prompt service: cache ISlashCommandDiscoveryInfo and IAgentDiscoveryInfo

[aeschli]

No description provided.

[Copilot]

Pull request overview

This PR updates the chat prompt service caching strategy to cache discovery info objects (for agents, slash commands, and skills) rather than caching only the derived arrays, so discovery details can be reused without recomputation.

Changes:

• Cache ISlashCommandDiscoveryInfo and derive IChatPromptSlashCommand[] from it.
• Cache IAgentDiscoveryInfo and derive ICustomAgent[] from it.
• Cache IPromptDiscoveryInfo for skills while keeping telemetry emission in the discovery computation.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
src/vs/workbench/contrib/chat/common/promptSyntax/service/promptsServiceImpl.ts	Switches caches to store discovery info and derives agents/commands/skills from those cached results.
src/vs/workbench/contrib/chat/common/promptSyntax/service/promptsService.ts	Adds new discovery interfaces that embed parsed/resolved objects for slash commands and agents.

Comments suppressed due to low confidence (1)

src/vs/workbench/contrib/chat/common/promptSyntax/service/promptsServiceImpl.ts:739

• onDidLogDiscovery is fired with discoveryInfo that now contains full ICustomAgent objects (including instructions content). The debug bridge stores discoveryInfo for later resolution and only needs file-level metadata; keeping full agent objects there can significantly increase memory usage and retain potentially sensitive prompt/instructions text. Suggest emitting a sanitized/lightweight IPromptDiscoveryInfo for logging (no agent payload), while still caching full agents for getCustomAgents().

			this._onDidLogDiscovery.fire({
				sessionResource,
				name: localize("promptsService.loadAgents", "Load Agents"),
				details,
				discoveryInfo,
				category: 'discovery',
			});