…ssion events

…rInterruption

…aused handling (review)

…e-download audio guard (final review)

- configure() no longer resolves the shared mixer on the default path
  (.sdkOwned, no injection) — develop's configure never touched the mixer,
  and resolving .shared builds the CoreAudio graph, which hangs headless
  CircleCI runs that merely construct + configure a player
- gate AudioSessionOwnershipTests behind CI env check: every test in the
  suite constructs PlayolaMainMixer (same failure class as e8604a5)
- guard handleAudioEngineConfigurationChange on handlesSessionEventsInternally:
  auto-resume is interruption policy and must not race a host-driven resume
  (greptile outside-diff #1)
- pauseForInterruption cancels playTask for symmetry with stop()
  (greptile outside-diff #2)
- seam test: graceful skip when sources aren't present at runtime
  (compile-time #filePath; greptile outside-diff #4)
- lint: file_length disable pair on PlayolaStationPlayer.swift (matches
  SpinPlayer precedent), for-where + line length in seam test

The SDK no longer manages the AVAudioSession at all. Removes the
.sdkOwned/.hostOwned dual mode and all of its transitional machinery,
which was the source of repeated review churn (split-brain release
fallback, late-application ordering, double-configure divergence) and
had no value given a single consumer that migrates in lockstep.

Deleted: PlayolaAudioSessionOwnership, AudioSessionManager +
NoOpAudioSessionManager + AudioSessionManaging (whole file),
applyOwnership/appliedOwnership/sessionTouched/hasAppliedOwnershipToMixer,
handlesSessionEventsInternally, observer gating, and the legacy
interruption/route/engine-config handlers (removing the two known
pre-existing legacy bugs with them). configure() loses its
audioSessionOwnership parameter.

The host now owns the AVAudioSession: it configures/activates it and
drives pauseForInterruption()/resumeAfterInterruption() from its own
interruption handlers. SpinPlayer/PlayolaMainMixer no longer touch the
session; engine.start() throwing on an inactive session surfaces through
the normal error path.

Unchanged: pauseForInterruption/resumeAfterInterruption/.paused, lazy
mixer resolution, stale-download guard. The seam invariant test now
asserts the SDK references AVAudioSession nowhere in Sources/. Example
app gains its own session setup. README documents the host contract and
a 0.19->0.20 migration guide.

BREAKING CHANGE: host apps must own the AVAudioSession (see README
migration guide). Ships as 0.20.0.

…ure (review)

Adversarial review (Codex challenge) findings on the host-only rework:

- [P1] resumeAfterInterruption() cleared the armed resume token in a defer
  even when restartEngine()/play() threw, permanently disarming retry. Now
  disarms only after a successful resume; a failed resume (e.g. host hasn't
  reactivated the session yet) stays armed for the next attempt. (This was
  unsafe to do under the old dual-mode config-change observer; that observer
  is gone, so preserving the token can no longer cause a double-resume.)

- [P1] removing the engine-config observer left no recovery when AVAudioEngine
  stops itself on a hardware/format/route reconfiguration — silent dead audio
  while state stayed .playing. Re-added a PURE engine-recovery observer
  (AVAudioEngineConfigurationChange, not an AVAudioSession API — seam intact):
  restarts the engine and re-syncs to wall clock, guarded to skip while
  host-paused or not playing. object: nil avoids resolving the shared mixer at
  construction (no CI hang). This is engine ownership, not session ownership.

- README: corrected the stale 'session management' architecture bullet.
- Example app: demonstrates the full host contract (interruption observer
  driving pause/resume), not just launch-time activation.

Accepted as follow-ups (noted on PR): cold-start engine-start failure is
retried like a transient download failure and surfaces as .scheduleError
(only reachable when the host violates the activate-before-play contract,
caught at dev time); the seam test is a substring tripwire, not a complete
invariant (documented in-test).

…o own engine

- Add CHANGELOG 0.20.0 entry (pre-1.0 breaking = minor bump) documenting the
  host-owns-AVAudioSession change + migration steps, in the project's style.
- Scope the AVAudioEngineConfigurationChange observer to the SDK's OWN engine
  (registered lazily on first playback) instead of object: nil. Fixes the
  Greptile 4/5 concern: a host running its own AVAudioEngine no longer triggers
  spurious SDK restartEngine()+play() on unrelated config changes. Lazy
  registration keeps construction from building the CoreAudio graph (no CI hang).
- README migration guide: drop the phantom 'audioSessionOwnership parameter'
  step (that param never shipped in a release) — configure() is otherwise
  unchanged.

…level-audio

refactor!: host-only audio-session ownership + host-driven pause/resume

fix(sdk): one-shot retryable resume; stop() clears interruption state

…-generation-gate

fix(sdk): generation-gate + .error state in engine-config recovery