Adds 22 new tests on top of the existing 7 _on* / stopPreview ones.
startPreview happy path: invokes audio_preview_play with the configured
args (id, url, durationSec, startSec, volume) and stores the previewing
track + duration + reset elapsed / audioStarted. Short tracks
(duration <= previewDuration * 1.5) start at 0; longer tracks seek to
duration * trackPreviewStartRatio. Camel-case IPC keys pinned
(startSec / durationSec, not snake_case -- CLAUDE.md gotcha).
Cross-store guard tests: no-op when previews globally disabled, no-op
when disabled at the calling location, no-op while a host or guest is
inside any Orbit phase (active / joining / starting), falls through to
play when role is null (no session).
Same-id re-click: treats it as a stop -- audio_preview_stop fires,
audio_preview_play does not.
Failure path: engine invoke rejects -> store state rolls back
(previewingId / previewingTrack / audioStarted) and the error propagates
to the caller.
Loudness pre-attenuation folding: with normalizationEngine=loudness +
loudnessPreAnalysisAttenuationDb=-6 dB, volume is multiplied by
10^(-6/20). normalizationEngine=off keeps volume verbatim. Positive
pre-attenuation values are pulled to 0 by the Math.min(0, ...) guard.
Main-player volume sync side-effect (module-level
usePlayerStore.subscribe): pings audio_preview_set_volume when volume
changes during a preview, skips when no preview is active, skips when
the new value equals the prior value (subscription guard).
previewStore.ts coverage 33% -> 100% lines. Added to the hot-path gate.
Plus the typed `OrbitRole` is `'host' | 'guest'` (null when no session),
not 'idle' as a string -- minor type-correctness alignment.
Frank Stellmacher