fix(proxy): include input in streamed tool starts

[topjohncian]

Summary

• Add empty input: {} objects to streamed Anthropic tool_use content_block_start events
• Cover OpenAI-compatible streaming, Responses streaming, and Gemini streaming conversion paths
• Prevent clients from receiving malformed streaming tool blocks before argument deltas arrive

Closes #2556

Test plan

• GitHub Actions

🤖 Generated with Claude Code

[farion1231]

@codex review
@claude review

[claude]

Claude finished @farion1231's task in 1m 1s —— View job

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Claude PR Review

• Read changed files
• Compare against linked issue Claude Code crashes on Windows when OpenAI Responses streaming tool_use starts without input #2556
• Check Anthropic streaming spec compliance
• Post review

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LGTM.

The fix is correctly scoped and complete. Anthropic's streaming spec requires tool_use content_block_start events to carry an input field (the actual JSON arrives later via input_json_delta events). Without it, strict clients can choke on the initial block.

I verified all four content_block_start sites that emit "type": "tool_use" are updated:

• streaming.rs:448 — OpenAI tool_calls path
• streaming.rs:557 — OpenAI function_call fallback path
• streaming_gemini.rs:528 — Gemini functionCall path
• streaming_responses.rs:423 — Responses API output_item.added (normal path)
• streaming_responses.rs:465 — Responses API function_call_arguments.delta (fallback path)

Other content_block_start emissions in these files are for text / thinking blocks, which don't take input, so the surface is fully covered.

Test coverage looks good:

• Existing OpenAI tests tightened to assert input == {} on tool starts.
• The Gemini test was rewritten to parse SSE and assert structurally rather than via output.contains(...) — a strict improvement.
• New streaming_responses tests cover both the normal and fallback paths independently.

No blocking issues found. Leaving the merge call to the maintainer.
• Branch: claude-fix

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. 👍

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