feat: user path to resume BT from low-memory pause via reader menu toggle

Field session: after a recovery teardown the heap settles at ~72 KB --
below the 100 KB start floor -- and never recovers on its own (the
defrag silent-restart only fires when a build FAILS, and builds succeed
now). BT stayed paused forever, the menu toggle claimed ON, and toggling
off/on changed nothing.

- Menu label tells the truth: ON / PAUSED (enabled but stack down) / OFF
  (new STR_STATE_PAUSED string)
- Toggling BT on below the heap floor silent-restarts into the current
  book: the fresh boot's ~118 KB passes the gate and BT auto-starts on
  resume. Explicit user intent is the right trigger for the defrag.
- Hoist the floor to bleinput::kStartMinFreeHeap, shared by the
  lifecycle gate and the toggle

lib/I18n/translations/english.yaml

@@ -299,6 +299,8 @@ STR_BT_NO_PAIRED: "No paired devices"
 STR_BT_MAP_BUTTONS: "Map Remote Buttons"
 STR_BT_PRESS_REMOTE: "Press a button on your remote"
 STR_BT_CONNECTING_POPUP: "BT Connecting..."
+STR_BT_PAUSED_LOW_MEM_POPUP: "BT paused (low memory)"
+STR_STATE_PAUSED: "PAUSED"
 STR_BT_PAGE_FORWARD: "Page Forward"
 STR_BT_PAGE_BACK: "Page Back"
 STR_BT_FORGET_PROMPT: "Hold Confirm to forget"

src/BleInput.h

@@ -25,6 +25,12 @@ namespace bleinput {
 // Advertised central name shown to peripherals during pairing.
 inline constexpr const char* kHostName = "CrossPoint";
 
+// Heap floor for starting the NimBLE stack (~57 KB) while leaving the reader's
+// section-build pre-flight (40 KB) satisfiable afterwards. Shared by the main-loop
+// lifecycle gate and the reader menu's toggle (which offers a defrag restart when a
+// user turns BT on below the floor).
+inline constexpr size_t kStartMinFreeHeap = 100 * 1024;
+
 // Start the BLE HID host (idempotent). Returns false if BLE is compiled out or
 // NimBLE init failed. Safe to call repeatedly.
 bool ensureStarted();

src/activities/reader/EpubReaderMenuActivity.cpp

@@ -2,9 +2,12 @@
 
 #include <GfxRenderer.h>
 #include <I18n.h>
+#include <Logging.h>
 
+#include "BleInput.h"
 #include "CrossPointSettings.h"
 #include "MappedInputManager.h"
+#include "SilentRestart.h"
 #include "components/UITheme.h"
 #include "fontIds.h"
 
@@ -84,6 +87,15 @@ void EpubReaderMenuActivity::loop() {
       // so start/stop has a single owner.
       SETTINGS.bluetoothEnabled = SETTINGS.bluetoothEnabled ? 0 : 1;
       SETTINGS.saveToFile();
+      // Turning BT on below the lifecycle's heap floor would otherwise sit in PAUSED
+      // until the heap happens to recover -- which a long session's fragmentation never
+      // gives back. The user asked for BT *now*: silent-restart into this book to
+      // defrag (fresh boot is ~118 KB free, comfortably above the floor), and BT
+      // auto-starts on the way back in.
+      if (SETTINGS.bluetoothEnabled && !BleHid.isRunning() && ESP.getFreeHeap() < bleinput::kStartMinFreeHeap) {
+        LOG_INF("ERM", "BT enabled below heap floor (%u); silent restart to defrag", ESP.getFreeHeap());
+        silentRestartToReader();
+      }
       requestUpdate();
       return;
     }
@@ -138,8 +150,12 @@ void EpubReaderMenuActivity::render(RenderLock&&) {
           // Render current page turn value on the right edge of the content area.
           return pageTurnLabels[selectedPageTurnOption];
         } else if (value == MenuAction::TOGGLE_BLUETOOTH) {
-          // Render current Bluetooth on/off state on the right edge.
-          return SETTINGS.bluetoothEnabled ? tr(STR_STATE_ON) : tr(STR_STATE_OFF);
+          // Render current Bluetooth state on the right edge. "Enabled but the stack
+          // isn't running" is the low-memory deferral -- show PAUSED, not a lie.
+          if (SETTINGS.bluetoothEnabled) {
+            return BleHid.isRunning() ? tr(STR_STATE_ON) : tr(STR_STATE_PAUSED);
+          }
+          return tr(STR_STATE_OFF);
         } else {
           return "";
         }

src/main.cpp

@@ -514,18 +514,18 @@ void updateBluetoothLifecycle() {
   static constexpr uint32_t BLE_RESTART_COOLDOWN_MS = 30 * 1000;
   const bool inCooldown = recoveryTeardownMs != 0 && millis() - recoveryTeardownMs < BLE_RESTART_COOLDOWN_MS;
   // Heap gate: NimBLE needs ~57 KB, and the section-build pre-flight needs 40 KB free
-  // AFTER the stack is up -- so anything below ~100 KB just re-enters build recovery
+  // AFTER the stack is up -- so anything below the floor just re-enters build recovery
   // and tears BLE straight back down. (A first cut used 70 KB for restarts; 70-57=13 KB
   // left for builds, guaranteeing the oscillation above.) Defer and retry next loop;
-  // the build path's silent-restart defrag yields ~118 KB and passes this gate.
-  static constexpr size_t BLE_START_MIN_FREE_HEAP = 100 * 1024;
+  // the reader menu's toggle offers a defrag restart, and the build path's silent
+  // restart also yields ~118 KB and passes this gate.
   static bool deferralAnnounced = false;
-  if (wanted && !BleHid.isRunning() && (inCooldown || ESP.getFreeHeap() < BLE_START_MIN_FREE_HEAP)) {
+  if (wanted && !BleHid.isRunning() && (inCooldown || ESP.getFreeHeap() < bleinput::kStartMinFreeHeap)) {
     static uint32_t lastGateLogMs = 0;
     if (millis() - lastGateLogMs > 10000) {
       lastGateLogMs = millis();
       LOG_INF("BLELC", "start deferred: heap %u floor %u cooldown=%d", ESP.getFreeHeap(),
-              (unsigned)BLE_START_MIN_FREE_HEAP, inCooldown ? 1 : 0);
+              (unsigned)bleinput::kStartMinFreeHeap, inCooldown ? 1 : 0);
     }
     // Tell the reader once per deferral episode that the remote is paused -- otherwise
     // the only symptom is a remote that silently stopped working. Draws into the