Fix spectrum-strip peak-block crash when bin count grows between frames

[patrickrb]

Summary

ColumnarView (the spectrum strip's bar view) can throw an
IndexOutOfBoundsException on the UI thread — an unrecoverable app crash —
while drawing the peak-hold "falling block" overlay. This fixes the root cause
and adds tests.

Root cause

In ColumnarView.setWaveData(int[]) the peak-block section rebuilt its block
list to the current frame's bin count (binsToShow) whenever the size
changed:

for (int i = 0; i < binsToShow; i++) { blockData.add(new Rect(...)); }
for (int i = 0; i < blockData.size(); i++) {
    blockData.get(i).left = newData.get(i).left;   // <-- newData is the PREVIOUS frame
    ...
}

but the copy loop reads geometry from newData, which at that point still
holds the previous frame's (smaller) bar set — newData is not rebuilt
until later in the method. When the visible bin count grows between two
frames, the loop indexes past the previous bars → IndexOutOfBoundsException.
Drawing is not wrapped in try/catch, so it crashes the app.

The bin count changes whenever binsToShow = min(len, round(spectrumWidth / nyquist * len)) changes — i.e. on a spectrum-width change (the
NumberInputDialog, 2500–5000 Hz, in Radio/Audio settings) or an audio
sample-rate change — both reachable at runtime while the peak blocks are
shown (setShowBlock(true) is set on the waterfall's ColumnarView).

Fix

Drive the peak-hold state off the bars actually present this frame. The
sizing/geometry decision is extracted into a pure, JVM-testable PeakBlocks
helper (mirroring the existing BinAggregation extraction). It always returns
exactly one block per current bar, so the copy can never over-index. A
bin-count change resets the peak-hold to the floor (matching the legacy
full-rebuild); when the count is unchanged the geometry is bit-for-bit
identical to the pre-fix code. The Composable/View wrapper stays a thin
caller, per the project's testability guidance.

Testing

• PeakBlocksTest (pure JVM, no Robolectric):
  • growingBinCountDoesNotThrow — asserts the reconstructed legacy inline
    logic throws on a grown bin count and the fix does not.
  • stableSizeMatchesLegacyMath — bit-for-bit parity with the legacy math
    when the size is unchanged.
  • first-frame floor start, rise-snap, fall-by-one-step, shrinking-bin-count
    reset, empty-bars cases.
• ./gradlew :app:testDebugUnitTest — full suite green.
• ./gradlew :app:assembleDebug — native cpp + APK build succeeds.

Risk

Low and localized to ColumnarView's peak-block overlay. No DSP, decoder,
encoder, protocol, or CAT behavior touched. Steady-state rendering is
unchanged (verified by the parity test); only the previously-crashing
size-change transient now renders instead of throwing. Same per-frame Rect
reuse as before, so no allocation/perf regression.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 23.35%. Comparing base (6135d45) to head (9172a7a).

Additional details and impacted files

@@            Coverage Diff            @@
##                dev     #496   +/-   ##
=========================================
  Coverage     23.35%   23.35%           
  Complexity      162      162           
=========================================
  Files           167      167           
  Lines         21450    21450           
  Branches       3154     3154           
=========================================
  Hits           5009     5009           
  Misses        16248    16248           
  Partials        193      193           

Flag	Coverage Δ
android	13.26% <ø> (ø)
native	9.93% <ø> (ø)

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