.keys())
-                        if keys and all(str(k).isdigit() for k in keys):
-                            # Convert to array
-                            sorted_keys = sorted(keys, key=lambda x: int(str(x)))
-                            feeds_config['custom_feeds'] = [custom_feeds_dict[k] for k in sorted_keys]
-                            logger.info(f"Force-converted feeds.custom_feeds from dict to array: {len(feeds_config['custom_feeds'])} items")
+                coerce_array_shapes(plugin_config, schema['properties'],
+                                    short_lists_take_default=True)
 
             # Fix unchecked boolean checkboxes: HTML checkboxes don't submit values
             # when unchecked, so the existing config value (potentially True) persists.
@@ -2104,8 +1833,6 @@ def save_plugin_config():
             try:
                 api_v3.config_manager.save_raw_file_content('secrets', current_secrets)
             except PermissionError as e:
-                # Log the error with more details
-                import os
                 secrets_path = api_v3.config_manager.secrets_path
                 secrets_dir = os.path.dirname(secrets_path) if secrets_path else None
                 
@@ -2126,12 +1853,9 @@ def save_plugin_config():
                     f"Failed to save secrets configuration: Permission denied. Check file permissions on {secrets_path}",
                     status_code=500
                 )
-            except Exception as e:
-                # Log the error but don't fail the entire config save
-                import os
+            except Exception:
                 secrets_path = api_v3.config_manager.secrets_path
                 logger.error("Error saving secrets config for %s (path=%s)", plugin_id, secrets_path, exc_info=True)
-                # Return error response with more context
                 return error_response(
                     ErrorCode.CONFIG_SAVE_FAILED,
                     "Failed to save secrets configuration; see logs for details",
@@ -2177,8 +1901,7 @@ def save_plugin_config():
                                 plugin_instance.on_disable()
                     except Exception as lifecycle_error:
                         # Log the error but don't fail the save - config is already saved
-                        import logging
-                        logging.warning(f"Lifecycle method error for {plugin_id}: {lifecycle_error}", exc_info=True)
+                        logger.warning("Lifecycle method error for %s: %s", plugin_id, lifecycle_error, exc_info=True)
         except Exception as hook_err:
             # Do not fail the save if hook fails; just log
             logger.warning("on_config_change failed: %s", hook_err)
@@ -2226,48 +1949,9 @@ def _prepare_plugin_config_for_save(plugin_id, plugin_config, schema, schema_mgr
     Returns ``(regular_config, secrets_config, None)``, or
     ``(None, None, error_response)`` when validation fails.
     """
-    # JSON path: fix numeric-keyed dicts that should be arrays.
-    # JS dotToNested() converts feeds.custom_feeds.0.name → {'0': {name:...}}
-    # instead of [{name:...}]. The form-data path has fix_array_structures for this;
-    # mirror that logic here for JSON submissions.
+    # The form path has already done this, before its checkbox pass.
     if is_json and schema and 'properties' in schema:
-        def _fix_json_arrays(cfg, props):
-            for k, ps in props.items():
-                if not isinstance(cfg, dict) or k not in cfg:
-                    continue
-                pt = ps.get('type')
-                val = cfg[k]
-                if pt == 'array':
-                    items_schema = ps.get('items', {})
-                    item_type = items_schema.get('type')
-                    if isinstance(val, dict):
-                        keys = list(val.keys())
-                        if keys and all(str(x).isdigit() for x in keys):
-                            sorted_keys = sorted(keys, key=lambda x: int(str(x)))
-                            arr = [val[sk] for sk in sorted_keys]
-                            if item_type in ('integer', 'number'):
-                                converted = []
-                                for v in arr:
-                                    if isinstance(v, str):
-                                        try:
-                                            converted.append(int(v) if item_type == 'integer' else float(v))
-                                        except (ValueError, TypeError, OverflowError):
-                                            converted.append(v)
-                                    else:
-                                        converted.append(v)
-                                arr = converted
-                            cfg[k] = arr
-                        elif not keys:
-                            cfg[k] = []
-                    # Recurse into each element when items are objects with properties,
-                    # covering both freshly-converted and already-list values.
-                    if item_type == 'object' and 'properties' in items_schema:
-                        for elem in (cfg[k] if isinstance(cfg[k], list) else []):
-                            if isinstance(elem, dict):
-                                _fix_json_arrays(elem, items_schema['properties'])
-                elif pt == 'object' and 'properties' in ps and isinstance(val, dict):
-                    _fix_json_arrays(val, ps['properties'])
-        _fix_json_arrays(plugin_config, schema['properties'])
+        coerce_array_shapes(plugin_config, schema['properties'])
 
     # PRE-PROCESSING: Preserve 'enabled' state if not in request
     # This prevents overwriting the enabled state when saving config from a form that doesn't include the toggle
@@ -2276,7 +1960,6 @@ def _prepare_plugin_config_for_save(plugin_id, plugin_config, schema, schema_mgr
             current_config = api_v3.config_manager.load_config()
             if plugin_id in current_config and 'enabled' in current_config[plugin_id]:
                 plugin_config['enabled'] = current_config[plugin_id]['enabled']
-                # logger.debug(f"Preserving enabled state for {plugin_id}: {plugin_config['enabled']}")
             elif api_v3.plugin_manager:
                 # Fallback to plugin instance if config doesn't have it
                 plugin_instance = api_v3.plugin_manager.get_plugin(plugin_id)
@@ -2311,9 +1994,8 @@ def _prepare_plugin_config_for_save(plugin_id, plugin_config, schema, schema_mgr
         defaults = schema_mgr.generate_default_config(plugin_id, use_cache=True)
         plugin_config = prepare_plugin_config(plugin_config, schema, defaults)
 
-    # After merging defaults, replace any None array values with their schema defaults.
-    # merge_with_defaults gives user config higher priority, so a None submitted by
-    # the client can survive the merge — this pass cleans those up.
+    # The defaults merge replaces a None only where the schema has a default,
+    # so an array the client sent as None, or left out, can still be one here.
     def _fix_none_arrays(cfg, props):
         for k, pschema in props.items():
             if pschema.get('type') == 'array':
@@ -2371,14 +2053,8 @@ def _prepare_plugin_config_for_save(plugin_id, plugin_config, schema, schema_mgr
                 # Check integer first (more specific than number)
                 if 'integer' in prop_type:
                     if isinstance(value, str):
-                        value_stripped = value.strip()
-                        if value_stripped == '':
-                            # Empty string with null allowed - already handled above, but double-check
-                            if 'null' in prop_type:
-                                normalized[key] = None
-                                continue
                         try:
-                            normalized[key] = int(value_stripped)
+                            normalized[key] = int(value.strip())
                             continue
                         except (ValueError, TypeError, OverflowError):
                             pass
@@ -2389,14 +2065,8 @@ def _prepare_plugin_config_for_save(plugin_id, plugin_config, schema, schema_mgr
                 # Check number (less specific, but handles floats)
                 if 'number' in prop_type:
                     if isinstance(value, str):
-                        value_stripped = value.strip()
-                        if value_stripped == '':
-                            # Empty string with null allowed - already handled above, but double-check
-                            if 'null' in prop_type:
-                                normalized[key] = None
-                                continue
                         try:
-                            normalized[key] = float(value_stripped)
+                            normalized[key] = float(value.strip())
                             continue
                         except (ValueError, TypeError, OverflowError):
                             pass
@@ -2410,21 +2080,7 @@ def _prepare_plugin_config_for_save(plugin_id, plugin_config, schema, schema_mgr
                         normalized[key] = value.strip().lower() in ('true', '1', 'on', 'yes')
                         continue
 
