diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7ef93ba..223ce8c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -90,10 +90,14 @@ add_executable(switch-pico
         switch_haptics.cpp
 )
 if(SWITCH_PICO_INPUT_BACKEND STREQUAL "BLUEPAD32")
-    target_sources(switch-pico PRIVATE bluepad32_input_backend.cpp)
+    target_sources(switch-pico PRIVATE
+            bluepad32_input_backend.cpp
+            bootsel_pairing_button.cpp
+    )
     target_compile_definitions(switch-pico PRIVATE
             SWITCH_PICO_BLUEPAD32=1
             SWITCH_PICO_HID_INSTANCE_COUNT=4
+            PICO_FLASH_ASSUME_CORE1_SAFE=0
     )
 else()
     target_compile_definitions(switch-pico PRIVATE
@@ -125,6 +129,7 @@ if(SWITCH_PICO_INPUT_BACKEND STREQUAL "BLUEPAD32")
             pico_btstack_classic
             pico_btstack_cyw43
             pico_multicore
+            pico_flash
     )
 endif()
 
diff --git a/README.md b/README.md
index 2dff74b..7e32b40 100644
--- a/README.md
+++ b/README.md
@@ -46,40 +46,38 @@ The default `python3 build.py` command and `firmware/switch-pico.*` artifacts re
 
 Both `build.py --aio` and direct AIO CMake configuration apply `patches/bluepad32-sdl3-imu.patch` idempotently before compiling Bluepad32. The patch makes supported motion controllers use SDL3-equivalent axes and fixed-point units before conversion to Nintendo samples. It intentionally leaves the dependency worktree dirty; the committed submodule revision remains Bluepad32 4.2.0.
 
-### Pairing two controllers
+### Pairing up to four controllers
 
 1. Flash and connect the Pico 2 W to the Switch.
 2. Enable `System Settings → Controllers and Sensors → Pro Controller Wired Communication`.
-3. Put the first controller into Bluetooth pairing mode:
+3. Hold the Pico's BOOTSEL button for about two seconds, until the onboard LED starts double-blinking. This opens a 60-second pairing window.
+4. Put a controller into Bluetooth pairing mode:
    - DualSense: hold Create + PS.
    - DualShock 4: hold Share + PS.
    - Switch Pro: press its sync button.
    - Xbox Bluetooth controller: hold its pair button.
    - 8BitDo: use a Bluetooth mode supported by Bluepad32; use Switch/S mode when motion is required.
-4. Wait for the first controller to connect and become ready. The LED continues slow-blinking because the second slot remains open. Pairing keys persist across Pico reboots.
-5. Put the second controller into pairing mode and wait for it to connect and become ready. The LED turns solid only after both controllers are active.
+5. Wait for the controller's player light to settle. Repeat step 4 for additional controllers while the window remains open. Holding BOOTSEL again extends the window by 60 seconds from that point.
 
-During initial setup, pairing order determines the initial slot assignment: the first controller paired occupies slot 0, and the second occupies slot 1. Pairing keys persist, so both controllers can reconnect after a Pico reboot without re-pairing. Slot numbers are not permanently bound to physical controllers: while one controller remains connected, a returning controller fills the other open slot; after a reboot or whenever both slots are empty, whichever persisted controller reconnects first receives slot 0, so the physical controllers can swap USB interfaces.
+Pairing order determines the initial USB slot assignment. Up to four controllers map 1:1 to the four emulated Switch Pro Controller interfaces.
+
+Outside the BOOTSEL-open window, Bluetooth discovery and incoming connections are disabled. The Pico does not scan for or reconnect disconnected controllers while locked. Pairing keys still persist, but reconnecting a previously paired controller also requires opening the BOOTSEL window before pressing its normal power button.
 
 ### LED meanings and device state
 
 The Pico 2 W onboard LED reports the overall Bluetooth state:
-- **Slow blink (0.5 s period)**: at least one slot is open and scanning for a Bluetooth controller.
-- **Fast blink (0.1 s period)**: at least one controller is connected but not yet ready (handshake in progress).
-- **Solid**: both slots are filled and both controllers are ready for input.
-- **Solid immediately after boot that never starts blinking**: Bluepad32 initialization did not complete; check firmware flashing and UART logs.
-
-The LED transitions to slow blink as soon as any slot becomes empty (e.g., a controller is turned off or unpaired). Scanning resumes automatically.
+- **Double blink**: the bounded pairing window is open.
+- **Fast blink**: a controller connection is still completing its handshake.
+- **Solid**: at least one controller is active.
+- **Slow blink**: no controller is active and pairing is locked.
+- **Solid immediately after boot that never transitions**: Bluepad32 initialization did not complete; check firmware flashing and UART logs.
 
