Emoji and other supplementary-plane characters in titles, file names, and
subtitle paths were corrupted on the Android MPV path, and malformed bytes
from mpv logs could abort under CheckJNI. NewStringUTF/GetStringUTFChars
speak JNI's modified UTF-8, not the standard UTF-8 mpv produces and
consumes; the native lead-byte filter and the Kotlin surrogate scrubber
ran on the wrong side of that conversion and could not recover it.
Both directions now go through UTF-16 (NewString/GetStringChars) with a
small JNI-free transcoder that replaces malformed input with U+FFFD, the
same policy as shared/cpp/sanitize_utf8.h on desktop. The header is
covered by the Android host native test harness.
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