fix(web): the installed-plugins list never waits on the registry download (#766)

GET /plugins/installed called get_registry_info() per plugin. Despite the
"no network call" comment, a cold or expired cache made that download
plugins.json (10 s timeout, three attempts), and with no cached copy each
plugin's lookup repeated it -- offline, every load waited out the timeouts.

The route now reads the registry copy already in memory, however old, via
get_cached_registry_info(). A missing or expired copy starts a single
background refresh (backing off after an offline failure), so a later load
gets update and verified badges. Store, install and update paths still fetch.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

test/test_installed_list_registry_offline.py

@@ -0,0 +1,188 @@
+"""GET /api/v3/plugins/installed never waits on the network for registry data.
+
+The route used `get_registry_info`, which goes through `fetch_registry`: on a
+cold (or expired) cache that downloads plugins.json from GitHub with a 10s
+timeout and three attempts -- and, with no registry to fall back on, every
+plugin's lookup repeated the whole cycle. The first plugin-list load after a
+restart waited on GitHub, and offline it waited out every timeout.
+
+Now the route reads the registry copy already in memory, however old, and a
+missing or expired copy only starts a background refresh. These tests block
+the network at the socket layer (DNS lookups hang, then fail) and assert the
+request returns quickly without a single network attempt on the request path.
+"""
+
+import functools
+import socket
+import threading
+import time
+from unittest.mock import MagicMock
+
+import pytest
+import requests
+
+from test._api_v3_test_helpers import (  # noqa: F401 - fixtures
+    api_v3_client, api_v3_module,
+)
+from src.plugin_system.store_manager import PluginStoreManager
+
+# How long a blocked lookup hangs before failing: long enough that a single
+# one on the request path blows the response budget below.
+HANG_SECONDS = 1.5
+FAST_SECONDS = 1.0
+
+REGISTRY = {'plugins': [
+    {'id': 'weather', 'name': 'Weather', 'verified': True, 'latest_version': '1.2.0'},
+]}
+
+
+@pytest.fixture
+def blocked_network(monkeypatch):
+    """Every DNS lookup hangs, then fails; records the thread it came from."""
+    attempts = []
+
+    def hang_then_fail(host, *args, **kwargs):
+        attempts.append((host, threading.current_thread().name))
+        time.sleep(HANG_SECONDS)
+        raise socket.gaierror(-3, 'Temporary failure in name resolution (blocked by test)')
+
+    monkeypatch.setattr(socket, 'getaddrinfo', hang_then_fail)
+    return attempts
+
+
+@pytest.fixture
+def store(tmp_path, monkeypatch):
+    store = PluginStoreManager(plugins_dir=str(tmp_path / 'plugins'))
+    # One attempt, no pause between attempts, so a background refresh against
+    # the blocked network ends within the test (teardown joins it).
+    monkeypatch.setattr(store, '_http_get_with_retries', functools.partial(
+        PluginStoreManager._http_get_with_retries, store, max_retries=1))
+    yield store
+    thread = getattr(store, '_registry_refresh_thread', None)
+    if thread is not None:
+        thread.join(timeout=30)
+
+
+@pytest.fixture
+def get_installed(api_v3_module, api_v3_client, store, tmp_path):
+    api = api_v3_module.api_v3
+    api.plugin_store_manager = store
+    api.plugin_catalog.plugins_dir = str(tmp_path / 'plugins')
+    api.plugin_catalog.get_all_plugin_info = MagicMock(return_value=[
+        {'id': 'weather', 'name': 'Weather', 'version': '1.0.0'},
+        {'id': 'clock', 'name': 'Clock', 'version': '2.0.0'},
+    ])
+    api.plugin_catalog.get_plugin_display_modes = MagicMock(return_value=[])
+    api.config_manager.load_config = MagicMock(return_value={})
+
+    def _get():
+        start = time.perf_counter()
+        response = api_v3_client.get('/api/v3/plugins/installed')
+        elapsed = time.perf_counter() - start
+        assert response.status_code == 200
