Summary

Codex Responses API sometimes reports finishReason as "stop" or undefined even when the turn ends with tool calls. OpenAI-compatible clients (e.g. any SDK that parses streaming chat.completions and drains tool_call deltas on finish_reason="tool_calls") silently drop accumulated tool calls when the final chunk carries finish_reason: null / "stop".

This PR overrides the mapped finish_reason to "tool_calls" in both the streaming and non-streaming paths whenever any tool calls were actually emitted during the turn.

Why this matters

OpenAI-compat clients accumulate tool_call argument deltas across streaming chunks (delta.tool_calls[].function.arguments chunks). They only flush the accumulated tool call into a real ToolCall event when the final chunk signals finish_reason="tool_calls" (or on [DONE], but clients that follow the OpenAI reference behavior rely on the former). If the proxy hands them finish_reason=null or "stop" on a turn that emitted tool_calls, the tool call is dropped and the assistant appears to return an empty response.

I hit this from a Rust client that uses the official OpenAI streaming format. Turn ends with a complete tool_calls delta stream for context_get(...), proxy emits finish_reason: null in the finish chunk, client never drains, agent loop exits with 0 tool calls, UI shows nothing.

Changes

• packages/openai-oauth/src/chat-stream.ts — in the "finish" case, if any tool calls were emitted during the stream (toolIndexes.size > 0) and the mapped finish_reason is not already "tool_calls", override it.
• packages/openai-oauth/src/chat-completions.ts — same defensive override in the non-streaming response builder when toolCalls.length > 0.

Test plan

• Hit /v1/chat/completions with stream: true and a prompt that triggers a tool call → verify the finish chunk carries finish_reason: "tool_calls".
• Same without streaming → verify the response's choices[0].finish_reason is "tool_calls".
• Verify regular text-only responses still emit "stop" (not overridden).

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