The gate hard-cloned `--branch ${patch_branch}`, so when that branch does not
exist it failed with "Remote branch ... not found in upstream origin". With
cascade detection live the proposer often has no candidates and never
(re)creates the branch, so "branch absent" is the normal "nothing to verify"
state, not an error.
Clone main, then fetch+checkout the patch branch only if it exists; otherwise
log and exit 0. A present branch is verified as before.
Companion to bincraft codefloe #65. Sets `BINCRAFT_VERBOSE_PATCH_BUILD=TRUE` in the trial-build gate so a failed isolated patched build prints the real compiler error instead of `System command 'R' failed`. Harmless on bincraft versions without the flag (unknown env var is ignored). Takes effect once bincraft #65 is released and the build-env images pick it up.
Reviewed-on: #129
Closes the classifier loop (issue #115, step 3): turns the auto-proposable candidates into an actual PR, gated by a real trial build **in our own build-env images**.
Chosen model (from the design discussion): **autonomous PR**, **PR-first with a CI trial-build gate**, **bounded top-N batch** per run.
## Creating the patch PR
- `propose-patches.R` gains:
- `--limit N` -- act on the top-N candidates by failure volume; the rest defer to the next run (logged).
- `--open-pr` -- write the entries onto the reused `auto/registry-patch-proposals` branch, push (with `REPO_RW_TOKEN`), and open/update **one** PR via the Forgejo API (so re-runs update the same PR instead of piling up).
- `.crow/auto-apply-patches.yaml` -- a single job that runs `--open-pr --limit` on a cron/manual trigger. Needs `FORGEJO_TOKEN` + a write-scoped `REPO_RW_TOKEN`.
Novel source diffs and unknown signatures are still never proposed; nothing merges.
## The merge gate (our build-env images)
- `.crow/trial-build-registry.yaml` -- matrixed over the real `OS/IMG` build-env matrix (alpine:3.24, redhat:8/9/10, ubuntu:jammy/noble/**resolute** for ubuntu-2604). Each platform runs `local/trial-build-registry.R`, which diffs the branch registry against `main` and trial-builds **only the entries the branch adds** that apply to that platform, inside `reg.devxy.io/rpkgs/build-env-*`. Green only if every new entry builds; a platform with no new entries is a fast no-op. Nothing is uploaded/archived/recorded.
- The base-registry read **fails loud** if it can't read `registry.json` at `main`, rather than silently treating the base as empty and trial-building the whole registry.
## Notes / follow-up
- The repo uses **no `pull_request` triggers**, so the gate runs manually or on a cron against the branch (`--var patch_branch=...`). Wiring it to fire automatically on the PR needs `event: pull_request` enabled on the Forgejo webhook -- a one-line addition once that's on.
- Two new crons to register in the crow UI: `auto-apply-patches` and `trial-build-registry`. New secret needed: `REPO_RW_TOKEN` (write scope) for the push.
## Verification
- New pure helpers `entry_applies_to_os()` / `new_registry_packages()` covered by tests (platform codename/family/wildcard matching; added-vs-unchanged entry detection; per-platform filtering).
- `--limit` smoke (stubbed DB): top-2 by volume proposed, 3 deferred, candidate registry validates.
- Full suite: 105 tests pass; all pre-commit hooks pass (air, prettier, markdownlint, yamllint, validate-patches).
Reviewed-on: #124
