fix: charge local input tokens when Gemini returns empty response

[seefs001]

Summary by CodeRabbit

Release Notes

• Bug Fixes

  • Improved response tracking and usage calculation accuracy when handling streaming responses.

• Refactor

  • Enhanced concurrency management for better resource utilization and reliability.

[coderabbitai]

Walkthrough

These changes introduce explicit response counting via a new ReceivedResponseCount field in RelayInfo to track received responses, replacing text-length-based detection. The code integrates goroutine pooling (gopool) for concurrent work management in stream scanning while maintaining existing synchronization semantics.

Changes

Cohort / File(s)	Summary
Response Tracking Infrastructure relay/common/relay_info.go, relay/channel/gemini/relay-gemini.go	Added ReceivedResponseCount field to RelayInfo struct; updated usage recalculation condition to check info.ReceivedResponseCount > 0 instead of len(responseText).
Goroutine Pooling & Response Counting relay/helper/stream_scanner.go	Replaced direct goroutine launches with gopool.Go calls in three locations (done channel closure, ping data write, data handling); added ReceivedResponseCount increment when non-[DONE] data is processed.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• fix: gemini 原生格式流模式中断请求未计费 #1272: Both PRs modify Gemini streaming response handling to determine when to recompute usage; this PR introduces explicit ReceivedResponseCount tracking while the related PR used accumulated responseText aggregation.

Poem

🐰 A counter hops through every stream,
Each response now tracked with gopool's gleam,
No more text lengths clouding the way,
Just count the responses, hip-hip-hooray! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main fix: addressing how local input tokens are charged when Gemini returns empty responses, which aligns with the logic changes in relay-gemini.go and the new ReceivedResponseCount tracking.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing touches

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