Cloud: tactically disable customAgents when > 1 git repo is detected

[joshspicer]

I think we need API changes in provideChatSessionProviderOptions or add some filter() to enable updating other options based on one option

[Copilot]

Pull request overview

Tactically disables the “Custom Agents” chat session option in multi-repo workspaces by avoiding remote custom agent retrieval and tightening the conditions under which the Custom Agents option group is shown.

Changes:

• Only fetch remote custom agents when exactly one repository is detected.
• Only show the Custom Agents option group when remote agents exist, or when exactly one repo is detected and local-only agent files exist.

Comments suppressed due to low confidence (1)

src/extension/chatSessions/vscode-node/copilotCloudSessionsProvider.ts:677

• When repoIds?.length !== 1, customAgents is forced to [] and the Custom Agents option group will never be shown, but the code still calls getLocalCustomAgentFiles(...), which triggers a workspace file search (vscode.workspace.findFiles). Consider skipping the local scan unless Custom Agents are actually eligible to be displayed (e.g., wrap the whole local-scan + option-group construction in a repoIds?.length === 1 guard).

			const { matches, localOnly } = await this.getLocalCustomAgentFiles(
				customAgents.status === 'fulfilled' ? customAgents.value : []
			);

			if ((customAgents.status === 'fulfilled' && customAgents.value.length > 0) || (repoIds?.length === 1 && localOnly.length > 0)) {