Fix the "update with merge commit" button for non-checked-out PRs

[alexr00]

No description provided.

[Copilot]

Pull request overview

Fixes the “Update with merge commit” (update branch) flow so it works for pull requests that are not currently checked out by routing conflict-free updates through the GitHub GraphQL API, and ensures the webview state reflects update availability after an update attempt.

Changes:

• Prefer updateBranchWithGraphQL() in tryMergeBaseIntoHead for non-conflicting, non-enterprise PRs (including when the PR isn’t checked out).
• Include canUpdateBranch in the pr.update-branch reply and propagate it into the webview PR state.
• Add coverage for the GraphQL update path and for canUpdateBranch being reported after a successful update.

Show a summary per file

File	Description
webviews/common/context.tsx	Applies canUpdateBranch updates returned from the extension host after pr.update-branch.
src/test/github/folderRepositoryManager.test.ts	Adds tests for GraphQL-based update when PR isn’t checked out and for canUpdateBranch reply semantics.
src/github/pullRequestReviewCommon.ts	Updates the webview reply payload to include canUpdateBranch for pr.update-branch.
src/github/folderRepositoryManager.ts	Reorders update logic to attempt GraphQL update before conflict-resolution/local-checkout paths.

Review details

Comments suppressed due to low confidence (1)

src/github/pullRequestReviewCommon.ts:185

• If tryMergeBaseIntoHead returns false, this handler still waits up to ~5 seconds polling mergeability (including setTimeout) before replying. That delays re-enabling the webview button and does unnecessary network work even though the branch update didn’t happen. Consider only polling when mergeSucceeded is true, and otherwise fetch mergeability once and reply immediately.

		const mergeSucceeded = await ctx.folderRepositoryManager.tryMergeBaseIntoHead(ctx.item, true);
		// The mergability of the PR doesn't update immediately. Poll.
		let mergability = PullRequestMergeability.Unknown;
		let attemptsRemaining = 5;
		do {

• Files reviewed: 4/4 changed files
• Comments generated: 0
• Review effort level: Low