 ### Managing controller disconnect and reconnect
 
-Controllers can disconnect and reconnect independently:
-- **Disconnect one controller**: that controller's slot becomes empty. The LED transitions to slow blink if both slots are no longer filled. The other controller continues sending input.
-- **Reconnect while the other controller remains connected**: the returning controller fills the only open slot, preserving the current assignment. The LED transitions through fast blink and back to solid.
-- **Reconnect after both slots become empty or after reboot**: reconnection/autoconnect order determines the assignments. The physical controllers can swap USB interfaces if their order changes.
-- **Turn off or unpair a controller**: delete it from Bluetooth settings on the Pico or reset pairing entirely using Bluepad32 commands. It will no longer auto-reconnect; the slot remains open for a new controller.
-
-When a controller disconnects, the Pico immediately publishes neutral buttons, sticks, and motion for that slot. The other controller is unaffected.
+- **Disconnect a controller**: its slot immediately publishes neutral buttons, sticks, and motion. Other connected controllers are unaffected.
+- **Reconnect a paired controller**: hold BOOTSEL until the LED double-blinks, then power on the controller normally.
+- **Pair a new controller**: hold BOOTSEL until the LED double-blinks, then put the controller into its explicit Bluetooth pairing mode.
+- **Pairing window expires**: scanning and incoming connections stop; already connected controllers remain connected.
 
 ### Controller capabilities
 
@@ -98,15 +96,15 @@ Rumble effects are per-slot and independent. The Switch sends rumble commands to
 
 ### Hardware validation
 
-The dual-interface AIO build has been verified on a real Switch with two DualSense controllers: the Switch assigned two controller slots; buttons, sticks, calibrated motion, and rumble remained independent; disconnecting either controller left the other working; scanning resumed and the disconnected controller reconnected to the open slot.
+The four-interface AIO build has been verified on a real Switch with two DualSense controllers: the Switch assigned independent controller slots, and buttons, sticks, calibrated motion, rumble, and disconnect isolation worked per controller. Fresh DualSense pairing through the BOOTSEL-open window has also been verified on hardware.
 
 To reproduce the validation:
 
-1. **Verify USB enumeration**: Connect the Pico 2 W to a USB host (PC, Mac, or USB analyzer). Confirm that two HID devices are present (e.g., `lsusb -v` on Linux shows interface 0 and interface 1, both with Product ID 0x2009).
-2. **Verify Bluetooth pairing**: Pair two controllers via Bluepad32. Confirm the LED transitions from scanning → fast blink → solid.
-3. **Verify input on one controller**: Move sticks, press buttons, and check that the controller paired first during initial setup appears in slot 0.
-4. **Verify input on two controllers**: Move sticks on the controller paired second during initial setup, and confirm its inputs appear in slot 1 while the first controller is unaffected.
-5. **Verify disconnect and reconnect**: Turn off one controller while leaving the other connected. The LED reverts to slow blink. Turn the disconnected controller back on; it reconnects to the only open slot. Verify the occupied slot continues reporting the other controller's input.
+1. **Verify USB enumeration**: Connect the Pico 2 W to a USB host or analyzer. Confirm that four HID interfaces are present, using IN/OUT endpoint pairs `0x81/0x01` through `0x84/0x04`.
+2. **Verify Bluetooth pairing**: Hold BOOTSEL until the LED double-blinks, put a controller into explicit pairing mode, and confirm its player light settles.
+3. **Verify input on one controller**: Move sticks and press buttons; confirm only its assigned Switch slot changes.
+4. **Verify input on two controllers**: Move the second controller independently and confirm the first controller's slot is unaffected.
+5. **Verify the pairing gate**: Disconnect a controller and confirm it does not reconnect while locked. Open the BOOTSEL window, power it on, and confirm it can connect.
 6. **Verify rumble per slot**: Send rumble to interface 0 and confirm only the slot 0 controller vibrates. Send rumble to interface 1 and confirm only the slot 1 controller vibrates.
 7. **Verify motion**: Enable gyro/accel on both controllers. Rotate each controller independently and confirm that motion is per-slot (rotating controller 0 does not affect controller 1's IMU output).
 
