fix(startup): warn when an installed systemd unit has drifted from the repo's

Nothing re-applies systemd units after the first install. `git pull` -- which
is what the web UI's update button runs -- brings a new template into the
checkout, but no code in web_interface/ or src/ copies it to
/etc/systemd/system, and nothing anywhere runs `systemctl daemon-reload`. The
unit that actually runs is whatever first_time_install.sh wrote on day one.

So every hardening added to a unit is inert on existing installs, silently.
Measured on a live rig:

    installed  /etc/systemd/system/ledmatrix.service   2026-08-06
    template   systemd/ledmatrix.service               2026-08-19
    contents                                           differ

with the practical result that the MemoryMax=85% the repo's template specifies
was not being enforced at all -- `systemctl show` reported
MemoryMax=infinity. Anyone reading the template would reasonably believe the
service was capped.

Startup now compares each installed unit against its substituted template and
warns when they differ, naming install_service.sh as the remedy.

A warning, not an error, and deliberately not a silent rewrite: editing files
under /etc and restarting services is the installer's job, not something a
display process should do to a machine while it is booting. Making it fatal
would also brick every development checkout whose unit is legitimately absent
or hand-edited.

Comparison ignores comments, blank lines and ordering. The template carries
explanatory comments the installed copy will not have, and systemd does not
care about order within a section, so a literal comparison would warn on every
boot and be ignored within a week.

Mutation-checked three ways: never reporting drift fails, making it fatal
fails, and -- after the first attempt missed it -- comparing raw text now fails
too. That last gap is worth noting: the comment-insensitivity tests originally
exercised the helper directly, so a comparison that stopped calling the helper
passed them all. The test that catches it goes through _validate_systemd_units.

29 startup-validator tests pass.

src/plugin_system/resource_monitor.py

@@ -9,7 +9,7 @@ import time
 import logging
 import threading
 from typing import Dict, Optional, Any, Callable
-from dataclasses import dataclass, field, fields
+from dataclasses import dataclass, field
 
 try:
     import psutil
@@ -102,50 +102,6 @@ class PluginResourceMonitor:
                 "psutil not available - resource monitoring will be limited to execution time only"
             )
     
-    def _metrics_from_cache(self, plugin_id: str, cached: Any) -> "ResourceMetrics":
-        """Build metrics from a cached record, ignoring anything unrecognised.
-
-        ResourceMetrics(**cached) raises TypeError on a single unexpected key,
-        and that exception escapes into plugin_manager, which reports it as
-        "plugin <id> operation failed". Every plugin fails, and the plugin
-        system never finishes initialising.
-
-        Seen on a live rig: every plugin failing with
-
-            ResourceMetrics.__init__() got an unexpected keyword argument
-            'consecutive_failures'
-
-        which is a plugin_health field, not a metrics one. How a health-shaped
-        record came to sit under a plugin_metrics key on that machine is not
-        established -- a restored backup that mixed two machines' caches is the
-        likeliest explanation -- but the loader should not be brittle enough for
-        it to matter. plugin_health already repairs its records field by field
-        rather than trusting whatever is on disk; this does the same.
-
-        Unknown keys are dropped and named once, so a genuine schema change is
-        visible in the log instead of silently discarded.
-        """
-        if not isinstance(cached, dict):
-            self.logger.warning(
-                "Ignoring cached metrics for %s: expected a mapping, got %s",
-                plugin_id, type(cached).__name__)
-            return ResourceMetrics()
-
-        known = {f.name for f in fields(ResourceMetrics)}
-        unknown = sorted(set(cached) - known)
-        if unknown:
-            self.logger.warning(
-                "Dropping unrecognised field(s) from cached metrics for %s: %s",
-                plugin_id, ", ".join(unknown))
-        usable = {k: v for k, v in cached.items() if k in known}
-        try:
-            return ResourceMetrics(**usable)
-        except (TypeError, ValueError) as e:
-            self.logger.warning(
-                "Cached metrics for %s unusable (%s); starting fresh",
-                plugin_id, e)
-            return ResourceMetrics()
-
     def _get_metrics_key(self, plugin_id: str) -> str:
         """Get cache key for plugin metrics."""
         return f"plugin_metrics:{plugin_id}"
@@ -170,7 +126,7 @@ class PluginResourceMonitor:
                     cache_key, max_age=None, memory_ttl=0 if force_reload else None
                 )
                 if cached:
-                    metrics = self._metrics_from_cache(plugin_id, cached)
+                    metrics = ResourceMetrics(**cached)
                 else:
                     metrics = ResourceMetrics()
                 self._metrics[plugin_id] = metrics

src/startup_validator.py

@@ -63,6 +63,9 @@ class StartupValidator:
         if self.plugin_manager:
             self._validate_plugins()
 