-                # If no conversion worked and null is allowed, try to set to None
-                # This handles cases where the value is an empty string or can't be converted
-                if 'null' in prop_type:
-                    if isinstance(value, str):
-                        value_stripped = value.strip()
-                        if value_stripped == '' or value_stripped.lower() in ('null', 'none', 'undefined'):
-                            normalized[key] = None
-                            continue
-                    # If it's already None, keep it
-                    if value is None:
-                        normalized[key] = None
-                        continue
-
-                # If no conversion worked, keep original value (will fail validation, but that's expected)
-                # Log a warning for debugging
+                # Nothing converted: keep the value for validation to report.
                 logger.warning(f"Could not normalize field {field_path}: value={repr(value)}, type={type(value)}, schema_type={prop_type}")
                 normalized[key] = value
                 continue
@@ -2550,37 +2206,24 @@ def _prepare_plugin_config_for_save(plugin_id, plugin_config, schema, schema_mgr
         enhanced_schema_for_filtering = _enhance_schema_with_core_properties(schema)
         plugin_config = _filter_config_by_schema(plugin_config, enhanced_schema_for_filtering)
 
-    # Debug logging for union type fields (temporary)
-    if 'rotation_settings' in plugin_config and 'random_seed' in plugin_config.get('rotation_settings', {}):
-        seed_value = plugin_config['rotation_settings']['random_seed']
-        logger.debug(f"After normalization, random_seed value: {repr(seed_value)}, type: {type(seed_value)}")
-
-    # Validate configuration against schema before saving
+    # A uniqueItems array can arrive with a repeat -- the form merges onto
+    # the stored list, so a stock symbol already saved and submitted again
+    # appears twice -- and validation would refuse the whole save for it.
     if schema:
-        # Log what we're validating for debugging
-        logger.info(f"Validating config for {plugin_id}")
-        # Only the shape. plugin_config still holds the submitted secret
-        # values at this point -- separate_secrets does not run until
-        # below -- so logging it wrote live credentials to the journal.
-        logger.info(f"Config keys being validated: {list(plugin_config.keys())}")
-
-        # Schema keys including the injected core properties, for the error
-        enhanced_schema = _enhance_schema_with_core_properties(schema)
+        dedup_unique_arrays(plugin_config, schema)
 
+    if schema:
         is_valid, validation_errors = schema_mgr.validate_config_against_schema(
             plugin_config, schema, plugin_id
         )
         if not is_valid:
-            # Log validation errors for debugging
-            logger.error(f"Config validation failed for {plugin_id}")
-            logger.error(f"Validation errors: {validation_errors}")
-            # Keys only, for the same reason as above.
-            logger.error(f"Config keys that failed: {list(plugin_config.keys())}")
-            logger.error(f"Schema properties: {list(enhanced_schema.get('properties', {}).keys())}")
-
-            # Also print to console for immediate visibility
-            logger.warning("Config validation failed for plugin (see debug logs)")
-
+            # Schema keys including the injected core properties, for the error
+            enhanced_schema = _enhance_schema_with_core_properties(schema)
+            # Keys, never values: plugin_config still holds the submitted
+            # secrets here (separate_secrets runs below), and logging it wrote
+            # live credentials to the journal.
+            logger.warning("Config validation failed for %s: %s (config keys: %s)",
+                           plugin_id, validation_errors, list(plugin_config.keys()))
             return None, None, error_response(
                 ErrorCode.CONFIG_VALIDATION_FAILED,
                 'Configuration validation failed',
@@ -2704,8 +2347,13 @@ def reset_plugin_config():
         # Replace all secrets with defaults
         current_secrets[plugin_id] = default_secrets
 
-    # Save updated configs
-    api_v3.config_manager.save_config(current_config)
+    success, error_msg = _pkg._save_config_atomic(api_v3.config_manager, current_config, create_backup=True)
+    if not success:
+        return error_response(
+            ErrorCode.CONFIG_SAVE_FAILED,
+            f"Failed to save configuration: {error_msg}",
+            status_code=500
+        )
     if default_secrets or not preserve_secrets:
         api_v3.config_manager.save_raw_file_content('secrets', current_secrets)
 
@@ -2715,7 +2363,8 @@ def reset_plugin_config():
             plugin_instance = api_v3.plugin_manager.get_plugin(plugin_id)
             if plugin_instance:
                 merged_config = api_v3.config_manager.load_config()
-                plugin_full_config = merged_config.get(plugin_id, {})
+                plugin_full_config = _pkg._prepared_plugin_config(
+                    plugin_id, merged_config.get(plugin_id, {}))
                 if hasattr(plugin_instance, 'on_config_change'):
                     plugin_instance.on_config_change(plugin_full_config)
     except Exception as hook_err:
@@ -2761,13 +2410,8 @@ def execute_plugin_action():
         if plugin_id is None:
             return jsonify({'status': 'error', 'message': 'Invalid plugin_id'}), 400
 
-        # Get plugin directory
-        if api_v3.plugin_manager:
-            plugin_dir = api_v3.plugin_manager.get_plugin_directory(plugin_id)
-        else:
-            plugin_dir = PROJECT_ROOT / 'plugins' / plugin_id
-
-        if not plugin_dir or not Path(plugin_dir).exists():
+        plugin_dir = _plugin_directory(plugin_id)
+        if not plugin_dir:
             return jsonify({'status': 'error', 'message': 'Plugin not found'}), 404
 
         # Load manifest to get action definition
@@ -2989,6 +2633,10 @@ sys.exit(proc.returncode)
                                     'message': 'Could not generate authorization URL'
                                 }), 400
                         except Exception as e:
+                            # Not a copy of the blueprint handler: without it, a
+                            # TimeoutExpired from the plugin's script would reach
+                            # this route's own `except subprocess.TimeoutExpired`
+                            # and be answered as a 408 "Action timed out".
                             logger.error("Error executing action step 1", exc_info=True)
                             return jsonify({
                                 'status': 'error',
@@ -3121,7 +2769,7 @@ def upload_plugin_asset():
         if total_size + file_size > max_total_size:
             return jsonify({
                 'status': 'error',
-                'message': f'Upload would exceed 50MB total storage limit'
+                'message': 'Upload would exceed 50MB total storage limit'
             }), 400
 
         # Validate file is actually an image (check magic bytes)
@@ -3222,13 +2870,8 @@ def serve_plugin_static(plugin_id, file_path):
     if not safe_parts:
         return jsonify({'status': 'error', 'message': 'Invalid file path'}), 400
 
-    # Get plugin directory
-    if api_v3.plugin_manager:
-        plugin_dir = api_v3.plugin_manager.get_plugin_directory(safe_plugin_id)
-    else:
-        plugin_dir = PROJECT_ROOT / 'plugins' / safe_plugin_id
-
-    if not plugin_dir or not Path(plugin_dir).exists():
+    plugin_dir = _plugin_directory(safe_plugin_id)
+    if not plugin_dir:
         return jsonify({'status': 'error', 'message': 'Plugin not found'}), 404
 
