Document Agent Merge draft PR and changes workflows

[ntrogh]

Product change

• Sources: agentHost: add draft PR Agent Merge operation vscode#333964 and agentHost: Show Agent Merge changes in Agents Window vscode#334045
• Merged: 2026-09-02T16:17:59Z to 2026-09-02T21:25:14Z

The experimental Agent Merge workflow now includes Create Draft PR & Agent Merge. The pull request remains a draft while Agent Merge addresses blockers and can then be marked ready. The Agents Window can also show Agent Merge Changes, which compares the latest completed Agent Merge repair turn with the preceding completed user turn.

Why the docs need an update

docs/agents/run/agents-window.md describes enabling Agent Merge after a pull request exists and lists the available changesets, but it does not cover the draft pull request workflow or the Agent Merge Changes comparison.

Suggested documentation

• docs/agents/run/agents-window.md: Add the draft pull request entry point, explain when Mark Ready is available, and describe Agent Merge Changes and when it contains results.

Details to verify

• Both additions are part of the experimental Agent Merge workflow.
• Agent Merge Changes is populated only after a completed repair turn and compares it with the preceding completed user turn.

Acceptance criteria

• The Agent Merge documentation covers creating a draft pull request and moving it to ready status.
• The Changes guidance accurately describes Agent Merge Changes and when it is available.