diff --git a/bluepad32_config/btstack_config.h b/bluepad32_config/btstack_config.h
index c2880e2..424d437 100644
--- a/bluepad32_config/btstack_config.h
+++ b/bluepad32_config/btstack_config.h
@@ -15,6 +15,7 @@
 #define ENABLE_LE_DATA_LENGTH_EXTENSION
 #define ENABLE_LE_PERIPHERAL
 #define ENABLE_LE_PRIVACY_ADDRESS_RESOLUTION
+#define ENABLE_LE_RESOLVING_LIST
 #define ENABLE_LE_SECURE_CONNECTIONS
 #else
 #error "BP32: ENABLE_BLE should be defined"
diff --git a/bluepad32_input_backend.cpp b/bluepad32_input_backend.cpp
index e515da2..1b84169 100644
--- a/bluepad32_input_backend.cpp
+++ b/bluepad32_input_backend.cpp
@@ -2,10 +2,12 @@
 
 #include <limits.h>
 #include <stddef.h>
+#include <string.h>
 
 #include <btstack_run_loop.h>
 #include <pico/critical_section.h>
 #include <pico/cyw43_arch.h>
+#include <pico/flash.h>
 #include <pico/multicore.h>
 #include <pico/stdlib.h>
 #include <uni.h>
@@ -20,6 +22,7 @@ constexpr int32_t kTriggerThreshold = (kTriggerMaximum * 35) / 100;
 constexpr uint16_t kRumbleDurationMs = 50;
 constexpr uint32_t kRumblePollIntervalMs = 5;
 constexpr uint8_t kSlotCount = BLUEPAD32_INPUT_BACKEND_SLOT_COUNT;
+constexpr uint32_t kPairingWindowDurationMs = 60000;
 
 static_assert(kSlotCount == 4);
 static_assert(SWITCH_PICO_HID_INSTANCE_COUNT == kSlotCount);
@@ -31,6 +34,14 @@ enum class ConnectionStatus {
     Ready,
 };
 
+enum class ConnectionPolicyState {
+    Uninitialized,
+    Open,
+    Locked,
+    Paused,
+    FailedClosed,
+};
+
 struct RumbleEnvelope {
     uint8_t slot;
     uint32_t connection_generation;
@@ -51,16 +62,22 @@ struct BackendSlot {
 critical_section_t g_state_lock;
 BackendSlot g_slots[kSlotCount];
 
-// These acknowledgement generations are only read or written by Core 0.
+// These acknowledgement generations and the pairing request producer are only
+// used by Core 0. The request is transferred under the cross-core state lock.
 uint32_t g_consumed_generation[kSlotCount]{};
 uint32_t g_last_snapshot_generation[kSlotCount]{};
+bool g_pairing_window_requested = false;
 bool g_initialized = false;
 bool g_started = false;
 
-// The timer and connection status are only read or written by Core 1 / BTstack.
+// These fields are only read or written by Core 1 / BTstack.
 btstack_timer_source_t g_rumble_timer{};
 ConnectionStatus g_connection_status = ConnectionStatus::Initializing;
+ConnectionPolicyState g_connection_policy_state =
+    ConnectionPolicyState::Uninitialized;
+uint32_t g_pairing_window_deadline_ms = 0;
 uint16_t g_status_led_tick = 0;
+bool g_pairing_window_open = false;
 bool g_status_led_on = false;
 
 SwitchInputState make_neutral_state() {
@@ -76,6 +93,26 @@ bool valid_slot(uint8_t slot) {
     return slot < kSlotCount;
 }
 
+bool has_free_slot() {
+    critical_section_enter_blocking(&g_state_lock);
+    bool free_slot = false;
+    for (const BackendSlot& slot : g_slots) {
+        free_slot = free_slot || slot.device == nullptr;
+    }
+    critical_section_exit(&g_state_lock);
+    return free_slot;
+}
+
+bool has_active_controller() {
+    critical_section_enter_blocking(&g_state_lock);
+    bool active_controller = false;
+    for (const BackendSlot& slot : g_slots) {
+        active_controller = active_controller || slot.active;
+    }
+    critical_section_exit(&g_state_lock);
+    return active_controller;
+}
+
 int slot_for_device(const uni_hid_device_t* device) {
     if (device == nullptr) {
         return -1;
@@ -125,6 +162,8 @@ void publish_all_neutral() {
     }
     critical_section_exit(&g_state_lock);
     g_connection_status = ConnectionStatus::Initializing;
+    g_connection_policy_state = ConnectionPolicyState::FailedClosed;
+    g_pairing_window_open = false;
     g_status_led_tick = 0;
 }
 
