feat(audio): shuffle the soundtrack across gauntlet/contract runs + trim dead air

[prabu-openclaw]

Two related audio fixes for the replay modes.

1. Runs shuffle instead of looping one track

Gauntlet/Contract picked one random track and set numberOfLoops = -1 — so an entire run was that same song on repeat.

A run is now a shuffle: play a random pool track once, then hand off to a fresh random pick 1s before it ends, for as long as the run lasts. The next pick always excludes the current track, so nothing plays back to back.

• playMissionMusic is idempotent — crossing a room boundary keeps the run going rather than restarting on a new song.
• Menu loops, boss tracks, boss chains, and stop() all take over the shuffle.
• Ducking (mini-games) defers through the existing deferredResumeKind, via a new .shuffleRun case.
• A missing file retries up to 3 other picks rather than stranding the run in silence.

2. Trimmed trailing dead air (29 tracks)

Most tracks ended with 2–13s of sub -45dB tail. Harmless while a track looped, but under the shuffle each tail became an audible gap between songs.

Trimmed to the last non-silent moment with a stream copy (ffmpeg -c copy) — a container-level cut, no re-encode, no quality loss. 148s of dead air removed; longest cuts intro_m5_music (-12.8s), m2_a (-12.7s), drop_intro (-8.3s).

Validation

Ran a gauntlet floor in the iOS Simulator for ~90 minutes:

• 35 handoffs across 25 distinct tracks, zero back-to-back repeats
• Handoff pacing matches trimmed durations exactly (e.g. intro_m1(60) + intro_m5_5(114) + m6_b(204) + m5_5_coldtrace(180) + intro_m4_5(118) = 676s, observed 11:38→11:50)
• Trimmed assets confirmed live in the build (m6_b reports 204s, not 210s)

Assets only + one Swift file; no files added/removed, so no XcodeGen regeneration needed.

🤖 Generated with Claude Code