     # Containment is still checked after resolving: name validation cannot
@@ -3300,14 +2943,8 @@ def upload_calendar_credentials():
             'message': 'File does not appear to be a valid Google OAuth credentials file'
         }), 400
 
-    # Get plugin directory
-    plugin_id = 'calendar'
-    if api_v3.plugin_manager:
-        plugin_dir = api_v3.plugin_manager.get_plugin_directory(plugin_id)
-    else:
-        plugin_dir = PROJECT_ROOT / 'plugins' / plugin_id
-
-    if not plugin_dir or not Path(plugin_dir).exists():
+    plugin_dir = _plugin_directory('calendar')
+    if not plugin_dir:
         return jsonify({'status': 'error', 'message': 'Plugin not found'}), 404
 
     # Save file to plugin directory
@@ -3316,7 +2953,6 @@ def upload_calendar_credentials():
     # Backup existing file if it exists
     if credentials_path.exists():
         backup_path = Path(plugin_dir) / f'credentials.json.backup.{int(_pkg.time.time())}'
-        import shutil
         shutil.copy2(credentials_path, backup_path)
         _prune_credential_backups(Path(plugin_dir))
 
diff --git a/web_interface/blueprints/api_v3/starlark.py b/web_interface/blueprints/api_v3/starlark.py
index 08d592c7..cdc21fa4 100644
--- a/web_interface/blueprints/api_v3/starlark.py
+++ b/web_interface/blueprints/api_v3/starlark.py
@@ -1,7 +1,7 @@
 """Starlark / Tronbyte app management routes.
 
-Routes decorate the shared `api_v3` Blueprint from ._common, so their
-endpoint names are unchanged by living here.
+Routes decorate the shared `api_v3` Blueprint from the package `__init__`,
+so their endpoint names are unchanged by living here.
 """
 import signal
 import threading
@@ -333,7 +333,6 @@ def uninstall_starlark_app(app_id):
         else:
             # Standalone: remove app dir and manifest entry. app_dir is the
             # path _validate_starlark_app_path checked, not a fresh join.
-            import shutil
             if app_dir.exists():
                 shutil.rmtree(app_dir)
             with _starlark_manifest_lock():
@@ -716,7 +715,6 @@ def install_from_tronbyte_repository():
                     success = _install_star_file(app_id, temp_path, install_metadata, assets_dir=temp_assets_dir)
             finally:
                 # Clean up temp assets directory
-                import shutil
                 try:
                     shutil.rmtree(temp_assets_dir)
                 except OSError:
diff --git a/web_interface/blueprints/api_v3/system.py b/web_interface/blueprints/api_v3/system.py
index 405c425f..ab3403a2 100644
--- a/web_interface/blueprints/api_v3/system.py
+++ b/web_interface/blueprints/api_v3/system.py
@@ -1,7 +1,7 @@
 """Service control, updates, versions and system status.
 
-Routes decorate the shared `api_v3` Blueprint from ._common, so their
-endpoint names are unchanged by living here.
+Routes decorate the shared `api_v3` Blueprint from the package `__init__`,
+so their endpoint names are unchanged by living here.
 """
 from web_interface.blueprints.api_v3 import (
     Any, Dict, PROJECT_ROOT, Path, _GIT, _UPDATE_CHECK_TTL,
@@ -14,6 +14,8 @@ from web_interface.blueprints.api_v3 import (
 )
 import threading
 
+from web_interface.cache import get_cached, set_cached
+from web_interface.system_metrics import collect_system_metrics, format_uptime
 import web_interface.blueprints.api_v3 as _pkg
 # Read through the module rather than bound by value: tests patch these
 # as module attributes, and a value binding would not see the patch.
@@ -23,91 +25,25 @@ import web_interface.blueprints.api_v3 as _pkg
 
 @api_v3.route('/system/status', methods=['GET'])
 def get_system_status():
-    """Get system status"""
-    # Check cache first (10 second TTL for system status)
-    try:
-        from web_interface.cache import get_cached, set_cached
-        cached_result = get_cached('system_status', ttl_seconds=10)
-        if cached_result is not None:
-            return jsonify({'status': 'success', 'data': cached_result})
-    except ImportError:
-        # Cache not available, continue without caching
-        get_cached = None
-        set_cached = None
+    """CPU, memory, disk, temperature and uptime, plus the display service state.
 
-    # Import psutil for system monitoring
-    try:
-        import psutil
-    except ImportError:
-        # Fallback if psutil not available
-        return jsonify({
-            'status': 'error',
-            'message': 'psutil not available for system monitoring'
-        }), 503
+    ``data`` carries every key of system_metrics.collect_system_metrics() --
+    the numbers the live status stream sends -- and ``timestamp``, ``uptime``
+    (formatted) and ``service_active``. A metric that cannot be read is null.
+    Cached for 10 seconds.
+    """
+    cached_result = get_cached('system_status', ttl_seconds=10)
+    if cached_result is not None:
+        return jsonify({'status': 'success', 'data': cached_result})
 
-    # Get system metrics using psutil
-    cpu_percent = psutil.cpu_percent(interval=0.1)  # Short interval for responsiveness
-    memory = psutil.virtual_memory()
-    memory_percent = memory.percent
-    disk = psutil.disk_usage('/')
-    disk_percent = disk.percent
-
-    # Calculate uptime
-    boot_time = psutil.boot_time()
-    uptime_seconds = _pkg.time.time() - boot_time
-    uptime_hours = uptime_seconds / 3600
-    uptime_days = uptime_hours / 24
-
-    # Format uptime string
-    if uptime_days >= 1:
-        uptime_str = f"{int(uptime_days)}d {int(uptime_hours % 24)}h"
-    elif uptime_hours >= 1:
-        uptime_str = f"{int(uptime_hours)}h {int((uptime_seconds % 3600) / 60)}m"
-    else:
-        uptime_str = f"{int(uptime_seconds / 60)}m"
-
-    # Get CPU temperature (Raspberry Pi)
-    cpu_temp = None
-    try:
-        temp_file = '/sys/class/thermal/thermal_zone0/temp'
-        if os.path.exists(temp_file):
-            with open(temp_file, 'r') as f:
-                temp_millidegrees = int(f.read().strip())
-                cpu_temp = temp_millidegrees / 1000.0  # Convert to Celsius
-    except (IOError, ValueError, OSError):
-        # Temperature sensor not available or error reading
-        cpu_temp = None
-
-    # Get display service status
-    service_status = _get_display_service_status()
-
-    status = {
-        'timestamp': _pkg.time.time(),
-        'uptime': uptime_str,
-        'uptime_seconds': int(uptime_seconds),
-        'service_active': service_status.get('active', False),
-        'cpu_percent': round(cpu_percent, 1),
-        'memory_used_percent': round(memory_percent, 1),
-        'memory_total_mb': round(memory.total / (1024 * 1024), 1),
-        'memory_used_mb': round(memory.used / (1024 * 1024), 1),
-        # MemAvailable, not total-minus-used: it accounts for reclaimable
-        # page cache, so it is what actually predicts memory trouble. A
-        # board can read 70% "used" and be fine, or read the same and be
-        # about to fail fork(), and only this number tells them apart.
-        'memory_available_mb': round(memory.available / (1024 * 1024), 1),
-        'cpu_temp': round(cpu_temp, 1) if cpu_temp is not None else None,
-        'disk_used_percent': round(disk_percent, 1),
-        'disk_total_gb': round(disk.total / (1024 * 1024 * 1024), 1),
-        'disk_used_gb': round(disk.used / (1024 * 1024 * 1024), 1)
-    }
-
-    # Cache the result if available
-    if set_cached:
-        try:
-            set_cached('system_status', status, ttl_seconds=10)
-        except Exception:
-            pass  # Cache write failed, but continue
+    # A short blocking sample: this may be the first cpu_percent call in the
+    # process, and a non-blocking first call has nothing to measure against.
+    status = collect_system_metrics(cpu_interval=0.1)
+    status['timestamp'] = _pkg.time.time()
+    status['uptime'] = format_uptime(status['uptime_seconds'])
+    status['service_active'] = _get_display_service_status().get('active', False)
 