@@ -240,21 +279,79 @@ SwitchInputState map_gamepad(const uni_gamepad_t& gamepad) {
     return state;
 }
 
+bool pairing_window_active_at(uint32_t now_ms) {
+    return g_pairing_window_open &&
+           static_cast<int32_t>(now_ms - g_pairing_window_deadline_ms) < 0;
+}
+
+bool update_pairing_window(uint32_t now_ms) {
+    critical_section_enter_blocking(&g_state_lock);
+    const bool requested = g_pairing_window_requested;
+    g_pairing_window_requested = false;
+    critical_section_exit(&g_state_lock);
+
+    if (requested) {
+        g_pairing_window_open = true;
+        g_pairing_window_deadline_ms = now_ms + kPairingWindowDurationMs;
+        g_status_led_tick = 0;
+        return true;
+    }
+    if (g_pairing_window_open && !pairing_window_active_at(now_ms)) {
+        g_pairing_window_open = false;
+        g_status_led_tick = 0;
+        return true;
+    }
+    return false;
+}
+
+void apply_connection_policy(uint32_t now_ms) {
+    const bool free_slot = has_free_slot();
+    const bool pairing_open = pairing_window_active_at(now_ms);
+    if ((!free_slot &&
+         g_connection_policy_state == ConnectionPolicyState::Paused) ||
+        (free_slot && pairing_open &&
+         g_connection_policy_state == ConnectionPolicyState::Open) ||
+        (free_slot && !pairing_open &&
+         g_connection_policy_state == ConnectionPolicyState::Locked)) {
+        return;
+    }
+
+    uni_bt_allow_incoming_connections(false);
+    uni_bt_stop_scanning_unsafe();
+
+    if (!free_slot) {
+        g_connection_policy_state = ConnectionPolicyState::Paused;
+        return;
+    }
+
+    if (!pairing_open) {
+        g_connection_policy_state = ConnectionPolicyState::Locked;
+        return;
+    }
+
+    // Use Bluepad32's normal pairing/autoconnect path while the physical
+    // BOOTSEL gesture has explicitly opened the pairing window.
+    uni_bt_allow_incoming_connections(true);
+    uni_bt_start_scanning_and_autoconnect_unsafe();
+    g_connection_policy_state = ConnectionPolicyState::Open;
+}
+
 void update_status_led() {
     ++g_status_led_tick;
     bool led_on = false;
-    switch (g_connection_status) {
-        case ConnectionStatus::Initializing:
-        case ConnectionStatus::Ready:
-            led_on = true;
-            break;
-        case ConnectionStatus::Scanning:
-            led_on = (g_status_led_tick % 200) < 100;
-            break;
-        case ConnectionStatus::Connecting:
-            led_on = (g_status_led_tick % 40) < 20;
-            break;
+
+    if (pairing_window_active_at(btstack_run_loop_get_time_ms())) {
+        const uint16_t phase = g_status_led_tick % 200;
+        led_on = phase < 20 || (phase >= 40 && phase < 60);
+    } else if (g_connection_status == ConnectionStatus::Connecting) {
+        led_on = (g_status_led_tick % 40) < 20;
+    } else if (g_connection_status == ConnectionStatus::Initializing ||
+               has_active_controller()) {
+        led_on = true;
+    } else {
+        led_on = (g_status_led_tick % 200) < 100;
     }
+
     if (led_on != g_status_led_on) {
         cyw43_arch_gpio_put(CYW43_WL_GPIO_LED_PIN, led_on);
         g_status_led_on = led_on;
@@ -262,6 +359,11 @@ void update_status_led() {
 }
 
 void process_rumble_timer(btstack_timer_source_t* timer) {
+    const uint32_t now_ms = btstack_run_loop_get_time_ms();
+    if (update_pairing_window(now_ms)) {
+        apply_connection_policy(now_ms);
+    }
+
     for (uint8_t slot_index = 0; slot_index < kSlotCount; ++slot_index) {
         RumbleEnvelope envelope{};
         uni_hid_device_t* device = nullptr;
@@ -274,14 +376,16 @@ void process_rumble_timer(btstack_timer_source_t* timer) {
             slot.rumble_pending = false;
             dispatch = envelope.slot == slot_index && slot.active &&
                        slot.device != nullptr &&
-                       envelope.connection_generation == slot.connection_generation;
+                       envelope.connection_generation ==
+                           slot.connection_generation;
             if (dispatch) {
                 device = slot.device;
             }
         }
         critical_section_exit(&g_state_lock);
 
