Implements steps 3 + 4 of #115, building on the classifier merged in #116. Now that bincraft **v4.4.3** applies registry `patch`/`makevars`/`configure_args` to the *target* package build (previously deps-only), a trial patched build is a meaningful acceptance gate, so the "propose" half is viable.
## Step 3 — propose, do not apply
- **`local/propose-patches.R`** — for each classified, safe fix affecting a package with no current registry entry, emits a pre-filled `registry.json` entry and validates the candidate set against a *temporary* merged registry (the real one is never touched unless asked).
- default: print candidates + validation, **take no action**
- `--write`: append entries to `registry.json` + the proposals ledger (you commit + open the PR)
- `--open-issue`: post/update a Forgejo tracking issue (reuses the weekly-audit `httr2` + `FORGEJO_TOKEN` pattern)
- **`local/trial-build-patch.R`** — isolated bincraft build of one package with the registry applied (no upload/archive/metadata; `patchhash` keeps it out of the real cache). Exit 0/1, so it gates a CI step or manual pre-merge check.
The human gate stays: nothing merges. Acceptance = `validate-patches.R` passes (checked automatically) **and** the trial build succeeds. Novel source diffs and unknown signatures are never proposed (they carry `auto = FALSE`).
## Step 4 — feedback loop
- **`local/proposal-tracking.R`** (read-only) — signature hit rate (builds/pkgs/addressed/open per signature), proposed-vs-merged (a proposal counts merged once its package is in the registry), and retirement candidates (registry entries whose package no longer fails, i.e. likely fixed upstream).
- **`local/proposal-tracking-lib.R`** — the pure metric/ledger helpers.
## Supporting changes
- Refactored the classify helpers to expose a pure `build_triage_report()` + a list-returning entry builder; `failing-builds-report.R` now renders from the shared function (no behaviour change).
- `validate-patches.R` gains optional `PATCH_DIR`/`REGISTRY_FILE` overrides (backward-compatible) so a candidate registry can be validated in isolation.
- Documented the propose/trial-build/tracking workflow in `local/patches/README.md`.
## Verification
- 71 unit tests pass (incl. new `test-proposal-tracking-lib.R`) under the Dockerized R 4.5.3 build env.
- All pre-commit hooks pass (`air-format`, `validate-patches`, prettier, etc.).
- Smoke-tested all three entrypoints end-to-end with a stubbed DB: dry-run, `--write` (produces a registry that passes the canonical validator + a valid ledger, then reverted), and the tracker.
Closes#115
Reviewed-on: #117
## Summary
Adds the curated **patch registry** and wiring that drives bincraft's new package-patching mechanism (see bincraft PR `feat/package-patching`).
Lets specific packages be patched (env/configure/Makevars overrides or source diffs) before pak installs them — including as transitive dependencies — so compiler-/OS-specific failures like RcppParallel's bundled TBB stop cascading.
## What's included
- `local/patches/registry.json` — initial entry: RcppParallel with `RCPP_PARALLEL_USE_TBB=0` for alpine / ubuntu-2604, plus `local/patches/README.md` schema docs.
- `local/validate-patches.R` — validates schema, referenced patch files, and ambiguous overlaps; clean failure + exit 1 (no stacktrace).
- `.pre-commit-config.yaml` — a `validate-patches` hook (re-runs when the registry or the validator changes).
- `local/build-one.R` / `local/build-all.R` — pass `patches = "local/patches"` to `bincraft::build_binary_package()`.
- `specs/2026-06-30-package-patching-design.md` and `plans/2026-06-30-package-patching-implementation.md`.
## ⚠️ Merge ordering (blocker)
This PR adds a `patches = ...` argument to `build_binary_package()` calls.
The `.crow/*.yaml` workflows currently pin bincraft **v4.2.3**, which does not accept that argument — CI will error with `unused argument (patches=...)` until:
1. bincraft **v4.3.0** is released (PR `feat/package-patching`), and
2. the pin is bumped in `.crow/build-all-versions-install-deps.yaml`, `.crow/build-all-versions.yaml`, and `.crow/process-updates.yaml`.
The `.crow` pin bump will be added to this PR once bincraft v4.3.0 is tagged. Do not merge before then.
Reviewed-on: #103
