Verification — R93 B2 audit_verify_chain Cross-Task Partition

Round: R93 debug-sweep Branch: feature/r93-b2-verifier-partition β task: 635d0ed2-5ee5-4414-93d4-489a07fee1bc

§1. Gates

Gate	Command	Result
Build	`npm run build`	✅ exit 0
Lint	`npm run lint`	✅ exit 0 (initial run flagged unused `ListThoughtRecordsFilters` import; removed; rerun clean)
Test	`npm test`	✅ 3499 / 3500 (1 documented flake: `reputation/tools.test.ts:227` parallel-migration prefix race, per `MEMORY.md`; retry-clean and unrelated to this slice)

Baseline was 3492. Delta = +8 (the 8 new Group D tests added to verifier.test.ts).

§2. Invariant check

ID	Verified by
I-1 (filtered path unchanged)	Existing 24 verifier tests pass — Group B tests at lines 302-353 cover the per-task chain workflow
I-2 (by_task field present when unfiltered)	New: `verifyChainsByTask — two intact chains` asserts `by_task.length === 2`
I-3 (aggregate valid = AND of partition valid)	New: `aggregate valid is false when ANY partition is broken`
I-4 (aggregate broken_count = sum of partitions)	New: `aggregate broken_count equals sum of per-partition broken_counts`
I-5 (record_count = total)	New: assertions on `result.record_count` in multiple tests
I-6 (first_broken_at first across partitions)	New: `aggregate first_broken_at points to the first broken record across partitions (insertion order)`
I-7 (by_task ordered by first-appearance / rowid)	New: `by_task order matches first-appearance (rowid / insertion) order of task_ids`
I-8 (pure verifyChain unchanged)	`git diff` shows `verifyChain` function body unchanged
I-9 (empty DB)	New: `verifyChainsByTask — empty input`
I-10 (single-task DB unfiltered)	New: `verifyChainsByTask — single-task input`

§3. Diff summary

$ git diff --stat origin/main..HEAD
 docs/audits/r93-b2-verifier-partition-audit.md                  | (new ~110 lines)
 docs/contracts/r93-b2-verifier-partition-contract.md            | (new ~70 lines)
 docs/packets/r93-b2-verifier-partition-packet.md                | (new ~110 lines)
 docs/verification/r93-b2-verifier-partition-verification.md     | (new, this doc)
 src/domains/trail/verifier.ts                                   | +110 -3
 src/__tests__/domains/trail/verifier.test.ts                    | +144 -1

Source change: added VerifyChainByTaskRow + VerifyChainsByTaskResult interfaces and the pure verifyChainsByTask(records) helper. Handler closure refactored to delegate to the helper. Unused ListThoughtRecordsFilters import removed (it was used in the inlined version of the handler but not after refactor).

§4. Refactor decision (post-packet)

The packet originally proposed inlining all partition logic inside the handler closure. During implementation, the logic was extracted into the exported verifyChainsByTask(records) helper so the Group D tests could drive it directly with fabricated ThoughtRecord[] arrays — mirroring how Group A tests drive verifyChain directly. The handler is now a 1-line return verifyChainsByTask(listThoughtRecords(db));. This avoids the alternative of constructing a paired Client+InMemoryTransport fixture inside verifier.test.ts and overriding the getDb() singleton, which would have added significant fixture surface.

VerifyChainByTaskRow and VerifyChainsByTaskResult are now public exports from src/domains/trail/verifier.ts. They are additive; existing consumers of VerifyChainResult (verifier.test.ts line 34, and any external callers — none found in src/** grep) are unaffected.

§5. Result

PASS. Ready to commit, push, PR. Writeback to follow.