diff --git a/libs/hardware/BatteryMonitor/include/BatteryMonitor.h b/libs/hardware/BatteryMonitor/include/BatteryMonitor.h
index bcef6f80..2ec37d38 100644
--- a/libs/hardware/BatteryMonitor/include/BatteryMonitor.h
+++ b/libs/hardware/BatteryMonitor/include/BatteryMonitor.h
@@ -71,6 +71,21 @@ class BatteryMonitor {
     //     a board with a gauge but no charger IC (e.g. X3) still reports it.
     bool isCharging() const;
 
+    // True when external power (a USB cable or charger) is physically present.
+    //
+    // This is NOT isCharging(): a full battery stops charging while still
+    // plugged in, so isCharging() goes false with the cable still attached.
+    // Only a source that reports the input rail itself can answer this, so it
+    // is currently the BQ25896's REG0B — VBUS_STAT[7:5] plus PG_STAT — and
+    // nothing else. Boards without that charger IC cannot observe it.
+    //
+    // `known` (optional, out) is set false when the board has no way to tell,
+    // or the read failed. Callers MUST branch on it: a bare false means "no
+    // opinion" just as often as it means "unplugged", and treating the two the
+    // same is how you get a device that thinks the cable is gone because it
+    // never had a way to see it.
+    bool isExternalPowerPresent(bool* known = nullptr) const;
+
     // Percentage from a millivolt value, off a standard 1S Li-ion discharge
     // curve. The result is always a multiple of 10: voltage cannot resolve a
     // Li-ion pack any finer than that, and pretending otherwise just produces a
diff --git a/libs/hardware/BatteryMonitor/src/BatteryMonitor.cpp b/libs/hardware/BatteryMonitor/src/BatteryMonitor.cpp
index 1687668c..bb556fe0 100644
--- a/libs/hardware/BatteryMonitor/src/BatteryMonitor.cpp
+++ b/libs/hardware/BatteryMonitor/src/BatteryMonitor.cpp
@@ -290,6 +290,35 @@ bool readGaugeCharging(bool& known) {
   known = false;
   return false;
 }
+
+// External-power presence from the charger IC, out of the SAME REG0B read that
+// readGaugeCharging() uses for CHRG_STAT:
+//   VBUS_STAT [7:5] — 000 no input, 001 USB host SDP, 010 USB CDP, 011 adapter,
+//                     111 OTG (we are SOURCING power, not receiving it)
+//   PG_STAT   [2]   — power good
+// Anything but "no input" and "OTG" means a cable is supplying us. Unlike
+// charge state this stays true at 100%, which is exactly the case that makes
+// charge-based USB inference wrong.
+//
+// Only the BQ25896 answers this. The BQ27220 gauge measures the BATTERY, not
+// the input rail, so there is deliberately no gauge fallback here — reporting
+// "no external power" from a gauge that cannot see the input would be a lie.
+bool readChargerExternalPower(bool& known) {
+  const auto& g = BoardConfig::ACTIVE.batteryGauge;
+  if (g.chargerAddr == 0) {
+    known = false;
+    return false;
+  }
+  uint8_t status = 0;
+  if (!readReg8(g.chargerAddr, BQ25896_REG_STATUS, status)) {
+    known = false;
+    return false;
+  }
+  known = true;
+  const uint8_t vbus = (status >> 5) & 0x07;
+  const bool powerGood = (status & 0x04) != 0;
+  return (vbus != 0x00 && vbus != 0x07) || powerGood;
+}
 }  // namespace
 #endif  // FREEINK_BATTERY_I2C_GAUGE
 
@@ -506,6 +535,29 @@ bool BatteryMonitor::isCharging() const {
   return digitalRead(_chargeStatusPin) == chargeActiveLevel();
 }
 
