Background - handle empty git repositories

[lszomoru]

Fixes #308596

[Copilot]

Pull request overview

Fixes Copilot Chat Sessions “Background” flows when the workspace is a newly-initialized/empty Git repository (no commits), avoiding Git operations that expect a resolvable HEAD.

Changes:

• Skip branch base resolution when the repository has no HEAD commit.
• Skip baseline/post-turn checkpoint creation when the repository has no HEAD commit.

Show a summary per file

File	Description
extensions/copilot/src/extension/chatSessions/vscode-node/folderRepositoryManagerImpl.ts	Avoids calling branch-base resolution in empty repositories by requiring a headCommitHash.
extensions/copilot/src/extension/chatSessions/vscode-node/chatSessionWorktreeCheckpointServiceImpl.ts	Avoids checkpoint creation in empty repositories by requiring a headCommitHash.

Copilot's findings

Comments suppressed due to low confidence (2)

extensions/copilot/src/extension/chatSessions/vscode-node/chatSessionWorktreeCheckpointServiceImpl.ts:88

• Same as above: this warning now fires when the repo exists but has no HEAD commit. Consider adjusting the message to explicitly mention the empty-repo/no-commit case to avoid confusing "No repository found" logs.

		if (!repository || !repository.headCommitHash) {
			this.logService.warn(`[ChatSessionWorktreeCheckpointService][handleRequestCompleted] No repository found for session ${sessionId}, skipping post-turn checkpoint`);
			return;

extensions/copilot/src/extension/chatSessions/vscode-node/chatSessionWorktreeCheckpointServiceImpl.ts:170

• This warning is now emitted both when no repo is found and when the worktree repo is empty (no HEAD commit). Please tweak the message to reflect the empty-repository case so it’s clear why checkpoint creation is being skipped.

			if (!repository || !repository.headCommitHash) {
				this.logService.warn(`[ChatSessionWorktreeCheckpointService][handleAdditionalWorktreesRequest] No repository found for additional worktree ${props.worktreePath}`);
				continue;

• Files reviewed: 2/2 changed files
• Comments generated: 2