diff --git a/README.md b/README.md
index 3b47d4d..2107e43 100644
--- a/README.md
+++ b/README.md
@@ -73,20 +73,20 @@ cd <cloned folder>
 west init -l zephcore
 west update
 
-# Companion (with logging)
+# Companion (production — default, no extra conf needed)
 west build -b wio_tracker_l1 zephcore --pristine
 
-# Companion (production, no logging, no USB)
+# Companion (debug logging)
 west build -b wio_tracker_l1 zephcore --pristine -- \
-  -DEXTRA_CONF_FILE="boards/common/prod.conf"
+  -DEXTRA_CONF_FILE="boards/common/debug.conf"
 
-# Repeater (with logging)
+# Repeater
 west build -b rak4631 zephcore --pristine -- \
   -DEXTRA_CONF_FILE="boards/common/repeater.conf"
 
-# Repeater (production)
+# Repeater (debug logging)
 west build -b rak4631 zephcore --pristine -- \
-  -DEXTRA_CONF_FILE="boards/common/repeater.conf;boards/common/prod.conf"
+  -DEXTRA_CONF_FILE="boards/common/repeater.conf;boards/common/debug.conf"
 
 # Repeater with packet logging (clean RAW/RX/TX lines only, no debug spam)
 west build -b rak4631 zephcore --pristine -- \
@@ -175,7 +175,7 @@ The old `txdelay`, `rxdelay`, and `direct.txdelay` commands are still accepted f
 
 - **LoRa RX duty cycle**: CAD-based receive windowing reduces LoRa RX current from ~10-15mA to ~3-5mA. Auto-enabled for SX1262 companion and repeater builds (toggleable at runtime via `set rxduty on/off`). Disabled for LR1110 (mid-preamble lock issue) and SX127x.
 - **Adaptive Power Control (APC)**: compiled in by default but disabled at runtime. Enable per-node with `set tx apc` -- automatically reduces TX power when echo SNR shows excess margin, ramping back up if echoes drop. See [apc.md](zephcore/apc.md).
-- **USB disabled in production**: Saves ~2-5mA and 62KB flash when logging is off
+- **Production by default**: No logging, no asserts, reboot-on-fatal. Add `debug.conf` to enable logging.
 - **GPIO-gated GPS**: Powered on only during fix acquisition
 
 ## Configuration
diff --git a/build.sh b/build.sh
index ef4343a..649478c 100644
--- a/build.sh
+++ b/build.sh
@@ -37,19 +37,19 @@ if [[ $1 == "nrf" ]]; then
     for board in "${nRF_boards[@]}"; do
         board_clean_for_path=$(echo "$board" | sed -e 's/\//-/g')
         
-        # build nRF companions
+        # build nRF companions (production is the default — no extra conf needed)
         echo "Now building $board companion"
         if [[ $board == "wio_tracker_l1" ]]; then
-            west build -b "$board" zephcore --pristine -- -DEXTRA_CONF_FILE="boards/common/prod.conf" -DCONFIG_ZEPHCORE_EASTER_EGG_DOOM=y
+            west build -b "$board" zephcore --pristine -- -DCONFIG_ZEPHCORE_EASTER_EGG_DOOM=y
         else
-            west build -b "$board" zephcore --pristine -- -DEXTRA_CONF_FILE="boards/common/prod.conf"
+            west build -b "$board" zephcore --pristine
         fi
         mv build/zephyr/zephyr.uf2 firmware/"$board"-companion-"$COMMIT_HASH".uf2
         mv build/zephyr/zephyr.zip firmware/"$board"-companion-"$COMMIT_HASH".zip
-        
+
         # build nRF repeaters
         echo "Now building $board repeater"
-        west build -b "$board" zephcore --pristine -- -DEXTRA_CONF_FILE="boards/common/repeater.conf;boards/common/prod.conf"
+        west build -b "$board" zephcore --pristine -- -DEXTRA_CONF_FILE="boards/common/repeater.conf"
         mv build/zephyr/zephyr.uf2 firmware/"$board"-repeater-"$COMMIT_HASH".uf2
         mv build/zephyr/zephyr.zip firmware/"$board"-repeater-"$COMMIT_HASH".zip
 
@@ -58,12 +58,12 @@ if [[ $1 == "nrf" ]]; then
         # Heltec_t114_without_display_* PIO envs.
         if [[ $board == "heltec_t114" ]]; then
             echo "Now building $board companion (noscreen)"
-            west build -b "$board" zephcore --pristine -- -DEXTRA_CONF_FILE="boards/common/prod.conf;boards/nrf52840/heltec_t114/no_display.conf"
+            west build -b "$board" zephcore --pristine -- -DEXTRA_CONF_FILE="boards/nrf52840/heltec_t114/no_display.conf"
             mv build/zephyr/zephyr.uf2 firmware/"$board"-companion-noscreen-"$COMMIT_HASH".uf2
             mv build/zephyr/zephyr.zip firmware/"$board"-companion-noscreen-"$COMMIT_HASH".zip
 
             echo "Now building $board repeater (noscreen)"
-            west build -b "$board" zephcore --pristine -- -DEXTRA_CONF_FILE="boards/common/repeater.conf;boards/common/prod.conf;boards/nrf52840/heltec_t114/no_display.conf"
+            west build -b "$board" zephcore --pristine -- -DEXTRA_CONF_FILE="boards/common/repeater.conf;boards/nrf52840/heltec_t114/no_display.conf"
             mv build/zephyr/zephyr.uf2 firmware/"$board"-repeater-noscreen-"$COMMIT_HASH".uf2
             mv build/zephyr/zephyr.zip firmware/"$board"-repeater-noscreen-"$COMMIT_HASH".zip
         fi
@@ -82,9 +82,9 @@ if [[ $1 == "esp32" ]]; then
         fi
         
