feat(LocalAPI): OpenAI-compatible transcription API

[souljorje]

Description

Added OpenAI-compatible transcription API support for local API. Useful when you need to give some apps endpoint to custom transcriber :)

• POST /v1/audio/transcriptions
• Only json and text response formats are currently supported
• OpenAI-style multipart/form-data uploads
• OpenAI-shaped error responses

The model multipart field is accepted but ignored, FluidVoice's currently selected Voice Engine remains the source of truth.

Type of Change

• 🐞 Bug fix
• ✨ New feature
• 💥 Breaking change
• 🧹 Chore
• 📝 Documentation update

Related Issue or Discussion

#871

Testing

• Tested on Intel Mac
• Tested on Apple Silicon Mac
• Tested on macOS version: 26.5.2 (25F84)
• Ran linter locally: swiftlint --strict --config .swiftlint.yml Sources Tests Package.swift
• Ran formatter locally: swiftformat --config .swiftformat Sources
• Ran tests locally:
• multipart parsing
• multipart boundary bytes inside uploaded audio
• JSON transcription response
• plain-text transcription response
• unsupported response_format
• unavailable ASR handling
• unexpected ASR failures
• temporary upload cleanup

Screenshots / Video

• No UI/visual changes; screenshots/video are not applicable.

Notes

GPT 5.6-Sol High coded and reviewed 🤖

[greptile-apps]

Greptile Summary

Adds an OpenAI-compatible local transcription API and model-discovery endpoint.

• Parses multipart audio uploads and supports JSON or plain-text transcription responses.
• Normalizes audio decoding failures into client-facing errors and cleans up temporary files.
• Adds OpenAI-shaped error responses, including a 503 response when the transcription service is unavailable.
• Moves shared transcription behavior into a dedicated service and adds multipart, response-format, error-handling, and cleanup tests.

Confidence Score: 5/5

The PR appears safe to merge; the prior findings are resolved and the latest change correctly handles the 503 HTTP reason phrase.

No actionable new issues were identified, and all previous findings are resolved.

_{Reviews (4): Last reviewed commit: "fix(api): serialize 503 reason phrase" | Re-trigger Greptile}

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

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Reviewed commit: 6188dfb045

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