[WalkerTech15]

Summary

• Adds the Phase 2 chat foundation
• Adds conversation state and message validation
• Adds a deterministic mock provider
• Adds the provider adapter interface and registry
• Adds safe provider error handling
• Fixes Windows secret-store concurrency reliability

Security

• No real model API calls
• No network requests
• No plaintext secrets
• No filesystem or shell tools
• Existing permission, audit, and emergency-stop boundaries preserved

Verification

• Unit tests passed
• Electron/Playwright tests passed
• Build passed
• TypeScript passed
• ESLint passed
• Prettier passed
• npm audit: 0 vulnerabilities