+    set_cached('system_status', status, ttl_seconds=10)
     return jsonify({'status': 'success', 'data': status})
 @api_v3.route('/system/version', methods=['GET'])
 def get_system_version():
diff --git a/web_interface/blueprints/api_v3/wifi.py b/web_interface/blueprints/api_v3/wifi.py
index 7700ea82..f504a8a8 100644
--- a/web_interface/blueprints/api_v3/wifi.py
+++ b/web_interface/blueprints/api_v3/wifi.py
@@ -1,7 +1,7 @@
 """Wi-Fi scanning, connection and status routes.
 
-Routes decorate the shared `api_v3` Blueprint from ._common, so their
-endpoint names are unchanged by living here.
+Routes decorate the shared `api_v3` Blueprint from the package `__init__`,
+so their endpoint names are unchanged by living here.
 """
 import threading
 import time
diff --git a/web_interface/blueprints/pages_v3.py b/web_interface/blueprints/pages_v3.py
index e2b82c3d..3f55bc4c 100644
--- a/web_interface/blueprints/pages_v3.py
+++ b/web_interface/blueprints/pages_v3.py
@@ -1,6 +1,5 @@
 from flask import Blueprint, Response, render_template, jsonify, url_for
 from jinja2 import TemplateNotFound
-from markupsafe import escape
 from html.parser import HTMLParser
 import json
 import logging
@@ -163,41 +162,13 @@ def index():
 
 @pages_v3.route('/partials/<partial_name>')
 def load_partial(partial_name):
-    """Load HTMX partials dynamically"""
+    """One tab's HTML for HTMX, by the names in _PARTIAL_LOADERS; 404 otherwise."""
+    loader = _PARTIAL_LOADERS.get(partial_name)
+    if loader is None:
+        return "Partial not found", 404
     try:
-        # Map partial names to specific data loading
-        if partial_name == 'overview':
-            return _load_overview_partial()
-        elif partial_name == 'general':
-            return _load_general_partial()
-        elif partial_name == 'display':
-            return _load_display_partial()
-        elif partial_name == 'durations':
-            return _load_durations_partial()
-        elif partial_name == 'schedule':
-            return _load_schedule_partial()
-        elif partial_name == 'plugins':
-            return _load_plugins_partial()
-        elif partial_name == 'fonts':
-            return _load_fonts_partial()
-        elif partial_name == 'logs':
-            return _load_logs_partial()
-        elif partial_name == 'raw-json':
-            return _load_raw_json_partial()
-        elif partial_name == 'backup-restore':
-            return _load_backup_restore_partial()
-        elif partial_name == 'wifi':
-            return _load_wifi_partial()
-        elif partial_name == 'cache':
-            return _load_cache_partial()
-        elif partial_name == 'operation-history':
-            return _load_operation_history_partial()
-        elif partial_name == 'tools':
-            return _load_tools_partial()
-        else:
-            return "Partial not found", 404
-
-    except Exception as e:
+        return loader()
+    except Exception:
         logger.error("Error loading partial %s", partial_name, exc_info=True)
         return "Error loading partial", 500
 
@@ -297,19 +268,7 @@ def serve_plugin_web_ui(plugin_id, filename):
         return 'Plugin manager not available', 503, {'Content-Type': 'text/plain'}
 
     try:
-        _plugins_base = Path(pages_v3.plugin_manager.plugins_dir).resolve()
-
-        _plugin_dir = resolve_under(_plugins_base, safe_id)
-        if _plugin_dir is None:
-            return 'Forbidden', 403, {'Content-Type': 'text/plain'}
-
-        # Mirror PluginManager's ledmatrix- prefix fallback.
-        if not _plugin_dir.exists():
-            _alt = resolve_under(_plugins_base, f'ledmatrix-{safe_id}')
-            if _alt is not None:
-                _plugin_dir = _alt
-
-        web_ui_path = resolve_under(_plugin_dir / 'web_ui', safe_fn)
+        web_ui_path = resolve_under(_plugin_dir_for(safe_id) / 'web_ui', safe_fn)
         if web_ui_path is None:
             return 'Forbidden', 403, {'Content-Type': 'text/plain'}
 
@@ -362,10 +321,11 @@ def serve_plugin_web_ui(plugin_id, filename):
 
 
 def _plugin_dir_for(safe_id):
-    """Resolve a sanitised plugin id to its directory, or None.
+    """A sanitised plugin id's directory, which may not exist.
 
-    Mirrors serve_plugin_web_ui: containment-guarded against the configured
-    plugins directory, with PluginManager's ``ledmatrix-`` prefix fallback.
+    Contained under the configured plugins directory, with PluginManager's
+    ``ledmatrix-`` prefix fallback. Raises ValueError for an id that would
+    leave it; the routes answer that with a 403.
     """
     plugins_base = Path(pages_v3.plugin_manager.plugins_dir).resolve()
     plugin_dir = resolve_under(plugins_base, safe_id)
@@ -479,45 +439,33 @@ def serve_plugin_widget(plugin_id, widget_name):
 
 def _load_overview_partial():
     """Load overview partial with system stats"""
-    try:
-        if pages_v3.config_manager:
-            main_config = pages_v3.config_manager.load_config()
-            # This would be populated with real system stats via SSE
-            return render_template('v3/partials/overview.html',
-                                 main_config=main_config)
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+    if pages_v3.config_manager:
+        main_config = pages_v3.config_manager.load_config()
+        # This would be populated with real system stats via SSE
+        return render_template('v3/partials/overview.html',
+                             main_config=main_config)
 
 def _load_general_partial():
     """Load general settings partial"""
-    try:
-        if pages_v3.config_manager:
-            main_config = pages_v3.config_manager.load_config()
-            try:
-                from web_interface.auto_update import describe_status
-                auto_update_status = describe_status(main_config)
-            except Exception:
-                logger.debug("Could not read auto-update status", exc_info=True)
-                auto_update_status = None
-            return render_template('v3/partials/general.html',
-                                 main_config=main_config,
-                                 auto_update_status=auto_update_status)
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+    if pages_v3.config_manager:
+        main_config = pages_v3.config_manager.load_config()
+        try:
+            from web_interface.auto_update import describe_status
+            auto_update_status = describe_status(main_config)
+        except Exception:
+            logger.debug("Could not read auto-update status", exc_info=True)
+            auto_update_status = None
+        return render_template('v3/partials/general.html',
+                             main_config=main_config,
+                             auto_update_status=auto_update_status)
 
