fix(routing/proxy): emit finish_reason: tool_calls when tool call pre…

[crashf]

…cedes empty completion

GPT/Codex streaming can emit response.output_item.added with a function_call before response.completed, whose output array is empty. Previously the adapter only checked output for function_call items, producing finish_reason: stop and causing the client to end the turn prematurely.

• Track sawToolCall in ReasoningStreamState
• Set sawToolCall = true on response.output_item.added function_call
• In handleCompletedEvent, use hasFunctionCalls || sawToolCall to decide finish_reason
• Add regression tests for empty-completion + tool-call, text-only completion, and normal function-call completion

Fixes the "GPT no-respond / stops after one tool call" symptom in streaming mode.

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Summary by cubic

Fixes the ChatGPT/Codex streaming adapter emitting finish_reason: stop when a tool call precedes an empty response.completed output, which made clients end the turn before running the tool. The adapter now emits finish_reason: tool_calls when any function_call was streamed, even if the completed event's output is empty.

• Tracks tool-call presence in the stream transformer state on response.output_item.added events.
• Uses the tracked state, alongside existing output inspection, to decide finish_reason.
• Adds regression tests for empty-completion tool calls, text-only completions, and normal function-call completions.

^{Written for commit f2a798f. Summary will update on new commits.}

[cubic-dev-ai]

All reported issues were addressed across 2 files

<sub>Reply with feedback, questions, or to request a fix.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.50%. Comparing base (1431f74) to head (10436f1).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2773   +/-   ##
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  Coverage   96.50%   96.50%           
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  Files         604      604           
  Lines       36048    36050    +2     
  Branches    10081    10083    +2     
=======================================
+ Hits        34788    34790    +2     
  Misses        702      702           
  Partials      558      558           

Flag	Coverage Δ
backend	95.69% <100.00%> (+<0.01%)	⬆️
frontend	97.36% <ø> (ø)
shared	99.45% <ø> (ø)

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