Add Homebrew release rehearsal and implementation selection

[irl-dan]

Add a provider-free Homebrew packaging gate to the existing four-platform distribution rehearsal. It consumes this build's verified development archives, tests both implementations and exact executable hashes, rejects link overwrites, checks switching and removes only the owned rehearsal installations. Development rehearsal bytes remain non-publishing and do not qualify a release.

The unsigned native RC build also tests its exact already-built release archives. A shared Homebrew execution body consumes a separate native custody adapter binding expected workflow source/version, all report-bound files, four package artifacts, five structured probes, standalone/npm binary equality and compiled binary hashes. It never rebuilds, relabels or grants live qualification. Results retain source, report/manifest/archive identities and cleanup checks. Workflow policy rejects removed, skipped, reordered or unretained Homebrew gates and substituted source/version anchors.

Document prose-bun and prose-rust, both providing prose, with no default alias. Follow-up tap updates use digest-bound public release manifests and installation/upgrade-checked PRs. Actions prepares and tests the update branch; the release owner opens its PR using existing GitHub authentication, preserving organization policy without another publishing token.

Related tap PR1 passes four-platform installation/switching checks and adds conditional genuine-version upgrades with either implementation selected. Distribution PR14 preserves Homebrew renderer style.

Current revision 8a1ed308edb0cfb3a4641a821a0e3a6d59f5d7ee incorporates newly merged overnight main e5aa922b1bbbf9db23b1722094869d98329a7e33 (PRs43–46). Independent reconciliation review confirms all 27 incoming runtime/docs/fixture paths match main byte-for-byte; all non-ownership PR41 files match the prior branch. Both complete ownership blocks are retained. All 15 final-head checks pass: source admission (53 gates each platform), distribution, native builds and exact-release Homebrew, and CodeQL. Checked merge 8c314db6301df05c9a4dba0e701aafe94142d489 has the identical branch tree 74f5c5cb40c32211e327136fbaf3d0631d9d3688. Four native Homebrew receipts bind that source and actual report/manifest/archive/binary identities, with 21 checks each. Default-RC1 PR build bytes are a private rehearsal, not RC3 or a public release.

Local validation: 20 archive/native-custody admission tests, 18 workflow-policy tests and 17 contributor-documentation tests pass. All four original RC2 native artifact trees pass read-only custody controls; root independently verifies the original macOS ARM64 Bun/Rust hashes. Credential/private-path and diff checks pass. Previous 86b05c5 combined-head validation passed both source suites (53 provider-free gates each), four-platform distribution, four native builds and exact-archive Homebrew gates, and CodeQL. Each exact-archive Homebrew receipt records 21 checks, expected source, native report/manifest/archive/binary hashes and owned cleanup. The automatic build uses its existing RC1 label solely for a private, nonpublishing PR rehearsal; these are not RC3 artifacts.

Two retained macOS source failures exposed fixture timing assumptions: draining 4 MiB through a capacity-one channel inside 250 ms, and expecting terminal output inside a 150 ms run deadline despite allowing escaped-descendant setup two seconds. This revision gives only those fixtures explicit finite budgets (two-second drain; three-second run and five-second elapsed guard). All lossless-drain, cleanup-failure and terminal-observation assertions remain. Production cleanup deadlines and separate short-deadline tests are unchanged. All 27 supervisor unit and 23 fake-harness tests, formatting, staged credential/private-path and diff checks pass locally; independent review confirmed the fixture-only scope.

These changes do not resolve or qualify the separate Bun cleanup observation. No model calls, published release-byte changes, stable promotion or default implementation selection occurred.