fix: try fix retry /v1/audio/transcriptions

[seefs001]

fix #2403

Summary by CodeRabbit

Bug Fixes

• Fixed Content-Type header handling during audio request retries for OpenAI integrations. The system now correctly preserves multipart form-data formatting when rebuilding requests, ensuring audio content is properly processed during retry operations.

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[coderabbitai]

Walkthrough

Captures the original Content-Type header from incoming requests and restores it during retry handling for OpenAI audio endpoints, preserving multipart/form-data boundary information required for proper request body parsing on retries.

Changes

Cohort / File(s)	Summary
Audio retry Content-Type preservation controller/relay.go	Adds capture of original Content-Type header and restores it during OpenAI audio endpoint retries when multipart/form-data is detected, preventing buffer parsing errors

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

• Minimal scope: single file with straightforward header preservation logic
• Low density: targeted bug fix with clear intent and limited conditional logic
• No architectural or control-flow changes

Possibly related PRs

• fix: boundary parser error (error parsing multipart NextPart: bufio: buffer full) #2235: Also addresses multipart/form-data boundary handling for audio/transcription requests by fixing boundary parsing and memory limits; complements this PR's Content-Type header preservation approach

Poem

🐰 A header lost, a retry failed,
But now we guard the multipart trail,
With boundary safe and form intact,
Audio flows through, fact on fact—
One small fix, transcription restored! 🎵

Pre-merge checks and finishing touches

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title clearly summarizes the main change: fixing retry issues for the /v1/audio/transcriptions endpoint. It directly relates to the changeset's objective.
Linked Issues check	✅ Passed	The code changes address the linked issue #2403 by capturing the original Content-Type and restoring it during retries, which fixes the multipart form parsing error that occurred on retry attempts.
Out of Scope Changes check	✅ Passed	All changes in controller/relay.go are directly scoped to fixing the retry handling for /v1/audio/transcriptions by managing Content-Type headers, with no unrelated modifications.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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📜 Recent review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between fca015c and e28de47.

📒 Files selected for processing (1)

• controller/relay.go (2 hunks)

🧰 Additional context used

🧬 Code graph analysis (1)

controller/relay.go (1)

types/relay_format.go (1)

• RelayFormatOpenAIAudio (10-10)

🔇 Additional comments (2)

controller/relay.go (2)

69-69: LGTM! Proper capture of the original Content-Type header.

Capturing the Content-Type at the beginning of the request ensures the multipart boundary is preserved for retry attempts, which directly addresses the root cause of the 500 error described in issue #2403.

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171-173: The Content-Type restoration logic is already safe and doesn't require the suggested check. The condition strings.Contains(originalContentType, "multipart/form-data") safely returns false when originalContentType is empty, making an additional empty string check redundant. The code correctly preserves the multipart boundary on retry for audio requests.

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