HFP call audio silent over hci_bridge + hci-socket (SCO/eSCO payload not delivered; USER channel filter error / RAW channel unstable)

We use Bumble as an HCI bridge to provide Bluetooth for Android emulator. Pairing and A2DP media work, but during phone calls (HFP) the call UI appears and SCO connects, yet there is no audio (no mic/speaker audio on the Android emulator side; sometimes phone audio behavior changes depending on settings). This looks like SCO/eSCO payload (HCI packet type 0x03) is not flowing through the Bumble ↔ host-controller path. also bridged controller there is no PCM

Setup

Host: Ubuntu Linux
Target: Android emulator

What works
Pairing
media audio works

What fails

HFP call audio: call control works, SCO connect happens, but audio is silent / not routed.

Evidence
Android logs show SCO connect events and HeadsetClientService: connectAudio, but no audio follows.
Bumble logs show eSCO setup commands/events (e.g. HCI_ACCEPT_SYNCHRONOUS_CONNECTION_REQUEST_COMMAND and HCI_SYNCHRONOUS_CONNECTION_COMPLETE_EVENT) but we do not see evidence of SCO data payload being forwarded/received.