Fix RejectedExecutionException crash on ViewModel teardown

[patrickrb]

Problem

Pulled from a crashing device (debug.log + logcat crash buffer, 07-05). One of two distinct app crashes found:

FATAL EXCEPTION: Thread-139
java.util.concurrent.RejectedExecutionException: Task
  com.k1af.ft8af.MainViewModel$GetQTHRunnable rejected from
  ThreadPoolExecutor[Terminated, pool size = 0, ...]
    at com.k1af.ft8af.MainViewModel$4.afterDecode(MainViewModel.java)
    at com.k1af.ft8af.ft8listener.FT8SignalListener$4.run(FT8SignalListener.java:251)

A late deep-decode pass delivers afterDecode() on a background decode thread after MainViewModel.onCleared() has shut getQTHThreadPool / sendWaveDataThreadPool down (ViewModel destroyed on activity teardown/recreate). The raw execute() on the terminated pool throws RejectedExecutionException (default AbortPolicy), which is uncaught on the decode thread and crashes the process.

Fix

New SafeExecutor.tryExecute(pool, task) helper: fast-paths on isShutdown(), and wraps execute() in a try/catch (RejectedExecutionException) to cover the check→execute race with onCleared(). Drops the task and returns false instead of throwing.

Wired into all three submit sites in MainViewModel (1× getQTHThreadPool, 2× sendWaveDataThreadPool).

Tests

SafeExecutorTest (pure JUnit + Truth, no Robolectric needed): live-pool execution, shutdown pool, shutdownNow(), null pool, null task. :app:testDebugUnitTest green.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 21.57%. Comparing base (f23faaa) to head (eeaabbe).

Additional details and impacted files

@@             Coverage Diff              @@
##                dev     #432      +/-   ##
============================================
+ Coverage     21.47%   21.57%   +0.09%     
- Complexity      133      140       +7     
============================================
  Files           150      154       +4     
  Lines         19755    19945     +190     
  Branches       2909     2947      +38     
============================================
+ Hits           4243     4303      +60     
- Misses        15344    15474     +130     
  Partials        168      168              

Flag	Coverage Δ
android	12.42% <ø> (+0.26%)	⬆️
native	9.93% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.
see 5 files with indirect coverage changes

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.