audiobook player guide updated.

Summary of what changed in each file, all confined to the change points shown in the diffs:
ChannelScreen.h — ChannelMessage gains a session-only scope_idx (initialised to 0xFF in the constructor and explicitly reset to 0xFF on SD load, since region is not persisted); addMessage gains a trailing defaulted scope_idx and stores it. The message-list line now renders (Xh)(Xb) Xm, with the byte figure taken from path_len's upper bits for floods and from the_mesh.getNodePrefs()->path_hash_mode + 1 for the 0xFF/0 sentinels. The path overlay shows Route: ... (N-byte) and a new Region: line (name, or (reg unknown), or nothing when unscoped).
MyMesh.h / .cpp — a fixed 28-entry SCOPE_NAMES table, a _scope_keys array precomputed once at the end of begin() via initScopeKeys(), resolveScopeIndex() (matches pkt->transport_codes[0] against the candidates; 0xFF unscoped, 0xFE unmatched), and the public getScopeName() accessor. onChannelMessageRecv resolves the index and passes it to newMsg.
AbstractUITask.h / UITask.h / UITask.cpp — newMsg gains a trailing uint8_t scope_idx = 0xFF; only the channel addMessage call forwards it. DMs and sent echoes keep the default, so they stay unscoped.
MsgFileRecord and the SD save/load format are untouched, so there's no version bump.

Audiobook Player Guide.md

@@ -1,7 +1,8 @@
-## Audiobook Player (Audio variant only)
+## Audiobook Player
 
-Press **P** from the home screen to open the audiobook player.
-Place `.mp3`, `.m4b`, `.m4a`, or `.wav` files in `/audiobooks/` on the SD card.
+The audiobook player is available on the T-Deck Pro audio variant and on all
+T-Deck Max variants. Press **P** from the home screen to open it.
+Place `.mp3`, `.m4a`, or `.wav` files in `/audiobooks/` on the SD card.
 Files can be organised into subfolders (e.g. by author) — use **Enter** to
 browse into folders and **.. (up)** to go back.
 
@@ -11,13 +12,15 @@ browse into folders and **.. (up)** to go back.
 | Enter | Select book or folder / Play-Pause |
 | A | Seek back 30 seconds |
 | D | Seek forward 30 seconds |
-| [ | Previous chapter (M4B only) |
-| ] | Next chapter (M4B only) |
+| [ | Previous chapter |
+| ] | Next chapter |
+| N | Next track |
+| Z | Toggle 45-minute sleep timer |
 | Q | Leave player (audio continues) / Close book (when paused) / Exit (from file list) |
 
 ### Recommended Format
 
-**MP3 is the recommended format.** M4B/M4A files are supported but currently
+**MP3 is the recommended format.** M4A files are supported but currently
 have playback issues with the ESP32-audioI2S library — some files may fail to
 decode or produce silence. MP3 files play reliably and are the safest choice.
 
@@ -25,17 +28,94 @@ MP3 files should be encoded at a **44100 Hz sample rate**. Lower sample rates
 (e.g. 22050 Hz) can cause distortion or playback failure due to ESP32-S3 I2S
 hardware limitations.
 
+Check a file's sample rate with ffprobe:
+
+```bash
+ffprobe -i "yourfile.mp3" 2>&1 | grep "Audio:"
+# Audio: mp3, 48000 Hz, stereo, fltp, 192 kb/s    ← won't play
+# Audio: mp3, 44100 Hz, stereo, fltp, 192 kb/s    ← will play
+```
+
+Re-encode in place if needed:
+
+```bash
+ffmpeg -i input.mp3 -ar 44100 output.mp3
+```
+
+For a whole album folder:
+
+```bash
+cd "/path/to/Album"
+mkdir converted
+for f in *.mp3; do ffmpeg -i "$f" -ar 44100 "converted/$f"; done
+```
+
+Verify by re-running ffprobe on a converted file and confirming `44100 Hz`. Once
+happy, move the contents of `converted/` up and delete the originals.
+
 **Bookmarks** are saved automatically every 30 seconds during playback and when
 you stop or exit. Reopening a book resumes from your last position.
 