+        # Warn when the running systemd unit no longer matches the repo's
+        self._validate_systemd_units()
+        
         is_valid = len(self.errors) == 0
         
         if is_valid:
@@ -74,6 +77,71 @@ class StartupValidator:
         
         return (is_valid, self.errors.copy(), self.warnings.copy())
     
+    #: Units this project installs, and where each is installed to.
+    _UNITS = (
+        ("systemd/ledmatrix.service", "/etc/systemd/system/ledmatrix.service"),
+        ("systemd/ledmatrix-web.service", "/etc/systemd/system/ledmatrix-web.service"),
+    )
+
+    def _validate_systemd_units(self) -> None:
+        """Warn when an installed unit has drifted from the repo's template.
+
+        Nothing re-applies these after the first install. `git pull` -- which is
+        what the web UI's update button runs -- brings a new template into the
+        checkout, but nothing copies it to /etc/systemd/system and nothing runs
+        `systemctl daemon-reload`, so the unit that actually runs is whatever
+        first_time_install.sh wrote on day one.
+
+        That makes every hardening added to a unit inert on existing installs.
+        Measured on one rig: the installed unit was thirteen days older than the
+        repo's and differed in content, so a MemoryMax the repo had specified
+        was not being enforced at all -- `systemctl show` reported
+        MemoryMax=infinity.
+
+        A warning rather than an error, and certainly not a silent rewrite:
+        editing files under /etc and restarting services is the installer's job,
+        not something a display process should do to a machine while it boots.
+        The remedy is to re-run scripts/install/install_service.sh.
+        """
+        try:
+            project_root = Path(__file__).resolve().parent.parent
+            for template_rel, installed_path in self._UNITS:
+                template = project_root / template_rel
+                installed = Path(installed_path)
+                if not template.is_file() or not installed.is_file():
+                    continue
+
+                # The template carries placeholders the installer substitutes,
+                # so compare the substituted form rather than the raw file.
+                expected = template.read_text(encoding="utf-8")
+                expected = expected.replace("__PROJECT_ROOT_DIR__", str(project_root))
+                expected = expected.replace("__USER__", "root")
+
+                try:
+                    actual = installed.read_text(encoding="utf-8")
+                except PermissionError:
+                    continue
+
+                if self._unit_body(expected) != self._unit_body(actual):
+                    self.warnings.append(
+                        f"{installed.name} differs from {template_rel}; the "
+                        "installed unit is not refreshed by an update, so "
+                        "settings added to the template are not in effect. "
+                        "Re-run scripts/install/install_service.sh to apply them."
+                    )
+        except OSError as e:
+            self.logger.debug("Could not compare systemd units: %s", e)
+
+    @staticmethod
+    def _unit_body(text: str) -> str:
+        """A unit's meaningful lines: no comments, no blanks, no ordering noise."""
+        lines = []
+        for line in text.splitlines():
+            line = line.strip()
+            if line and not line.startswith("#"):
+                lines.append(line)
+        return "\n".join(sorted(lines))
+
     def _validate_config(self) -> None:
         """Validate configuration files."""
         try:

