fix(round-4): review findings — backfill keying, ratchet evasion, pull guard

[leeovery]

Summary

• Round-4 fresh-eyes review of the unreviewed tail (feat(scoping): promotion routes through first-phase choice + bridge #515–fix(discovery): first-written briefs join the full brief lifecycle #521): 3 minors, 0 majors, all fixed here.
• Backfill keys on the pointer, not the file (brief-synthesis.md): triggering on "had no brief before this write" missed briefs orphaned by a crash between the file write and the un-committed apply, and every brief first-written under the pre-fix(discovery): first-written briefs join the full brief lifecycle #521 prose. Keying on "committed topic whose map item lacks brief_path" (one get per written topic) self-heals both classes in-flow — no migration needed.
• Ratchet evasion closed: the first-phase menu placeholder wrapped across two lines, invisible to check 13's single-line classifier — in both complexity-check.md and its sibling first-phase-routing.md. Un-wrapped so the ratchet counts them; pinned deliberately (these menus carry a model-authored one-line read — genuinely judgment-only prose).
• pull joins the shadow-field guard (fields.cjs): a typo'd phase-headed pull answered ok:true (no-op) where set/push refuse loudly; now refused identically, guard comment describes the real coverage, refusal pinned in the fields suite.

Test plan

• npm test 1590 pass (incl. the simulation suite), test:cli, typecheck, conventions lint green.

🤖 Generated with Claude Code

Stack

1. feat(engine): discovery-map add-batch — the harvest persists in one call (D7) #505
2. feat(engine): manifest apply — batched set/delete across one work unit (D7) #506
3. refactor(prose): task-map family folds onto existing batch forms (D7, stage 3) #507
4. feat(engine): manifest set — two grammars, never mixed #508
5. refactor(prose): dump/read folds — subtree gets replace per-topic loops (D7, stage 5) #509
6. feat(engine): commit --plan — plan storage stages from recorded state (D7, stage 6) #510
7. fix: batching-stack review round — re-resolve rewired, guards symmetric, hardening pinned #512
8. fix: deep-dive round 2 — backbone rule flipped, pre-upgrade paths routed, flow bugs closed #513
9. fix(review-r3): engine hardening + crash-resume seams #514
10. feat(scoping): promotion routes through first-phase choice + bridge #515
11. fix(spec): pin the bugfix source name to the topic #516
12. fix(skills): gate-skip sentence accurate in gate-less phases #517
13. fix(review-entry): name the real upstream — specification and plan #518
14. fix(shared): strip triage-landing's unreachable superseded-research arm #519
15. feat(engine): refuse work-unit-level fields that shadow the phases tree #520
16. fix(discovery): first-written briefs join the full brief lifecycle #521
17. test(sim): pipeline simulation — engine driven end-to-end as a black box #522
18. fix(round-4): review findings — backfill keying, ratchet evasion, pull guard #523 👈 current