fix(discovery): first-written briefs join the full brief lifecycle

[leeovery]

Summary

• Pre-existing gap found while reviewing fix: deep-dive round 2 — backbone rule flipped, pre-upgrade paths routed, flow bugs closed #513's propagation skip: a brief first-written for an existing committed topic (materially deepened this session; topic originally added by research-analysis/gap-analysis/migration, before briefs existed) produced a file with no brief_path pointer — confirm-and-persist only sets pointers for new working-list topics. The brief was invisible to read-brief-context (silent fallback to the description seed) and exempt from reconcile flagging.
• brief-synthesis B gains a pointer backfill: one set op per first-written existing topic, riding the same ops file as the restructure cleanup.
• C widens from regenerated-only to every brief written in A: in-flight downstream work is flagged whether the brief changed under it or appeared after it started brief-less. The zero-briefs gate keeps the H4 conditional shape from fix: deep-dive round 2 — backbone rule flipped, pre-upgrade paths routed, flow bugs closed #513's review.
• reconcile-advisory wording follows ("written or regenerated", "latest discovery brief").

Test plan

• Conventions lint green (29 checks).

🤖 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 fix(shared): strip triage-landing's unreachable superseded-research arm #519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 👈 current
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