Summary

• Add createCliRuntime(provider) factory function that maps provider name strings to AgentRuntime instances
• Export SUPPORTED_PROVIDERS array and SupportedProvider type for validation and help text
• Input normalized (case-insensitive, whitespace-trimmed); unknown providers throw descriptive Error

Test plan

• 12 tests in src/middleware/runtime-factory.test.ts covering:
  • Provider mapping (4 providers + interface check)
  • Input normalization (case, whitespace, mixed)
  • Error handling (descriptive message, lists supported providers)
  • Instance freshness (distinct instances per call)
  • SUPPORTED_PROVIDERS export validation
• npx vitest run src/middleware/runtime-factory.test.ts — 12 passed
• pnpm lint — 0 warnings, 0 errors
• pnpm format — clean

Closes #19

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