Loads Bassline For Doppler Song longer.wav and plays the golden
loop (11.9886 s → 14.6008 s, cycle 2.6122 s) via LoopPlayer's native
source.loop. Press Play: (1) the suspended
AudioContext must resume inside play(); (2) setVolume(0.1) must land on
the gain node; (3) an AnalyserNode taps the source and records the RMS
energy envelope for ~9 s (3+ cycles) — the envelope's autocorrelation
peak (the recurring loop-start energy fingerprint) must sit at the loop
period 2.612 s ±20 ms, proving native looping honors the exact points.