Add dummy action to checkout the PR from session toolbar

[alexr00]

Part of microsoft/vscode#282428

[Copilot]

Pull request overview

This PR adds a "Checkout" action button to the session toolbar for cloud agent pull request sessions. The button appears only when the GitHub Pull Request extension is not activated and allows users to checkout the associated pull request by opening a URI that redirects to the GitHub PR extension.

Changes:

• Adds a new command github.copilot.chat.checkoutPullRequestReroute that constructs a URI to trigger the GitHub PR extension's checkout flow
• Configures the command to appear in the session toolbar for copilot-cloud-agent sessions when the PR extension is not activated
• Adds localization string for the "Checkout" button title

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
src/extension/chatSessions/vscode-node/copilotCLIChatSessionsContribution.ts	Implements the checkoutPullRequestReroute command that parses the session URI and constructs a checkout URL for the GitHub PR extension
package.json	Registers the command and adds it to the session toolbar menu with appropriate visibility conditions
package.nls.json	Adds localization entry for the checkout button title

Comments suppressed due to low confidence (2)

src/extension/chatSessions/vscode-node/copilotCLIChatSessionsContribution.ts:1108

• The variable is named pullRequestNumber but receives a string from SessionIdForCLI.parse(). This creates a type mismatch since pull request numbers should be numeric values. Additionally, the validation check on line 1109 doesn't verify that the value is actually a valid number before using it in the URI construction on line 1118.

		const pullRequestNumber = SessionIdForCLI.parse(resource);

src/extension/chatSessions/vscode-node/copilotCLIChatSessionsContribution.ts:39

• This import should be SessionIdForPr instead of just getRepoId since the function needs to parse copilot-cloud-agent session URIs using SessionIdForPr.parsePullRequestNumber() rather than SessionIdForCLI.parse().

import { getRepoId } from '../vscode/copilotCodingAgentUtils';