         if [[ $2 == "companions" ]]; then
-            # build ESP32 companions
+            # build ESP32 companions (production is the default)
             echo "Now building $board companion"
-            west build -b "$board" zephcore --pristine --sysbuild -- -DEXTRA_CONF_FILE="boards/common/prod.conf"
+            west build -b "$board" zephcore --pristine --sysbuild
             FLASH_SIZE=$(
                 python3 -c '
 import re
@@ -127,7 +127,7 @@ print(str(size // 1048576) + "MB")
         if [[ $2 == "repeaters" ]]; then
             # build ESP32 repeaters
             echo "Now building $board repeater"
-            west build -b "$board" zephcore --pristine --sysbuild -- -DEXTRA_CONF_FILE="boards/common/repeater.conf;boards/common/prod.conf"
+            west build -b "$board" zephcore --pristine --sysbuild -- -DEXTRA_CONF_FILE="boards/common/repeater.conf"
             FLASH_SIZE=$(
                 python3 -c '
 import re
diff --git a/zephcore/ARCHITECTURE.md b/zephcore/ARCHITECTURE.md
index 3395486..1ea2fc6 100644
--- a/zephcore/ARCHITECTURE.md
+++ b/zephcore/ARCHITECTURE.md
@@ -511,11 +511,11 @@ Wolf3D-style raycaster on OLED: textured walls, 2 enemy types, shooting, HUD. By
 ### 9.1 Config Layering
 
 ```
-prj.conf (base: console, logging)
+prj.conf (base: console; production defaults — LOG=n, ASSERT=n)
   → boards/common/zephcore_common.conf (ALL boards: BLE, crypto, FS, LoRa, sensors)
     → boards/common/<platform>_common.conf (nrf52/esp32/nrf54l/mg24 specifics)
       → boards/<mcu>/<board>/board.conf (board-specific pins, features)
-        → [optional] repeater.conf, prod.conf (user extras, LAST = highest priority)
+        → [optional] repeater.conf, debug.conf (user extras, LAST = highest priority)
 ```
 
 ### 9.2 Key Kconfig Choices
diff --git a/zephcore/CMakeLists.txt b/zephcore/CMakeLists.txt
index b58a9b2..668ce0b 100644
--- a/zephcore/CMakeLists.txt
+++ b/zephcore/CMakeLists.txt
@@ -306,17 +306,7 @@ if(ZEPHCORE_BOARD_CONF AND EXISTS ${ZEPHCORE_BOARD_CONF})
     zephcore_auto_pair_overlay("${ZEPHCORE_BOARD_CONF}")
 endif()
 
-# Include logging tuning only for debug builds (when prod.conf is NOT active).
-# This avoids Kconfig warnings from log settings that depend on CONFIG_LOG.
-set(ZEPHCORE_LOGGING_CONF "${CMAKE_CURRENT_SOURCE_DIR}/boards/common/logging.conf")
-if(EXTRA_CONF_FILE MATCHES "prod\\.conf")
-    message(STATUS "  Production build — skipping logging.conf")
-else()
-    if(EXISTS ${ZEPHCORE_LOGGING_CONF})
-        list(APPEND ZEPHCORE_CONF_FILES ${ZEPHCORE_LOGGING_CONF})
-        zephcore_auto_pair_overlay("${ZEPHCORE_LOGGING_CONF}")
-    endif()
-endif()
+# Production is the default. Debug logging is opt-in via debug.conf.
 
 # Auto-include WiFi OTA for ESP32 repeater builds.
 # Enables WiFi AP + HTTP server + MCUboot image management.
diff --git a/zephcore/Kconfig b/zephcore/Kconfig
index 6194f25..75f9450 100644
--- a/zephcore/Kconfig
+++ b/zephcore/Kconfig
@@ -66,6 +66,27 @@ config ZEPHCORE_ROLE_COMPANION
 	  BLE companion device that connects to ZephCore mobile app.
 	  Includes BLE stack, contact management, offline queue, channels.
 
+config ZEPHCORE_COMPANION_USB
+	bool "Enable USB CDC companion transport"
+	depends on USB_DEVICE_STACK_NEXT
+	default y if ZEPHCORE_ROLE_COMPANION
+	help
+	  Compile and init the USB CDC-ACM companion protocol stack
+	  (ZephyrCompanionUSB / ZephyrUSBCDC) independently of CONFIG_LOG.
+	  The full ~60-opcode binary protocol is available over USB even in
+	  production builds (CONFIG_LOG=n).  USB and BLE arbitrate the active
+	  interface first-come-first-served: CMD_APP_START claims it for USB only
+	  if no BLE session is already active (and is ignored while BLE is live);
+	  on USB unplug the interface is handed back to BLE or released to idle.
+
+	  Enabled by default for all companion builds on platforms that already
+	  have CONFIG_USB_DEVICE_STACK_NEXT=y (all nRF52840 boards).  On
+	  platforms without USB hardware (MG24, ESP32 classic, C3/C6) the
+	  depends forces this to n automatically — no conf change needed.
+
+	  For ESP32-S3 boards, USB_DEVICE_STACK_NEXT must be enabled first via
+	  boards/common/esp32s3_usb.conf before this becomes active.
+
 config ZEPHCORE_ROLE_REPEATER
 	bool "Repeater"
 	help
diff --git a/zephcore/adapters/ble/ZephyrBLE.cpp b/zephcore/adapters/ble/ZephyrBLE.cpp
index 89065b4..8818730 100644
--- a/zephcore/adapters/ble/ZephyrBLE.cpp
+++ b/zephcore/adapters/ble/ZephyrBLE.cpp
@@ -122,6 +122,44 @@ static int64_t ble_tx_start_time = 0;
 /* Active interface tracking */
 static enum zephcore_iface active_iface = ZEPHCORE_IFACE_NONE;
 
