Problem2: in song mode UI shows 6m(Am) but MIDI played AM7
(E2 A2 E3 G#3 C#4 E4). Root cause: BL_Set_led wrote the LED frame's
chord code into chord_type_index_map of the group middle key
(LED_L6 -> key17), so a guidance frame carrying 0x02 (M7) turned the
Am key into AM7. Remapping on the chord page only helped until the
next LED frame.
- BL_Set_led: light LED only, drop all chord_type_index_map writes;
chord quality is owned by map page 02 03/02 04 (BT_Chord_offset_map)
- handleReadRhythmMap / Return_Light_buff: fix type->protocol read-back
encoding (m7->0x0A, M7->0x02, ad9->0x04, m7-5->0x0B, sus2->0x1F,
sus4->0x1E), re-landing the 0917 verified fix
- BT_Chord_offset_map: accept dominant-7 doc code 0x0D (legacy 0x13 kept)
- tests: test_chord_map_fix.py (16/16 PASS on device),
test_fret_positions.py, test_problem2_song_am.py (7/7 PASS:
post-LED strum stays E2 A2 E3 A3 C4 E4)
Co-authored-by: Cursor <cursoragent@cursor.com>
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