+bool BatteryMonitor::isExternalPowerPresent(bool* known) const {
+  bool observed = false;
+#if FREEINK_BATTERY_I2C_GAUGE
+  const bool present = readChargerExternalPower(observed);
+  if (observed) {
+    if (known) *known = true;
+    return present;
+  }
+#endif
+  if (hasM5Pm1Backend()) {
+    // The M5 PMIC reports its supply source directly (PWR_SRC 5VIN/5VINOUT),
+    // which readM5Pm1Status() already decodes into externalPower — the right
+    // field here, rather than the `charging` one it derives from it.
+    Status status;
+    if (readM5Pm1Status(status) && status.externalPowerKnown) {
+      if (known) *known = true;
+      return status.externalPower;
+    }
+  }
+  if (known) *known = false;
+  return false;
+}
+
 bool BatteryMonitor::readM5Pm1Status(Status& status) const {
   status.supported = true;
   if (!hasM5Pm1Backend()) return false;
diff --git a/libs/hardware/BoardConfig/include/BoardConfig.h b/libs/hardware/BoardConfig/include/BoardConfig.h
index 5489a653..85a415dd 100644
--- a/libs/hardware/BoardConfig/include/BoardConfig.h
+++ b/libs/hardware/BoardConfig/include/BoardConfig.h
@@ -211,13 +211,26 @@
 #define FREEINK_CAP_WARMLIGHT (FREEINK_DEVICE_X4PRO || FREEINK_DEVICE_MURPHY_M4 || FREEINK_DEVICE_EEGO_A4)
 #endif
 // USB Mass Storage ("USB Transfer" mode): exposes the SD card to a host over
-// USB-MSC. OPT-IN (default off), NOT board-derived: it forces the build into
-// USB-OTG mode (ARDUINO_USB_MODE=0 + CONFIG_TINYUSB_MSC_ENABLED), which changes
-// how the USB serial console works — so a board enables it in its OWN env
-// alongside those flags (e.g. X4 Pro adds -DFREEINK_CAP_USB_MSC=1
-// -DARDUINO_USB_MODE=0 -DARDUINO_USB_CDC_ON_BOOT=1). Native-USB (ESP32-S3/C3
-// OTG) targets only. When 0, UsbMassStorage links stub bodies and pulls in no
-// TinyUSB/MSC code. Requires SDMMC/SPI storage exposing a block device.
+// USB-MSC. OPT-IN (default off), NOT board-derived, so a board enables it in
+// its OWN env (e.g. -DFREEINK_CAP_USB_MSC=1). Native-USB (ESP32-S3/C3 OTG)
+// targets only. When 0, UsbMassStorage links stub bodies and pulls in no
+// TinyUSB/MSC code.
+//
+// ARDUINO_USB_MODE=0 is one way to reach the OTG PHY, not a requirement of this
+// library. A firmware can equally keep ARDUINO_USB_MODE=1 — so USB Serial/JTAG
+// stays the board's normal USB personality for monitoring and flashing — and
+// switch the shared PHY to OTG at runtime for the duration of a transfer,
+// handing it back before it reboots out of the mode. X4 Pro and LilyGo T5 S3
+// both ship that way in CrossPoint.
+//
+// What this DOES require is the platform's prebuilt Arduino core, whose TinyUSB
+// component is built with CONFIG_TINYUSB_MSC_ENABLED: an env that rebuilds the
+// core from source (custom_sdkconfig / custom_component_remove) drops that
+// component and USBMSC will not link.
+//
+// Storage must expose a 512-byte-sector block device. Both SDCardManager
+// backends do — SDMMC natively, and SPI through SdFat's own SdCard — so this is
+// no longer an SDMMC-only capability.
 #ifndef FREEINK_CAP_USB_MSC
 #define FREEINK_CAP_USB_MSC 0
 #endif
diff --git a/libs/hardware/SDCardManager/include/SDCardManager.h b/libs/hardware/SDCardManager/include/SDCardManager.h
index 4fe8df8a..d14b8377 100644
--- a/libs/hardware/SDCardManager/include/SDCardManager.h
+++ b/libs/hardware/SDCardManager/include/SDCardManager.h
@@ -75,16 +75,20 @@ class SDCardManager {
   using PowerHook = void (*)();
   void setPowerHook(PowerHook hook) { _powerHook = hook; }
 