+/* active_iface is mutated from two threads — the Bluetooth callback thread
+ * (connect / security / pairing / disconnect) and the USB workqueue
+ * (CMD_APP_START / DTR drop).  This mutex makes the check-then-act claim and
+ * release sequences atomic so the two transports can never both believe they
+ * own the interface (or lose a write to it). */
+K_MUTEX_DEFINE(ble_iface_lock);
+
+/* Atomically claim the interface for `who` iff it is currently idle.
+ * Returns true only if this call performed the NONE -> who transition. */
+static bool iface_claim_if_idle(enum zephcore_iface who)
+{
+	k_mutex_lock(&ble_iface_lock, K_FOREVER);
+	bool claimed = (active_iface == ZEPHCORE_IFACE_NONE);
+	if (claimed) {
+		active_iface = who;
+	}
+	k_mutex_unlock(&ble_iface_lock);
+	return claimed;
+}
+
+/* Atomically release the interface if `who` currently owns it. */
+static void iface_release(enum zephcore_iface who)
+{
+	k_mutex_lock(&ble_iface_lock, K_FOREVER);
+	if (active_iface == who) {
+		active_iface = ZEPHCORE_IFACE_NONE;
+	}
+	k_mutex_unlock(&ble_iface_lock);
+}
+
+/* Claim the active interface for BLE, but only if nothing else owns it.
+ * First-come-first-served: a live USB session must not be evicted by BLE
+ * connecting/pairing in the background.  Returns true if BLE now owns it. */
+static bool ble_claim_iface_if_idle(void)
+{
+	return iface_claim_if_idle(ZEPHCORE_IFACE_BLE);
+}
+
 /* DLE tracking — set after successful DLE request to avoid double-request */
 static bool dle_requested;
 
@@ -298,6 +336,16 @@ static void connected(struct bt_conn *conn, uint8_t err)
 		return;
 	}
 	LOG_INF("connected: %s", addr);
+
+	/* Reject BLE connections while USB is the active transport.
+	 * The user connected via BLE expecting to exchange messages, but
+	 * USB owns the interface — they would get nothing and be confused. */
+	if (active_iface == ZEPHCORE_IFACE_USB) {
+		LOG_INF("connected: USB active — rejecting BLE connection from %s", addr);
+		bt_conn_disconnect(conn, BT_HCI_ERR_REMOTE_USER_TERM_CONN);
+		return;
+	}
+
 	current_conn = bt_conn_ref(conn);
 
 	/* Zephyr stops advertising internally when the conn slot is consumed
@@ -349,9 +397,7 @@ static void disconnected(struct bt_conn *conn, uint8_t reason)
 	conn_params_pending = false;
 
 	/* Clear interface state if BLE was active */
-	if (active_iface == ZEPHCORE_IFACE_BLE) {
-		active_iface = ZEPHCORE_IFACE_NONE;
-	}
+	iface_release(ZEPHCORE_IFACE_BLE);
 
 	/* Clear queues, retry state, and congestion */
 	k_msgq_purge(&ble_send_queue);
@@ -397,7 +443,7 @@ static void security_changed(struct bt_conn *conn, bt_security_t level, enum bt_
 	if (level >= BT_SECURITY_L2 && !ble_tx_ready) {
 		LOG_INF("security established, enabling TX");
 		ble_tx_ready = true;
-		active_iface = ZEPHCORE_IFACE_BLE;
+		ble_claim_iface_if_idle();
 
 		/* If CCC was already subscribed (bonded reconnect — phone writes
 		 * CCC before security_changed fires), kick TX now.  On fresh
@@ -532,14 +578,12 @@ static void pairing_complete(struct bt_conn *conn, bool bonded)
 	ARG_UNUSED(conn);
 	LOG_INF("pairing complete: bonded=%d", bonded);
 
-	/* Switch to BLE interface (fresh pairing only).
-	 * Conn params and TX enable are handled in security_changed(),
-	 * which fires for both fresh pairing and bonded reconnects. */
-	if (active_iface == ZEPHCORE_IFACE_USB) {
-		LOG_INF("switching from USB to BLE");
-		/* Main handles USB state clearing via on_connected callback */
+	if (ble_claim_iface_if_idle()) {
+		LOG_INF("pairing complete, activating BLE interface");
+	} else {
+		LOG_INF("pairing complete, %s already active — BLE paired but not promoted",
+			active_iface == ZEPHCORE_IFACE_USB ? "USB" : "BLE");
 	}
-	active_iface = ZEPHCORE_IFACE_BLE;
 }
 
 static void pairing_failed(struct bt_conn *conn, enum bt_security_err reason)
@@ -985,12 +1029,28 @@ uint32_t zephcore_ble_get_passkey(void)
 
 enum zephcore_iface zephcore_ble_get_active_iface(void)
 {
-	return active_iface;
+	k_mutex_lock(&ble_iface_lock, K_FOREVER);
+	enum zephcore_iface iface = active_iface;
+	k_mutex_unlock(&ble_iface_lock);
+	return iface;
 }
 
 void zephcore_ble_set_active_iface(enum zephcore_iface iface)
 {
+	k_mutex_lock(&ble_iface_lock, K_FOREVER);
 	active_iface = iface;
+	k_mutex_unlock(&ble_iface_lock);
+}
+
+bool zephcore_ble_iface_try_claim(enum zephcore_iface who)
+{
+	k_mutex_lock(&ble_iface_lock, K_FOREVER);
+	bool ok = (active_iface == ZEPHCORE_IFACE_NONE || active_iface == who);
+	if (ok) {
+		active_iface = who;
+	}
+	k_mutex_unlock(&ble_iface_lock);
+	return ok;
 }
 
 struct k_msgq *zephcore_ble_get_recv_queue(void)
diff --git a/zephcore/adapters/ble/ZephyrBLE.h b/zephcore/adapters/ble/ZephyrBLE.h
index f8a18ab..b1df197 100644
--- a/zephcore/adapters/ble/ZephyrBLE.h
+++ b/zephcore/adapters/ble/ZephyrBLE.h
@@ -65,10 +65,17 @@ bool zephcore_ble_is_advertising(void);
 void zephcore_ble_set_passkey(uint32_t passkey);
 uint32_t zephcore_ble_get_passkey(void);
 
