Drives ConformManager for every audio-streaming footage with the same
AudioParams the export will use, before starting ExportTask - matching
the app's preview prewarm semantics. Root-cause analysis showed the
export's own wait-for-conform path already worked; this remains as a
first-export speedup and a belt-and-braces guarantee
- oakengine_export_render drives ExportTask synchronously (offline
render + encode) with a progress callback, codec probing, and a
thread-local error channel; exporter.h keeps clear of the visibility
macro header
- oak-cli transcode now defaults to mp4 (H.264/AAC) with --format ppm
keeping the raw output path
- two real concurrency bugs found by the facade's own test: ExportTask
deadlocks when start()ed synchronously (queued conform handshake
needs an event loop), and the progress callback must be captured by
value because it fires on the task thread
Mike-Solar