feat(start): announce auto-merge default before the run

[OGtwelve]

Summary

Auto-merge is on by default and merges PRs via a gh subprocess — outside Claude Code's tool boundary, so a host repo's git-guard hook can't intercept it. start now prints a banner when auto-merge is active, making the default explicit and pointing at the off switch. Per the chosen direction, the default stays ON (non-breaking).

Changes

• src/cli/commands.ts — new exported autoMergeNotice(autoMerge) helper; runStart prints it (via a new optional stdout seam on StartCtx) before launching the loop.
• docs/commands/start.md — new "Auto-merge" section documenting the default, the banner, and how to disable.

Testing

• New tests in src/cli/commands.test.ts: pure autoMergeNotice on/off, plus runStart emits the banner by default and suppresses it under --no-automerge.
• bun test + node --test green; biome check and tsc --noEmit clean.

Closes #73

Summary by CodeRabbit

• New Features

  • Added an auto-merge notice when starting a PR workflow, so you can see when merges will happen automatically after checks pass.
  • Improved start behavior to support opening PRs without auto-merging, with clear guidance on how to finish later.

• Documentation

  • Updated the start command docs with the new auto-merge behavior and the option to disable it.

[coderabbitai]

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Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

Run ID: 92409219-a863-4e5d-aa5e-338cd68b94d9

📥 Commits

Reviewing files that changed from the base of the PR and between 507cd4b and 1f4d9b0.

📒 Files selected for processing (3)

• packages/aitm/docs/commands/start.md
• packages/aitm/src/cli/commands.test.ts
• packages/aitm/src/cli/commands.ts

📝 Walkthrough

Walkthrough

Adds a autoMergeNotice(autoMerge: boolean) helper that returns a formatted warning banner or null. StartCtx gains an optional stdout sink. runStart emits the notice before runLoop. Tests cover banner presence/absence. Docs describe the auto-merge default and opt-out flags.

Auto-merge notice banner

Layer / File(s)	Summary
autoMergeNotice helper and runStart wiring packages/aitm/src/cli/commands.ts	StartCtx gets an optional stdout callback; autoMergeNotice returns a multi-line warning or null; runStart emits it via ctx.stdout or process.stdout before runLoop.
Tests for banner behavior packages/aitm/src/cli/commands.test.ts	Imports autoMergeNotice; adds unit tests for the helper's return values and two integration-style tests asserting runStart stdout output with and without autoMerge.
Docs packages/aitm/docs/commands/start.md	New ### Auto-merge subsection documents default behavior, the gh subprocess merge path, banner text, and --no-automerge / autoMerge: false opt-out.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~5 minutes

Possibly related issues

• #73 (Reconsider auto-merge-on-by-default): This PR directly addresses option 2 from that issue — surfacing auto-merge prominently in start output with a banner and documenting the --no-automerge / autoMerge: false opt-out path.
• Reconsider auto-merge-on-by-default: subprocess merges bypass host git-guard hooks claude-task-master#104: Raises the same auto-merge subprocess bypass concern; this PR's banner and docs address that same user-facing gap.

Possibly related PRs

• developerz-ai/ai-task-master#11: Modifies the same runStart/StartCtx wiring in cli/commands.ts.
• developerz-ai/ai-task-master#13: Touches --no-automerge flag parsing in parseStart, directly adjacent to this PR's banner logic.
• developerz-ai/ai-task-master#24: Extends StartCtx and adds pre-runLoop behavior in runStart, same extension point as this PR.

Suggested labels

claudetm

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main change: announcing the default auto-merge behavior before start runs.
Linked Issues check	✅ Passed	The changes match issue #73 by surfacing auto-merge in start output and documenting the existing opt-out path.
Out of Scope Changes check	✅ Passed	The PR stays focused on auto-merge notice, docs, and tests with no obvious unrelated code changes.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/automerge-notice-73

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