fix(queue): count a multi-family message's rows without crashing its batch

[JSONbored]

Closes metagraphed-infra#370. Prerequisite for metagraphed-infra#359.

The sync-batches consumer opens with a batch summary:

const { valid, invalid } = classifySyncBatch(batch.messages);
const rows = valid.reduce((n: number, m) => n + m.rows.length, 0);

A chain-detail message carries families and no rows at all — packMultiFamilyMessage deletes the key by construction (src/sync-batch-queue.ts). So that read throws a TypeError.

Why a log line could take out four healthy lanes

It throws above the per-message try/catch, so the failure is not scoped to the offending message. The whole batch of up to 10 fails, is retried five times, and dead-letters — every lane co-batched with it. account-balances, hotkey-alpha, validator-nominator-counts and nominator-positions all share this consumer.

syncBatchRowCount was written for exactly this case (it already sums families) and was never imported.

Why nothing caught it

SyncBatchMessage.rows was declared required, and stayed required when families was added alongside it in #9678. m.rows.length therefore typechecks on a shape that has no rows. The only tests driving the real worker.queue covered nominator-positions and account-balances — both single-family — so the multi-family path had unit coverage of its parts and none of its handler.

The fix

• the count goes through syncBatchRowCount
• rows is now optional on the wire type, so the type system enforces the distinction rather than the reader remembering it. packSyncBatchMessages returns a narrowed SyncBatchRowsMessage[] that still guarantees rows, so every existing caller keeps its non-null reads and the tests needed no !
• syncBatchRows — the only other reader — answers [] rather than throwing

Regression test

tests/data-api-sync-queue-consumer.test.ts drives a real multi-family message through worker.queue alongside a single-family neighbour, and asserts the neighbour still acks and still writes. That neighbour is the property that was lost; a families-only test would pass against the broken code's intent and miss the blast radius.

Verified the test reproduces the bug: reverting only the syncBatchRowCount call fails it with TypeError: Cannot read properties of undefined (reading 'length').

Not fixed here

Nothing routes chain-detail today (SYNC_QUEUE_LANES names four lanes and this is not one), so this was a landmine, not an outage. Two things still stand between this and the #359 cutover, both recorded there rather than papered over here:

• the producer posts ~350–662 KiB per chain-detail POST, over the 128 KB transport cap, so packMultiFamilyMessage would throw on the first tick
• the lane declares no pass_total, and the family writer discards the tally argument

Validation

npm run typecheck        # clean
npm run lint             # clean
npx prettier --check     # clean on all four changed files
npx vitest run tests/sync-batch-queue.test.ts tests/data-api-sync-queue-consumer.test.ts \
  tests/data-api-{nominator-positions,account-balances,hotkey-alpha,neurons,validator-nominator-counts}-d1.test.ts \
  tests/chain-detail-sync-route.test.ts   # 232 passed

Patch coverage measured by intersecting the diff's changed lines with a v8 report over both changed files: 0 uncovered statements, 0 uncovered branches.

Template Used

• Backend/code change

[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.

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