 def _load_display_partial():
     """Load display settings partial"""
-    try:
-        if pages_v3.config_manager:
-            main_config = pages_v3.config_manager.load_config()
-            return render_template('v3/partials/display.html',
-                                 main_config=main_config,
-                                 is_pi5=is_raspberry_pi_5())
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+    if pages_v3.config_manager:
+        main_config = pages_v3.config_manager.load_config()
+        return render_template('v3/partials/display.html',
+                             main_config=main_config,
+                             is_pi5=is_raspberry_pi_5())
 
 def _plugin_default_duration(plugin_id, plugin_config):
     """Seconds a plugin shows each screen when the Rotation page sets none.
@@ -553,199 +501,168 @@ def _load_durations_partial():
     value overrides the plugin (see DisplayController._get_display_duration).
     Pre-filling every mode would pin them all on the first save.
     """
-    try:
-        if pages_v3.config_manager:
-            main_config = pages_v3.config_manager.load_config()
-            duration_groups = []
-            covered_keys = set()
-            if pages_v3.plugin_manager:
-                try:
-                    pages_v3.plugin_manager.discover_plugins()
-                    saved = (main_config.get('display', {}) or {}).get('display_durations', {}) or {}
-                    infos = sorted(pages_v3.plugin_manager.get_all_plugin_info(),
-                                   key=lambda i: (i.get('name') or i.get('id') or '').lower())
-                    for info in infos:
-                        pid = info.get('id')
-                        if not pid or not (main_config.get(pid, {}) or {}).get('enabled', False):
-                            continue
-                        modes = pages_v3.plugin_manager.get_plugin_display_modes(pid) or [pid]
-                        covered_keys.update(modes)
-                        default = _plugin_default_duration(pid, main_config.get(pid, {}) or {})
-                        duration_groups.append({
-                            'plugin_id': pid,
-                            'plugin_name': info.get('name') or pid,
-                            'modes': [{'key': m, 'value': saved.get(m, ''), 'default': default}
-                                      for m in modes],
-                        })
-                    # Saved keys not owned by any enabled plugin (disabled or
-                    # uninstalled plugins) stay visible rather than vanishing.
-                    leftovers = [{'key': k, 'value': v} for k, v in saved.items()
-                                 if k not in covered_keys]
-                    if leftovers:
-                        duration_groups.append({
-                            'plugin_id': '',
-                            'plugin_name': 'Other saved entries',
-                            'modes': leftovers,
-                        })
-                except Exception:
-                    logger.warning("durations: could not enumerate plugin modes", exc_info=True)
-            return render_template('v3/partials/durations.html',
-                                 main_config=main_config,
-                                 duration_groups=duration_groups)
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+    if pages_v3.config_manager:
+        main_config = pages_v3.config_manager.load_config()
+        duration_groups = []
+        covered_keys = set()
+        if pages_v3.plugin_manager:
+            try:
+                pages_v3.plugin_manager.discover_plugins()
+                saved = (main_config.get('display', {}) or {}).get('display_durations', {}) or {}
+                infos = sorted(pages_v3.plugin_manager.get_all_plugin_info(),
+                               key=lambda i: (i.get('name') or i.get('id') or '').lower())
+                for info in infos:
+                    pid = info.get('id')
+                    if not pid or not (main_config.get(pid, {}) or {}).get('enabled', False):
+                        continue
+                    modes = pages_v3.plugin_manager.get_plugin_display_modes(pid) or [pid]
+                    covered_keys.update(modes)
+                    default = _plugin_default_duration(pid, main_config.get(pid, {}) or {})
+                    duration_groups.append({
+                        'plugin_id': pid,
+                        'plugin_name': info.get('name') or pid,
+                        'modes': [{'key': m, 'value': saved.get(m, ''), 'default': default}
+                                  for m in modes],
+                    })
+                # Saved keys not owned by any enabled plugin (disabled or
+                # uninstalled plugins) stay visible rather than vanishing.
+                leftovers = [{'key': k, 'value': v} for k, v in saved.items()
+                             if k not in covered_keys]
+                if leftovers:
+                    duration_groups.append({
+                        'plugin_id': '',
+                        'plugin_name': 'Other saved entries',
+                        'modes': leftovers,
+                    })
+            except Exception:
+                logger.warning("durations: could not enumerate plugin modes", exc_info=True)
+        return render_template('v3/partials/durations.html',
+                             main_config=main_config,
+                             duration_groups=duration_groups)
 
 def _load_schedule_partial():
     """Load schedule settings partial"""
-    try:
-        if pages_v3.config_manager:
-            main_config = pages_v3.config_manager.load_config()
-            schedule_config = main_config.get('schedule', {})
-            dim_schedule_config = main_config.get('dim_schedule', {})
-            # Get normal brightness for display in dim schedule UI
-            normal_brightness = main_config.get('display', {}).get('hardware', {}).get('brightness', 90)
-            return render_template('v3/partials/schedule.html',
-                                 schedule_config=schedule_config,
-                                 dim_schedule_config=dim_schedule_config,
-                                 normal_brightness=normal_brightness)
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+    if pages_v3.config_manager:
+        main_config = pages_v3.config_manager.load_config()
+        schedule_config = main_config.get('schedule', {})
+        dim_schedule_config = main_config.get('dim_schedule', {})
+        # Get normal brightness for display in dim schedule UI
+        normal_brightness = main_config.get('display', {}).get('hardware', {}).get('brightness', 90)
+        return render_template('v3/partials/schedule.html',
+                             schedule_config=schedule_config,
+                             dim_schedule_config=dim_schedule_config,
+                             normal_brightness=normal_brightness)
 
 
 def _load_plugins_partial():
     """Load plugins management partial"""
-    try:
-        import json
-        from pathlib import Path
-        
-        # Load plugin data from the plugin system
-        plugins_data = []
+    # Load plugin data from the plugin system
+    plugins_data = []
 
-        # Get installed plugins if managers are available
-        if pages_v3.plugin_manager and pages_v3.plugin_store_manager:
-            try:
-                # Get all installed plugin info
-                all_plugin_info = pages_v3.plugin_manager.get_all_plugin_info()
+    # Get installed plugins if managers are available
+    if pages_v3.plugin_manager and pages_v3.plugin_store_manager:
+        try:
+            # Get all installed plugin info
+            all_plugin_info = pages_v3.plugin_manager.get_all_plugin_info()
 
-                # Load config once before the loop (not per-plugin)
-                full_config = pages_v3.config_manager.load_config() if pages_v3.config_manager else {}
+            # Load config once before the loop (not per-plugin)
+            full_config = pages_v3.config_manager.load_config() if pages_v3.config_manager else {}
 
-                # Format for the web interface
-                for plugin_info in all_plugin_info:
-                    plugin_id = plugin_info.get('id')
+            # Format for the web interface
+            for plugin_info in all_plugin_info:
+                plugin_id = plugin_info.get('id')
 