-/** Get/set active interface (BLE/USB coexistence). */
+/** Get/set active interface (BLE/USB coexistence). Both are thread-safe —
+ *  active_iface is mutated from the BLE callback thread and the USB workqueue. */
 enum zephcore_iface zephcore_ble_get_active_iface(void);
 void zephcore_ble_set_active_iface(enum zephcore_iface iface);
 
+/** Atomically claim the active interface for `who` unless the other transport
+ *  already owns it. Succeeds (returns true) if the interface is idle or already
+ *  held by `who`; fails if a different interface is active. Thread-safe — use
+ *  this instead of a get-then-set sequence to avoid a check-then-act race. */
+bool zephcore_ble_iface_try_claim(enum zephcore_iface who);
+
 /** Get recv/send queues for USB path sharing. */
 struct k_msgq *zephcore_ble_get_recv_queue(void);
 struct k_msgq *zephcore_ble_get_send_queue(void);
diff --git a/zephcore/adapters/usb/ZephyrCompanionUSB.cpp b/zephcore/adapters/usb/ZephyrCompanionUSB.cpp
index 5a1a64a..f535b6b 100644
--- a/zephcore/adapters/usb/ZephyrCompanionUSB.cpp
+++ b/zephcore/adapters/usb/ZephyrCompanionUSB.cpp
@@ -115,13 +115,17 @@ static void usb_rx_work_fn(struct k_work *work)
 				 * is actually CMD_SEND_CHANNEL_TXT_MSG and meant the USB
 				 * handshake silently dropped the app's first frame.) */
 				if (payload_len >= 1 && payload[0] == 0x01 /* CMD_APP_START */) {
-					if (zephcore_ble_get_active_iface() == ZEPHCORE_IFACE_BLE &&
-					    zephcore_ble_is_connected()) {
-						LOG_INF("usb_rx: CMD_APP_START, disconnecting BLE");
-						zephcore_ble_disconnect();
+					/* Atomically claim the interface for USB unless BLE
+					 * already owns it.  try_claim succeeds when idle or
+					 * already USB (reconnect) and fails only while a BLE
+					 * session is live, so USB can't steal it — and the
+					 * compare-and-set can't race a concurrent BLE claim. */
+					if (zephcore_ble_iface_try_claim(ZEPHCORE_IFACE_USB)) {
+						zephcore_ble_set_enabled(false);
+						LOG_INF("usb_rx: CMD_APP_START → IFACE_USB");
+					} else {
+						LOG_INF("usb_rx: CMD_APP_START ignored, BLE is active");
 					}
-					zephcore_ble_set_active_iface(ZEPHCORE_IFACE_USB);
-					LOG_INF("usb_rx: active_iface = IFACE_USB");
 				}
 
