Fix Sentry error on Compose.io GitHub commit webhook events

[Al629176]

Summary

Investigate and fix Sentry error triggered when Compose.io sends GitHub commit events to backend webhook pipeline.

Scope

• Reproduce failing event path from webhook ingest to handler.
• Identify root cause of Sentry exception.
• Implement fix and add guardrails/logging.

Acceptance Criteria

• Error no longer appears for valid GitHub commit events.
• Webhook events process successfully without failure.
• Sentry signal quality improved (no noisy false failures).