AssMatroskaExtractor and MatroskaLatmSupport reflect MatroskaExtractor's private extractorOutput/subtitleSample fields by name, but no keep rule covered them: R8 renames the fields and every MKV direct-play in a release build fails constructing the extractor. Adds the keepclassmembernames rule (descriptors verified against media3 1.11.0 in the Gradle cache) and extends check_shrinker_rules.py to scan Kotlin/Java reflection across all android src/main roots including libass.