spawn_blocking uses arbitrary thread-pool threads that don't have the
Android JNI context initialized, causing ndk_context::android_context()
to panic. Switch to run_on_main_thread (where the context is always
valid) via a oneshot channel, with a 2s timeout. Panic is caught and
forwarded as an Err so the debug log captures it rather than crashing.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
bc1668ed96