chat session actions: parse slash command

[aeschli]

No description provided.

[Copilot]

Pull request overview

This PR adjusts chat session actions to recognize prompt-file slash commands (e.g. /troubleshoot) and attach the corresponding prompt file to the request context, aligning programmatic session creation more closely with the interactive chat widget behavior.

Changes:

• Exported slashReg from the common chat request parser so other components can detect slash commands consistently.
• Updated chat session actions (openSessionWithPrompt and initial prompt sending in openChatSession) to resolve prompt slash commands and attach the corresponding prompt file as context.

Reviewed changes

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

File	Description
src/vs/workbench/contrib/chat/common/requestParser/chatRequestParser.ts	Exports slashReg for reuse outside the parser.
src/vs/workbench/contrib/chat/browser/chatSessions/chatSessions.contribution.ts	Resolves prompt slash commands and appends the prompt file as an attached context entry before sending requests.

Comments suppressed due to low confidence (1)

src/vs/workbench/contrib/chat/browser/chatSessions/chatSessions.contribution.ts:1386

• The prompt-slash-command attachment logic here duplicates the existing implementation in ChatWidget._applyPromptFileIfSet (resolve prompt slash command → compute tool refs → toPromptFileVariableEntry). To avoid these implementations drifting over time, consider extracting a shared helper (e.g. in chatVariableEntries or a prompt-slash-command utility) and using it from both call sites.

		// need to resolve the slash command to get the prompt file
		const slashCommand = await promptsService.resolvePromptSlashCommand(slashMatch[1], CancellationToken.None);
		if (slashCommand) {
			const parseResult = slashCommand.parsedPromptFile;
			// add the prompt file to the context
			const refs = parseResult.body?.variableReferences.map(({ name, offset }) => ({ name, range: new OffsetRange(offset, offset + name.length + 1) })) ?? [];
			const toolReferences = toolsService.toToolReferences(refs);
			return toPromptFileVariableEntry(parseResult.uri, PromptFileVariableKind.PromptFile, undefined, true, toolReferences);
		}