fix(v2): finalize pending OpenAI Responses tool calls at response completion

[opencode-agent]

Summary

OpenCode V2 can leave a local tool call permanently pending when an OpenAI Responses-compatible stream announces a function call but reaches response.completed without a matching response.output_item.done event.

This was observed as an empty Patch card stuck for 13 minutes. Interrupting the session finally changed it to Tool execution interrupted.

Source report: https://slack.com/archives/C0BE69AHCQP/p1784134227920579

Deterministic reproduction

A focused provider-stream test reproduces the issue with this sequence:

{"type":"response.output_item.added","item":{"type":"function_call","id":"item_1","call_id":"call_1","name":"patch","arguments":""}}
{"type":"response.completed","response":{"usage":{"input_tokens":5,"output_tokens":1}}}

Run from packages/ai:

bun test test/provider/openai-responses.test.ts -t "finalizes an empty function call"

Current events are:

step-start
tool-input-start (patch)
step-finish (stop)
finish (stop)

The stream produces no tool-input-end, tool-call, or tool failure. This leaves the Patch card in a pending state until the session is interrupted.

Expected behavior

At terminal response handling, any pending function-call assembly should be finalized from its accumulated arguments. For empty arguments, the canonical parser should produce {}. The resulting Patch invocation can then fail normal schema validation immediately rather than remaining pending.

Expected terminal events include:

tool-input-end
tool-call (patch, input: {})
step-finish (tool-calls)

Likely cause

packages/ai/src/protocols/openai-responses.ts only finalizes pending ToolStream entries in onOutputItemDone. onResponseFinish closes the lifecycle without flushing state.tools, and hasFunctionCall remains false.

The V2 session publisher then has evidence for tool-input-start, but no actual call to settle or fail.

Notes

Blank patch text and a marker-only patch already fail synchronously in PatchTool; the hang occurs before PatchTool.execute is reached.

Related legacy reports include #30653 and #31843, but this issue has a minimal deterministic V2/OpenAI Responses protocol reproduction.