-**Cover art** from M4B files is displayed as dithered monochrome on the e-ink
-screen, along with title, author, and chapter information.
-
 **Metadata caching** — the first time you open the audiobook player, it reads
 title and author tags from each file (which can take a few seconds with many
 files). This metadata is cached to the SD card so subsequent visits load
 near-instantly. If you add or remove files the cache updates automatically.
 
+### WAV Files
+
+WAV playback works, but the player has a narrower compatibility window than MP3.
+Files must be:
+
+- **Format code 0x0001** (linear PCM). Not 0xFFFE (`WAVE_FORMAT_EXTENSIBLE`),
+  which is what most DAWs export by default for 24-bit, 32-bit, or
+  multichannel sessions.
+- **16-bit samples.** 24-bit and 32-bit PCM either produce silence or
+  distortion.
+- **44.1 kHz sample rate.** Same constraint as MP3.
+- **Mono or stereo.** Multichannel files fail the format check.
+
+A non-compliant WAV refuses to start. The decoder only accepts format code
+0x0001, so anything in the `EXTENSIBLE` wrapper is rejected even when the
+underlying samples are plain PCM.
+
+Inspect a WAV's actual format with ffprobe:
+
+```bash
+ffprobe -i "yourfile.wav" 2>&1 | grep "Audio:"
+# Audio: pcm_s24le, 48000 Hz, stereo, s32, 2304 kb/s    ← won't play
+# Audio: pcm_s16le, 44100 Hz, stereo, s16, 1411 kb/s    ← will play
+```
+
+Re-encode a single file:
+
+```bash
+ffmpeg -i "input.wav" -acodec pcm_s16le -ar 44100 "output.wav"
+```
+
+For a whole album folder:
+
+```bash
+cd "/path/to/Album"
+mkdir converted
+for f in *.wav; do ffmpeg -i "$f" -acodec pcm_s16le -ar 44100 "converted/$f"; done
+```
+
+Verify with ffprobe and check the output line shows `pcm_s16le, 44100 Hz`. Once
+you're happy, move the contents of `converted/` up to the album folder and
+delete the originals.
+
+### Album Art
+
+Strip embedded album art (cover images) from your audio files before copying
+them to the SD card. Large embedded artwork can make a track slow to start when
+you open it, and in some cases fail or reboot the device, because the player has
+to read past the embedded image data before it reaches the start of the audio.
+The player does not currently display embedded cover art, so removing it costs
+nothing and recovers SD card space.
+
+Most tag editors can strip embedded artwork — for example Mp3tag, Kid3, or
+MusicBrainz Picard. Remove the cover / picture field from each file and save.
+
 ### Background Playback
 
 Audio continues playing when you leave the audiobook player screen. Press **Q**
@@ -51,10 +131,12 @@ and you're returned to the file list instead.
 
 The audiobook player uses the PCM5102A I2S DAC on the audio variant of the
 T-Deck Pro (I2S pins: BCLK=7, DOUT=8, LRC=9). Audio is output via the 3.5mm
-headphone jack.
+headphone jack. On the T-Deck Max, it uses the ES8311 audio codec and is
+available on every Max variant.
 
-> **Note:** The audiobook player is not available on the 4G modem variant
-> due to I2S pin conflicts.
+> **Note:** On the T-Deck Pro, the audiobook player is not available on the 4G
+> modem variant due to I2S pin conflicts. The T-Deck Max runs both the modem
+> and audio at once, so the player is available there regardless of variant.
 
 ### SD Card Folder Structure
 
@@ -75,4 +157,20 @@ SD Card
 ├── books/                   (existing — text reader)
 │   └── ...
 └── ...
-```
+```
+
+### Troubleshooting
+
+**A track stalls for several seconds when you open it, then fails or reboots the
+device.** The file has a large embedded album-art image and the player is
+working through it before it reaches the audio. Strip the embedded art — see
+Album Art.
+
+**An MP3 refuses to start.** Past the obvious "the file is corrupt" check, the
+usual cause is a sample rate other than 44.1 kHz. Inspect it with ffprobe and
+re-encode if needed — see Recommended Format.
+
+**A WAV refuses to start.** The file is outside the compatibility window — most
+often `pcm_s24le` or `pcm_s32le` at 48 kHz (the default DAW export), or a
+`WAVE_FORMAT_EXTENSIBLE` wrapper. Check it with ffprobe and convert — see WAV
+Files.