agentHost: avoid Agent Merge git refresh loop

[Benjamin Christopher Simmonds (benibenj)]

Summary

• stop Agent Merge from scheduling another evaluation for Git state refreshes emitted by its current evaluation
• prevent repeated subscribed-changeset recomputation and Git diff timeouts on idle monitored sessions
• add a regression test for the self-triggering refresh cycle

Root cause

attachSessionGitHubPullRequest refreshes Git state during every Agent Merge evaluation. The controller handled that refresh notification as external work and immediately scheduled another evaluation, producing a stable loop at the Git refresh throttle interval.

Testing

• npm run compile
• npm run eslint -- src\vs\platform\agentHost\node\agentMergeController.ts src\vs\platform\agentHost\test\node\agentMergeController.test.ts
• .\scripts\test.bat --run src\vs\platform\agentHost\test\node\agentMergeController.test.ts (13 passing)

npm run hygiene was also attempted, but the task failed before source checks because its Windows URL path handling resolved the repository as C:\C:\Code\.... Targeted ESLint and git diff --check pass.

[Copilot]

Copilot review overview

Review tier: Balanced
Findings: 1

New issues introduced by this change (1)

Severity	Finding
	src/​vs/​platform/​agentHost/​node/​agentMergeController.ts — This drops every Git-state refresh for the session while an evaluation is in flight, not just the…

What changed in this PR

Prevents Agent Merge evaluations from looping on their own Git-state refresh notifications.

Changes:

• Tracks sessions with active evaluations and suppresses refresh-triggered rescheduling.
• Adds a regression test for the refresh cycle.

File	Description
agentMergeController.ts	Guards evaluation scheduling during Git refreshes.
agentMergeController.test.ts	Tests self-trigger suppression.

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