workflow-fix: Step 9c selector does not map .claude/agents prose files to their token-pin tests

Provenance: surfaced by the Claude code-reviewer on #2364 round 1 (2026-08-27) while auditing the round's Gate-scope line; pre-existing on trunk (Step 0.9 subclass pre-existing-on-trunk), not introduced by #2364.

The gap

The #2364 round edited .claude/agents/codex-code-reviewer.md (Blocker-tags line) and .claude/agents/code-reviewer.md. Two committed tests pin exactly those artifacts byte-identically:

• tests/test_codex_code_reviewer_step09_tag_parity.py (pins the codex Blocker-tags line + the Step 5c-bis strip-subset sentence),
• tests/test_verdict_disagree_observer.py (Blocker-tags vocabulary consumer).

Neither appeared in the implementer's 96-file local union NOR the selector's 205-file Step 9c selection: select_step9c_tests.py has no mapping arm from an edited .claude/agents/*.md file to the prose/token-pin tests that read it (a text-pin test neither imports nor importlib-loads the agent file, so the import-map arm from #1299 and the importlib-literal arm proposed in #2380 both structurally miss it). Edits to agent specs are therefore not gated by their own pin tests at Step 9c; #2364's reviewer discharged the NOT-RUN presumption by hand (71 passed).

Proposed fix (implementing session refines)

Extend the selector's file→test mapping so .claude/agents/<name>.md (and sibling agent-prose surfaces) map to their token-pin tests — either a maintained explicit map (the FAMILY_agents vetted-membership list in .claude/skills/issue/steps/09-step-5.md already enumerates candidates) or a cheap content-scan arm (tests whose source contains the literal edited path). Add a membership assert so the map cannot silently rot (the guard-20 convention in tests/test_issue_skill_lint_family_sync.py).

Acceptance

• Editing .claude/agents/codex-code-reviewer.md alone makes the selector select tests/test_codex_code_reviewer_step09_tag_parity.py.
• The mapping is enumerable + pinned (a new agent-pin test either joins the map or a named exempt list; a lint/test asserts completeness).
• No regression in selector wall-time worth noting (the map is static).