Handle missing task in comment workflow as no-op

[xmtp-coder-agent]

Resolves #116

Summary

When a comment is posted on an issue or PR with no associated Coder task, runComment previously threw NonRetryableError from the locate-task step. That transitioned the workflow instance to errored state — visible in wrangler workflows instances list and Workers Logs as a failure — even though the situation is benign (e.g. a comment on an issue that was never assigned to the agent).

Changes

• src/workflows/steps/comment.ts: locate-task returns null when findTaskByName returns null. runComment checks for this and returns early, silently matching the existing "PR comment with no linked issue" short-circuit. The same pattern is already used in src/workflows/steps/failed-check.ts.
• Malformed SDK shapes (present task but missing id/owner_id scalars) still throw NonRetryableError — that failure mode is distinct and should remain loud.
• src/workflows/steps/comment.test.ts: replaced the "throws NonRetryableError when task not found (PR path)" test with two tests covering silent short-circuit on both PR and issue paths.

Test plan

• npm run check passes locally (typecheck + lint + format + 374 vitest tests).
• New tests assert step.calls ends at locate-task with no reaction, no send-task-input, and no thrown error.
• Regression coverage for the happy path and the malformed-SDK path is unchanged.

🤖 Generated with Claude Code

Note

Handle missing task in comment workflow as a silent no-op instead of throwing

When runComment cannot find a task for an issue or PR, the locate-task step now returns null and the workflow exits early instead of throwing a NonRetryableError. No task input is sent and no GitHub reactions are added.

• Behavioral Change: previously a missing task caused a NonRetryableError; it now silently short-circuits with no error and no side effects.

^{Macroscope summarized 50c156e.}