Two guards, one number: bound the published check to the retention it must live with

Gates only. No release, no version bump, no binary published; the agent stays
v0.128.0 at 28ba8593b8 and nothing on a customer's machine changes.

THE COUPLING DEFECT. The registry stopped serving 0.120.0 and older while
check-published-versions.py demanded every tag still be downloadable. Both rules
are sensible and together they are impossible, so CI went red at a commit whose
own run had been GREEN the day before -- and would have gone red again at the
next publish when 0.121.0 was evicted. scripts/retention-policy.json is now THE
number and both readers take it from there.

WHAT CI NO LONGER COVERS, and it prints this on every run rather than leaving it
to be discovered: a released version older than the retention window is no longer
asserted downloadable. Its git tag and its config tree ARE still asserted -- only
the binary's presence is dropped. A missing policy file is INCONCLUSIVE (exit 2),
never silently unbounded.

THE NUMBER IS NOT A LOCATED RULING and the file says so in its own header. Ten is
what the registry demonstrably holds; no register row records a prune, R-210 says
"Nothing was deleted; this is a list, not an action" and concerns local Docker
images, and container packages hold 19 each. The principled bound is the hub's
vouched min_agent floor -- nothing can install below it -- and that is the
recorded follow-up.

check-release-complete.py is the tag half as a machine. release-agent.sh already
warned that "a released version without a git tag 404s a box mid-install, as
root" and the step was still missed, so this is a gate and not a reminder. Legs
1-2 need no network and run in --fast, so the pre-push hook is the earliest
catch. Red-proved by repointing the CHANGELOG head at an unreleased v0.129.0:
both legs convicted and each named its fix command.

Three controls run: green at 10 naming what it dropped; widened to 11 the evicted
version re-enters and convicts; policy removed gives INCONCLUSIVE naming the path.

scripts/check-published-versions.py

@@ -95,6 +95,25 @@ PROBE_CONFIG = "configs/felhom-agent.service"
 
 TAG_RE = re.compile(r"^v(\d+\.\d+\.\d+)$")
 
+# THE retention number, read from the one file that owns it. A check and the policy it enforces
+# must read the same number from the same place, or they drift and the drift looks like a defect
+# in something else — which is exactly what happened on 2026-08-08/09 (R-287).
+RETENTION_FILE = os.path.join(os.path.dirname(os.path.abspath(__file__)), "retention-policy.json")
+
+
+def retention_kept():
+    """How many of the newest generic versions the registry is expected to still serve.
+
+    Fails CLOSED and LOUD: a missing or unreadable policy file makes the check INCONCLUSIVE
+    rather than silently unbounded. An unbounded check would re-create the red this fixed; a
+    silently-bounded one would be worse.
+    """
+    with open(RETENTION_FILE, encoding="utf-8") as fh:
+        n = json.load(fh)["generic_versions_kept"]
+    if not isinstance(n, int) or n < 1:
+        raise ValueError("generic_versions_kept must be a positive int, got %r" % (n,))
+    return n
+
 tried = []
 
 
@@ -189,7 +208,28 @@ def main():
         print("  no v<semver> tags in this repo yet — nothing to check, and nothing proven")
         print("\ncheck-published-versions: NOTHING TO CHECK")
         return 0
-    print("  %d released version(s) to verify: %s" % (len(versions), ", ".join(versions)))
+    all_versions = versions
+    try:
+        keep = retention_kept()
+    except Exception as e:
+        inconclusive("cannot read the retention policy (%s): %s" % (RETENTION_FILE, e))
+
+    # Bound the assertion to what the registry is expected to still hold. Sorted by SEMVER, not
+    # lexically: "0.9.0" > "0.10.0" as strings, and that would silently drop the wrong end.
+    def _key(v):
+        return tuple(int(x) for x in v.split("."))
+    versions = sorted(all_versions, key=_key)[-keep:]
+    dropped = [v for v in all_versions if v not in versions]
+
+    print("  %d released version(s); retention policy keeps the newest %d" % (len(all_versions), keep))
+    print("  verifying: %s" % ", ".join(versions))
+    if dropped:
+        # NEVER silent. A bounded check that does not say what it stopped covering is how a
+        # narrowing becomes permanent by accident.
+        print("  NOT ASSERTED (older than the retention window, and therefore not expected to be")
+        print("  downloadable): %s" % ", ".join(dropped))
+        print("  ^ these versions still have git TAGS and are still installable in the sense that")
+        print("    their configs resolve; what is no longer asserted is the BINARY's presence.")
 
     bad = []
     for v in versions: