fix(ai): accept responses calls without item ids - #45081

Summary

• accept valid Responses function_call output items that include required call_id but omit optional provider item id
• route streamed arguments and terminal reconciliation using the actual item ID when present or call_id otherwise
• preserve public tool identity and call/result pairing by call_id without inventing provider item metadata
• retain required event-level item_id validation and existing WebSocket incremental continuation

Before and after

The Responses API permits a completed function call without an item ID:

{
  "type": "response.output_item.done",
  "item": {
    "type": "function_call",
    "call_id": "call_1",
    "name": "lookup",
    "arguments": "{\"query\":\"weather\"}"
  }
}

Before: OpenCode ignored the call because item.id was absent.

After: OpenCode emits the normal tool call with ID call_1, parses its arguments, and replays the subsequent history without fabricating a provider item ID:

[
  { "type": "function_call", "call_id": "call_1", "name": "lookup", "arguments": "{\"query\":\"weather\"}" },
  { "type": "function_call_output", "call_id": "call_1", "output": "{\"forecast\":\"sunny\"}" }
]

Argument-stream events still require their own protocol-level item_id; when it differs from call_id, registered output_index routes the event to the correct pending call.

Verification

• bun test test/partial-json.test.ts test/tool-stream.test.ts test/provider/openai-responses.test.ts test/provider/openai-compatible-responses.test.ts test/provider/openai-responses-images.recorded.test.ts test/provider/openai-responses-websocket.recorded.test.ts test/provider/openai-chat.test.ts test/provider/anthropic-messages.test.ts test/provider/bedrock-converse.test.ts test/provider/xai-responses.test.ts test/response.test.ts test/tool-runtime.test.ts --timeout 30000 --only-failures (379 passing)
• RECORDED_PREFIX=openai-responses bun test test/provider/golden.recorded.test.ts --timeout 30000 --only-failures
• bun typecheck from packages/ai
• bunx prettier --check packages/ai/src/protocols/open-responses.ts packages/ai/test/provider/openai-responses.test.ts packages/ai/test/provider/openai-compatible-responses.test.ts