Step 5a spec-freshness: couple agents prose-pin tests (test_mapping_baselines_wiring_pins.py class) to the .claude/agents family — half-sync gate red

kind: infra

Goal

Close a Step 5a spec-freshness family-coupling gap: prose-pin tests over .claude/agents/*.md content that live OUTSIDE the coupled globs (tests/test_issue_skill_*.py, tests/test_workflow_lint*.py, tests/test_guard_*.py) are not members of any FAMILY_OF entry, so the blind sync refreshes .claude/agents (a singleton family) to current origin/main while those pin tests stay branch-era — the #1824/#1860 half-sync class, reproduced 2026-08-12 in the #2251 session.

Incident (reproduced evidence)

• #2251's Step 5a sync checked out .claude/agents from origin/main; main had (a) removed the prefix-based AND context-based both-arms row from .claude/agents/planner.md AND (b) deleted the pinning test tests/test_mapping_baselines_wiring_pins.py::test_wired_files_name_both_mapping_arms in the same main-side change.
• tests/test_mapping_baselines_wiring_pins.py is in the Step 9c selector universe but in NO Step 5a family, so the worktree kept the branch-era copy (which still carried the deleted test).
• The Step 9c gate ran 8,255 tests; the ONLY failure was that stale pin asserting against the freshly-synced planner.md — a 74-minute gate red on pure vintage skew, costing a full gate re-run.

Proposed fix (implementer to verify the right grain)

Either (a) add a FAMILY_OF coupling in the Step 5a block (.claude/skills/issue/SKILL.md) binding .claude/agents with the agent-prose pin-test files (enumerate the concrete files that pin agents prose — at minimum tests/test_mapping_baselines_wiring_pins.py; sweep tests/ for other .claude/agents readers outside the already-coupled globs, e.g. grep -rl 'claude/agents' tests/ | grep -v test_issue_skill_ | grep -v test_workflow_lint | grep -v test_guard_), or (b) generalize: any test file whose text references .claude/agents/ joins the agents family dynamically. Keep the fail-safe direction (dirty family ⇒ skip whole family, never clobber). Update the FAMILY_OF comment block + the lint --check-lessons-index-adjacent docs if the family table is documented elsewhere; add/extend a pin test for the coupling (the existing tests/test_issue_skill_lint_family_sync.py is the likely home).

Acceptance criteria

1. A Step 5a sync that refreshes .claude/agents also refreshes (or family-skips together with) every test file pinning agents prose outside the already-coupled globs.
2. The coupling is pinned by a test so a future FAMILY_OF edit cannot silently drop it.
3. No change to the fail-safe direction (dirty ⇒ whole-family skip).

Provenance

Surfaced by the /issue 2251 session (2026-08-12) after the Step 9c gate red described above; fingerprint: (step5a-FAMILY_OF, agents-prose-pin-tests-uncoupled).