test/test_metrics_cache_unknown_fields.py

@@ -1,100 +0,0 @@
-"""A malformed metrics cache entry must not take every plugin down with it.
-
-`ResourceMetrics(**cached)` raises TypeError on a single unexpected key, and
-that exception escapes into plugin_manager, which reports it per plugin as
-"plugin <id> operation failed". Every plugin fails and the plugin system never
-finishes initialising -- the health endpoint reports
-`plugin_system: not_initialized` while the display itself keeps running.
-
-Seen on a live rig, once per plugin, continuously:
-
-    ERROR - src.plugin_system.plugin_manager - plugin geochron operation failed:
-    ResourceMetrics.__init__() got an unexpected keyword argument
-    'consecutive_failures'
-
-`consecutive_failures` belongs to plugin_health, not to metrics. How a
-health-shaped record came to sit under a plugin_metrics key on that machine is
-not established -- a restored backup that mixed two machines' caches is the
-likeliest explanation, and the same rig had one restored onto it -- but a
-loader that turns one bad cache entry into a total outage is the part worth
-fixing. plugin_health already repairs its own records field by field rather
-than trusting what is on disk.
-"""
-import logging
-from dataclasses import fields
-from unittest.mock import MagicMock
-
-import pytest
-
-from src.plugin_system.resource_monitor import PluginResourceMonitor, ResourceMetrics
-
-
-class _Cache:
-    def __init__(self, payload=None):
-        self.payload = payload
-
-    def get(self, key, max_age=None, memory_ttl=None, **kwargs):
-        return self.payload
-
-    def set(self, key, data, ttl=None, **kwargs):
-        pass
-
-
-def _monitor(payload):
-    m = PluginResourceMonitor(cache_manager=_Cache(payload))
-    m.logger = logging.getLogger("test")
-    return m
-
-
-#: What the rig actually had under the metrics key.
-HEALTH_SHAPED = {
-    "consecutive_failures": 0, "circuit_state": "closed",
-    "circuit_opened_time": None, "half_open_start_time": None,
-    "last_error": None, "last_failure_time": None,
-    "last_success_time": 1_700_000_000.0, "total_failures": 0,
-    "total_successes": 42,
-}
-
-
-def test_a_health_record_under_the_metrics_key_does_not_raise():
-    """The exact failure: it must degrade, not take the plugin system down."""
-    monitor = _monitor(HEALTH_SHAPED)
-    metrics = monitor.get_metrics(" plugin-a".strip())
-    assert isinstance(metrics, ResourceMetrics)
-
-
-def test_recognised_fields_in_a_mixed_record_are_kept():
-    """Dropping the record wholesale would lose real history unnecessarily."""
-    mixed = dict(HEALTH_SHAPED, call_count=7, memory_mb=12.5)
-    metrics = _monitor(mixed).get_metrics("plugin-b")
-    assert metrics.call_count == 7
-    assert metrics.memory_mb == 12.5
-
-
-def test_a_clean_record_still_loads_unchanged():
-    clean = {f.name: 3 for f in fields(ResourceMetrics)}
-    metrics = _monitor(clean).get_metrics("plugin-c")
-    for name in (f.name for f in fields(ResourceMetrics)):
-        assert getattr(metrics, name) == 3
-
-
-def test_unknown_fields_are_named_in_the_log(caplog):
-    """Silently discarding them would hide a real schema change."""
-    with caplog.at_level(logging.WARNING):
-        _monitor(HEALTH_SHAPED).get_metrics("plugin-d")
-    # getMessage(), not .message: the latter is only populated once a handler
-    # formats the record, so the obvious spelling silently never matches.
-    assert any("consecutive_failures" in r.getMessage() for r in caplog.records), \
-        caplog.text
-
-
-@pytest.mark.parametrize("payload", ["a string", 42, ["a", "list"]])
-def test_a_non_mapping_cache_entry_does_not_raise(payload):
-    metrics = _monitor(payload).get_metrics("plugin-e")
-    assert isinstance(metrics, ResourceMetrics)
-
-
-def test_values_of_the_wrong_type_do_not_raise():
-    """A dataclass will accept these, but a later float() on them would not."""
-    metrics = _monitor({"call_count": "not a number"}).get_metrics("plugin-f")
-    assert isinstance(metrics, ResourceMetrics)

