refactor(adapters): address PR review — jsdoc, casts, zod, finishReason Apply review feedback from PR #545: - Restore JSDoc removed during the openai-base media/summarize refactor (26 blocks across ai-openai, ai-grok, ai-anthropic, ai-gemini, ai-openrouter adapters). Only restore where the documented symbol still exists post-refactor; skip JSDoc tied to removed classes / provider- options interfaces. - Drop `as` casts on stream chunks in ai-openrouter (responses-text.ts output_item.{added,done} handlers, response.completed handler) by typing `NormalizedStreamEvent.item` as the SDK's `OutputItems` discriminated union and `.response` as `Partial`. Discriminated- union narrowing now works without bypass. - Drop request-builder casts in ai-openrouter/{text,responses-text}.ts: `as InputsItem`, `as ChatMessages`, `as ChatContentItems`, `as ResponsesRequest['tools' | 'text' | 'input']`, `as Omit`, `as Record` on modelOptions spread. - Drop SDK-return casts `as AsyncIterable` / `as AsyncIterable` — `EventStream` already is `AsyncIterable`. - Drop `tool as Tool` in the webSearchTool guard — `Tool` is assignable to `Tool` directly. - Remove `'function_call'` from RunFinishedEvent.finishReason union. Normalize OpenAI's legacy v1 function_call termination to `tool_calls` inside chat-completions-text — the SDK-vocabulary value no longer leaks into the public AG-UI type. - Drop redundant `satisfies StreamChunk` from yield/array-element sites across adapters and ai-client tests. The contextual type from `AsyncIterable` / `Array` already validates every emission; the suffix added no extra safety. - Annotate the `ev.*` builders in ai/tests/test-utils.ts with explicit return types (RunStartedEvent, TextMessageStartEvent, …) instead of `satisfies StreamChunk`. Each builder now returns the precise event variant rather than the wide union. - Drop zod from ai-openrouter peerDependencies — no source imports zod; it's only used in tests, where it stays as a devDep. (OpenRouter SDK already declares zod as a regular dep, so transitive consumers aren't affected.) - Clean up mid-PR rename leftovers: stale "openai-compatible adapters" jsdoc in ai-openai/utils/client.ts, and `'openai-compatible'` / `'openai-compatible-responses'` default-name strings in the openai-base test subclasses (now `openai-base` / `openai-base-responses`).