feat(music): switch station music to live PCM streaming

Move music playback off the HLS/download-first path and stream 48k mono PCM chunks over WebSocket so stations can start playing immediately. Add station-side PCM chunk playback support and stream lifecycle logging to make no-audio issues easier to trace.

station_broadcast.lua

@@ -654,6 +654,19 @@ local function playChunkOnSpeakers(samples, volume, playSeq)
     return true
 end
 
+local function decodePcmS8Chunk(chunk)
+    if type(chunk) ~= "string" or #chunk == 0 then return nil end
+    local samples = {}
+    for i = 1, #chunk do
+        local b = string.byte(chunk, i)
+        if b >= 128 then
+            b = b - 256
+        end
+        samples[i] = b
+    end
+    return samples
+end
+
 local function areHqSpeakersBusy(speakers)
     for _, sp in ipairs(speakers) do
         local playing = false
@@ -824,10 +837,47 @@ function Audio.playDfpwmItem(item)
     end
 end
 
+function Audio.playPcmItem(item)
+    if not Peripherals.speakers or #Peripherals.speakers == 0 then
+        Utils.log("WARN", "No speakers found; cannot play audio")
+        return
+    end
+
+    local playSeq = State.interruptSeq
+    local source = item.audioData
+
+    if type(source) == "table" and source.read then
+        source = source.read
+    end
+
+    if type(source) ~= "function" then
+        local data = source
+        source = function()
+            local chunk = data
+            data = nil
+            return chunk
+        end
+    end
+
+    while true do
+        if shouldStop(playSeq) then break end
+        local chunk = source()
+        if chunk == nil then break end
+        if type(chunk) == "string" and #chunk > 0 then
+            local samples = decodePcmS8Chunk(chunk)
+            if samples and not playChunkOnSpeakers(samples, CONFIG.AUDIO_VOLUME, playSeq) then
+                break
+            end
+        end
+    end
+end
+
 function Audio.playItem(item)
     local format = tostring(item.audioFormat or "dfpwm"):lower()
     if format == "wav" or format == "file" or format == "stream" or format == "hls" then
         return playHqAudioItem(item)
+    elseif format == "pcm" then
+        return Audio.playPcmItem(item)
     end
     return Audio.playDfpwmItem(item)
 end
@@ -1160,9 +1210,12 @@ function Network.messageLoop()
                             audioId = data.audioId
                         })
                         State.audioRx = nil
-                    elseif audioFormat == "dfpwm" then
+                    elseif audioFormat == "dfpwm" or audioFormat == "pcm" then
                         local stream = Audio.createStream()
                         State.audioRx.stream = stream
+                        if audioFormat == "pcm" then
+                            Utils.log("INFO", "Receiving live PCM audio stream")
+                        end
                         Audio.enqueueItem({
                             audioData = stream,
                             audioFormat = audioFormat,
@@ -1204,7 +1257,8 @@ function Network.messageLoop()
             else
                     if State.audioRx then
                         -- Memory protection: limit to 10MB per audio item
-                        if State.audioRx.receivedBytes + #msg > 10 * 1024 * 1024 then
+                        local isLiveStream = State.audioRx.stream and (tonumber(State.audioRx.expectedBytes) or 0) <= 0
+                        if (not isLiveStream) and State.audioRx.receivedBytes + #msg > 10 * 1024 * 1024 then
                             Utils.log("ERROR", "Audio item too large, discarding")
                             if State.audioRx.stream then
                                 State.audioRx.stream.finish()