The replacements and policy Bats cases are retired where Go covers them #878

Problem

tests/skills/agent-merge-pr/replacements.bats (235 lines, 19 cases) and policy.bats (409 lines, 31 cases) test gate replacement pairing, owner approval, required-check selection, review readers, APM lockfile reading and protection through the shell scripts. After the wrappers exec Go, those behaviors have Go tests from several children, so the Bats cases either duplicate them or need a real shell.

Part of #324, within #588. Child 16 in #324's Children list. Retires cases of tests/skills/agent-merge-pr/replacements.bats and tests/skills/agent-merge-pr/policy.bats.

Acceptance criteria

1. AC1: Given each of the 50 cases in the files named above, when the ledger is read, then the case is deleted with the name of the Go test that covers it, or kept with a one-line reason it needs a real shell. The ledger also lists any case a prerequisite issue added to these files before this change, with the same disposition.
2. AC2: Given the Go tests named in the ledger, when mise run test-go runs, then each passes and asserts the same outcome as the Bats case it replaces (the coverage comes from children 01 to 03, the review-reader tests, and the protection tests of build(agents): protect replacement Go enforcement paths #753).
3. AC3: Given the cases kept, when mise run test-hooks runs on the files, then they pass against the wrappers.
4. AC4: Given a deleted case, when a regression is introduced in the behavior it covered, then a named Go test fails; the pull request shows one such mutation per ten deleted cases.
5. AC5: Given a search of both test families (tests/skills and tests/hooks) and of the documentation for the helper names and files this change leaves unused, when it runs, then no reference to a removed Bats case or helper remains, and the shared helpers that other suites still load stay in place for child 24.
6. AC6: Non-functional: the Bats suite wall time does not increase.

Scope and non-goals

Scope: the Bats files named in the problem, helpers loaded by them alone, and the ledger in the pull request description.

Non-goal: porting new behavior or editing production code. Non-goal: removing shared helpers other suites still load, which child 24 does. Non-goal: the other agent-merge-pr suites.

Approach

Meet AC1 to AC6 by building the ledger first, then deleting cases whose Go counterpart exists, then mutation-checking a sample and running the reference audit.

Dependencies

Blocked by: #874, #875, #876, #333.

Prerequisites: #333.

Size

S. One pull request, about 645 lines changed, almost all deletions.

Verify plan

• AC1: the ledger lists all 50 cases, plus prerequisite additions, with a disposition each.
• AC2, AC3: mise run test-go and mise run test-hooks tests/skills/agent-merge-pr at the merged head.
• AC4: the sampled mutation runs, with the failing test names.
• AC5: the search output, run over both test families and the documentation.
• AC6: Bats wall times before and after.
• Definition of done: D1 each AC is verified at the merged head, with the commands and results cited in the pull request's Verification. D2 an independent review approves the exact merged head, and every finding has a recorded disposition. D3 required checks pass with no gate loosened. D4 the leak scans the repository specifies are clean, and every post made for this work passes the per-post leak review before it is posted. D5 every commit is signed. D6 the documentation matches the change or the Verification says why there is no impact. D7 every commit has an Assisted-by trailer and the pull request has the provenance:agent-assisted label. D8 the pull request stays within the size limits. D9 follow-ups are filed as issues and listed under Related. D10 the merge closes the issue through a closing reference, the board shows Done, and the final Status: comment names the merge commit.

Risks

A deleted case with no true Go equivalent loses coverage of the gates that decide owner approval and protected paths. The ledger and the mutation sample are the controls. Undo: revert the deletion.

Operator authority

None.