-                    # Re-read manifest from disk to ensure we have the latest metadata
-                    manifest_path = Path(pages_v3.plugin_manager.plugins_dir) / plugin_id / "manifest.json"
-                    if manifest_path.exists():
-                        try:
-                            with open(manifest_path, 'r', encoding='utf-8') as f:
-                                fresh_manifest = json.load(f)
-                            # Update plugin_info with fresh manifest data
-                            plugin_info.update(fresh_manifest)
-                        except Exception as e:
-                            # If we can't read the fresh manifest, use the cached one
-                            logger.warning("Could not read fresh manifest for plugin: %s", plugin_id)
+                # Re-read manifest from disk to ensure we have the latest metadata
+                manifest_path = Path(pages_v3.plugin_manager.plugins_dir) / plugin_id / "manifest.json"
+                if manifest_path.exists():
+                    try:
+                        with open(manifest_path, 'r', encoding='utf-8') as f:
+                            fresh_manifest = json.load(f)
+                        # Update plugin_info with fresh manifest data
+                        plugin_info.update(fresh_manifest)
+                    except Exception:
+                        # If we can't read the fresh manifest, use the cached one
+                        logger.warning("Could not read fresh manifest for plugin: %s", plugin_id)
 
-                    # Get enabled status from config (source of truth)
-                    # Read from config file first, fall back to plugin instance if config doesn't have the key
-                    enabled = None
-                    if pages_v3.config_manager:
-                        plugin_config = full_config.get(plugin_id, {})
-                        # Check if 'enabled' key exists in config (even if False)
-                        if 'enabled' in plugin_config:
-                            enabled = bool(plugin_config['enabled'])
-                    
-                    # Fallback to plugin instance if config doesn't have enabled key
-                    if enabled is None:
-                        plugin_instance = pages_v3.plugin_manager.get_plugin(plugin_id)
-                        if plugin_instance:
-                            enabled = plugin_instance.enabled
-                        else:
-                            # Default to True if no config key and plugin not loaded (matches BasePlugin default)
-                            enabled = True
+                # Get enabled status from config (source of truth)
+                # Read from config file first, fall back to plugin instance if config doesn't have the key
+                enabled = None
+                if pages_v3.config_manager:
+                    plugin_config = full_config.get(plugin_id, {})
+                    # Check if 'enabled' key exists in config (even if False)
+                    if 'enabled' in plugin_config:
+                        enabled = bool(plugin_config['enabled'])
+                
+                # Fallback to plugin instance if config doesn't have enabled key
+                if enabled is None:
+                    plugin_instance = pages_v3.plugin_manager.get_plugin(plugin_id)
+                    if plugin_instance:
+                        enabled = plugin_instance.enabled
+                    else:
+                        # Default to True if no config key and plugin not loaded (matches BasePlugin default)
+                        enabled = True
 
-                    # Get verified status from store registry (no GitHub API calls needed)
-                    store_info = pages_v3.plugin_store_manager.get_registry_info(plugin_id)
-                    verified = store_info.get('verified', False) if store_info else False
+                # Get verified status from store registry (no GitHub API calls needed)
+                store_info = pages_v3.plugin_store_manager.get_registry_info(plugin_id)
+                verified = store_info.get('verified', False) if store_info else False
 
-                    last_updated = plugin_info.get('last_updated')
-                    last_commit = plugin_info.get('last_commit') or plugin_info.get('last_commit_sha')
-                    branch = plugin_info.get('branch')
+                last_updated = plugin_info.get('last_updated')
+                last_commit = plugin_info.get('last_commit') or plugin_info.get('last_commit_sha')
+                branch = plugin_info.get('branch')
 
-                    if store_info:
-                        last_updated = last_updated or store_info.get('last_updated') or store_info.get('last_updated_iso')
-                        last_commit = last_commit or store_info.get('last_commit') or store_info.get('last_commit_sha')
-                        branch = branch or store_info.get('branch') or store_info.get('default_branch')
+                if store_info:
+                    last_updated = last_updated or store_info.get('last_updated') or store_info.get('last_updated_iso')
+                    last_commit = last_commit or store_info.get('last_commit') or store_info.get('last_commit_sha')
+                    branch = branch or store_info.get('branch') or store_info.get('default_branch')
 
-                    plugins_data.append({
-                        'id': plugin_id,
-                        'name': plugin_info.get('name', plugin_id),
-                        'author': plugin_info.get('author', 'Unknown'),
-                        'category': plugin_info.get('category', 'General'),
-                        'description': plugin_info.get('description', 'No description available'),
-                        'tags': plugin_info.get('tags', []),
-                        'enabled': enabled,
-                        'verified': verified,
-                        'loaded': plugin_info.get('loaded', False),
-                        'last_updated': last_updated,
-                        'last_commit': last_commit,
-                        'branch': branch
-                    })
-            except Exception as e:
-                logger.error("Error loading plugin data", exc_info=True)
+                plugins_data.append({
+                    'id': plugin_id,
+                    'name': plugin_info.get('name', plugin_id),
+                    'author': plugin_info.get('author', 'Unknown'),
+                    'category': plugin_info.get('category', 'General'),
+                    'description': plugin_info.get('description', 'No description available'),
+                    'tags': plugin_info.get('tags', []),
+                    'enabled': enabled,
+                    'verified': verified,
+                    'loaded': plugin_info.get('loaded', False),
+                    'last_updated': last_updated,
+                    'last_commit': last_commit,
+                    'branch': branch
+                })
+        except Exception:
+            logger.error("Error loading plugin data", exc_info=True)
 
-        return render_template('v3/partials/plugins.html',
-                             plugins=plugins_data)
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+    return render_template('v3/partials/plugins.html',
+                         plugins=plugins_data)
 
 def _load_fonts_partial():
     """Load fonts management partial"""
-    try:
-        # This would load font data from the font system
-        fonts_data = {}  # Placeholder for font data
-        return render_template('v3/partials/fonts.html',
-                             fonts=fonts_data)
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+    # This would load font data from the font system
+    fonts_data = {}  # Placeholder for font data
+    return render_template('v3/partials/fonts.html',
+                         fonts=fonts_data)
 
 def _load_logs_partial():
     """Load logs viewer partial"""
-    try:
-        return render_template('v3/partials/logs.html')
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+    return render_template('v3/partials/logs.html')
 
 def _load_raw_json_partial():
     """Load raw JSON editor partial"""
-    try:
-        if pages_v3.config_manager:
-            main_config_data = pages_v3.config_manager.get_raw_file_content('main')
-            secrets_config_data = pages_v3.config_manager.get_raw_file_content('secrets')
-            main_config_json = json.dumps(main_config_data, indent=4)
-            secrets_config_json = json.dumps(secrets_config_data, indent=4)
+    if pages_v3.config_manager:
+        main_config_data = pages_v3.config_manager.get_raw_file_content('main')
+        secrets_config_data = pages_v3.config_manager.get_raw_file_content('secrets')
+        main_config_json = json.dumps(main_config_data, indent=4)
+        secrets_config_json = json.dumps(secrets_config_data, indent=4)
 
-            return render_template('v3/partials/raw_json.html',
-                                 main_config_json=main_config_json,
-                                 secrets_config_json=secrets_config_json,
-                                 main_config_path=pages_v3.config_manager.get_config_path(),
-                                 secrets_config_path=pages_v3.config_manager.get_secrets_path())
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+        return render_template('v3/partials/raw_json.html',
+                             main_config_json=main_config_json,
+                             secrets_config_json=secrets_config_json,
+                             main_config_path=pages_v3.config_manager.get_config_path(),
+                             secrets_config_path=pages_v3.config_manager.get_secrets_path())
 
 def _load_backup_restore_partial():
     """Load backup & restore partial."""
-    try:
-        return render_template('v3/partials/backup_restore.html')
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+    return render_template('v3/partials/backup_restore.html')
 
