feat(conformance): L0 guard that the external-dns annotationPrefix matches the tree

Add assertion (8) to internal-services-publish-no-public-dns. The external-dns
HelmRelease must declare annotationPrefix explicitly, and every
external-dns annotation in apps/, platform/, runbooks/ and catalog/render.py
must use that prefix. The v0.23.0 default-prefix change on 2026-11-07
ignored the controller: none, target and hostname annotations while
assertions (1)-(3) stayed green.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

conformance/tests/l0-static/internal-services-publish-no-public-dns/check.sh

@@ -26,7 +26,10 @@
 #       KNOWN_NON_CATALOG_PUBLISHERS — shrink-only, stale entries FAIL;
 #   (7) the check is LOAD-BEARING: whole-repo scope declared in chainsaw-test.yaml, honoured by
 #       ci/l0.sh's --include-scope union, and ci/gate.sh blocks on an l0 failure. NO hand-written
-#       ci/l0.sh stage (whole-repo-invariants-wired fails the gate if one appears).
+#       ci/l0.sh stage (whole-repo-invariants-wired fails the gate if one appears);
+#   (8) the external-dns HelmRelease declares `annotationPrefix` explicitly and it matches the
+#       prefix of EVERY external-dns annotation in the tree and in catalog/render.py — added after
+#       the 2026-11-07 v0.23.0 default-prefix change silently voided (1)-(3) at runtime.
 #
 # WHAT THIS DOES *NOT* PROVE (honest gaps — it is STATIC, offline, cluster-free):
 #   - That the record is gone from Cloudflare. Live read; belongs beside
@@ -90,9 +93,18 @@ CHECKS = 0
 #   ControllerValue = "dns-controller"                  -> the value that CLAIMS an object
 # source/annotations/processors.go IsControllerMismatch skips a source object when the key is
 # PRESENT and the value is NOT ControllerValue. So "disowned" == key present, value != claimed.
-CONTROLLER_KEY = "external-dns.alpha.kubernetes.io/controller"
+#
+# THE PREFIX IS NOT A CONSTANT OF NATURE. Every key external-dns reads is `<annotationPrefix><name>`,
+# and the prefix is a runtime flag whose DEFAULT moved in v0.22.0 (#6424: alpha -> GA, "with no
+# fallback"). On 2026-11-07 the chart bump to v0.23.0 made every key below invisible to the running
+# controller while this check — which only asserted the keys were PRESENT — stayed green. (8) now
+# ties ANNOTATION_PREFIX to the HelmRelease's explicit `annotationPrefix`.
+ANNOTATION_PREFIX = "external-dns.alpha.kubernetes.io/"
+CONTROLLER_KEY = ANNOTATION_PREFIX + "controller"
 CONTROLLER_CLAIMED = "dns-controller"
-HOSTNAME_KEY = "external-dns.alpha.kubernetes.io/hostname"
+HOSTNAME_KEY = ANNOTATION_PREFIX + "hostname"
+# Any key that looks like an external-dns annotation, under ANY prefix variant (alpha, GA, typos).
+EXTERNAL_DNS_KEY_RE = re.compile(r"^external-dns(\.[a-z0-9-]+)*\.kubernetes\.io/")
 
 
 def check(cond, msg):
@@ -231,9 +243,7 @@ for sub in SCAN_DIRS:
             ann = md.get("annotations") or {}
             if kind == "HTTPRoute":
                 routes.append((rel, d))
-            elif kind == "Service" and any(
+            elif kind == "Service" and any(EXTERNAL_DNS_KEY_RE.match(a) for a in ann):
-                a.startswith("external-dns.alpha.kubernetes.io/") for a in ann
-            ):
                 dns_services.append((rel, d))
 
 check(len(routes) > 0, "inventory: no HTTPRoute found under apps/ platform/ runbooks/ — parse "
@@ -444,6 +454,67 @@ check(
     "and the whole-repo-invariants-wired meta-test fails the gate on a hand-written stage.",
 )
 
