feat(ci): detect Gitea settings drift -- the blind spot that hid a month of outage

Every check in this repo reads the repository, the rendered manifests, or the cluster.
NONE could see Gitea's own database, and that is where branch protection and runner
registration live. Three failures came out of that blind spot on 2026-09-29, all the same
shape -- a setting that READ as enforced while not being, with nothing able to notice:

  * main had NO branch protection for ~a month while DECISIONS-LOG recorded it as a
    required status check;
  * ZERO Actions runners were registered, so PR #1 -- the first PR this repo ever had --
    sat pending for 30.6 minutes with nothing to execute it;
  * after enable_status_check and required_approvals were turned on they STILL did not
    bite, because block_admin_merge_override was false: PRs #5-#9 merged with zero
    approvals recorded against required_approvals: 1.

infra/gitea/*.sh ASSERT the desired state. Nothing DETECTED drift from it. This is the
detector.

ci/gitea-settings.sh runs as a merge-gate stage: it diffs the live rule at
/branch_protections/main against infra/gitea/expected-branch-protection.json and asserts at
least one runner is online. It reads the RULE object, not /branches/main -- the branch view
does not expose block_admin_merge_override and showed all-green while the rule was
overridable by the only account that merges.

Verified by test, not assumed:
  no token            -> exit 3, skips loudly, does NOT block
  live == declaration -> exit 0
  injected drift      -> exit 1, blocks, naming both the drifted key and the runner count

The skip is DELIBERATELY not in gate.sh's strict-skips loop. Making an absent credential
block every PR is precisely the lock-yourself-out failure this repo keeps walking into, so
a skip denies a PASS (exit 3) and says loudly what is unverified. REQUIRE_GITEA_SETTINGS=true
upgrades it to a block once the token is wired.

gate.yml's `|| [ "$?" -eq 3 ]` tolerance now covers a second stage. That widening is
declared in the file rather than left to be discovered, and it narrows back the moment
REQUIRE_GITEA_SETTINGS is set.

infra/gitea/set-ci-token.sh mints the token and stores it as the repo Actions secret without
ever printing the value.

UNTIL THAT TOKEN EXISTS THIS STAGE SKIPS, AND A SKIPPED DETECTOR DETECTS NOTHING.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

ci/gate.sh

@@ -112,6 +112,7 @@ run_stage lint          "${CI_DIR}/lint.sh"
 run_stage l0            "${CI_DIR}/l0.sh"
 run_stage render-golden "${CI_DIR}/render-golden.sh"
 run_stage l1            "${CI_DIR}/l1.sh"
+run_stage gitea-settings "${CI_DIR}/gitea-settings.sh"
 run_stage conformance   "${CI_DIR}/conformance.sh"
 
 echo >&2
@@ -188,6 +189,31 @@ case "${OUTCOME[spec-immutability]}" in
   pass) ok   "spec-immutability: green" ;;
 esac
 
+# gitea-settings: the ONLY check that can see Gitea's own database (branch protection +
+# runner registration). A FAIL is real drift and always blocks -- that is the whole point.
+# A SKIP means no token or unreachable Gitea, which is an UNWIRED CREDENTIAL, not a defect
+# in the change under test. It is deliberately NOT in the strict-skips loop below: making an
+# absent secret block every PR is precisely the lock-yourself-out failure this repo keeps
+# walking into (a required check with nothing able to satisfy it). So a skip denies a PASS
+# (exit 3) and says loudly what is unverified. Set REQUIRE_GITEA_SETTINGS=true once the
+# token is wired, and the skip becomes a block as it should.
+case "${OUTCOME[gitea-settings]}" in
+  fail) err "gitea-settings: Gitea DRIFTED from infra/gitea/expected-branch-protection.json -> blocks merge"; BLOCK=1 ;;
+  skip)
+    if truthy "${REQUIRE_GITEA_SETTINGS:-false}"; then
+      err "gitea-settings: skipped and REQUIRE_GITEA_SETTINGS=true -> blocks merge"
+      summary "- gitea-settings: **SKIPPED** (no token) — blocks merge (REQUIRE_GITEA_SETTINGS=true)"
+      BLOCK=1
+    else
+      warn "gitea-settings: skipped (no GITEA_SETTINGS_TOKEN) — branch protection and runner"
+      warn "  registration are UNVERIFIED. Both were silently wrong for a month. Wire the token"
+      warn "  (infra/gitea/set-ci-token.sh), then set REQUIRE_GITEA_SETTINGS=true."
+      summary "- gitea-settings: **SKIPPED** (no token — protection/runners unverified; not a pass)"
+      NOT_ESTABLISHED+=("gitea-settings")
+    fi ;;
+  pass) ok "gitea-settings: green" ;;
+esac
+
 # L0/L1 stages: any failure blocks. A SKIP here means a pinned tool is missing or a seam is
 # unwired — NEVER green. In CI (strict) that is a defect and blocks; on a workstation it
 # degrades to UNDETERMINED, which is still non-zero and still not a pass. render-golden is a