chat: add support for agent plugin sources

[connor4312]

• Adds support for agent plugins to reference sources as specified in
  PLUGIN_SOURCES, enabling installation from GitHub, npm, pip, and
  other package registries
• Integrates source parsing and validation into the plugin installation
  service and repository service
• Adds comprehensive test coverage for plugin source handling and
  installation from various sources
• Creates PLUGIN_SOURCES.md documentation describing how to specify
  plugin source configurations

(Commit message generated by Copilot)

[Copilot]

Pull request overview

Adds first-class support for installing Agent Plugins from multiple “source” types (relative path in a marketplace repo, GitHub/git URL, npm, pip), including parsing/validation of marketplace.json source and wiring install/update flows through repository + install services.

Changes:

• Introduces PluginSourceKind + sourceDescriptor on marketplace plugins and parsing/label helpers (parsePluginSource, getPluginSourceLabel).
• Extends repository/install services to clone/update git sources and run npm/pip installs via the terminal.
• Updates UI + discovery plumbing to use a new IAgentPlugin.label for display, and adds/updates tests accordingly.

Reviewed changes

Copilot reviewed 16 out of 16 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/vs/workbench/contrib/mcp/common/discovery/pluginMcpDiscovery.ts	Uses plugin-provided label for MCP collection display name.
src/vs/workbench/contrib/chat/test/common/promptSyntax/service/promptsService.test.ts	Updates test plugin objects to include label.
src/vs/workbench/contrib/chat/test/common/plugins/pluginMarketplaceService.test.ts	Adds unit tests for plugin source parsing/label formatting.
src/vs/workbench/contrib/chat/test/browser/plugins/pluginInstallService.test.ts	New tests covering install/update behavior for multiple source kinds.
src/vs/workbench/contrib/chat/test/browser/plugins/agentPluginRepositoryService.test.ts	Extends repo service tests for revision-aware git source URIs + updates.
src/vs/workbench/contrib/chat/common/plugins/pluginMarketplaceService.ts	Adds sourceDescriptor model, parsing/validation, labels, and storage migration.
src/vs/workbench/contrib/chat/common/plugins/agentPluginServiceImpl.ts	Populates IAgentPlugin.label during discovery.
src/vs/workbench/contrib/chat/common/plugins/agentPluginService.ts	Adds label to IAgentPlugin.
src/vs/workbench/contrib/chat/common/plugins/agentPluginRepositoryService.ts	Extends repository service interface for non-repo plugin sources.
src/vs/workbench/contrib/chat/browser/pluginInstallService.ts	Implements install/update flows for git/npm/pip sources via repo service + terminal.
src/vs/workbench/contrib/chat/browser/agentPluginsView.ts	Threads sourceDescriptor through UI items and uses plugin label for display.
src/vs/workbench/contrib/chat/browser/agentPluginRepositoryService.ts	Implements cache paths + clone/update/checkout for git sources; cache URIs for npm/pip.
src/vs/workbench/contrib/chat/browser/agentPluginEditor/agentPluginItems.ts	Adds sourceDescriptor to marketplace plugin item shape.
src/vs/workbench/contrib/chat/browser/agentPluginEditor/agentPluginEditor.ts	Uses plugin label for installed items and threads sourceDescriptor.
extensions/git/src/git.ts	Adds clone targetName support to clone into an exact folder name.
extensions/git/src/commands.ts	Changes _git.cloneRepository to take a localPath and adds _git.checkout command.

Comments suppressed due to low confidence (2)

src/vs/workbench/contrib/chat/common/plugins/pluginMarketplaceService.ts:705

• PR description mentions adding a PLUGIN_SOURCES.md document, but it doesn’t appear to be included in this change set (no file found in the repo). Either add the documentation file as described, or update the PR description to match what’s actually being shipped.

 * Parse a raw `source` field from marketplace.json into a structured
 * {@link IPluginSourceDescriptor}. Accepts either a relative-path string
 * or a JSON object with a `source` discriminant indicating the kind.
 */
export function parsePluginSource(

src/vs/workbench/contrib/chat/browser/pluginInstallService.ts:295

• _waitForTerminalCommandCompletion resolves undefined on timeout, but _runTerminalCommand treats any exitCode !== 0 as failure, so a timeout results in an error like “Command exited with code undefined”. Handle the timeout case explicitly (eg show a dedicated timeout error and/or return failure before formatting the exit code message).

			const timeoutHandle: CancelablePromise<void> = timeout(120_000);
			disposables.add(toDisposable(() => timeoutHandle.cancel()));
			void timeoutHandle.then(() => {
				if (isResolved) {
					return;
				}
				this._logService.warn('[PluginInstallService] Terminal command completion timed out');
				resolveAndDispose(undefined);
			});
		});

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[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

@lszomoru

Matched files:

• extensions/git/src/commands.ts
• extensions/git/src/git.ts

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

@lszomoru

Matched files:

• extensions/git/src/commands.ts
• extensions/git/src/git.ts