feat: delete worktrees when Linear issue moves to Done or Cancelled

[cyrusagent]

Assignee: @PaytonWebber (payton)

Summary

When a Linear issue transitions to "Done" or "Cancelled" state, automatically clean up associated worktrees. This replaces the previous external CYHOST-triggered cleanup flow, which no longer works with multi-repo sessions (CYPACK-910).

• Detect Linear issue state changes via new IssueStateChangeMessage type and isIssueStateChangeWebhook type guard
• Implement GitService.deleteWorktree() supporting both single-repo and multi-repo layouts
• Wire EdgeWorker to stop active sessions and delete worktrees when issues are completed/canceled

Implementation

New message type (packages/core)

• Added "issue_state_change" to the MessageAction union
• Created IssueStateChangeMessage interface with newStateType field
• Created LinearIssueStateChangePlatformData platform data type
• Added isIssueStateChangeMessage() type guard

Webhook detection (packages/core)

• Created IssueStateChangeWebhook type for Issue/update webhooks where stateId changed in updatedFrom
• Created isIssueStateChangeWebhook() type guard — checked before isIssueTitleOrDescriptionUpdateWebhook to avoid conflicts

Message translation (packages/linear-event-transport)

• Added translateIssueStateChange() to LinearMessageTranslator
• Extracts new state type from data.state.type (e.g., "completed", "canceled")

Worktree deletion (packages/edge-worker)

• GitService.deleteWorktree(workspaceBaseDir, issueIdentifier):
  • Detects worktrees under the path (single-repo: root dir is worktree; multi-repo: subdirs are worktrees)
  • Runs git worktree remove --force for each before rm -rf
  • Graceful no-op when directory doesn't exist
  • Prunes stale worktree references
• EdgeWorker.handleIssueStateChangeMessage():
  • Only acts on completed and canceled states
  • Stops all active sessions before worktree deletion
  • Searches across all repositories if cached repository not found

Edge cases handled

• Issue reopened after Done — worktree already deleted, new session re-creates it (existing behavior)
• Session still running — stopped before deletion
• Worktree already deleted manually — graceful no-op with info log
• git worktree remove fails — warns and continues with directory deletion

Testing

• 6 type guard tests (isIssueStateChangeWebhook)
• 4 translator tests (completed, canceled, precedence over title change, non-state updates)
• 4 GitService deletion tests (missing dir, single-repo, multi-repo, error handling)
• All 545 edge-worker tests passing
• TypeScript type checking clean
• Linting clean

Links

• Linear: CYPACK-958
• Parent: CYPACK-910