Find why Tier 3 never confirmed, and port detection to Go

Peter's report: the phone runs hot, uses a lot of battery, playback takes a
moment to start, and intelligent skipping has never done anything.

**The hot phone and the dead detection were one bug.** The candidate search
correlated 117 window positions against the whole of the other clip,
re-transforming that unchanged clip every time -- 199 seconds per episode end,
measured on a desktop, so minutes more on a phone. FingerprintWorker is a plain
WorkManager worker, Android stops one at ten minutes, and nothing was persisted
until a comparison returned. So it was killed mid-flight, saved nothing, and was
re-enqueued to start over, forever. IntroOutroDetectorScaleTest is the tripwire
whose absence allowed this: the unit tests ran on 300-sample clips while
production ran on 1,920,000.

Fixed coarse-to-fine, plus AudioCorrelation.prepareTarget so the target clip is
transformed once per search rather than 117 times. 10.6x, and a test asserts the
chosen reference window is byte-identical to what a full-resolution search picks.

**Midroll detection could never have run at all.** decodeFull buffered a whole
episode at its native rate -- 434MB for a 13-minute episode, no largeHeap -- to
produce 6MB of 8kHz mono. It threw OutOfMemoryError into a swallowing
runCatching and the episode was then marked checked forever. MonoResampler now
streams the decode so the peak allocation is the output, and maxDecodableMs skips
a longer episode before spending anything and without marking it checked.

**Detection is moving to a server**, Peter's call, in Go to match podkit and
doot. server/ holds the ported core, verified three ways because this is the
second port of this maths and the first shipped a normalization bug: numpy's
literals extracted mechanically from AudioCorrelationTest, the FFT against a
direct DFT, and the whole correlation path against a brute-force Pearson.

On four real Radiolab episodes it confirms the intro on 4 of 4, at 48.0s, 8.65s,
8.65s and 65.15s -- the varying pre-roll, observed in working code at last.

skips.SelfCheck verifies located segments against *each other* rather than
against the reference, which is a different claim: correlation is not transitive,
so two segments can each clear 0.6 against a reference and be unrelated. It
rejected the outro on its first real run (r=0.746), withholding offsets that
would have ended three episodes early. Offsets are published only when they
verify.

Also: the episode screen gets a working scrubber with ad-break marks and a
declared-versus-measured length readout, queue rows open the episode instead of
doing nothing, PrepareTrace logs playback-start timing against episode length
for the still-open pause question, and -PphoneOnly drops the emulator's CPython
from a sideload build (114MB -> 99MB).

Full history and numbers in docs/detection-findings.md.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018AwnALZL6bD4VBtATDVv3B

1 files changed, 14 insertions, 1 deletions

diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index bc8c4bd..36d6038 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -65,7 +65,20 @@ android {
         ndk {
             // CPython ships as native code, so every ABI included multiplies the APK size.
             // arm64 is the phone; x86_64 is the emulator.
-            abiFilters += listOf("arm64-v8a", "x86_64")
+            //
+            // `-PphoneOnly` drops the emulator's copy: measured at 114MB -> 99MB, so 15MB and
+            // not the halving it looks like it should be. The APK is dominated by 72MB of
+            // unminified debug dex, with Chaquopy's assets and one ABI's CPython adding ~25MB
+            // between them; shrinking it meaningfully means R8 on a debug build, not ABIs.
+            //
+            // Not the default: a build with no flag has to stay installable on the emulator too,
+            // or it stops being usable by whoever forgets. Pass it for a build only the phone
+            // will ever install.
+            abiFilters += if (project.hasProperty("phoneOnly")) {
+                listOf("arm64-v8a")
+            } else {
+                listOf("arm64-v8a", "x86_64")
+            }
         }
 
     }