Host: tuh_midi_mount_cb never fires for UAC2 audio+MIDI composite device (Zoom G5n)

[FellInk90923148]

Setup: RP2040 (Pico) native USB host, tinyusb via pico-sdk. tusb_config.h: CFG_TUH_ENABLED=1, CFG_TUH_MIDI=1, all other CFG_TUH_* classes disabled, CFG_TUH_ENUMERATION_BUFSIZE tried up to 65536.
Device: Zoom G5n (VID 0x1686, PID 0x02DF), a UAC2 audio + MIDI composite device.
Symptom: tuh_mount_cb() fires normally (generic enumeration succeeds, tuh_vid_pid_get() returns correct VID/PID), but tuh_midi_mount_cb() is never called.
I manually fetched the config descriptor via tuh_descriptor_get_configuration_sync() and parsed it myself: of 5 declared interfaces (7 interface descriptor entries incl. alt settings), one interface has bInterfaceClass=0x01 (AUDIO), bInterfaceSubClass=0x03 (MIDISTREAMING) — a standard MIDIStreaming interface is present. Despite this, the MIDI host driver never claims it.
This looks similar to #3382 (device side, fixed by #3383) where the audio driver interferes with MIDI interface claiming — possibly the same class of issue on the host side. Is this a known limitation, or is there a config I'm missing?