[Copilot]

The firmware was BLE-only. This PR adds runtime commands to turn BLE and Bluetooth Classic/A2DP on and off, so audio streaming can replace the FrSky/BLE behaviour without a reflash. BLE and A2DP are mutually exclusive, so the module switches between them rather than running both at once.

I couldn't compile or run this: there was no ESP-IDF or PlatformIO toolchain available. Please build and test it on a board.

Commands (existing AT-style parser)

AT+BLEON / AT+BLEOFF
AT+A2DPON / AT+A2DPOFF
AT+A2DPCON<12-hex-addr>   (only valid while A2DP is active)
AT+BTOFF
AT+BTBOTH                 -> ERROR (unsupported, logged)

Mode switching (terminal.c)

• Each mode is a role_t handled by the existing setRole().
• setRole() tears down the current stack first: A2DP deinit, then Bluedroid and controller disable.
• A partial AT command is dropped on every switch.
• FrSky byte parsing now runs only in BLE modes.
• AT+BLEON returns to the last BLE role (central by default).
• The active mode is logged and sent over UART as Mode:<name> when BLE is off.

Persistence

• ROLE_BTEDR_AUDIO_SOURCE and ROLE_BT_OFF are appended to role_t, so saved values keep their meaning. The mode is stored in the existing NVS settings blob.
• At boot, a saved A2DP mode on a build without A2DP falls back to BLE central.
• If A2DP fails to start, the module ends up in Bluetooth off.

BT stack (bt.c, new bt_a2dp.c/bt_a2dp.h)

• bt_init() is now a thin wrapper over a shared start path, and bt_classic_init() is new.
• Classic controller memory is released only on builds that can't use A2DP, because the release is permanent until reboot.
• The A2DP source has a minimal init and deinit path with a stubbed data callback that sends silence.
• Everything A2DP is compiled behind CONFIG_BT_CLASSIC_ENABLED and CONFIG_BT_A2DP_ENABLE, and bt_a2dp_supported() reports whether it's available.

Review notes

• A2DP is not enabled in any sdkconfig in this PR. Those sdkconfigs have CONFIG_BT_CLASSIC_ENABLED unset, so until a classic-ESP32 sdkconfig enables both options, AT+A2DPON returns ERROR and BLE behaves as before.
• UART audio ingestion, ring buffer and resampling are out of scope here.
• esp_bt_gap_set_scan_mode() and esp_a2d_source_register_data_cb() use the IDF 4.4/5.x signatures. Please check them against the IDF version PlatformIO resolves.

[Amigache]

Thanks for the PR. Some notes after reviewing it against the current development branch (develop), which has diverged significantly from main:

Base and conflicts

• This PR is based on main (pre-refactor): it uses btaddrtostr, btSetName, src/defines.h and an strncmp-based AT parser. On develop those were renamed/restructured (bt_addr_to_str, bt_set_name, role_t moved into board.h, and the AT parser now lives in at_command.c/h). Merging as-is would conflict heavily, so this would need to be ported, not merged.
• If you want to make changes, please do so on the develop branch, not main.

Hardware scope

• Bluetooth Classic / A2DP is not available on the ESP32-C3 (our primary target): the C3 is BLE-only. On C3SuperMini / C3Mini, AT+A2DPON can only ever return ERROR. The feature only makes sense on ESP32-classic boards (pico32, Node32s, and the Seeit ESP32-DEV-38P).
• Please expose A2DP only on ESP32-classic targets and keep returning ERROR on C3 (which bt_a2dp_supported() already handles).

Functionality

• The A2DP data callback currently sends silence, so audio streaming is not implemented yet — it is a stub. Could you clarify the intended scope (streaming the radio's audio?) and whether it belongs in this project at all?

Process

• The PR is a draft and has not been compiled or tested. Before it can be considered it must build cleanly and be validated on hardware (see doc/BENCH.md and tools/at_bench.py).
• New AT commands are a project extension (like AT+HTRESET); they should be added to the AT parser and documented.

Happy to help port it onto develop if there is interest.

[gagarinlg]

It was just a test run of Copilot, nothing too serious. In the end it would be great to be able to use bletooth audio, when the HW supports it.