fix(voice): honour the volume argument on Linux players

[m8ryx]

playAudio() accepts a volume multiplier and threads it all the way through to the player:

const proc = spawn(player.path, player.buildArgs(tempFile, volume))

The macOS branch honours it:

{ cmd: "afplay", buildArgs: (file, volume) => ["-v", volume.toString(), file] }

Every Linux candidate declares buildArgs: (file) => ... and silently discards the argument:

{ cmd: "ffplay", buildArgs: (file) => ["-nodisp", "-autoexit", "-loglevel", "quiet", file] },
{ cmd: "mpg123", buildArgs: (file) => ["-q", file] },
{ cmd: "paplay", buildArgs: (file) => [file] },
{ cmd: "aplay",  buildArgs: (file) => ["-q", file] },

So per-voice volume in the config, and the volume field on the notification API, do nothing on Linux — playback is always at system level. There is no error; the value is simply dropped. FALLBACK_VOLUME = 1.0 and per-voice entry.volume ?? 1.0 confirm the intended scale is a multiplier where 1.0 is normal, matching afplay's -v.

Fix

Map that multiplier onto each player's own integer scale, taken from the tools' own help output:

$ ffplay -h | grep volume
-volume volume      set startup volume 0=min 100=max

$ paplay --help | grep volume
      --volume=VOLUME    Specify the initial (linear) volume in range 0...65536

A shared helper clamps and rounds:

function scaleVolume(volume: number, max: number): number {
  if (!Number.isFinite(volume) || volume < 0) return max
  return Math.min(max, Math.round(volume * max))
}

A non-finite or negative value falls back to the player's normal level rather than silencing playback, which seemed the safer failure direction for a notification system.

Deliberately not changed

• aplay has no volume-set option — only --disable-softvol. Volume cannot be honoured on this fallback.
• mpg123 scales with -f, but I could not verify its range on the machine I tested on, and guessing a factor risks making playback quieter for everyone else. Left as-is, with a comment marking it.

Both are noted inline so the gap is visible rather than silent.

Verification

Flags confirmed present rather than assumed — a deliberately misspelled variant is rejected while the real one is accepted:

$ ffplay -nodisp -autoexit -loglevel error -volume 50 tone.mp3     # accepted
$ ffplay -nodisp -autoexit -loglevel error -vollume 50 tone.mp3
Failed to set value '50' for option 'vollume': Option not found

$ paplay --volume=32768 tone.mp3                                    # exit 0
$ paplay --vollume=32768 tone.mp3
paplay: unrecognized option '--vollume=32768'

scaleVolume covered by unit checks: 1.0 → max, 0.5 → half, 0 → 0, 2.0 → clamped (no amplification), NaN → normal, -1 → normal.

bun build VoiceServer/voice.ts --target=bun compiles clean in place.

No change to macOS behaviour — the darwin branch is untouched.

[danielmiessler]

Ported into source as-is, thank you. The per-player scaling with clamping is right, and the restraint on mpg123 (unverified range) and aplay (no flag) is the kind of honesty we want in the tree; both comments survive. Merge-back note: the public repo is generated from private source at release, so this closes as ported, with credit in the README. Ships with the next release.