fix(renovate): the workflow still named renovate.json, so every run since #79 died with ENOENT

#79 renamed the config to renovate.json5 and left configurationFile pointing at the old
name. Runs 315-322 (2026-10-22..29) all failed in ~1s before Renovate started.

Also add a ci/lint.sh assertion that every workflow configurationFile: resolves to a real
path — valid YAML, so yamllint could not catch it, and the gate stayed green throughout.

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

decisions/2026-10-29-renovate-config-filename.md

@@ -0,0 +1,48 @@
+---
+date: 2026-10-29
+branch: fix/renovate-config-filename
+title: Renovate has failed every run since #79 — the workflow still named renovate.json
+---
+
+## What changed
+
+**`.gitea/workflows/renovate.yaml`** — `configurationFile: renovate.json` → `renovate.json5`.
+
+PR #79 (`fix/renovate-invalid-config`) renamed the config to `renovate.json5` and did not update
+the one line in the workflow that names it. Measured 2026-10-29 from the Gitea Actions log of run
+322 (task 513, schedule, 08:15 UTC):
+
+    Error: ENOENT: no such file or directory, stat '/workspace/Home-Network/home-network-k3s-impl/renovate.json'
+
+Runs 315–322 (2026-10-22 → 10-29, every one listed) are all `failure` on the `schedule` event,
+each failing in about one second. Renovate never started. `RENOVATE_TOKEN` **does** exist as a
+repository Actions secret (listed by name via the API; value not read), so the token preflight
+passes and this filename is the only blocker observed.
+
+**`ci/lint.sh`** — a new assertion after yamllint: every non-comment `configurationFile:` key in
+`.gitea/workflows/*.y*ml` must name a path that exists. This is valid YAML, so yamllint cannot see
+it, and the gate stayed green through 11 days of failures.
+
+## What I verified
+
+- The root cause, from the run log quoted above, and that `origin/main` has `renovate.json5` and
+  no `renovate.json` (`git ls-tree`).
+- The new guard, both ways, run standalone: on this branch it prints
+  `workflow configurationFile references resolve`, rc 0. With the line reverted to `renovate.json`
+  it prints `configurationFile 'renovate.json' does not exist in the repo`, rc 1. My first version
+  also matched its own explanatory comment in the workflow and failed. That is why the grep is
+  anchored to non-comment lines.
+- Toolbox gate: result and rc are reported in the PR, not predicted here.
+
+## What I did NOT verify
+
+- **Renovate has still never completed a run.** This removes the observed blocker. Others may
+  follow it. The test is a `workflow_dispatch` with `dry_run: true` after merge, and its log is
+  the first evidence that Renovate authenticates, extracts dependencies, and honours `.json5`.
+- **The `enabledManagers: ["regex"]` vs `custom.regex` question** (#73, #77) is still open. The
+  same dry-run log answers it: look for the regex/custom manager's dependency-extraction count.
+- **No alert for "Renovate keeps failing".** The guard prevents this specific cause from recurring.
+  Nothing notices a scheduled workflow that is red every day. That gap stays open.
+- **Sensitive path.** `.gitea/**` and `ci/**` are both in `approval-policy.json`. CI will block
+  on `approval-policy` until the operator posts `/approve-override` as a review. The local gate
+  reports that stage as N/A.