feat(ai): lazy-load provider modules for faster startup fixes #2297

AGENTS.md

@@ -136,14 +136,16 @@ Adding a new provider requires changes across multiple files:
 ### 2. Provider Implementation (`packages/ai/src/providers/`)
 Create provider file exporting:
 - `stream<Provider>()` function returning `AssistantMessageEventStream`
+- `streamSimple<Provider>()` for `SimpleStreamOptions` mapping
+- Provider-specific options interface
 - Message/tool conversion functions
 - Response parsing emitting standardized events (`text`, `tool_call`, `thinking`, `usage`, `stop`)
 
-### 3. Stream Integration (`packages/ai/src/stream.ts`)
-- Import provider's stream function and options type
-- Add credential detection in `getEnvApiKey()`
-- Add case in `mapOptionsForApi()` for `SimpleStreamOptions` mapping
-- Add provider to `streamFunctions` map
+### 3. Provider Exports and Lazy Registration
+- Add a package subpath export in `packages/ai/package.json` pointing at `./dist/providers/<provider>.js`
+- Add `export type` re-exports in `packages/ai/src/index.ts` for provider option types that should remain available from the root entry
+- Register the provider in `packages/ai/src/providers/register-builtins.ts` via lazy loader wrappers, do not statically import provider implementation modules there
+- Add credential detection in `packages/ai/src/env-api-keys.ts`
 
 ### 4. Model Generation (`packages/ai/scripts/generate-models.ts`)
 - Add logic to fetch/parse models from provider source