build-cran-binaries/.superpowers/handoff/final-fix2-bincraft-report.md

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# final-fix2-bincraft-report
## Summary
Critical correctness fix for the `bincraftr` package-patching feature.
Without `Built:` in the PACKAGES index, pak recompiles from the source tarball, silently discarding build-time fixes baked in at patch time (e.g. `RCPP_PARALLEL_USE_TBB=0`).
---
## Fix 1 — production code (`R/patches.R`)
One-line change in `prepare_patched_repo()`:
```r
# BEFORE (broken)
tools::write_PACKAGES(contrib, type = "source")
# AFTER (fixed)
tools::write_PACKAGES(contrib, type = "source", fields = "Built")
```
`tools::write_PACKAGES` only emits extra fields when explicitly requested via the `fields` argument.
Without it, the `Built:` line present in the tarball's DESCRIPTION is silently dropped from the PACKAGES index.
---
## Fix 2 — regression test (`tests/testthat/test-patches.R`)
Test: `"prepare_patched_repo src/contrib layout is resolvable by available.packages"`
Two additions:
1. The minimal `pkgfoo` DESCRIPTION written into the tarball now includes a `Built:` line:
```
Built: R 4.5.3; x86_64-pc-linux-gnu; 2026-06-30 00:00:00 UTC; unix
```
This makes the tarball look like a real prebuilt binary package.
2. After `prepare_patched_repo(...)`, a new assertion checks the index:
```r
pkgs <- readLines(file.path(out, "src", "contrib", "PACKAGES"))
expect_true(any(grepl("^Built:", pkgs)))
```
The real `tools::write_PACKAGES` is used (not mocked) so the assertion is meaningful.
The older "serves a cached binary and writes an index" test continues to mock `tools::write_PACKAGES` — that is intentional (it tests orchestration only).
---
## RED / GREEN evidence
Verified with a standalone script calling the real `tools::write_PACKAGES` on an identical tarball:
```
RED (old, type="source", no fields) — Built in PACKAGES: FALSE
GREEN (new, type="source", fields="Built") — Built in PACKAGES: TRUE
```
---
## Test run (post-fix)
```
[ FAIL 0 | WARN 0 | SKIP 1 | PASS 42 ]
```
SKIP: e2e test (`BINCRAFT_PATCH_E2E` not set) — expected.
All 42 unit/integration tests pass.
---
## Commit
```
10e610f fix(patches): preserve Built field so pak installs patched binary without recompiling
```
Branch: `feat/package-patching`
Repo: `/Users/pjs/git/codefloe.com/rpkgs/bincraftr`