Greptile Summary

This PR makes two complementary changes to the OpenAI TTS provider:

1. Speed config fix (line 84): Replaces || with ?? (nullish coalescing) when applying the default speed value of 1.0. This is semantically correct because config.speed is typed as number | undefined. The change ensures that an explicitly provided 0 is not incorrectly overridden as falsy — only null or undefined will trigger the fallback.

2. Function relocation: Extracts pcmToMulaw and linearToMulaw utility functions from tts-openai.ts to telephony-audio.ts for better code organization, with the import properly updated.

The changes are low-risk and correct. The model and voice fields on lines 82–83 continue to use || for their defaults, which is acceptable (empty strings are invalid inputs regardless). No other logic is affected.

Confidence Score: 5/5

• This PR is safe to merge — the nullish coalescing fix is correct and the function relocation is properly executed with imports maintained.
• The speed config change from || to ?? is semantically correct and solves the edge case where an explicitly passed 0 would be incorrectly overridden. The function relocation to telephony-audio.ts is a low-risk refactor that properly maintains imports. No files are broken, no logic is altered beyond the intended fix, and the change is minimal and well-scoped. The model and voice defaults can remain with || since empty strings are invalid inputs regardless.
• No files require special attention

_{Last reviewed commit: ce3b961}