+        plugins = {p['id']: p for p in response.get_json()['data']['plugins']}
+        return plugins, elapsed
+    return _get
+
+
+def _request_path_attempts(attempts):
+    return [a for a in attempts if a[1] != 'registry-refresh']
+
+
+def test_a_cold_cache_offline_returns_fast_without_registry_info(get_installed, blocked_network):
+    plugins, elapsed = get_installed()
+
+    assert _request_path_attempts(blocked_network) == []
+    assert elapsed < FAST_SECONDS, f"installed list took {elapsed:.2f}s with the network blocked"
+    weather = plugins['weather']
+    assert weather['latest_version'] == ''
+    assert weather['update_available'] is False
+    assert weather['verified'] is False
+
+
+def test_a_stale_cache_is_used_as_is_without_a_fetch(get_installed, store, blocked_network):
+    store.registry_cache = REGISTRY
+    store.registry_cache_time = time.time() - store.registry_cache_timeout - 3600
+
+    plugins, elapsed = get_installed()
+
+    assert _request_path_attempts(blocked_network) == []
+    assert elapsed < FAST_SECONDS
+    weather = plugins['weather']
+    assert weather['latest_version'] == '1.2.0'
+    assert weather['update_available'] is True
+    assert weather['verified'] is True
+    assert plugins['clock']['latest_version'] == ''
+
+
+def test_a_fresh_cache_starts_no_refresh(get_installed, store, blocked_network):
+    store.registry_cache = REGISTRY
+    store.registry_cache_time = time.time()
+
+    plugins, _ = get_installed()
+
+    assert blocked_network == []
+    assert store._registry_refresh_thread is None
+    assert plugins['weather']['update_available'] is True
+
+
+def test_a_cold_cache_is_filled_in_the_background_for_the_next_load(get_installed, store, monkeypatch):
+    response = MagicMock()
+    response.json.return_value = REGISTRY
+    fetched_on = []
+
+    def fake_get(url, **kwargs):
+        fetched_on.append(threading.current_thread().name)
+        return response
+
+    monkeypatch.setattr(store, '_http_get_with_retries', fake_get)
+
+    first, _ = get_installed()
+    assert first['weather']['update_available'] is False
+    store._registry_refresh_thread.join(timeout=10)
+
+    second, _ = get_installed()
+    assert second['weather']['latest_version'] == '1.2.0'
+    assert second['weather']['update_available'] is True
+    # One background fetch for the whole listing, none on the request path.
+    assert fetched_on == ['registry-refresh']
+
+
+def test_an_offline_background_refresh_backs_off(store, monkeypatch):
+    def offline(url, **kwargs):
+        raise requests.ConnectionError('blocked by test')
+
+    monkeypatch.setattr(store, '_http_get_with_retries', offline)
+
+    assert store.refresh_registry_in_background() is True
+    store._registry_refresh_thread.join(timeout=10)
+    assert store.registry_cache is None
+    # Offline: the next page load does not start another attempt straight away.
+    assert store.refresh_registry_in_background() is False
+    store._registry_refresh_retry_after = 0.0
+    assert store.refresh_registry_in_background() is True
+
+
+def test_only_one_background_refresh_runs_at_a_time(store, monkeypatch):
+    release = threading.Event()
+
+    def slow(url, **kwargs):
+        release.wait(10)
+        raise requests.ConnectionError('blocked by test')
+
+    monkeypatch.setattr(store, '_http_get_with_retries', slow)
+    try:
+        assert store.refresh_registry_in_background() is True
+        assert store.refresh_registry_in_background() is False
+    finally:
+        release.set()
+
+
+def test_get_registry_info_still_fetches_for_the_store(store, monkeypatch):
+    """The store, install and update paths keep fetching a cold registry."""
+    response = MagicMock()
+    response.json.return_value = REGISTRY
+    monkeypatch.setattr(store, '_http_get_with_retries', MagicMock(return_value=response))
+
+    assert store.get_registry_info('weather')['latest_version'] == '1.2.0'
+    store._http_get_with_retries.assert_called_once()