fix: process @/file references in slash command content

[roomote]

Summary

This PR fixes an issue where slash commands were not expanding @/file references when they were included in the command description or body. The files remained as plain text instead of being included in the context.

Problem

When users created slash commands in .roo/commands/ that referenced project files using @/ mentions, these references were not being expanded. The model would receive the literal text @/README.md instead of the actual file contents.

Solution

• Integrated the parseMentions function into runSlashCommandTool to process command content before returning it
• File references in command descriptions and bodies are now properly expanded and included
• Added comprehensive test coverage for the new functionality
• Handles errors gracefully by falling back to original content if processing fails

Changes

• Modified src/core/tools/runSlashCommandTool.ts to process mentions in command content
• Added tests in src/core/tools/__tests__/runSlashCommandTool.spec.ts to verify:
  • Single file reference processing
  • Multiple file references in a single command
  • Error handling when mention processing fails

Testing

• All existing tests pass ✅
• Added 3 new test cases for mention processing ✅
• Type checking passes ✅
• Linting passes ✅

Fixes #8602

---

Important

Fixes slash command file reference processing by integrating parseMentions in runSlashCommandTool.ts.

• Behavior:
  • runSlashCommandTool in runSlashCommandTool.ts now processes @/file references in slash command content using parseMentions.
  • If mention processing fails, logs a warning and uses original content.
• Testing:
  • Added tests in runSlashCommandTool.spec.ts for single and multiple file references, and error handling during mention processing.
• Misc:
  • Mocks parseMentions and UrlContentFetcher in runSlashCommandTool.spec.ts.

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[roomote]

Reviewing my own code again—at least I know who to blame when it breaks.

[roomote]

Critical: Potential null pointer dereference. The provider could be undefined if task.providerRef.deref() returns undefined, but you're using the non-null assertion operator (!) on line 85. This will cause a runtime error if provider is undefined.

You should add a null check before using provider.context:

Suggested change

	const urlContentFetcher = new UrlContentFetcher(provider!.context)
	const provider = task.providerRef.deref()
	if (!provider) {
	pushToolResult(
	formatResponse.toolError("Provider not available for processing mentions in slash command"),
	)
	return
	}
	const urlContentFetcher = new UrlContentFetcher(provider.context)