-        if (dispatch && device->report_parser.play_dual_rumble != nullptr) {
+        if (dispatch &&
+            device->report_parser.play_dual_rumble != nullptr) {
             device->report_parser.play_dual_rumble(
                 device, 0, kRumbleDurationMs,
                 envelope.rumble.high_frequency_magnitude,
@@ -294,19 +398,12 @@ void process_rumble_timer(btstack_timer_source_t* timer) {
     btstack_run_loop_add_timer(timer);
 }
 
-void resume_connections() {
-    uni_bt_allow_incoming_connections(true);
-    uni_bt_start_scanning_and_autoconnect_unsafe();
-}
 void recompute_connection_status() {
+    const uint32_t now_ms = btstack_run_loop_get_time_ms();
+    update_pairing_window(now_ms);
     g_connection_status = compute_connection_status();
     g_status_led_tick = 0;
-    if (g_connection_status == ConnectionStatus::Ready) {
-        uni_bt_stop_scanning_unsafe();
-        uni_bt_allow_incoming_connections(false);
-    } else {
-        resume_connections();
-    }
+    apply_connection_policy(now_ms);
 }
 
 void platform_init(int argc, const char** argv) {
@@ -315,23 +412,35 @@ void platform_init(int argc, const char** argv) {
 }
 
 void platform_on_init_complete() {
+    // Discovery and incoming connections remain disabled until BOOTSEL opens
+    // the bounded pairing window.
     btstack_run_loop_set_timer_handler(&g_rumble_timer, process_rumble_timer);
     btstack_run_loop_set_timer(&g_rumble_timer, kRumblePollIntervalMs);
     btstack_run_loop_add_timer(&g_rumble_timer);
     recompute_connection_status();
 }
 
-uni_error_t platform_on_device_discovered(bd_addr_t addr, const char* name, uint16_t cod, uint8_t rssi) {
+uni_error_t platform_on_device_discovered(bd_addr_t addr, const char* name,
+                                          uint16_t cod, uint8_t rssi) {
     (void)addr;
     (void)name;
     (void)cod;
     (void)rssi;
-    return compute_connection_status() == ConnectionStatus::Ready
-               ? UNI_ERROR_IGNORE_DEVICE
-               : UNI_ERROR_SUCCESS;
+    return has_free_slot() &&
+                   g_connection_policy_state == ConnectionPolicyState::Open
+               ? UNI_ERROR_SUCCESS
+               : UNI_ERROR_IGNORE_DEVICE;
 }
 
 void platform_on_device_connected(uni_hid_device_t* device) {
+    if (device == nullptr) {
+        return;
+    }
+    if (g_connection_policy_state != ConnectionPolicyState::Open) {
+        uni_hid_device_disconnect(device);
+        return;
+    }
+
     const int slot_index = slot_for_device(device);
     if (slot_index < 0) {
         return;
@@ -453,22 +562,26 @@ uni_platform* get_platform() {
     return &platform;
 }
 
+[[noreturn]] void halt_wireless_backend() {
+    publish_all_neutral();
+    while (true) {
+        tight_loop_contents();
+    }
+}
+
 [[noreturn]] void core1_main() {
+    if (!flash_safe_execute_core_init()) {
+        halt_wireless_backend();
+    }
     if (cyw43_arch_init() != 0) {
-        publish_all_neutral();
-        while (true) {
-            tight_loop_contents();
-        }
+        halt_wireless_backend();
     }
     cyw43_arch_gpio_put(CYW43_WL_GPIO_LED_PIN, true);
     g_status_led_on = true;
 
     uni_platform_set_custom(get_platform());
     if (uni_init(0, nullptr) != 0) {
-        publish_all_neutral();
-        while (true) {
-            tight_loop_contents();
-        }
+        halt_wireless_backend();
     }
 
     btstack_run_loop_execute();
@@ -493,6 +606,11 @@ void bluepad32_input_backend_init() {
         g_consumed_generation[slot_index] = 0;
         g_last_snapshot_generation[slot_index] = 0;
     }
+    g_pairing_window_requested = false;
+    g_connection_status = ConnectionStatus::Initializing;
+    g_connection_policy_state = ConnectionPolicyState::Uninitialized;
+    g_pairing_window_deadline_ms = 0;
+    g_pairing_window_open = false;
     g_initialized = true;
 }
 
