# Task ID: 52

**Title:** Implement tool call intercept with briefing injection

**Status:** done

**Dependencies:** 50 ✓, 51 ✓

**Priority:** high

**Description:** When a gated session calls a tool without first calling begin_session, intercept the call, extract keywords, match prompts, and inject the briefing alongside the real tool result.

**Details:**

1. Implement handleInterceptedCall in `/src/mcplocal/src/router.ts`:
   ```typescript
   async handleInterceptedCall(
     sessionId: string,
     toolName: string,
     args: any
   ): Promise<ToolResult> {
     // 1. Extract keywords from tool call
     const keywords = this.keywordExtractor.extractKeywords(toolName, args);
     
     // 2. Match prompts using keywords
     const { fullContent, indexOnly, remaining } = 
       await this.promptSelector.selectPrompts(keywords, this.promptIndex);
     
     // 3. Execute the actual tool call
     const actualResult = await this.routeToolCall(toolName, args);
     
     // 4. Build briefing with intercept preamble
     const briefing = this.buildBriefing(fullContent, indexOnly, remaining, 'intercept');
     
     // 5. Ungate session
     this.ungateSession(sessionId);
     
     // 6. Send notifications/tools/list_changed
     await this.sendToolsListChanged();
     
     // 7. Return combined result
     return {
       content: [{
         type: 'text',
         text: `${briefing}\n\n---\n\n${actualResult.content[0].text}`
       }]
     };
   }
   ```

2. Use gate-intercept-preamble system prompt for the briefing prefix

**Test Strategy:**

- Unit test: Tool call while gated triggers intercept
- Unit test: Keywords extracted from tool name and args
- Unit test: Prompts matched using extracted keywords
- Unit test: Actual tool still executes and returns result
- Unit test: Briefing prepended to tool result
- Unit test: Session ungated after intercept
- Unit test: notifications/tools/list_changed sent
- Unit test: Intercept preamble included in briefing
- Integration test: End-to-end intercept flow