Disprove the leading Tier 3 detection hypothesis on real Up First audio

The brief's leading hypothesis -- an 8-second reference window too wide for
a ~6-second sting -- does not survive contact with real data. Simulating
IntroOutroDetector.findCandidate exactly (the same normalized_xcorr/best_match
math AudioCorrelation.kt uses, unmodified) against the four Up First episodes
already cached from the original prototype: every one of six pairs confirms
cleanly at both ends, at the app's real DEFAULT_REFERENCE_SECONDS=8 and
MIN_SCORE=0.6 -- intro r 0.79-0.998, outro r 0.994-0.999.

Also ruled out: the naive linear-interpolation resampler MediaCodecClipSource
actually uses. Reproduced it exactly against a fresh re-fetch's native 44.1kHz
audio and compared to a proper ffmpeg decode -- 0.9991 correlation, and the
production simulation confirms identically either way.

Two findings beyond the original brief:
- Pre-roll length varies a lot (44s-94s across four episodes) but the global
  search already handles that; it isn't the blocker the first draft worried
  it might be.
- The same episode URL, fetched fresh today against a copy from 2026-09-26,
  is byte-identical for the first ~50 seconds and then diverges completely --
  sharper evidence for "dynamic ad insertion is the environment" than the
  Radiolab duration mismatch alone, though it lands after the useful intro
  signal so doesn't threaten detection specifically.

Experiment 6 (re-check the Darknet Diaries trap) didn't need a new fetch --
the midroll prototype session's already-cached data answers it: the shared
~51s segment still matches at r=1.000 across a nine-year gap, which a truly
rotating per-request ad could not do by chance. Looks like a real intro, not
the trap the threshold exists to catch.

Net effect: the algorithm and its tuned constants are no longer plausible
suspects on real audio. What's left points at the specific on-device run
rather than the approach -- see "What to check on the phone" for the three
concrete things to look at that this sandbox has no way to check itself.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Sj3CoWEedM56bebByKgNxA

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