 				/* Only process if USB is active interface */
@@ -155,9 +159,21 @@ static void on_dtr_change(bool dtr_active)
 		return;
 	}
 	LOG_INF("usb_dtr: DTR dropped, USB disconnected");
+	/* While USB owns the interface, BLE claims are rejected (see connected()),
+	 * so this thread is the only writer of active_iface here — the get/set
+	 * pair below needs no extra locking beyond the thread-safe accessors. */
 	if (zephcore_ble_get_active_iface() == ZEPHCORE_IFACE_USB) {
-		zephcore_ble_set_active_iface(ZEPHCORE_IFACE_NONE);
-		LOG_INF("usb_dtr: active_iface = IFACE_NONE");
+		if (zephcore_ble_is_connected()) {
+			/* BLE client is physically connected — hand off to it. */
+			zephcore_ble_set_active_iface(ZEPHCORE_IFACE_BLE);
+			LOG_INF("usb_dtr: → IFACE_BLE (BLE was connected)");
+		} else {
+			/* Nobody connected — go idle and restart advertising
+			 * so the phone can find the companion again. */
+			zephcore_ble_set_active_iface(ZEPHCORE_IFACE_NONE);
+			zephcore_ble_set_enabled(true);
+			LOG_INF("usb_dtr: → IFACE_NONE, BLE advertising restarted");
+		}
 	}
 	ring_buf_reset(&usb_ring_buf);
 	usb_frame_len = 0;
diff --git a/zephcore/boards/common/debug.conf b/zephcore/boards/common/debug.conf
new file mode 100644
index 0000000..261c2ac
--- /dev/null
+++ b/zephcore/boards/common/debug.conf
@@ -0,0 +1,40 @@
+# Debug Config — opt-in logging and diagnostics.
+#
+# Production is the default.  Pass this conf to get the full debug experience:
+#
+#   west build -b rak4631 zephcore --pristine -- \
+#     -DEXTRA_CONF_FILE="boards/common/debug.conf"
+#
+#   # With repeater role:
+#   west build -b rak4631 zephcore --pristine -- \
+#     -DEXTRA_CONF_FILE="boards/common/repeater.conf;boards/common/debug.conf"
+
+# ========== Core debug features ==========
+CONFIG_LOG=y
+CONFIG_ASSERT=y
+CONFIG_USE_SEGGER_RTT=y
+CONFIG_SEGGER_RTT_BUFFER_SIZE_UP=4096
+CONFIG_THREAD_NAME=y
+
+# Halt-and-inspect on fatal faults instead of the production reboot-on-fatal
+# (prj.conf sets CONFIG_RESET_ON_FATAL_ERROR=y).  A debugger needs the core
+# stopped at the fault with a stack dump, not rebooted out from under it.
+CONFIG_RESET_ON_FATAL_ERROR=n
+
+# ========== Log tuning ==========
+# ZephCore BLE modules at INF level (connection lifecycle, pairing, TX/RX).
+CONFIG_ZEPHCORE_BLE_LOG_LEVEL_INF=y
+
+# Deferred logging — non-blocking so BLE/LoRa timing is not disturbed.
+CONFIG_LOG_BUFFER_SIZE=8192
+CONFIG_LOG_PROCESS_TRIGGER_THRESHOLD=1
+CONFIG_LOG_PROCESS_THREAD_STACK_SIZE=2048
+
+# RTT backend only — no UART backend on nRF52.
+# UART backend stalls on uart_poll_out() when the USB host disconnects;
+# RTT DROP mode discards messages without blocking.
+CONFIG_LOG_BACKEND_RTT=y
+CONFIG_LOG_BACKEND_RTT_MODE_DROP=y
+
+# Silence noisy subsystems
+CONFIG_CFB_LOG_LEVEL_ERR=y
diff --git a/zephcore/boards/common/esp32s3_console_uart0.dtsi b/zephcore/boards/common/esp32s3_console_uart0.dtsi
new file mode 100644
index 0000000..deb4bc2
--- /dev/null
+++ b/zephcore/boards/common/esp32s3_console_uart0.dtsi
@@ -0,0 +1,45 @@
+/*
+ * Reroute console + shell off USB Serial/JTAG onto uart0 (physical TX/RX).
+ *
+ * ESP32-S3 USB Serial/JTAG shares the D+/D- pins with USB OTG and only one
+ * controller can own the port at a time.  Boards that default their console to
+ * USB Serial/JTAG include this alongside esp32s3_usb_otg.dtsi so that, when
+ * esp32s3_usb.conf disables USB Serial/JTAG and hands the port to USB OTG, the
+ * console still has a home.  Boards with a dedicated UART console (e.g. Heltec)
+ * do not need this.
+ *
+ * uart0 is disabled by default in the ESP32-S3 SoC dtsi, so we enable it and
+ * pin it to the chip's ROM-default UART0 pads (GPIO43 TX / GPIO44 RX) — the
+ * same pins Heltec uses.  Without this the console would point at a disabled,
+ * un-pinned node and produce no output at all.
+ */
+#include <zephyr/dt-bindings/pinctrl/esp-pinctrl-common.h>
+#include <zephyr/dt-bindings/pinctrl/esp32s3-pinctrl.h>
+#include <zephyr/dt-bindings/pinctrl/esp32s3-gpio-sigmap.h>
+
+&pinctrl {
+	uart0_default: uart0_default {
+		group1 {
+			pinmux = <UART0_TX_GPIO43>;
+			output-high;
+		};
+		group2 {
+			pinmux = <UART0_RX_GPIO44>;
+			bias-pull-up;
+		};
+	};
+};
+
+&uart0 {
+	status = "okay";
+	current-speed = <115200>;
+	pinctrl-0 = <&uart0_default>;
+	pinctrl-names = "default";
+};
+
+/ {
+	chosen {
+		zephyr,console    = &uart0;
+		zephyr,shell-uart = &uart0;
+	};
+};
diff --git a/zephcore/boards/common/esp32s3_usb.conf b/zephcore/boards/common/esp32s3_usb.conf
new file mode 100644
index 0000000..9b76185
--- /dev/null
+++ b/zephcore/boards/common/esp32s3_usb.conf
@@ -0,0 +1,24 @@
+# ESP32-S3 USB CDC-ACM companion support
+#
+# ESP32-S3 has a DWC2 USB OTG peripheral (snps,dwc2 compatible) that supports
+# the Zephyr USB NEXT stack.  This conf enables it and turns on the companion
+# USB transport on S3 boards.  Do NOT use on ESP32 (original) or C3/C6 — those
+# chips have no DWC2 controller.
+#
+# Build with:
+#   -DEXTRA_CONF_FILE="boards/common/esp32s3_usb.conf"
+#
+# Also add the cdc_acm_uart DTS node to the board overlay (the overlays include
+# boards/common/esp32s3_usb_otg.dtsi).  Without the DT node,
+# DT_HAS_COMPAT_STATUS_OKAY(zephyr_cdc_acm_uart) is false and
+# zephcore_usbd_init() is compiled out at the #if check.
+
+CONFIG_USB_DEVICE_STACK_NEXT=y
+CONFIG_ZEPHCORE_COMPANION_USB=y
+CONFIG_CDC_ACM_SERIAL_INITIALIZE_AT_BOOT=n
+CONFIG_UART_LINE_CTRL=y
+
+# Disable USB Serial/JTAG so it doesn't fight USB OTG for the D+/D- pins.
+# ESP32-S3 has an internal mux — only one controller can own the port at a time.
+# With USB companion active, the port IS the companion protocol channel.
+CONFIG_ESP_USB_SERIAL_JTAG_ENABLED=n
diff --git a/zephcore/boards/common/esp32s3_usb_otg.dtsi b/zephcore/boards/common/esp32s3_usb_otg.dtsi
new file mode 100644
index 0000000..1e8dbcb
--- /dev/null
+++ b/zephcore/boards/common/esp32s3_usb_otg.dtsi
@@ -0,0 +1,21 @@
+/*
+ * ESP32-S3 USB OTG (DWC2) — companion USB transport.
+ *
+ * Enables the snps,dwc2 USB OTG controller and attaches a CDC-ACM UART node
+ * for the binary companion protocol.  The DWC2 driver is only compiled when
+ * CONFIG_USB_DEVICE_STACK_NEXT=y (set by boards/common/esp32s3_usb.conf);
+ * without that conf this node is inert.
+ *
+ * Boards whose default console rides USB Serial/JTAG (shares D+/D- with USB
+ * OTG) must also reroute the console off the shared pins — see
+ * esp32s3_console_uart0.dtsi.
+ */
+zephyr_udc0: &usb_otg {
+	status = "okay";
+};
+
+&zephyr_udc0 {
+	cdc_acm_uart: cdc_acm_uart {
+		compatible = "zephyr,cdc-acm-uart";
+	};
+};
diff --git a/zephcore/boards/common/logging.conf b/zephcore/boards/common/logging.conf
deleted file mode 100644
index c828825..0000000
--- a/zephcore/boards/common/logging.conf
+++ /dev/null
@@ -1,23 +0,0 @@
-# Logging Tuning — included automatically for debug builds only.
-# Prod builds (CONFIG_LOG=n via prod.conf) skip this file entirely,
-# avoiding Kconfig warnings from log settings that depend on CONFIG_LOG.
-
-# ZephCore BLE modules at INF level (connection lifecycle, pairing, TX/RX)
-# Default level is WRN — this ensures our INF messages come through.
-# Avoid DBG level — it causes system workqueue stack overflow.
-CONFIG_ZEPHCORE_BLE_LOG_LEVEL_INF=y
-
-# Deferred mode (non-blocking) — buffer/thread config
-CONFIG_LOG_BUFFER_SIZE=8192
-CONFIG_LOG_PROCESS_TRIGGER_THRESHOLD=1
-CONFIG_LOG_PROCESS_THREAD_STACK_SIZE=2048
-
-# Backends
-# NOTE: UART backend on nRF52 routes through USB CDC ACM (zephyr,console = &cdc_acm_uart).
-# There is no LOG_BACKEND_UART_MODE_DROP in Zephyr — if the USB host disconnects, the log
-# processing thread stalls on uart_poll_out(). Disable UART backend on nRF52 to avoid this;
-# RTT (below) is the reliable debug path and already configured with drop mode.
-CONFIG_LOG_BACKEND_RTT=y
-
-# Suppress noisy subsystem logs
-CONFIG_CFB_LOG_LEVEL_ERR=y
diff --git a/zephcore/boards/common/mg24_common.conf b/zephcore/boards/common/mg24_common.conf
index 8e7b4ef..9d07191 100644
--- a/zephcore/boards/common/mg24_common.conf
+++ b/zephcore/boards/common/mg24_common.conf
@@ -16,10 +16,13 @@ CONFIG_BT_TX_PROCESSOR_STACK_SIZE=2048
 