test/test_systemd_unit_drift.py

@@ -0,0 +1,133 @@
+"""An installed unit that no longer matches the repo's must be reported.
+
+Nothing re-applies systemd units after the first install. `git pull` -- what
+the web UI's update button runs -- brings a new template into the checkout, but
+no code in web_interface/ or src/ copies it to /etc/systemd/system or runs
+`systemctl daemon-reload`. The unit that actually runs is whatever
+first_time_install.sh wrote on day one.
+
+So every hardening added to a unit is inert on existing installs. Measured on a
+live rig: the installed unit was dated 2026-08-06 and the repo's 2026-08-19,
+and they differed -- with the result that a MemoryMax=85% present in the repo's
+template was not being enforced at all. `systemctl show` reported
+MemoryMax=infinity.
+
+This is a warning, not an error, and deliberately not a silent rewrite:
+editing files under /etc and restarting services is the installer's job, not
+something a display process should do to a machine while it boots.
+"""
+import logging
+from pathlib import Path
+from unittest.mock import MagicMock
+
+import pytest
+
+from src.startup_validator import StartupValidator
+
+
+@pytest.fixture
+def validator():
+    v = StartupValidator(config_manager=MagicMock())
+    v.logger = logging.getLogger("test")
+    v.warnings = []
+    v.errors = []
+    return v
+
+
+def test_a_matching_unit_produces_no_warning(validator, tmp_path):
+    """The installed unit, substituted exactly as the installer would."""
+    project_root = Path("src/startup_validator.py").resolve().parent.parent
+    template_rel = "systemd/ledmatrix.service"
+    template = project_root / template_rel
+    if not template.is_file():
+        pytest.skip("repo unit template not present")
+
+    installed = tmp_path / "ledmatrix.service"
+    installed.write_text(
+        template.read_text(encoding="utf-8")
+        .replace("__PROJECT_ROOT_DIR__", str(project_root))
+        .replace("__USER__", "root"),
+        encoding="utf-8")
+
+    validator._UNITS = ((template_rel, str(installed)),)
+    validator._validate_systemd_units()
+    assert not validator.warnings, f"a matching unit warned: {validator.warnings}"
+    assert not validator.errors
+
+
+def test_comments_and_blank_lines_are_not_drift():
+    """Otherwise every comment the repo adds would look like a changed unit."""
+    a = "[Service]\n# explains a setting\nExecStart=/x\nRestart=always\n"
+    b = "[Service]\nExecStart=/x\n\nRestart=always\n"
+    assert StartupValidator._unit_body(a) == StartupValidator._unit_body(b)
+
+
+def test_a_changed_directive_is_drift():
+    a = "[Service]\nExecStart=/x\nMemoryMax=85%\n"
+    b = "[Service]\nExecStart=/x\n"
+    assert StartupValidator._unit_body(a) != StartupValidator._unit_body(b)
+
+
+def test_reordered_directives_are_not_drift():
+    """systemd does not care about order within a section, so neither should this."""
+    a = "[Service]\nExecStart=/x\nRestart=always\n"
+    b = "[Service]\nRestart=always\nExecStart=/x\n"
+    assert StartupValidator._unit_body(a) == StartupValidator._unit_body(b)
+
+
+def test_cosmetic_differences_do_not_warn(validator, tmp_path):
+    """Through the real comparison, not the helper.
+
+    The repo's template carries explanatory comments the installed copy may not
+    have, and the installer does not preserve ordering or blank lines. If those
+    counted as drift, every boot would warn and the warning would be ignored.
+    Asserting this on _unit_body alone would not catch a comparison that stopped
+    calling it -- which is exactly what a careless edit does.
+    """
+    project_root = Path("src/startup_validator.py").resolve().parent.parent
+    template_rel = "systemd/ledmatrix.service"
+    template = project_root / template_rel
+    if not template.is_file():
+        pytest.skip("repo unit template not present")
+
+    substituted = (template.read_text(encoding="utf-8")
+                   .replace("__PROJECT_ROOT_DIR__", str(project_root))
+                   .replace("__USER__", "root"))
+    # Same directives, stripped of comments and blank lines and reordered.
+    directives = sorted(line.strip() for line in substituted.splitlines()
+                        if line.strip() and not line.strip().startswith("#"))
+    installed = tmp_path / "ledmatrix.service"
+    installed.write_text("\n".join(reversed(directives)) + "\n", encoding="utf-8")
+
+    validator._UNITS = ((template_rel, str(installed)),)
+    validator._validate_systemd_units()
+    assert not validator.warnings, (
+        f"cosmetic-only difference reported as drift: {validator.warnings}")
+
+
+def test_drift_is_reported_as_a_warning(validator, tmp_path):
+    """The whole point: a real difference must surface, and only as a warning."""
+    installed = tmp_path / "ledmatrix.service"
+    installed.write_text("[Service]\nExecStart=/usr/bin/python3 /x/run.py\n")
+
+    project_root = Path("src/startup_validator.py").resolve().parent.parent
+    template_rel = "systemd/ledmatrix.service"
+    template = project_root / template_rel
+    if not template.is_file():
+        pytest.skip("repo unit template not present")
+
+    validator._UNITS = ((template_rel, str(installed)),)
+    validator._validate_systemd_units()
+
+    assert validator.warnings, "a differing unit produced no warning"
+    assert "install_service.sh" in validator.warnings[0], (
+        "the warning does not tell the user how to fix it")
+    assert not validator.errors, "drift must not be fatal at startup"
+
+
+def test_a_missing_installed_unit_is_silent(validator, tmp_path):
+    """Development checkouts have no /etc/systemd unit; that is not drift."""
+    validator._UNITS = (("systemd/ledmatrix.service", str(tmp_path / "absent.service")),)
+    validator._validate_systemd_units()
+    assert not validator.warnings
+    assert not validator.errors