-#if FREEINK_SD_SDMMC
-  // The raw SDMMC block device (512-byte sector I/O) backing the volume, for
-  // exposing the card over USB-MSC ("USB Transfer" mode). Null until begin()
-  // succeeds. The returned pointer implements SdFat's FsBlockDeviceInterface.
+  // The raw block device (512-byte sector I/O) backing the volume, for exposing
+  // the card over USB-MSC ("USB Transfer" mode). Null until begin() succeeds.
   // Do NOT touch the filesystem while the card is handed to the USB host.
-  freeink::SdmmcBlockDevice* rawBlockDevice() { return _dev; }
-  // End the FsVolume mount while keeping the native block device alive for a
-  // raw USB-MSC owner. The caller must reinitialize the manager after the
-  // owner releases the card.
+  //
+  // Both backends answer this: SDMMC boards hand back their native esp-idf
+  // device, SPI boards hand back SdFat's own SdCard (SdCardInterface derives
+  // from FsBlockDeviceInterface, so the card object IS a block device — no
+  // second driver is needed for the SPI path).
+  FsBlockDeviceInterface* rawBlockDevice();
+  // End the FsVolume mount while keeping the block device alive for a raw
+  // USB-MSC owner. The caller must reinitialize the manager (begin()) after the
+  // owner releases the card. Returns null when nothing is mounted.
   FsBlockDeviceInterface* detachFilesystemForRawAccess();
+#if FREEINK_SD_SDMMC
   // Stop the card for deep sleep: unmount the volume, stop the SDMMC host, and
   // float the bus pads so their pull-ups stop back-feeding the card's VDD net
   // through sleep. Idempotent; call only after all file users have stopped. A
diff --git a/libs/hardware/SDCardManager/inject_build_flags.py b/libs/hardware/SDCardManager/inject_build_flags.py
index e55b08b4..3ea34027 100644
--- a/libs/hardware/SDCardManager/inject_build_flags.py
+++ b/libs/hardware/SDCardManager/inject_build_flags.py
@@ -1,23 +1,50 @@
-# SDCardManager build hook: force SdFat's UTF-8 long-filename support on for
-# the WHOLE build (SdFat compiles as its own library, so a define in our
-# library.json "flags" would not reach it).
+# SDCardManager build hook: force two SdFat options on for the WHOLE build.
+# SdFat compiles as its own library, so a define in our library.json "flags"
+# would not reach it — it has to be appended to every lib builder's env here.
 #
-# Without USE_UTF8_LONG_NAMES, SdFat returns mangled names for any file with
-# a non-ASCII character ("The 7½ Deaths..." listed but unopenable — no
-# metadata, no cover, no reading). There is no situation where a FreeInk
-# firmware wants that, so this is not a user-facing option.
+# 1. USE_UTF8_LONG_NAMES, always. Without it, SdFat returns mangled names for
+#    any file with a non-ASCII character ("The 71/2 Deaths..." listed but
+#    unopenable — no metadata, no cover, no reading). There is no situation
+#    where a FreeInk firmware wants that, so this is not a user-facing option.
+#
+# 2. USE_BLOCK_DEVICE_INTERFACE, but only when the build enables USB Mass
+#    Storage (FREEINK_CAP_USB_MSC). It is what makes SdSpiCard derive from
+#    FsBlockDeviceInterface, which is how SDCardManager hands the SPI-attached
+#    card to a USB host as a raw block device — without it SdSpiCard is a plain
+#    concrete class and detachFilesystemForRawAccess() has nothing to return.
+#    The SDMMC backend needs the same option for its FsVolume, so coupling both
+#    to the capability keeps it off the boards that pay for it in vtables and
+#    indirect calls for nothing.
 Import("env")
 
