Poison-pill SQS message can crash ingestion handler before partial-batch failure handling

[m75gyqbsrw-boop]

Summary

A malformed SQS message body can throw an uncaught exception in ingestion-lambda, causing the whole invocation to fail before it returns batchItemFailures. This enables a poison-pill DoS where one bad message repeatedly retries and blocks/co-retries healthy messages in the same batch.

Evidence in code

ingestion-lambda/src/handler.ts

1. processSQSRecord does raw parse with no try/catch:

• const { externalId, objectKey } = JSON.parse(record.body) as ...

2. main processes records via Promise.all(records.map(async ...)).

• If processSQSRecord throws, the mapped promise rejects.
• Promise.all(...) rejects immediately.
• Handler exits without constructing per-item batchItemFailures response.

3. Existing per-record failure pathway (failureWith(...)) only handles returned OperationResult failures, not thrown parse exceptions from processSQSRecord.

Why this matters

• One malformed SQS body can fail the entire Lambda invocation.
• Good records in the same batch are retried unnecessarily.
• In sustained conditions, this can create queue backlog and ingestion delay (availability impact).

Repro (conceptual)

Send a record with non-JSON body (e.g. body: "{") into ingestion queue.
Expected with current code path:

• JSON.parse throws in processSQSRecord
• invocation fails instead of returning { batchItemFailures: [{ itemIdentifier: badMessageId }] }

Recommended fix

1. Make processSQSRecord exception-safe:
   • Wrap JSON.parse in try/catch and return status: 'failure' with reason for malformed body.
2. Keep per-record isolation:
   • Ensure all record-level parsing/validation errors become BatchItemFailure entries, not invocation-level exceptions.
3. Add regression tests:
   • mixed batch (1 malformed + 1 valid) should return only malformed message in batchItemFailures.
   • valid record should still process successfully in same invocation.

Severity

Medium-High (availability / queue processing reliability).