advisory-scan: derive windows from a compose diff (--compose-to)

Typing --from/--to/--image by hand means someone has to remember the recipe also
bumped its redis. That is how sidecar CVEs went uncounted for months. Point this
at a PR's compose.yml and it reads the windows off the diff instead.

  advisory-scan.py plausible --compose-to <.../branch/<pr>/compose.yml>
    -> community-edition: v2.0.0 -> v3.2.1
    -> clickhouse-server: 23.4.2.11-alpine -> 24.12-alpine
    -> 6 CVEs, identical to the hand-specified args

Details that mattered:

- keyed by SERVICE, not image repo. plausible moved plausible/analytics ->
  ghcr.io/plausible/community-edition; keyed by repo that reads as one image
  vanishing and an unrelated one appearing, and the app window - the one carrying
  the critical - is lost entirely.
- the baseline is the repo's DEFAULT BRANCH resolved from the API, never assumed
  to be main, because several recipes keep a stale main beside a live master.
- image names are matched against advisory sources BOTH ways: an image name is
  often longer than its source repo (clickhouse/clickhouse-server vs
  ClickHouse/ClickHouse) and sometimes shorter (redis vs redis/redis). One
  direction silently dropped the clickhouse window.
- credentials go in an Authorization header, never the URL: in-URL creds leak
  into shell history and process lists, and urllib mis-parses a password
  containing a colon.

--from/--to/--image remain for finer-grained checks (scanning a window that is
not a literal compose diff). 71 tests; discourse 140 / gitea 2 / mailu 2
unchanged.

cc-ci-plan/test-advisory-scan.py

@@ -537,6 +537,80 @@ class TestReleaseLineSemantics(unittest.TestCase):
         self.assertEqual(rep["fixed_by_this_upgrade"], ["CVE-2025-49844"])
 
 
+class TestComposeDerivedWindows(unittest.TestCase):
+    """Windows read off a compose diff, so nobody has to remember which --image args an upgrade needs."""
+
+    OLD = """
+services:
+  app:
+    image: "plausible/analytics:v2.0.0"
+  db:
+    image: pgautoupgrade/pgautoupgrade:18-alpine
+  plausible_events_db:
+    image: clickhouse/clickhouse-server:23.4.2.11-alpine
+volumes:
+  data:
+"""
+    NEW = """
+services:
+  app:
+    image: "ghcr.io/plausible/community-edition:v3.2.1"
+  db:
+    image: pgautoupgrade/pgautoupgrade:18-alpine
+  plausible_events_db:
+    image: clickhouse/clickhouse-server:24.12-alpine
+volumes:
+  data:
+"""
+
+    def _windows(self, old=None, new=None):
+        pages = {"to": new if new is not None else self.NEW,
+                 "from": old if old is not None else self.OLD}
+        with unittest.mock.patch.object(A, "_fetch", lambda u, h=None: pages["to" if "to" in u else "from"]), \
+             unittest.mock.patch.object(A, "_gitea_auth", lambda u: {}):
+            return A.windows_from_compose("http://x/to", "http://x/from")[0]
+
+    def test_app_service_leads_and_sidecars_follow(self):
+        w = self._windows()
+        self.assertEqual(w[0], ("community-edition", "v2.0.0", "v3.2.1"))
+        self.assertIn(("clickhouse-server", "23.4.2.11-alpine", "24.12-alpine"), w)
+
+    def test_unchanged_images_are_not_windows(self):
+        # pgautoupgrade is identical in both; inventing a window for it would be a false count.
+        self.assertNotIn("pgautoupgrade", [n for n, _, _ in self._windows()])
+
+    def test_a_changed_image_REPO_is_still_the_same_service(self):
+        # plausible/analytics -> ghcr.io/plausible/community-edition. Keyed by image repo this reads
+        # as one image vanishing and another appearing, and the app window is lost entirely.
+        w = self._windows()
+        self.assertTrue(any(n == "community-edition" and f == "v2.0.0" for n, f, _ in w))
+
+    def test_no_change_yields_no_windows(self):
+        self.assertEqual(self._windows(old=self.NEW, new=self.NEW), [])
+
+    def test_templated_tags_are_skipped(self):
+        new = self.NEW.replace('ghcr.io/plausible/community-edition:v3.2.1', 'ghost:${IMAGE_VERSION}')
+        self.assertNotIn("ghost", [n for n, _, _ in self._windows(new=new)])
+
+
+class TestImageNameMatching(unittest.TestCase):
+    """An image name and its advisory source rarely spell each other exactly."""
+
+    def test_matches_when_the_image_name_is_LONGER_than_the_source(self):
+        # clickhouse/clickhouse-server vs source ClickHouse/ClickHouse — one-directional matching
+        # dropped this window silently when the key came from a compose file.
+        rep = run_scan([gh("ClickHouse/ClickHouse", [adv("CVE-1", patched="23.10.2.13")])],
+                       images=[("clickhouse-server", "23.4.2.11", "24.12")],
+                       urls=["https://github.com/ClickHouse/ClickHouse"])
+        self.assertIn("github-advisories:ClickHouse/ClickHouse", rep["windows"])
+        self.assertEqual(rep["cve_count_fixed"], 1)
+
+    def test_matches_when_the_image_name_is_SHORTER_than_the_source(self):
+        rep = run_scan([gh("redis/redis", [adv("CVE-2", patched="7.4.1")])],
+                       images=[("redis", "7.4", "8.10")], urls=["https://github.com/redis/redis"])
+        self.assertEqual(rep["cve_count_fixed"], 1)
+
+
 class TestAdjudicationEvidenceAssembly(unittest.TestCase):
     """Pass 2's JUDGEMENT is a model's and not testable; what IS testable is what it gets shown."""