-_DEFINE = ("USE_UTF8_LONG_NAMES", "1")
+_ALWAYS = [("USE_UTF8_LONG_NAMES", "1")]
+_IF_USB_MSC = [("USE_BLOCK_DEVICE_INTERFACE", "1")]
+
+
+def _defines(e):
+    return {d[0] if isinstance(d, (tuple, list)) else d for d in e.get("CPPDEFINES", [])}
+
+
+def _usb_msc_enabled(e):
+    for d in e.get("CPPDEFINES", []):
+        if isinstance(d, (tuple, list)) and d[0] == "FREEINK_CAP_USB_MSC":
+            return str(d[1]) not in ("0", "")
+    return False
+
 
+def _append(e, wanted):
+    have = _defines(e)
+    missing = [d for d in wanted if d[0] not in have]
+    if missing:
+        e.Append(CPPDEFINES=missing)
 
-def _append(e):
-    defines = {d[0] if isinstance(d, tuple) else d for d in e.get("CPPDEFINES", [])}
-    if _DEFINE[0] not in defines:
-        e.Append(CPPDEFINES=[_DEFINE])
 
+_wanted = list(_ALWAYS)
+# Read the capability off the project env: a lib builder's env may not carry it.
+if _usb_msc_enabled(env) or _usb_msc_enabled(DefaultEnvironment()):
+    _wanted += _IF_USB_MSC
 
-_append(env)
-_append(DefaultEnvironment())
+_append(env, _wanted)
+_append(DefaultEnvironment(), _wanted)
 for lb in env.GetLibBuilders():
-    _append(lb.env)
+    _append(lb.env, _wanted)
diff --git a/libs/hardware/SDCardManager/src/SDCardManager.cpp b/libs/hardware/SDCardManager/src/SDCardManager.cpp
index eafd25ac..a57c5502 100644
--- a/libs/hardware/SDCardManager/src/SDCardManager.cpp
+++ b/libs/hardware/SDCardManager/src/SDCardManager.cpp
@@ -65,6 +65,8 @@ bool SDCardManager::begin() {
   return initialized;
 }
 
+FsBlockDeviceInterface* SDCardManager::rawBlockDevice() { return _dev; }
+
 FsBlockDeviceInterface* SDCardManager::detachFilesystemForRawAccess() {
   if (!initialized || !_dev) return nullptr;
   _vol.end();
@@ -195,7 +197,45 @@ bool SDCardManager::begin() {
 
   return initialized;
 }
-#endif
+
+// SdFat's card object already IS a block device: with USE_BLOCK_DEVICE_INTERFACE
+// (or HAS_SDIO_CLASS) set, SdSpiCard derives from FsBlockDeviceInterface and
+// implements the same readSector(s)/writeSector(s) contract SdmmcBlockDevice
+// does. So the SPI path needs no second driver for USB-MSC — it only needs the
+// volume dropped while the card session stays up.
+//
+// Without that option SdSpiCard is a plain concrete class with no such base, so
+// there is nothing to hand out. The build hook (inject_build_flags.py) turns the
+// option on whenever FREEINK_CAP_USB_MSC is set, so the stubs below are what a
+// board that never asked for USB Drive links.
+#if USE_BLOCK_DEVICE_INTERFACE || HAS_SDIO_CLASS
+
+FsBlockDeviceInterface* SDCardManager::rawBlockDevice() { return initialized ? sd.card() : nullptr; }
+
+FsBlockDeviceInterface* SDCardManager::detachFilesystemForRawAccess() {
+  if (!initialized) return nullptr;
+  auto* const card = sd.card();
+  if (!card) return nullptr;
+  // FsVolume::end() ONLY — deliberately not sd.end(), which would also call
+  // SdCard::end() and tear down the card session the USB host is about to read
+  // through. The card stays initialized and selected; remounting later goes
+  // back through begin(), whose sd.begin() re-runs SdCard::begin() on the same
+  // (factory-owned, statically allocated) card object.
+  sd.FsVolume::end();
+  initialized = false;
+  cachedTotalBytes = 0;
+  cachedUsedBytes = 0;
+  cachedUsedBytesValid = false;
+  return card;
+}
+
+#else  // USE_BLOCK_DEVICE_INTERFACE || HAS_SDIO_CLASS
+
+FsBlockDeviceInterface* SDCardManager::rawBlockDevice() { return nullptr; }
+FsBlockDeviceInterface* SDCardManager::detachFilesystemForRawAccess() { return nullptr; }
+
+#endif  // USE_BLOCK_DEVICE_INTERFACE || HAS_SDIO_CLASS
+#endif  // FREEINK_SD_SDMMC
 