 @pages_v3.route('/setup')
 def captive_setup():
@@ -754,27 +671,15 @@ def captive_setup():
 
 def _load_wifi_partial():
     """Load WiFi setup partial"""
-    try:
-        return render_template('v3/partials/wifi.html')
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+    return render_template('v3/partials/wifi.html')
 
 def _load_cache_partial():
     """Load cache management partial"""
-    try:
-        return render_template('v3/partials/cache.html')
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+    return render_template('v3/partials/cache.html')
 
 def _load_operation_history_partial():
     """Load operation history partial"""
-    try:
-        return render_template('v3/partials/operation_history.html')
-    except Exception as e:
-        logger.error("Error loading partial", exc_info=True)
-        return "Error loading partial", 500
+    return render_template('v3/partials/operation_history.html')
 
 
 def _load_tools_partial():
@@ -789,6 +694,24 @@ def _load_tools_partial():
         return "[Pages V3][Tools] Failed to load due to a file system error. Check logs.", 500
 
 
+_PARTIAL_LOADERS = {
+    'overview': _load_overview_partial,
+    'general': _load_general_partial,
+    'display': _load_display_partial,
+    'durations': _load_durations_partial,
+    'schedule': _load_schedule_partial,
+    'plugins': _load_plugins_partial,
+    'fonts': _load_fonts_partial,
+    'logs': _load_logs_partial,
+    'raw-json': _load_raw_json_partial,
+    'backup-restore': _load_backup_restore_partial,
+    'wifi': _load_wifi_partial,
+    'cache': _load_cache_partial,
+    'operation-history': _load_operation_history_partial,
+    'tools': _load_tools_partial,
+}
+
+
 def _load_plugin_config_partial(plugin_id):
     """
     Load plugin configuration partial - server-side rendered form.
@@ -960,7 +883,7 @@ def _load_plugin_config_partial(plugin_id):
             web_ui_actions=web_ui_actions
         )
         
-    except Exception as e:
+    except Exception:
         logger.error("Error loading plugin config partial for %s", plugin_id, exc_info=True)
         return '<div class="text-red-500 p-4">Error loading plugin config; see logs for details</div>', 500
 
@@ -1041,6 +964,6 @@ def _load_starlark_config_partial(app_id):
             last_render_time=None,
         )
 
-    except Exception as e:
+    except Exception:
         logger.error("[Pages V3] Error loading starlark config for app", exc_info=True)
         return '<div class="text-red-500 p-4">Error loading starlark config; see logs for details</div>', 500
diff --git a/web_interface/cache.py b/web_interface/cache.py
index 977600a2..643826b1 100644
--- a/web_interface/cache.py
+++ b/web_interface/cache.py
@@ -6,8 +6,8 @@ seconds or minutes (the font catalog, the system-status snapshot, systemctl
 checks). It is per-process and in-memory only; data shared with the display
 service goes through ``src.cache_manager.CacheManager`` instead.
 
-Separated from app.py to avoid circular imports: blueprints import the
-module-level helpers below lazily, inside their request handlers.
+Separate from app.py so the blueprints can import it without importing the
+app; it imports nothing from the project, so they import it at module top.
 """
 import threading
 import time
diff --git a/web_interface/display_preview.py b/web_interface/display_preview.py
new file mode 100644
index 00000000..47f3790a
--- /dev/null
+++ b/web_interface/display_preview.py
@@ -0,0 +1,36 @@
+"""The display preview the web UI shows, read from the display service's snapshot.
+
+GET /api/v3/display/current and the /api/v3/stream/display SSE stream both
+answer with preview_payload(). Free of Flask and app imports, like
+system_metrics, so a blueprint can use it without constructing the app.
+"""
+
+import base64
+import time
+from typing import Any, Dict, Optional
+
+#: Where DisplayManager writes the snapshot. Written atomically (a temp file
+#: and os.replace), so a read never sees half a PNG.
+SNAPSHOT_PATH = "/tmp/led_matrix_preview.png"  # nosec B108 - fixed path shared with display_manager
+
+
+def read_snapshot_base64(path: Optional[str] = None) -> str:
+    """The snapshot PNG's bytes, base64-encoded.
+
+    The file already is a PNG, so it is passed through as it is: decoding and
+    re-encoding it produced the same image for more CPU on the Pi. Raises
+    OSError when there is no snapshot or it cannot be read.
+    """
+    with open(path or SNAPSHOT_PATH, 'rb') as f:
+        return base64.b64encode(f.read()).decode('ascii')
+
+
+def preview_payload(width: int, height: int, image: Optional[str]) -> Dict[str, Any]:
+    """``{timestamp, width, height, image}``; ``image`` is None when there is
+    no snapshot to show."""
+    return {
+        'timestamp': time.time(),
+        'width': width,
+        'height': height,
+        'image': image,
+    }
diff --git a/web_interface/start.py b/web_interface/start.py
index f62ff086..7b37de78 100644
--- a/web_interface/start.py
+++ b/web_interface/start.py
@@ -11,10 +11,16 @@ import sys
 import logging
 from pathlib import Path
 
+logger = logging.getLogger('web_interface.start')
+
+# No route to host, broken pipe, connection reset: a client went away.
+_CLIENT_DISCONNECT_ERRNOS = (113, 32, 104)
+
+
 def get_local_ips():
     """Get list of local IP addresses the service will be accessible on."""
     ips = []
-    
+
     # Check if AP mode is active
     try:
         result = subprocess.run(
@@ -27,7 +33,7 @@ def get_local_ips():
             ips.append("192.168.4.1 (AP Mode)")
     except Exception:  # nosec B110 - AP mode IP detection is non-critical startup info; systemctl may not exist
         pass
-    
+
     # Get IPs from hostname -I
     try:
         result = subprocess.run(
@@ -43,7 +49,7 @@ def get_local_ips():
                     ips.append(ip)
     except Exception:  # nosec B110 - hostname -I output parsing; non-critical startup info
         pass
-    
+
     # Fallback: try socket method
     if not ips:
         try:
@@ -57,7 +63,7 @@ def get_local_ips():
                 s.close()
         except Exception:
             pass
-    
+
     return ips if ips else ["localhost"]
 
 def main():
@@ -65,15 +71,15 @@ def main():
     # Change to project root directory
     project_root = Path(__file__).parent.parent
     os.chdir(project_root)
-    
+
     # Add to Python path
     sys.path.insert(0, str(project_root))
-    
+
     # Configure logging to suppress non-critical socket errors
     # These occur when clients disconnect and are harmless
     werkzeug_logger = logging.getLogger('werkzeug')
     original_log_exception = werkzeug_logger.error
-    
+
     def log_exception_filtered(message, *args, **kwargs):
         """Filter out non-critical socket errors from werkzeug logs."""
         if isinstance(message, str):
@@ -90,51 +96,38 @@ def main():
         if 'exc_info' in kwargs and kwargs['exc_info']:
             exc_type, exc_value, exc_tb = kwargs['exc_info']
             if isinstance(exc_value, OSError):
-                # Suppress common non-critical socket errors
-                if exc_value.errno in (113, 32, 104):  # No route to host, Broken pipe, Connection reset
+                if exc_value.errno in _CLIENT_DISCONNECT_ERRNOS:
                     werkzeug_logger.debug(message, *args, **kwargs)
                     return
         # Log everything else normally
         original_log_exception(message, *args, **kwargs)
-    
+
     werkzeug_logger.error = log_exception_filtered
-    
-    # Import and run the Flask app
+
+    # Importing the app also sets up logging, so the lines below reach the
+    # journal through it.
     from web_interface.app import app, start_auto_update_scheduler
     start_auto_update_scheduler()
 