@@ -503,11 +621,28 @@ void bluepad32_input_backend_start() {
     if (g_started) {
         return;
     }
+    // Core 0 services USB from flash while Core 1 owns BTstack. Register both
+    // cores before either side can initiate a flash-backed BTstack TLV write.
+    if (!flash_safe_execute_core_init()) {
+        g_connection_policy_state = ConnectionPolicyState::FailedClosed;
+        return;
+    }
+
 
     g_started = true;
     multicore_launch_core1(core1_main);
 }
 
+void bluepad32_input_backend_open_pairing_window() {
+    if (!g_initialized) {
+        bluepad32_input_backend_init();
+    }
+
+    critical_section_enter_blocking(&g_state_lock);
+    g_pairing_window_requested = true;
+    critical_section_exit(&g_state_lock);
+}
+
 bool bluepad32_input_backend_snapshot(uint8_t slot_index, SwitchInputState* out) {
     if (out == nullptr || !valid_slot(slot_index)) {
         return false;
diff --git a/bluepad32_input_backend.h b/bluepad32_input_backend.h
index 16b7e00..b969635 100644
--- a/bluepad32_input_backend.h
+++ b/bluepad32_input_backend.h
@@ -9,6 +9,7 @@ constexpr uint8_t BLUEPAD32_INPUT_BACKEND_SLOT_COUNT = 4;
 