 # Controller assert handler — without this, a controller assert silently
 # freezes the CPU at highest IRQ priority with zero log output.
+# Harmless when CONFIG_ASSERT=n, so it stays on for prod and debug.
 CONFIG_BT_CTLR_ASSERT_HANDLER=y
 
 # ========== Debug ==========
-CONFIG_ASSERT=y
+# CONFIG_ASSERT is debug-only (boards/common/debug.conf, opt-in).  Setting it
+# here would override the prj.conf production default (CONFIG_ASSERT=n) on every
+# MG24 build, since this file loads after prj.conf.
 
 # ========== Heap ==========
 # Silabs BLE stack requires larger heap (override zephcore_common 2KB default)
diff --git a/zephcore/boards/common/nrf52_common.conf b/zephcore/boards/common/nrf52_common.conf
index eb0ce10..588cd07 100644
--- a/zephcore/boards/common/nrf52_common.conf
+++ b/zephcore/boards/common/nrf52_common.conf
@@ -44,11 +44,12 @@ CONFIG_SOC_FLASH_NRF_PARTIAL_ERASE=y
 # Silently ignored when QSPI is not present (Kconfig guard: if NORDIC_QSPI_NOR).
 CONFIG_NORDIC_QSPI_NOR_FLASH_LAYOUT_PAGE_SIZE=4096
 
-# ========== SEGGER RTT (J-Link debug) ==========
-# RTT log backend is in boards/common/logging.conf (only included for debug builds).
-CONFIG_USE_SEGGER_RTT=y
-CONFIG_SEGGER_RTT_BUFFER_SIZE_UP=4096
-
 # ========== Debug ==========
-CONFIG_ASSERT=y
+# SEGGER RTT and CONFIG_ASSERT are debug-only and live in boards/common/debug.conf
+# (opt-in).  Keeping them here would override the production defaults from
+# prj.conf (CONFIG_USE_SEGGER_RTT=n, CONFIG_ASSERT=n) on every nRF52 build,
+# since this file loads after prj.conf.
+#
+# BT_CTLR_ASSERT_HANDLER is harmless when CONFIG_ASSERT=n (no RAM/flash cost,
+# the handler is simply never invoked) so it stays on for both prod and debug.
 CONFIG_BT_CTLR_ASSERT_HANDLER=y
diff --git a/zephcore/boards/common/nrf54l_common.conf b/zephcore/boards/common/nrf54l_common.conf
index 756a255..67e5989 100644
--- a/zephcore/boards/common/nrf54l_common.conf
+++ b/zephcore/boards/common/nrf54l_common.conf
@@ -23,11 +23,9 @@ CONFIG_BT_CTLR_DATA_LENGTH_MAX=251
 # Coded PHY — enable in nRF LL controller (host auto-request in zephcore_common.conf)
 CONFIG_BT_CTLR_PHY_CODED=y
 