+# =============================================================================================
+# (8) THE RUNNING CONTROLLER READS THE PREFIX THIS TREE WRITES.
+#     (a) the external-dns HelmRelease sets `values.annotationPrefix` EXPLICITLY (an upstream
+#         default is exactly what moved under us) and it equals ANNOTATION_PREFIX;
+#     (b) it does not ALSO enable `--enable-legacy-annotation-prefix` (dual-read hides a
+#         half-migration; upstream says the flag will be removed);
+#     (c) every external-dns-looking annotation key on any object under apps/ platform/ runbooks/
+#         uses ANNOTATION_PREFIX — a key under another prefix is silently ignored at runtime;
+#     (d) catalog/render.py emits no external-dns key under another prefix.
+#     Migrating to the GA prefix = change ANNOTATION_PREFIX, the HelmRelease value, the renderer
+#     and every manifest in ONE commit; this assertion fails on any partial state.
+# =============================================================================================
+HR_PATH = ROOT / "platform/externaldns/helmrelease.yaml"
+hr = next((d for d in docs_of(HR_PATH) if d.get("kind") == "HelmRelease"
+           and (d.get("metadata") or {}).get("name") == "external-dns"), None)
+check(hr is not None, f"(8) {HR_PATH.relative_to(ROOT)} holds no HelmRelease `external-dns` — "
+                      f"cannot prove which annotation prefix the controller reads")
+values = ((hr or {}).get("spec") or {}).get("values") or {}
+hr_prefix = values.get("annotationPrefix")
+check(
+    hr_prefix == ANNOTATION_PREFIX,
+    f"(8a) external-dns HelmRelease `values.annotationPrefix` is {hr_prefix!r}, but every "
+    f"external-dns annotation in this tree uses {ANNOTATION_PREFIX!r}. A mismatch (or relying on "
+    f"the upstream default, which changed in v0.22.0) makes the controller IGNORE `controller: "
+    f"none`, the Gateway `target` and Service `hostname` — internal names go public, public names "
+    f"answer RFC1918 (incident 2026-11-07).",
+)
+extra = values.get("extraArgs") or []
+extra_s = " ".join(f"{k}={v}" for k, v in extra.items()) if isinstance(extra, dict) \
+    else " ".join(map(str, extra))
+check("enable-legacy-annotation-prefix" not in extra_s and "annotation-prefix" not in extra_s,
+      "(8b) external-dns extraArgs must not set --annotation-prefix or "
+      "--enable-legacy-annotation-prefix; the prefix is declared ONLY via values.annotationPrefix "
+      "so this check can see it")
+
+foreign: list[str] = []
+seen_keys = 0
+for sub in SCAN_DIRS:
+    base = ROOT / sub
+    if not base.is_dir():
+        continue
+    for p in sorted(base.rglob("*.yaml")):
+        rel = p.relative_to(ROOT).as_posix()
+        for d in docs_of(p):
+            for k in annotations_of(d):
+                if isinstance(k, str) and EXTERNAL_DNS_KEY_RE.match(k):
+                    seen_keys += 1
+                    if not k.startswith(ANNOTATION_PREFIX):
+                        foreign.append(f"{rel}:{'/'.join(ident(d))} {k}")
+check(seen_keys > 0, "(8c) no external-dns annotation found anywhere — parse contract broken "
+                     "(the Gateway target alone guarantees at least one)")
+check(not foreign,
+      f"(8c) external-dns annotations under a prefix the controller does NOT read "
+      f"({ANNOTATION_PREFIX!r} is configured): {foreign}")
+render_src = read(CATALOG / "render.py")
+bad_render = sorted({m for m in re.findall(r"external-dns(?:\.[a-z0-9-]+)*\.kubernetes\.io/",
+                                           render_src) if m != ANNOTATION_PREFIX})
+check(not bad_render,
+      f"(8d) catalog/render.py emits external-dns keys under {bad_render}, but the controller "
+      f"reads {ANNOTATION_PREFIX!r}")
+
 # =============================================================================================
 if FAILURES:
     for f in FAILURES:

decisions/2026-11-07-l0-externaldns-annotation-prefix.md

@@ -0,0 +1,51 @@
+---
+date: 2026-11-07
+branch: feat/l0-externaldns-annotation-prefix
+title: L0 guard — external-dns annotationPrefix must match every external-dns annotation in the tree
+---
+
+## What changed
+
+`conformance/tests/l0-static/internal-services-publish-no-public-dns/check.sh` gains assertion
+(8). The check is already whole-repo-scoped, so it runs on every gate.
+
+- **(8a)** `platform/externaldns/helmrelease.yaml` must set `values.annotationPrefix` explicitly,
+  and it must equal the check's `ANNOTATION_PREFIX` (`external-dns.alpha.kubernetes.io/`). The
+  check does not trust the upstream default, because that default is what changed.
+- **(8b)** `extraArgs` must not carry `--annotation-prefix` or `--enable-legacy-annotation-prefix`,
+  so the prefix has one declared place.
+- **(8c)** Every external-dns-looking annotation key under apps/, platform/ and runbooks/ must use
+  that prefix. The match is any `external-dns(.x)*.kubernetes.io/` key.
+- **(8d)** catalog/render.py must emit no external-dns key under any other prefix.
+
+`CONTROLLER_KEY` and `HOSTNAME_KEY` are now derived from `ANNOTATION_PREFIX`. The Service
+inventory matches any external-dns prefix variant, not only the alpha one.
+
+Why: on 2026-11-07, external-dns v0.23.0 (whose default prefix is GA) ignored every alpha
+annotation. Assertions (1) to (3) stayed green, because they prove the annotations are present,
+not that the controller reads them. See `decisions/2026-11-07-public-dns-wan-a-record.md`.
+
+This branch is stacked on `fix/public-dns-wan-a-record` (PR #140). Without that fix, (8a) fails,
+which is correct. Merge #140 first.
+
+## What I verified
+
+Run on the host (PyYAML):
+
+- the check passes on this tree: `check OK: 62 assertions passed`.
+- it **fails (8a)** with origin/main's HelmRelease, which has no `annotationPrefix`.
+- it **fails (8c)** when `platform/gateway/gateway.yaml`'s `target` key is changed to the GA
+  prefix.
+
+Toolbox gate: see the PR description.
+
+## What I did NOT verify
+
+- Whether a future chart could read the prefix from somewhere other than `values.annotationPrefix`,
+  for example a renamed chart value. (8a) would then pass while the flag silently vanished from the
+  rendered args. Rendering the chart in the gate would close that gap. Not done: it needs network
+  access or a vendored chart in L0.
+- `conformance/**` is a **sensitive path**. This PR needs the operator's approving review or
+  `/approve-override`. The agent did not post one.
+- The header of the sibling chainsaw-test.yaml still says "external-dns v0.21.0". That is cosmetic
+  and I left it alone.