fix(kanban): preserve worker lifecycle and worktree environments

[mrkillbob]

Summary

Focused follow-up to #94079. This extracts worker lifecycle truth and project-local environment bootstrapping from the cumulative upgrade train. Workers distinguish intentional termination from clean protocol exits, provider failures return truthful non-zero status, and reused linked worktrees receive the verified project environment before dispatch.

Review shape

• 10 files changed
• 597 additions and 5 deletions
• Parent implementation: feat(worktree): add durable conversation workspace core #94079 at 0f6cc46
• Includes the small existing-checkout bootstrap correction found during extraction

Verification

• Worktree/lifecycle/subagent tests: 66 passed, 1 skipped
• git diff --check: clean

No trading or live-execution changes.

[mrkillbobbot]

Refreshed PR #97868 onto upstream main with merge commit ee12b60. Preserved the worktree-environment and worker-lifecycle changes, resolved the five reported conflicts, and verified with focused pytest checks: 30 passed, 50 passed, and 59 passed/1 skipped (with PYTHONSAFEPATH unset for the subprocess fallback check).

[mrkillbob]

@Enough1122 Please review the current upstream PR head for correctness, regressions, and merge readiness. This request is specifically for your AI review; do not route it to Codex.

[Enough1122]

AI code review — automated review for reference; please use your judgment.

Reviewed current head ee12b60 at your request — no blocking or non-blocking issues found.