## Summary
Closes the deferred-since-day-one cache-server gap (documented as "Cache server (deferred)" in `infra/README.md` and mentioned every time we hit a slow CI install).
**Root cause.** `act_runner`'s built-in cache server binds inside the runner container and advertises an IP on the compose-defined `apf-portal-act-runners` bridge — but jobs are spawned via the mounted `/var/run/docker.sock`, which puts them on Docker's anonymous default `bridge`. The advertised URL is unreachable from the job, every cache request burns a ~2 min `ETIMEDOUT` (restore + save), the hit rate is zero.
**Fix.** Tell `act_runner` to attach jobs to the same compose-defined bridge as the runners, via `container.network` in the shared `runner-config.yaml`. The advertised cache URL becomes a normal internal-network DNS hop, jobs reach the cache server, `cache: 'pnpm'` works end-to-end.
**Blast-radius trade-off** (bounded). Every container on `apf-portal-act-runners` is one of our runner containers, plus the jobs they spawn — all of which already have full docker-socket access. Sharing a network doesn't widen what a malicious workflow can already do; it just lets jobs reach the cache server.
## What lands
- `infra/runner-config.yaml` — add `container.network: apf-portal-act-runners`. Surface the `cache.enabled: true` default explicitly so the toggle is discoverable.
- `.gitea/workflows/ci.yml` — re-enable `cache: 'pnpm'` on every `actions/setup-node` step (5 jobs). Drop the now-stale block comment that explained the disablement.
- `.gitea/workflows/security-scheduled.yml` — same on the two setup-node steps.
- `infra/README.md` "Cache server" section rewritten — was `"(deferred)"`, now describes the working setup, rationale, and the disable toggle.
- `ci.yml`'s Trivy comment trimmed to drop the cross-reference to the deferred-cache-server section that no longer exists.
## Roll-out (manual, post-merge, on the runner host)
```bash
cd <repo>/infra
git pull
./ci-runners.sh rotate
```
`rotate` recreates the containers with the new `runner-config.yaml` mount intact (rolling restart, ~15 s pause between each runner so the CI pipeline stays online).
## Test plan
- [ ] CI green on this PR (the gates run on the runners as configured **before** rollout, so this PR's run is one last "uncached" cycle).
- [ ] After rollout, the next CI run's `Set up Node.js` step shows the cache restore attempt **succeed quickly** (no ETIMEDOUT). The `Run pnpm install --frozen-lockfile` step on the first post-rollout run still reports `Progress: resolved N, reused 0, downloaded N` (cold seed).
- [ ] The **second** post-rollout run reports `reused N, downloaded 0` (or a small downloaded delta if Renovate moved a dep meanwhile) — the cache hit is real.
- [ ] `Complete job` step at the end no longer shows `reserveCache failed: connect ETIMEDOUT` warnings.
- [ ] Wall-clock for a typical PR's CI drops by ~5-10 min (5 jobs × ~30-90 s saved on `pnpm install` + the 2× ~2 min ETIMEDOUTs we used to eat).
---------
Co-authored-by: Julien Gautier <julien.gautier@apf.asso.fr>
Reviewed-on: #82
julien
a463199728