# Task ID: 55

**Title:** Implement system prompt fetching and caching in mcplocal

**Status:** done

**Dependencies:** 54 ✓

**Priority:** high

**Description:** Add functionality to mcplocal router to fetch system prompts from mcpd and cache them with 60s TTL, supporting template variable replacement.

**Details:**

1. Add system prompt fetching in `/src/mcplocal/src/router.ts`:
   ```typescript
   private systemPromptCache: Map<string, { content: string; expiresAt: number }> = new Map();
   
   async getSystemPrompt(name: string): Promise<string> {
     const cached = this.systemPromptCache.get(name);
     if (cached && cached.expiresAt > Date.now()) {
       return cached.content;
     }
     
     const prompts = await this.mcpdClient.fetch(
       '/api/v1/projects/mcpctl-system/prompts/visible'
     );
     const prompt = prompts.find(p => p.name === name);
     if (!prompt) {
       throw new Error(`System prompt not found: ${name}`);
     }
     
     this.systemPromptCache.set(name, {
       content: prompt.content,
       expiresAt: Date.now() + 60000,  // 60s TTL
     });
     
     return prompt.content;
   }
   ```

2. Add template variable replacement:
   ```typescript
   replaceTemplateVariables(content: string, vars: Record<string, string>): string {
     return content
       .replace(/\{\{prompt_index\}\}/g, vars.prompt_index || '')
       .replace(/\{\{project_name\}\}/g, vars.project_name || '')
       .replace(/\{\{matched_prompts\}\}/g, vars.matched_prompts || '')
       .replace(/\{\{remaining_prompts\}\}/g, vars.remaining_prompts || '');
   }
   ```

**Test Strategy:**

- Unit test: System prompt fetched from mcpd
- Unit test: Cached prompt returned within TTL
- Unit test: Cache miss triggers fresh fetch
- Unit test: Missing system prompt throws error
- Unit test: Template variables replaced correctly
- Unit test: Unknown template variables left as-is
- Integration test: End-to-end fetch and cache