feat(mcp): implement SearchAdapter with token-efficient formatters (Issue #28)

[prosdev]

Implements Issue #28 - First Adapter + Formatters (SearchAdapter)

Overview

Adds the first concrete MCP adapter: SearchAdapter with token-efficient formatters for semantic code search.

What's New

🎯 SearchAdapter

• Exposes dev_search MCP tool for semantic code search
• Integrates with RepositoryIndexer for vector search
• Input validation: query, format, limit (1-50), scoreThreshold (0-1)
• Structured error handling with error codes
• Token estimation for cost awareness

📊 Formatters

• CompactFormatter: Token-efficient summaries (~20 tokens/result)
  • Format: [score%] type: name (path:line)
  • Default mode for cost optimization
• VerboseFormatter: Full details (~100+ tokens/result)
  • Includes signatures, metadata, line counts
  • Opt-in for detailed exploration
• Token Estimation: ~4 chars/token heuristic
• Empty result handling

✅ Comprehensive Tests (135 passing)

• Formatters: 30 tests (formatting, tokens, edge cases)
• Utils: 15 tests (estimation accuracy, truncation)
• SearchAdapter: 25 tests (validation, execution, mocking)
• Existing: 65 tests (registry, protocol, integration)

🔧 Test Restructuring

• ✅ Moved ALL tests from tests/ to co-located __tests__/
• ✅ Consistent with packages/core and packages/subagents
• ✅ Simpler imports (../module vs ../../../src/module)
• ✅ Works with root vitest.config.ts automatically

API

Tool: dev_search

{
  query: string;              // Natural language search
  format?: 'compact' | 'verbose';  // Default: 'compact'
  limit?: number;             // 1-50, default: 10
  scoreThreshold?: number;    // 0-1, default: 0
}

Response

{
  success: true;
  data: {
    query: string;
    format: 'compact' | 'verbose';
    resultCount: number;
    results: string;          // Formatted results
    tokenEstimate: number;    // Estimated token cost
  }
}

Benefits

• 🎯 Token-efficient by default (compact mode)
• 🔍 Semantic search over exact matching
• 📈 Cost-aware (token estimation)
• ✅ Extensible formatter framework
• 🧪 Well-tested (100% coverage on utils)
• 📁 Consistent monorepo structure

Testing

pnpm test -- mcp-server  # All 135 tests pass
pnpm build               # Clean build
pnpm typecheck           # No errors

Next Steps

• Real MCP client testing (Claude Desktop, Cursor)
• More adapters (GitHub, Explorer, Planner)
• Performance benchmarking

Closes #28