AudioShare USB v3.0.0-rc.4

AudioShare USB v3.0.0-rc.4

Fourth public release candidate of the portable Windows-to-Android USB audio
product. The ZIP remains self-contained and normally runs without installation
or administrator access.

Reliability fixes

• Embeds and cryptographically verifies the permanently signed Android
  1.0.0-rc.4 companion (version code 7).
• Fixes a reproduced Android startup race in which the playback thread could
  reach speaker-route validation before its route-grace state was initialized.
• Preserves nested Android playback causes across the USB protocol.
• When phone-local music or video takes Android media audio focus, Windows now
  stops the session once, removes its exact ADB forward, and shows a beginner
  recovery instruction instead of repeatedly disconnecting/reconnecting.

Validation improvements

• Adds a Windows supervisor regression proving audio-focus loss creates exactly
  one actionable failure and no replacement companion launch or ADB forward.
• Adds Android tests for bounded cause-chain propagation while retaining stable
  protocol and transport error wording.
• Updates the physical-device protocol tool for the current 92-byte playback
  diagnostics and validates write/head progress, play state, and performance
  mode.

Current evidence

• Android clean unit/lint/debug-build matrix: passed.
• Flutter formatting, localization generation, analysis, and all 39 tests:
  passed.
• The exact signed RC4 APK on a Samsung Galaxy A52s / Android 14 passed a
  60-second stream with 2,880,000 frames received/written, zero dropped frames,
  zero underruns, confirmed speaker route/audio focus, active wake lock, and
  clean service/ADB-forward teardown.
• A controlled Samsung Music focus takeover returned the exact terminal cause
  AudioTrack playback failed: Android audio focus was lost.

RC4 remains a prerelease until the documented longer screen-off, repeated USB
reconnect, measured latency, restricted-PC, and two-hour endurance gates are
completed.