Add optional head_ref property to RemoteAgentJobPayload for async branching support (#7088)

* Initial plan

* Add optional head_ref property to RemoteAgentJobPayload for async branching

Co-authored-by: joshspicer <23246594+joshspicer@users.noreply.github.com>

* Update async branch naming to follow copilot/vscode<TIMESTAMP> spec

Co-authored-by: joshspicer <23246594+joshspicer@users.noreply.github.com>

* Remove low-value tests for RemoteAgentJobPayload interface

Co-authored-by: joshspicer <23246594+joshspicer@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: joshspicer <23246594+joshspicer@users.noreply.github.com>

Author: Copilot

src/github/copilotApi.ts

@@ -19,6 +19,7 @@ export interface RemoteAgentJobPayload {
 		body_placeholder?: string;
 		body_suffix?: string;
 		base_ref?: string;
+		head_ref?: string;
 	};
 	run_name?: string;
 }

src/github/copilotRemoteAgent.ts

@@ -213,7 +213,7 @@ export class CopilotRemoteAgentManager extends Disposable {
 			if (!this.autoCommitAndPushEnabled()) {
 				return { error: vscode.l10n.t('Uncommitted changes detected. Please commit or stash your changes before starting the remote agent. Enable \'{0}\' to push your changes automatically.', CODING_AGENT_AUTO_COMMIT_AND_PUSH), state: 'error' };
 			}
-			const asyncBranch = `continue-from-${Date.now()}`;
+			const asyncBranch = `copilot/vscode${Date.now()}`;
 			try {
 				await repository.createBranch(asyncBranch, true);
 				await repository.add([]);
@@ -256,7 +256,8 @@ export class CopilotRemoteAgentManager extends Disposable {
 			pull_request: {
 				title,
 				body_placeholder: problemContext,
-				base_ref: ref,
+				base_ref: hasChanges && autoPushAndCommit ? baseRef : ref,
+				...(hasChanges && autoPushAndCommit && { head_ref: ref })
 			}
 		};
 		const { pull_request } = await capiClient.postRemoteAgentJob(owner, repo, payload);