fix(indexer): skip malformed events in parseEvents instead of wedging the indexer

[Frun1na]

Closes #179

Summary

parseEvents called parseEvent in a bare loop, but parseEvent throws on malformed token events (and is tested to). The throw escaped pollOnce into the poll loop's catch in src/indexer.ts, which slept and retried the identical ledger range forever. One bad event on chain stopped indexing permanently, and the only symptom was a repeating log line. The docstring claimed it was "silently skipping unrecognised or malformed ones" — it wasn't.

Changes

• [MODIFY] src/decoder.ts

  • parseEvents wraps each parseEvent call in try/catch. A malformed event is logged with its event id, counted, and skipped; the good records in the batch are returned.
  • The malformed count is logged at warn, separately from the existing non-token count at debug, so "a contract we don't index" and "an event we failed to decode" don't read the same.
  • parseEvent is unchanged — it still throws. Only the batch wrapper changes.
  • Docstring corrected to describe what the function actually does.

• [MODIFY] src/metrics.ts

  • New counter events_skipped_total{reason}, registered in the module-local registry.
  • reason is one of two fixed values, malformed / unrecognised — no event ids, addresses or contract ids as label values.

• [MODIFY] README.md

  • Adds events_skipped_total to the /metrics table.

The fix is in the shared batch wrapper, so it also covers the other parseEvents callers (src/indexer/parallel.ts, src/ingest/backfill.ts), not just the single-poll path.

Tests

• [MODIFY] src/__tests__/decoder.test.ts — a [good, malformed, good] batch returns 2 records. The test also asserts that parseEvent alone still throws on the malformed event, so it pins both halves of the contract.

Verification Results

npx jest --runInBand src/__tests__/decoder.test.ts
✅ 8 passed

Same test against main's decoder.ts / metrics.ts
✅ fails (parseEvents throws on the malformed event) — the test is real

npx tsc --noEmit
✅ clean

npx tsc --noEmit -p tsconfig.test.json
✅ clean

npm run build
✅ clean

npm test
✅ 444 passed across 39 suites; coverage thresholds met

Notes

The Integration tests and Load test CI jobs were already red on main before this change (see #177 / #178), so a red result on either is unrelated to this PR.

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[Miracle656]

Verified locally.

• src/__tests__/decoder.test.ts → 8 passed with the fix; against main's src/decoder.ts the new parseEvents › skips a malformed event instead of failing the batch case is the single failure (1 failed, 7 passed). The test is real.
• The try/catch is per event inside the loop with continue, so one bad event cannot swallow the rest of the batch — the [good, malformed, good] case returns both good records.
• The skip is not silent: console.warn per event with the event id, an aggregate warn line, and events_skipped_total{reason}. reason is a two-value enum (malformed / unrecognised) — no event ids, addresses or contract ids as label values, so no cardinality risk.
• npx tsc --noEmit clean.

Your branch had picked up an additive conflict in src/metrics.ts against #209's ledgers_skipped_total, which landed after you opened this. I merged main in and kept both counters (caa97b7 on your branch) rather than bounce it back to you. Nothing else changed.

Merging. Thanks — the docstring on main claimed this already worked, which is the worst kind of bug to inherit.

https://claude.ai/code/session_01USgemLt4Rnz4SGB1Srf3GB