NaN/Inf from any JS caller (audio:setGain does no validation) previously
reached the gain atomics raw; a NaN master gain multiplies the whole device
output to NaN and poisons the peak meters (TLC deep-read §2). Clamp at the
four setters — the single choke point covering the legacy facade, the
source-indexed API, and the audio-effects executor.
Bounds 0..32 match the executor's clampGain (Phase 0.b compat pin); stream/
renderer-bus keep their historical 0..8 via the same JUCE-free helper, now
testable in the new tests/engine_units target (Phase 0.c harness).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
