diff --git a/backend/app/services/espidf_compiler.py b/backend/app/services/espidf_compiler.py
index edb387aa..157ba89c 100644
--- a/backend/app/services/espidf_compiler.py
+++ b/backend/app/services/espidf_compiler.py
@@ -1540,6 +1540,25 @@ class ESPIDFCompiler:
                 ' alloca=__builtin_alloca memcpy_P=memcpy memcmp_P=memcmp)\n'
             )
 
+        # The -Werror relaxations the main component gets, for the same reason
+        # but stronger: these are LIBRARY sources the user cannot even edit.
+        # M5Stack's own MahonyAHRS.cpp (the fast inverse square root reading a
+        # float through a long*) fails under -Werror=uninitialized, which made
+        # installing the vendor's library kill every build that used it. Same
+        # INTERFACE-library caveat as defs_block: no sources, no options.
+        warns_block = ''
+        if cpp_files:
+            warns_block = (
+                '# User libraries must compile as they do in the Arduino IDE.\n'
+                'target_compile_options(${COMPONENT_LIB} PRIVATE\n'
+                '    -Wno-error=comment -Wno-error=parentheses -Wno-error=sign-compare\n'
+                '    -Wno-error=narrowing -Wno-error=write-strings\n'
+                '    -Wno-error=missing-field-initializers -Wno-error=reorder\n'
+                '    -Wno-error=unused-variable -Wno-error=unused-but-set-variable\n'
+                '    -Wno-error=format -Wno-error=maybe-uninitialized\n'
+                '    -Wno-error=uninitialized)\n'
+            )
+
         cmake_content = (
             '# Auto-generated by Velxio — all user libraries merged into one component.\n'
             '# Directory structure preserved for libraries like ArduinoJson with src/ layout.\n'
@@ -1549,6 +1568,7 @@ class ESPIDFCompiler:
             f'    REQUIRES {arduino_comp_name}{extra_requires}\n'
             ')\n'
             f'{defs_block}'
+            f'{warns_block}'
         )
         (comp_dir / 'CMakeLists.txt').write_text(cmake_content, encoding='utf-8')
         logger.info(
diff --git a/frontend/src/simulation/Esp32Bridge.ts b/frontend/src/simulation/Esp32Bridge.ts
index a208ac01..d924f3ac 100644
--- a/frontend/src/simulation/Esp32Bridge.ts
+++ b/frontend/src/simulation/Esp32Bridge.ts
@@ -91,6 +91,11 @@ export interface Ws2812Pixel {
 export interface LedcDuty {
   channel: number;
   duty_pct: number;
+  /** Carrier frequency in Hz, when the engine knows it. The JS engines derive
+   *  it from the LEDC timer registers; without it a speaker on a PWM pin can
+   *  only ever play one fixed note, which is how the M5Stack Core's piano
+   *  spent months stuck on 660 Hz. */
+  freq_hz?: number;
 }
 /** GPIO Matrix routing event — `gpio_out_sel[gpio]` was set to
  *  `signal_id`.  Maintained by the backend SignalRouter; emitted on
diff --git a/frontend/src/simulation/PinManager.ts b/frontend/src/simulation/PinManager.ts
index 040231e8..764ebc83 100644
--- a/frontend/src/simulation/PinManager.ts
+++ b/frontend/src/simulation/PinManager.ts
@@ -280,6 +280,20 @@ export class PinManager {
     return this.pwmValues.get(pin) ?? 0;
   }
 
+  /** Last known PWM carrier frequency per pin, in Hz. Written by the LEDC
+   *  duty handler when the engine reports it; 0 = never reported. Kept as a
+   *  side table rather than a new callback parameter so the many existing
+   *  two- and three-arg PWM listeners stay untouched. */
+  private pwmFreqs: Map<number, number> = new Map();
+
+  setPwmFreq(pin: number, freqHz: number): void {
+    this.pwmFreqs.set(pin, freqHz);
+  }
+
+  getPwmFreq(pin: number): number {
+    return this.pwmFreqs.get(pin) ?? 0;
+  }
+
   // ── Analog voltage API ───────────────────────────────────────────────────
 
   /**
diff --git a/frontend/src/store/useSimulatorStore.ts b/frontend/src/store/useSimulatorStore.ts
index 61fc752b..6b5a2a27 100644
--- a/frontend/src/store/useSimulatorStore.ts
+++ b/frontend/src/store/useSimulatorStore.ts
@@ -696,7 +696,7 @@ class Esp32BridgeShim {
 // race window.
 
 function makeLedcDutyHandler(boardId: string) {
-  return (duty: { channel: number; duty_pct: number }) => {
+  return (duty: { channel: number; duty_pct: number; freq_hz?: number }) => {
     const boardPm = pinManagerMap.get(boardId);
     const router = signalRouterMap.get(boardId);
     if (!boardPm || !router) return;
@@ -707,6 +707,10 @@ function makeLedcDutyHandler(boardId: string) {
     // pins via the GPIO Matrix (rare but documented in TRM). Iterate
     // all of them — each gets its own updatePwm call.
     for (const pin of pins) {
+      // The carrier frequency rides alongside, when the engine knows it: a
+      // speaker listener reads it back with getPwmFreq to play the sketch's
+      // actual note rather than a canned one.
+      if (duty.freq_hz && duty.freq_hz > 0) boardPm.setPwmFreq(pin, duty.freq_hz);
       boardPm.updatePwm(pin, dutyCycle);
     }
   };