-# ========== SEGGER RTT (J-Link / CMSIS-DAP debug) ==========
-CONFIG_LOG_BACKEND_RTT=y
-CONFIG_USE_SEGGER_RTT=y
-CONFIG_SEGGER_RTT_BUFFER_SIZE_UP=4096
-
 # ========== Debug ==========
-CONFIG_ASSERT=y
+# SEGGER RTT and CONFIG_ASSERT are debug-only and live in boards/common/debug.conf
+# (opt-in).  Keeping them here would override the production defaults from
+# prj.conf on every nRF54L build, since this file loads after prj.conf.
+# BT_CTLR_ASSERT_HANDLER is harmless when CONFIG_ASSERT=n, so it stays on.
 CONFIG_BT_CTLR_ASSERT_HANDLER=y
diff --git a/zephcore/boards/common/prod.conf b/zephcore/boards/common/prod.conf
deleted file mode 100644
index 7ff951a..0000000
--- a/zephcore/boards/common/prod.conf
+++ /dev/null
@@ -1,22 +0,0 @@
-# Production Config - Common to ALL boards (Companion & Repeater)
-# Build: west build -b <board> zephcore --pristine -- \
-#   -DEXTRA_CONF_FILE="boards/common/prod.conf"
-#
-# Disables logging for smaller binary and lower power consumption.
-# USB CDC still works for CLI commands on repeaters.
-
-# Disable logging subsystem (saves ~62KB flash, ~2-5mA power)
-CONFIG_LOG=n
-
-# Disable asserts (saves flash, removes CMake warning)
-CONFIG_ASSERT=n
-
-# Disable SEGGER RTT (saves ~4KB RAM ring buffer + init code)
-CONFIG_USE_SEGGER_RTT=n
-
-# Disable thread name strings (saves flash — only useful for debug)
-CONFIG_THREAD_NAME=n
-
-# Max contacts: Kconfig default is 350 — fits nRF52840 RAM with ~10% headroom
-# and is safe for 100KB ExtraFS.  RAM-limited boards (xiao_nrf54l15=450,
-# xiao_esp32c3=300) override in their own board.conf.  Do not set here.
diff --git a/zephcore/boards/common/zephcore_common.conf b/zephcore/boards/common/zephcore_common.conf
index df18959..667e0e6 100644
--- a/zephcore/boards/common/zephcore_common.conf
+++ b/zephcore/boards/common/zephcore_common.conf
@@ -29,7 +29,6 @@ CONFIG_PSA_WANT_KEY_TYPE_HMAC=y
 
 # ========== Stack Protection ==========
 CONFIG_HW_STACK_PROTECTION=y
-CONFIG_THREAD_NAME=y
 
 # ========== Hardware Basics ==========
 CONFIG_ADC=y
@@ -195,10 +194,7 @@ CONFIG_INPUT_EVENT_DUMP=n
 CONFIG_INPUT_MODE_SYNCHRONOUS=y
 
 # ========== Logging ==========
-# RTT log backend: DROP mode (not BLOCK) — when no RTT host is connected the
-# buffer is always full; BLOCK mode sleeps 20ms per message with irq_lock held,
-# disrupting BLE timing and cascading into buffer exhaustion deadlocks.
-CONFIG_LOG_BACKEND_RTT_MODE_DROP=y
+# Log backend tuning lives in boards/common/debug.conf (opt-in).
 
 # Silence USB CH9 control-transfer spam (dozens of INF lines during enumeration).
 # WRN keeps real USB errors visible.
diff --git a/zephcore/boards/esp32/heltec_wifi_lora32_v4/board.overlay b/zephcore/boards/esp32/heltec_wifi_lora32_v4/board.overlay
index f51dc54..ce6e5c9 100644
--- a/zephcore/boards/esp32/heltec_wifi_lora32_v4/board.overlay
+++ b/zephcore/boards/esp32/heltec_wifi_lora32_v4/board.overlay
@@ -101,3 +101,6 @@
 
 /* LittleFS auto-mount — standard /lfs mount point */
 #include "../../common/filesystem.dtsi"
+/* USB CDC-ACM — companion USB transport (esp32s3_usb.conf). Heltec has a
+ * dedicated UART console, so no console reroute is needed. */
+#include "../../common/esp32s3_usb_otg.dtsi"
diff --git a/zephcore/boards/esp32/heltec_wifi_lora32_v43/board.overlay b/zephcore/boards/esp32/heltec_wifi_lora32_v43/board.overlay
index 6e42ee2..7047afd 100644
--- a/zephcore/boards/esp32/heltec_wifi_lora32_v43/board.overlay
+++ b/zephcore/boards/esp32/heltec_wifi_lora32_v43/board.overlay
@@ -101,3 +101,6 @@
 
 /* LittleFS auto-mount — standard /lfs mount point */
 #include "../../common/filesystem.dtsi"
+/* USB CDC-ACM — companion USB transport (esp32s3_usb.conf). Heltec has a
+ * dedicated UART console, so no console reroute is needed. */
+#include "../../common/esp32s3_usb_otg.dtsi"
diff --git a/zephcore/boards/esp32/station_g2/board.overlay b/zephcore/boards/esp32/station_g2/board.overlay
index 8b8174e..16b14a8 100644
--- a/zephcore/boards/esp32/station_g2/board.overlay
+++ b/zephcore/boards/esp32/station_g2/board.overlay
@@ -109,3 +109,8 @@
 
 /* LittleFS auto-mount — standard /lfs mount point */
 #include "../../common/filesystem.dtsi"
+
+/* USB OTG companion transport. station_g2 consoles over USB Serial/JTAG, which
+ * shares D+/D- with USB OTG, so the console is rerouted to uart0. */
+#include "../../common/esp32s3_console_uart0.dtsi"
+#include "../../common/esp32s3_usb_otg.dtsi"
diff --git a/zephcore/boards/esp32/xiao_esp32s3/board.overlay b/zephcore/boards/esp32/xiao_esp32s3/board.overlay
index 3ef121f..d433717 100644
--- a/zephcore/boards/esp32/xiao_esp32s3/board.overlay
+++ b/zephcore/boards/esp32/xiao_esp32s3/board.overlay
@@ -86,3 +86,8 @@
 
