The APRS stop endpoint terminated two processes sequentially (up to 4s
with PROCESS_TERMINATE_TIMEOUT=2s each) while the frontend fetch timed
out at 2.2s. This caused console errors and left the SDR device claimed
in the registry until termination finished, making the status panel show
the device as active after the user clicked stop.
Fix: release the SDR device from the registry immediately inside the
lock, clear process references, then terminate processes in a background
thread so the HTTP response returns instantly.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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