 bool SDCardManager::ready() const {
   return initialized;
diff --git a/libs/hardware/UsbMassStorage/include/UsbMassStorage.h b/libs/hardware/UsbMassStorage/include/UsbMassStorage.h
index 3c2b0269..210daa52 100644
--- a/libs/hardware/UsbMassStorage/include/UsbMassStorage.h
+++ b/libs/hardware/UsbMassStorage/include/UsbMassStorage.h
@@ -35,6 +35,20 @@ class UsbMassStorage {
   bool active() const { return _active; }
   UsbMassStorageState state() const;
   bool hostConnected() const;
+  // True while the USB bus is idle (no SOF for >3 ms), which is what the device
+  // sees when the cable is pulled.
+  //
+  // Needed because tud_mounted() CANNOT report an unplug on the ESP32-S3:
+  // Arduino's tinyusb init passes otg_io_conf = NULL (esp32-hal-tinyusb.c), so
+  // no VBUS line is routed to the OTG core and IDF forces B-session-valid on.
+  // The core therefore never detects session end, and state() stays Connected
+  // forever after the cable is gone. Bus suspend is detected by the core itself
+  // and is unaffected.
+  //
+  // A host suspending an idle bus looks identical, so this is a HINT, not a
+  // verdict: callers must require it to persist before acting on it, and should
+  // prefer a physical VBUS reading where the board has one.
+  bool hostSuspended() const;
   // Soft-disconnect the USB device from the host. Call from application/task
   // context, never from an MSC callback; end() still owns final teardown.
   bool disconnectHost() const;
@@ -64,6 +78,7 @@ class UsbMassStorage {
   UsbMassStorageState state() const { return UsbMassStorageState::Idle; }
   bool hostConnected() const { return false; }
   bool disconnectHost() const { return false; }
+  bool hostSuspended() const { return false; }
 };
 }  // namespace freeink
 
diff --git a/libs/hardware/UsbMassStorage/src/UsbMassStorage.cpp b/libs/hardware/UsbMassStorage/src/UsbMassStorage.cpp
index eef550c9..4cbbcab3 100644
--- a/libs/hardware/UsbMassStorage/src/UsbMassStorage.cpp
+++ b/libs/hardware/UsbMassStorage/src/UsbMassStorage.cpp
@@ -12,6 +12,7 @@
 
 extern "C" bool tud_mounted(void);
 extern "C" bool tud_disconnect(void);
+extern "C" bool tud_suspended(void);
 
 namespace freeink {
 namespace {
@@ -190,6 +191,8 @@ bool UsbMassStorage::hostConnected() const {
 
 bool UsbMassStorage::disconnectHost() const { return _active && tud_disconnect(); }
 
+bool UsbMassStorage::hostSuspended() const { return _active && tud_suspended(); }
+
 void UsbMassStorage::markAccessed() const {
   auto current = _state.load();
   while (current != UsbMassStorageState::Ejected && current != UsbMassStorageState::IoError) {