 /* LittleFS auto-mount — standard /lfs mount point */
 #include "../../common/filesystem.dtsi"
+
+/* USB OTG companion transport. Consoles over USB Serial/JTAG (shares D+/D-
+ * with USB OTG), so the console is rerouted to uart0. */
+#include "../../common/esp32s3_console_uart0.dtsi"
+#include "../../common/esp32s3_usb_otg.dtsi"
diff --git a/zephcore/boards/nrf52840/xiao_nrf52840/board.conf b/zephcore/boards/nrf52840/xiao_nrf52840/board.conf
index 9103fc0..db0b700 100644
--- a/zephcore/boards/nrf52840/xiao_nrf52840/board.conf
+++ b/zephcore/boards/nrf52840/xiao_nrf52840/board.conf
@@ -7,7 +7,7 @@ CONFIG_BT_DIS_MODEL_NUMBER_STR="Seeed XIAO nRF52840"
 
 CONFIG_ZEPHCORE_SD_FWID=0x0123
 
-# Default debug (logging.conf) sends LOG_* to RTT only. Plain XIAO is usually
+# Default debug (debug.conf) sends LOG_* to RTT only. Plain XIAO is usually
 # flashed/debugged over USB without an SWD J-Link — enable UART backend so
 # LOG_* appears on the CDC ACM serial port (same as zephyr,console).
 # RTT remains enabled for J-Link; use DROP mode (see zephcore_common.conf).
diff --git a/zephcore/prj.conf b/zephcore/prj.conf
index 474cb97..51fbf55 100644
--- a/zephcore/prj.conf
+++ b/zephcore/prj.conf
@@ -16,10 +16,16 @@ CONFIG_UART_CONSOLE=y
 CONFIG_UART_INTERRUPT_DRIVEN=y
 CONFIG_RING_BUFFER=y
 
-# Logging subsystem — enabled by default (prod.conf disables with CONFIG_LOG=n).
-# Log tuning (buffer size, backends, etc.) is in boards/common/logging.conf,
-# which CMake auto-includes only when prod.conf is NOT active.
-CONFIG_LOG=y
+# Production by default — add boards/common/debug.conf to enable logging.
+CONFIG_LOG=n
+CONFIG_ASSERT=n
+CONFIG_USE_SEGGER_RTT=n
+CONFIG_THREAD_NAME=n
+
+# Reboot on any fatal error (stack overflow, hard fault, etc.) instead of
+# spinning forever. Asserts are disabled so they won't reach here, but all
+# other fatal paths (k_panic, CPU exceptions) still get a clean reboot.
+CONFIG_RESET_ON_FATAL_ERROR=y
 
 # ========== Power Management ==========
 # Note: nRF52840 automatically uses WFI (Wait For Interrupt) in idle thread.
diff --git a/zephcore/src/main_companion.cpp b/zephcore/src/main_companion.cpp
index 201d72f..7176bb6 100644
--- a/zephcore/src/main_companion.cpp
+++ b/zephcore/src/main_companion.cpp
@@ -34,7 +34,13 @@ LOG_MODULE_REGISTER(zephcore_main, CONFIG_ZEPHCORE_MAIN_LOG_LEVEL);
 
 #include <ZephyrBLE.h>
 
-#if IS_ENABLED(CONFIG_LOG)
+/* The USB CDC companion stack is compiled when either logging needs the CDC
+ * console (debug builds) or the binary companion transport is explicitly
+ * enabled (CONFIG_ZEPHCORE_COMPANION_USB, default-y on USB-capable boards). */
+#define ZEPHCORE_USB_STACK \
+	(IS_ENABLED(CONFIG_LOG) || IS_ENABLED(CONFIG_ZEPHCORE_COMPANION_USB))
+
+#if ZEPHCORE_USB_STACK
 #include <ZephyrCompanionUSB.h>
 #include <ZephyrUSBCDC.h>
 #endif
@@ -181,7 +187,7 @@ static void ble_on_connected(void)
 /* BLE disconnected callback — clean up state and notify UI */
 static void ble_on_disconnected(void)
 {
-#if IS_ENABLED(CONFIG_LOG)
+#if ZEPHCORE_USB_STACK
 	zephcore_usb_companion_reset_rx();
 #endif
 #ifdef ZEPHCORE_LORA
@@ -562,8 +568,8 @@ int main(void)
 	/* USB CDC init up front so the host can enumerate, then block until the
 	 * host opens the port (DTR-high) — event-driven via the shared usbd
 	 * message callback.  Unplugged → 1 s timeout, banner is buffered for any
-	 * later attach.  CONFIG_LOG=n prod builds skip the whole stack. */
-#if IS_ENABLED(CONFIG_LOG) && DT_HAS_COMPAT_STATUS_OKAY(zephyr_cdc_acm_uart) && \
+	 * later attach. */
+#if ZEPHCORE_USB_STACK && DT_HAS_COMPAT_STATUS_OKAY(zephyr_cdc_acm_uart) && \
 	!IS_ENABLED(CONFIG_CDC_ACM_SERIAL_INITIALIZE_AT_BOOT)
 	zephcore_usbd_init();
 	zephcore_usbd_wait_dtr(1000);
@@ -780,10 +786,11 @@ int main(void)
 	zephcore_ble_init(&ble_cbs);
 
 	/*
-	 * USB CDC ACM - only enabled when logging is enabled (debug builds).
-	 * Production builds (CONFIG_LOG=n) skip USB entirely, saving ~2-5mA.
+	 * USB CDC ACM companion transport.
+	 * Enabled when logging is on (debug builds) OR when explicitly requested
+	 * via CONFIG_ZEPHCORE_COMPANION_USB (e.g. prod builds on USB-capable boards).
 	 */
-#if IS_ENABLED(CONFIG_LOG)
+#if ZEPHCORE_USB_STACK
 	zephcore_usb_companion_init(&mesh_events, &rx_process_work, MESH_EVENT_BLE_RX,
 				   &zephyr_board);
 #endif