The Zonos gateway returns a STREAMING wav header — the RIFF chunk size (offset 4)
and the data chunk size are both 0xFFFFFFFF ("unknown length"), because it can
stream. A browser <audio> element playing a fully-downloaded blob needs a finite,
correctly-sized WAV; a 0xFFFFFFFF length reads as raw/streaming PCM and won't play
(operator-reported: "zonos sends pcm by default, but the browser wants wav").
tts_synthesize now rewrites both size fields with the real byte counts — the whole
clip is buffered server-side, so the sizes are known. Idempotent on an already-
correct header; no-op-safe if the data chunk isn't found. Live-verified: /api/tts
output now opens as a valid finite WAV (wave.open: 1ch/16bit/44.1kHz), RIFF + data
sizes correct where they were 0xFFFFFFFF before.
TDD: +1 test (streaming 0xFFFFFFFF header -> real sizes, wave-module-decodable); the
_WAV fixtures upgraded from bare RIFF stubs to proper finite WAVs. 525 green.
vh
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