Support immediate re-triggering of completed tasks via TriggerComment

[axon-agent]

Summary

• When TriggerComment is configured and a completed (Succeeded/Failed) task exists, the spawner now compares the latest trigger comment's timestamp against the task's CompletionTime. If the trigger comment is newer, the completed task is deleted and a new one is created.
• This allows users to re-trigger work immediately by posting a new trigger comment, without waiting for TTL cleanup.
• Label-based flows and Cron sources are unaffected — retrigger only activates when TriggerComment is configured and a matching comment is found after task completion.

Key changes

1. internal/source/source.go: Added TriggerTime field to WorkItem to carry the latest trigger comment timestamp from source to spawner.
2. internal/source/github.go: Added CreatedAt to githubComment, refactored fetchComments to return structured comments (preserving timestamps), added latestTriggerTime helper and concatCommentBodies utility.
3. cmd/axon-spawner/main.go: Updated dedup logic — when a completed task exists and the trigger comment is newer than CompletionTime, delete the old task and allow recreation. Existing concurrency and budget limits are still respected.

Test plan

• TestRunCycleWithSource_RetriggerCompletedTask — verifies completed task is deleted and new one created when trigger is newer
• TestRunCycleWithSource_RetriggerSkippedWhenTriggerBeforeCompletion — verifies no retrigger when trigger is older than completion
• TestRunCycleWithSource_RetriggerFailedTask — verifies retrigger works for failed tasks too
• TestRunCycleWithSource_RetriggerSkippedWithoutTriggerComment — verifies no retrigger when TriggerComment not configured
• TestRunCycleWithSource_RetriggerSkippedForRunningTask — verifies running tasks are never retriggered
• TestRunCycleWithSource_RetriggerRespectsMaxConcurrency — verifies maxConcurrency is still enforced after retrigger
• TestLatestTriggerTime — unit tests for the timestamp extraction helper
• TestDiscoverSetsTriggerTime — integration test verifying TriggerTime is set on WorkItem
• TestDiscoverTriggerTimeZeroWithoutTriggerComment — verifies TriggerTime is zero when not configured
• All existing tests pass (make test, make verify)

Fixes #432

🤖 Generated with Claude Code

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Summary by cubic

Enable immediate re-triggering of completed tasks via TriggerComment. Satisfies axon-task-432 by recreating a task when a newer trigger comment is posted.

• New Features

  • Spawner compares WorkItem.TriggerTime to Task.CompletionTime; if the trigger is newer and the task is Succeeded/Failed, delete and recreate. Respects maxConcurrency and maxTotalTasks; running tasks are never retriggered. If creation is blocked, the item is picked up as new on the next cycle.
  • GitHub source captures comment timestamps (CreatedAt), computes the latest matching trigger, and sets WorkItem.TriggerTime.
  • Label-only and Cron-based flows are unchanged; retriggering activates only when TriggerComment is configured.

• Refactors

  • fetchComments now returns structured comments with timestamps; added latestTriggerTime helper and concatCommentBodies to keep existing comment filtering behavior.

^{Written for commit b6d383d. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 5 files