-    print("Starting LED Matrix Web Interface V3...")
-    print("Web server binding to: 0.0.0.0:5000")
-    
-    # Get and display accessible IP addresses
-    ips = get_local_ips()
-    if ips:
-        print("Access the interface at:")
-        for ip in ips:
-            if "AP Mode" in ip:
-                print("  - http://192.168.4.1:5000 (AP Mode - connect to LEDMatrix-Setup WiFi)")
-            else:
-                print(f"  - http://{ip}:5000")
-    else:
-        print("  - http://localhost:5000 (local only)")
-        print("  - http://<your-pi-ip>:5000 (replace with your Pi's IP address)")
-    
-    # Run the web server with error handling for client disconnections
+    logger.info("Starting LED Matrix Web Interface V3, binding to 0.0.0.0:5000")
+    # get_local_ips() always returns at least "localhost".
+    logger.info("Access the interface at:")
+    for ip in get_local_ips():
+        if "AP Mode" in ip:
+            logger.info("  - http://192.168.4.1:5000 (AP Mode - connect to LEDMatrix-Setup WiFi)")
+        else:
+            logger.info("  - http://%s:5000", ip)
+
     try:
         # threaded=True is Flask's default since 1.0, but set it explicitly
-        # so it's self-documenting: the two /api/v3/stream/* SSE endpoints
+        # so it's self-documenting: the three /api/v3/stream/* SSE endpoints
         # hold long-lived connections and would starve other requests under
         # a single-threaded server.
         app.run(host='0.0.0.0', port=5000, debug=False, threaded=True)
-    except (OSError, BrokenPipeError) as e:
-        # Suppress non-critical socket errors (client disconnections)
-        if isinstance(e, OSError) and e.errno in (113, 32, 104):  # No route to host, Broken pipe, Connection reset
-            werkzeug_logger.debug(f"Client disconnected: {e}", exc_info=True)
-            # Re-raise only if it's not a client disconnection error
-            if e.errno not in (113, 32, 104):
-                raise
-        else:
+    except OSError as e:
+        if e.errno not in _CLIENT_DISCONNECT_ERRNOS:
             raise
+        werkzeug_logger.debug("Client disconnected: %s", e, exc_info=True)
 
 if __name__ == '__main__':
     main()
diff --git a/web_interface/system_metrics.py b/web_interface/system_metrics.py
index 723bd85f..2d7ef585 100644
--- a/web_interface/system_metrics.py
+++ b/web_interface/system_metrics.py
@@ -1,4 +1,4 @@
-"""System metrics for the status stream.
+"""System metrics for the status stream and GET /api/v3/system/status.
 
 Deliberately free of Flask and app imports: importing web_interface.app
 constructs the Flask application and a CacheManager, and the latter claims the
@@ -11,9 +11,20 @@ the UI can render '--', because a confident wrong number is worse than a blank:
 on a card that was filling up.
 """
 
+import time
 from typing import Any, Dict, Optional
 
 _THERMAL_ZONE = '/sys/class/thermal/thermal_zone0/temp'
+_MB = 1024 * 1024
+_GB = 1024 * 1024 * 1024
+
+#: Every key collect_system_metrics() returns.
+METRIC_KEYS = (
+    'cpu_percent', 'cpu_temp',
+    'memory_used_percent', 'memory_total_mb', 'memory_used_mb', 'memory_available_mb',
+    'disk_used_percent', 'disk_total_gb', 'disk_used_gb',
+    'uptime_seconds',
+)
 
 
 def _cpu_temp_c() -> Optional[float]:
@@ -25,38 +36,53 @@ def _cpu_temp_c() -> Optional[float]:
         return None
 
 
-def collect_system_metrics() -> Dict[str, Any]:
+def collect_system_metrics(cpu_interval: Optional[float] = None) -> Dict[str, Any]:
     """Collect the numbers that predict trouble on a small board.
 
+    ``cpu_interval`` is passed to ``psutil.cpu_percent``. None does not block
+    and measures since the previous call (app startup primes it); a request
+    that may be the first call in its process passes a short interval instead.
+
     ``memory_available_mb`` is MemAvailable rather than a used percentage: it
     accounts for reclaimable page cache, so it is what separates a board at 70%
     "used" that is fine from one at 70% that is about to fail fork(). A 1GB Pi
     can sit at either and only this number tells them apart.
     """
+    metrics: Dict[str, Any] = dict.fromkeys(METRIC_KEYS)
+    metrics['cpu_temp'] = _cpu_temp_c()
     try:
         import psutil
     except ImportError:
-        return {
-            'cpu_percent': 0,
-            'memory_used_percent': 0,
-            'memory_available_mb': None,
-            'disk_used_percent': None,
-            'cpu_temp': _cpu_temp_c() or 0,
-        }
+        return metrics
+
+    metrics['cpu_percent'] = round(psutil.cpu_percent(interval=cpu_interval), 1)
 
-    # interval=None is non-blocking; app startup primes psutil's internal state.
-    cpu_percent = round(psutil.cpu_percent(interval=None), 1)
     memory = psutil.virtual_memory()
+    metrics['memory_used_percent'] = round(memory.percent, 1)
+    metrics['memory_total_mb'] = round(memory.total / _MB, 1)
+    metrics['memory_used_mb'] = round(memory.used / _MB, 1)
+    metrics['memory_available_mb'] = round(memory.available / _MB, 1)
 
     try:
-        disk_used_percent: Optional[float] = round(psutil.disk_usage('/').percent, 1)
+        disk = psutil.disk_usage('/')
     except OSError:
-        disk_used_percent = None
+        pass
+    else:
+        metrics['disk_used_percent'] = round(disk.percent, 1)
+        metrics['disk_total_gb'] = round(disk.total / _GB, 1)
+        metrics['disk_used_gb'] = round(disk.used / _GB, 1)
 
-    return {
-        'cpu_percent': cpu_percent,
-        'memory_used_percent': round(memory.percent, 1),
-        'memory_available_mb': round(memory.available / (1024 * 1024), 1),
-        'disk_used_percent': disk_used_percent,
-        'cpu_temp': _cpu_temp_c() or 0,
-    }
+    metrics['uptime_seconds'] = int(time.time() - psutil.boot_time())
+    return metrics
+
+
+def format_uptime(uptime_seconds: Optional[float]) -> Optional[str]:
+    """'3d 4h', '5h 12m' or '42m'; None when the uptime is unknown."""
+    if uptime_seconds is None:
+        return None
+    hours = uptime_seconds / 3600
+    if hours >= 24:
+        return f"{int(hours / 24)}d {int(hours % 24)}h"
+    if hours >= 1:
+        return f"{int(hours)}h {int((uptime_seconds % 3600) / 60)}m"
+    return f"{int(uptime_seconds / 60)}m"