feat: unified cpal audio engine with streaming decode and precomputed FFT waveforms

Replace HTML5 <audio> + Web Audio API with a Rust-native cpal audio engine.
One persistent output stream handles all playback — voice messages, audio
attachments, and notification sounds (desktop) — with real-time mixing.

Key changes:
- audio_engine.rs: singleton cpal stream, multi-source mixer, streaming
  decode for non-WAV formats, mixer-side linear interpolation for sample
  rate conversion, crossfade on seek, incremental FFT waveform computation
- Precomputed waveform data (64 bins x 30fps) sent to frontend once,
  eliminating per-frame IPC for visualization
- Voice recording preview plays through engine (no more Blob URLs/IPC)
- send_recording command keeps audio in Rust — WAV bytes never cross IPC
- audio_stop_all on chat navigation prevents ghost playback
- audio_probe for instant duration display before first play
- Removed voice_message Tauri command (now internal-only function)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: JSKitty

src-tauri/Cargo.lock

@@ -57,7 +57,8 @@ fast-thumbhash = "0.2"
 base64-simd = "0.8"
 cpal = "0.16.0"
 hound = "3.5.1"
-symphonia = { version = "0.5.5", features = ["mp3", "wav", "flac", "pcm"] }
+symphonia = { version = "0.5.5", features = ["mp3", "wav", "flac", "pcm", "aac", "isomp4", "ogg", "vorbis"] }
+rustfft = "6.2"
 rusqlite = { version = "0.32", features = ["bundled"] }
 # Pin OpenMLS crypto deps to versions MDK was tested with (newer versions pull broken sha3/digest pre-release chain)
 openmls_rust_crypto = "=0.5.0"

src-tauri/Cargo.toml

@@ -33,7 +33,6 @@ fn main() {
             // Message commands
             "message",
             "paste_message",
-            "voice_message",
             "file_message",
             "file_message_compressed",
             "get_file_info",
@@ -193,6 +192,16 @@ fn main() {
             "run_maintenance",
             // Debug commands (conditional)
             "debug_hot_reload_sync",
+            // Audio engine commands
+            "audio_probe",
+            "audio_load",
+            "audio_play",
+            "audio_pause",
+            "audio_seek",
+            "audio_stop",
+            "audio_stop_all",
+            "audio_set_volume",
+            "send_recording",
             // Encryption toggle commands
             "get_encryption_status",
             "disable_encryption",

src-tauri/build.rs

@@ -31,7 +31,6 @@
     "allow-toggle-chat-mute",
     "allow-message",
     "allow-paste-message",
-    "allow-voice-message",
     "allow-file-message",
     "allow-file-message-compressed",
     "allow-forward-attachment",
@@ -218,6 +217,15 @@
     "allow-is-directory",
     "allow-zip-directory",
     "allow-cleanup-zip",
-    "allow-update-group-metadata"
+    "allow-update-group-metadata",
+    "allow-audio-probe",
+    "allow-audio-load",
+    "allow-audio-play",
+    "allow-audio-pause",
+    "allow-audio-seek",
+    "allow-audio-stop",
+    "allow-audio-stop-all",
+    "allow-audio-set-volume",
+    "allow-send-recording"
   ]
 }

src-tauri/capabilities/default.json

@@ -0,0 +1,11 @@
+# Automatically generated - DO NOT EDIT!
+
+[[permission]]
+identifier = "allow-audio-load"
+description = "Enables the audio_load command without any pre-configured scope."
+commands.allow = ["audio_load"]
+
+[[permission]]
+identifier = "deny-audio-load"
+description = "Denies the audio_load command without any pre-configured scope."
+commands.deny = ["audio_load"]

src-tauri/permissions/autogenerated/audio_load.toml

@@ -0,0 +1,11 @@
+# Automatically generated - DO NOT EDIT!
+
+[[permission]]
+identifier = "allow-audio-pause"
+description = "Enables the audio_pause command without any pre-configured scope."
+commands.allow = ["audio_pause"]
+
+[[permission]]
+identifier = "deny-audio-pause"
+description = "Denies the audio_pause command without any pre-configured scope."
+commands.deny = ["audio_pause"]

src-tauri/permissions/autogenerated/audio_pause.toml

@@ -0,0 +1,11 @@
+# Automatically generated - DO NOT EDIT!
+
+[[permission]]
+identifier = "allow-audio-play"
+description = "Enables the audio_play command without any pre-configured scope."
+commands.allow = ["audio_play"]
+
+[[permission]]
+identifier = "deny-audio-play"
+description = "Denies the audio_play command without any pre-configured scope."
+commands.deny = ["audio_play"]

src-tauri/permissions/autogenerated/audio_play.toml

@@ -0,0 +1,11 @@
+# Automatically generated - DO NOT EDIT!
+
+[[permission]]
+identifier = "allow-audio-probe"
+description = "Enables the audio_probe command without any pre-configured scope."
+commands.allow = ["audio_probe"]
+
+[[permission]]
+identifier = "deny-audio-probe"
+description = "Denies the audio_probe command without any pre-configured scope."
+commands.deny = ["audio_probe"]

src-tauri/permissions/autogenerated/audio_probe.toml

@@ -0,0 +1,11 @@
+# Automatically generated - DO NOT EDIT!
+
+[[permission]]
+identifier = "allow-audio-seek"
+description = "Enables the audio_seek command without any pre-configured scope."
+commands.allow = ["audio_seek"]
+
+[[permission]]
+identifier = "deny-audio-seek"
+description = "Denies the audio_seek command without any pre-configured scope."
+commands.deny = ["audio_seek"]

src-tauri/permissions/autogenerated/audio_seek.toml

@@ -0,0 +1,11 @@
+# Automatically generated - DO NOT EDIT!
+
+[[permission]]
+identifier = "allow-audio-set-volume"
+description = "Enables the audio_set_volume command without any pre-configured scope."
+commands.allow = ["audio_set_volume"]
+
+[[permission]]
+identifier = "deny-audio-set-volume"
+description = "Denies the audio_set_volume command without any pre-configured scope."
+commands.deny = ["audio_set_volume"]