The backfill decided which objects were worth inspecting by looking the package
up in CRAN's current index. CRAN lists only what it currently ships, so a
package it has archived is absent, is never recognised as compiled, and is
never inspected. No verdict is ever recorded for it.
`union_index_records()` meanwhile reads the slot's *own* `NeedsCompilation`,
finds `yes`, and drops the record when the source classifier flags the package
and no safe verdict exists to clear it. The repair cannot rescue it either,
because it works from recorded verdicts and there is no row.
The record is therefore dropped from every per-minor index on every re-index,
permanently. `mixedMem` and `vcpen`, both removed from CRAN, were stuck out of
all three rhel8 per-minor indexes on both architectures that way, surviving a
backfill, two re-indexes and a repair.
Read `NeedsCompilation` from the slot's own flat index instead, which describes
exactly the objects being inspected. It is fetched from the bucket rather than
over HTTPS because this runs inside R, where the edge would route the request
to a per-minor index.
Keyed on `<package>_<version>` rather than the package name: a slot can carry
several versions and only some of them compile.
## 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
