BACK-686 - Watch task lists with the existing JSON output

[MrLesk]

Summary

Add backlog task list --json --watch so subscribers receive the full matching list immediately and changed full replacements afterwards. Each response uses the exact existing JSON fields, envelope, indentation, and trailing newline.

Both modes reuse the existing task-list operation, including filters, sorting, limits, and local scope. File notifications and periodic reconciliation trigger refreshes; writes are serialized and unchanged responses are suppressed. Includes shutdown and slow-consumer handling, CLI help, and public instructions.

Related Issue or Task

Closes #1014. Task: BACK-686.

Task Checklist

• Corresponding task in backlog/tasks/
• Clear acceptance criteria
• Implementation plan recorded
• Acceptance criteria verified and completed

Testing

• 71 tests pass across JSON output/watch, watch lifecycle, task lists, ordinal sorting, and agent instructions.
• bunx tsc --noEmit, bun run check ., and bun run build pass.
• Compiled binary verified for byte-identical initial JSON, documented help, and termination.
• Watch tests cover startup changes, missed notifications, atomic edits, removals, filters, readiness, duplicate identities, slow consumers, broken pipes, and termination with an unread 2 MB response.

[MrLesk]

@codex review

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-12T11:40:04.966225Z	ee00aa8	New commits
🔒 Security Review	✅ Completed 2026-09-12T11:39:47.196390Z	acb237e	PR opened

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[MrLesk]

@codex review the latest commit. The follow-up adds the watch tests to platform CI and makes the termination test account for Windows signal behavior.

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 🎉

Reviewed commit: 9a1367509d

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