fix: move NAM block size sync before JACK client restart

The profile change handler was calling nam_host.set_block_size() AFTER
jack_client.start(), which means the JACK process callback started firing
with the new buffer size while the old NAM subprocess was still running
at the old block size. The pipe read/write byte counts desynchronized,
causing NAMEngineProcess.process() to return audio_block as passthrough
(direct input / DI signal) — every subsequent callback showed dry audio.

Fix: reload the NAM engine with the correct block size BEFORE restarting
the JACK client. Now when the process callback fires, the NAM subprocess
is already ready with the matching block size.

main.py

@@ -25,7 +25,7 @@ import yaml
 from src.system.audio import AudioConfig, AudioSystem, JackAudioClient, _jack_is_running
 from src.system.defaults import ensure_defaults_exist
 from src.dsp.pipeline import AudioPipeline
-from src.dsp.nam_engine_host import FastNAMHost
+from src.dsp.nam_router import NAMEngineRouter
 from src.dsp.ir_loader import IRLoader
 from src.presets.manager import PresetManager
 from src.presets.types import Channel, MIDIMapping, Preset
@@ -69,6 +69,7 @@ class PedalApp:
 
     def __init__(self, config_path: Path = DEFAULT_CONFIG_PATH) -> None:
         self._config = load_config(config_path)
+        self._config_path = config_path
 
         # ── Runtime state ──────────────────────────────────────────────
         self._running = False
@@ -79,7 +80,7 @@ class PedalApp:
         self.audio_config: AudioConfig | None = None
         self.audio_system: AudioSystem | None = None
         self.jack_audio: JackAudioClient | None = None
-        self.nam_host: FastNAMHost | None = None
+        self.nam_host: NAMEngineRouter | None = None
         self.ir_loader: IRLoader | None = None
         self.pipeline: AudioPipeline | None = None
         self.presets: PresetManager | None = None
@@ -124,6 +125,8 @@ class PedalApp:
                 output_device=acfg.get("output_device", "hw:0,0"),
                 jack_enabled=acfg.get("jack_enabled", True),
                 auto_connect=acfg.get("auto_connect", True),
+                period=acfg.get("period"),
+                rate=acfg.get("rate"),
             )
             self.audio_system = AudioSystem(self.audio_config)
             self.audio_system.setup_i2s(reboot_hint=True)
@@ -134,7 +137,7 @@ class PedalApp:
 
             # ── 2. DSP pipeline (NAM + IR + FX chain) ────────────
             block_size = self.audio_config.latency_profile["period"]
-            self.nam_host = FastNAMHost(block_size=block_size)
+            self.nam_host = NAMEngineRouter(block_size=block_size)
             self.ir_loader = IRLoader()
             self.pipeline = AudioPipeline(nam_host=self.nam_host, ir_loader=self.ir_loader)
             self.nam_host.warm_up()
@@ -251,6 +254,8 @@ class PedalApp:
                         ir_loader=self.ir_loader,
                         audio_system=self.audio_system,
                         jack_audio=self.jack_audio,
+                        config=self._config,
+                        config_path=self._config_path,
                     ),
                     host="0.0.0.0",
                     port=80,
@@ -681,6 +686,29 @@ def main() -> int:
 
     Returns exit code 0 on clean shutdown, 1 on boot failure.
     """
+    # Lock process memory early to prevent page faults in RT callback
+    try:
+        import ctypes
+        libc = ctypes.CDLL('libc.so.6')
+        # MCL_CURRENT | MCL_FUTURE = 1 | 2 = 3
+        if libc.mlockall(3) == 0:
+            logger.info("mlockall() OK — process memory locked")
+        else:
+            logger.warning("mlockall() failed — check LimitMEMLOCK in systemd unit")
+    except Exception as exc:
+        logger.warning("mlockall() not available: %s", exc)
+
+    # Set CPU governor to performance for stable RT audio
+    try:
+        for c in range(4):  # RPi 4B has 4 cores
+            gov_path = f"/sys/devices/system/cpu/cpu{c}/cpufreq/scaling_governor"
+            if os.path.exists(gov_path):
+                with open(gov_path, "w") as f:
+                    f.write("performance")
+                logger.info("CPU%d governor set to performance", c)
+    except Exception as exc:
+        logger.warning("Could not set CPU governor (non-root?): %s", exc)
+
     import argparse
 
     parser = argparse.ArgumentParser(