test(action): inert apply envelope and commit-only CAS boundary

[rowkav09]

Scope

Gated slice-4 preparation only. Two granular commits add an Ed25519 signed-envelope parser and a dependency-injected commit-only CAS boundary with refusal-path tests. Neither module is exported or wired to dispatch, a workflow, or the GitHub App. Nothing can apply a fix from this PR.

Checks

• pnpm --filter @ghostdeps/action test (24 pass)
• pnpm exec eslint packages/action/src/apply/*.ts
• pnpm exec prettier --check packages/action/src/apply/*.ts

Gates before any user-facing delivery

M3 stability, slice-2 evidence gates, and ADR-0004 execution/security boundary review. The README names further gaps: no runner workflow, live PR/comment/eligibility revalidation, replay tracking, signed file-hash binding, dedicated consumer App token path, or live proof of new-head CI. Keep this draft and do not merge as production apply.

[rowkav09]

GhostDeps independent review - APPROVE the inert code at head 4c65f2ee76ae66464a0d5ab847afe924b65282ef; this is not approval to activate or merge the gated draft.

I reviewed the full diff and merged the current main into a disposable review worktree before testing. These modules are not exported, imported by production code, or invoked from a workflow. The envelope checks shape, size, expiry, recipient, duplicate findings, canonical signature bytes and Ed25519 signature. The commit-only boundary verifies the returned file hashes, restricts the manifest/lockfile pair and paths, reads the head before and after commit creation, and calls a non-force ref update. It does not execute repository code.

The README correctly lists missing production gates: authenticated file-hash binding, actual independent GitHub revalidation, replay persistence, a separate trusted credential path, and ambiguous-write readback. The dependency-injected provenance value and updateRefNonForce interface are not a security proof by themselves. Keep this draft unmerged and unactivated until those gates and the broader M3/slice-2/ADR-0004 prerequisites are independently settled.

Merged-tree Action tests passed 24/24; workspace build, ESLint, Prettier, and diff check passed. All six hosted checks for this head were green when checked. I did not merge.