 void bluepad32_input_backend_init();
 void bluepad32_input_backend_start();
+void bluepad32_input_backend_open_pairing_window();
 bool bluepad32_input_backend_snapshot(uint8_t slot, SwitchInputState* out);
 void bluepad32_input_backend_report_sent(uint8_t slot);
 void bluepad32_input_backend_queue_rumble(uint8_t slot,
diff --git a/bootsel_pairing_button.cpp b/bootsel_pairing_button.cpp
new file mode 100644
index 0000000..ab9de55
--- /dev/null
+++ b/bootsel_pairing_button.cpp
@@ -0,0 +1,99 @@
+#include "bootsel_pairing_button.h"
+
+#include "hardware/gpio.h"
+#include "hardware/structs/ioqspi.h"
+#include "hardware/structs/sio.h"
+#include "pico/flash.h"
+#include "pico/time.h"
+#if PICO_RP2350
+#include "hardware/regs/sio.h"
+#endif
+
+namespace {
+
+constexpr uint32_t kPollIntervalMs = 100;
+constexpr uint32_t kFlashSafeTimeoutMs = 100;
+constexpr uint32_t kQspiCsPinIndex = 1;
+
+BootselPairingButtonHoldFsm g_hold_fsm;
+uint32_t g_last_sample_ms = 0;
+
+// QSPI CSn sampling adapted from awalol/DS5Dongle's button_functions.cpp:
+// https://github.com/awalol/DS5Dongle/blob/master/src/button_functions.cpp
+// Copyright (c) 2026 awalol; used under the MIT License.
+//
+// This callback and everything it executes while CSn is floated must remain in
+// SRAM or be an inlined hardware-register operation. In particular, do not add
+// logging or ordinary flash-backed data access here.
+void __no_inline_not_in_flash_func(read_bootsel_callback)(void* parameter) {
+    auto* pressed = static_cast<bool*>(parameter);
+
+    hw_write_masked(
+        &ioqspi_hw->io[kQspiCsPinIndex].ctrl,
+        GPIO_OVERRIDE_LOW << IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_LSB,
+        IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_BITS);
+
+    for (volatile uint32_t delay = 0; delay < 1000; ++delay) {
+    }
+
+#if PICO_RP2350
+    *pressed =
+        (sio_hw->gpio_hi_in & SIO_GPIO_HI_IN_QSPI_CSN_BITS) == 0;
+#else
+    *pressed = (sio_hw->gpio_hi_in & (1u << kQspiCsPinIndex)) == 0;
+#endif
+
+    hw_write_masked(
+        &ioqspi_hw->io[kQspiCsPinIndex].ctrl,
+        GPIO_OVERRIDE_NORMAL << IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_LSB,
+        IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_BITS);
+}
+
+BootselPairingButtonSample sample_bootsel() {
+    bool pressed = false;
+    const int result = flash_safe_execute(read_bootsel_callback, &pressed,
+                                          kFlashSafeTimeoutMs);
+    if (result != PICO_OK) {
+        return BootselPairingButtonSample::kUnread;
+    }
+    return pressed ? BootselPairingButtonSample::kPressed
+                   : BootselPairingButtonSample::kReleased;
+}
+
+}  // namespace
+
+bool BootselPairingButtonHoldFsm::update(
+    BootselPairingButtonSample sample) {
+    if (sample == BootselPairingButtonSample::kUnread) {
+        return false;
+    }
+
+    if (sample == BootselPairingButtonSample::kReleased) {
+        pressed_samples_ = 0;
+        hold_reported_ = false;
+        return false;
+    }
+
+    if (hold_reported_) {
+        return false;
+    }
+
+    ++pressed_samples_;
+    if (pressed_samples_ < kHoldSamples) {
+        return false;
+    }
+
+    hold_reported_ = true;
+    return true;
+}
+
+bool bootsel_pairing_button_task() {
+    const uint32_t now_ms =
+        static_cast<uint32_t>(to_ms_since_boot(get_absolute_time()));
+    if (now_ms - g_last_sample_ms < kPollIntervalMs) {
+        return false;
+    }
+    g_last_sample_ms = now_ms;
+
+    return g_hold_fsm.update(sample_bootsel());
+}
diff --git a/bootsel_pairing_button.h b/bootsel_pairing_button.h
new file mode 100644
index 0000000..7a881b0
--- /dev/null
+++ b/bootsel_pairing_button.h
@@ -0,0 +1,23 @@
+#pragma once
+
+#include <cstdint>
+
+enum class BootselPairingButtonSample : uint8_t {
+    kUnread,
+    kReleased,
+    kPressed,
+};
+
+class BootselPairingButtonHoldFsm {
+public:
+    static constexpr uint8_t kHoldSamples = 20;
+
+    bool update(BootselPairingButtonSample sample);
+
+private:
+    uint8_t pressed_samples_ = 0;
+    bool hold_reported_ = false;
+};
+
+// Polls BOOTSEL at 10 Hz. Returns true once when a 20-sample hold completes.
+bool bootsel_pairing_button_task();
diff --git a/firmware/switch-pico-aio.elf b/firmware/switch-pico-aio.elf
index 9c1edc0..eb9df86 100755
Binary files a/firmware/switch-pico-aio.elf and b/firmware/switch-pico-aio.elf differ
diff --git a/firmware/switch-pico-aio.uf2 b/firmware/switch-pico-aio.uf2
index d5b54a8..e177a55 100644
Binary files a/firmware/switch-pico-aio.uf2 and b/firmware/switch-pico-aio.uf2 differ
diff --git a/switch-pico.cpp b/switch-pico.cpp
index ebe3007..ba3ba3f 100644
--- a/switch-pico.cpp
+++ b/switch-pico.cpp
@@ -7,6 +7,7 @@
 #include "hardware/uart.h"
 #else
 #include "bluepad32_input_backend.h"
+#include "bootsel_pairing_button.h"
 #endif
 
 #ifdef SWITCH_PICO_LOG
@@ -232,6 +233,9 @@ int main() {
     while (true) {
         tud_task();          // USB device tasks
 #ifdef SWITCH_PICO_BLUEPAD32
+        if (bootsel_pairing_button_task()) {
+            bluepad32_input_backend_open_pairing_window();
+        }
         for (uint8_t instance = 0;
              instance < BLUEPAD32_INPUT_BACKEND_SLOT_COUNT; ++instance) {
             bluepad32_input_backend_snapshot(instance,
diff --git a/tests/bluepad32_backend_lifecycle_test.cpp b/tests/bluepad32_backend_lifecycle_test.cpp
index d28cc88..253b74c 100644
--- a/tests/bluepad32_backend_lifecycle_test.cpp
+++ b/tests/bluepad32_backend_lifecycle_test.cpp
@@ -7,13 +7,29 @@
 
 namespace {
 
+
 bool incoming_connections = false;
 int scan_starts = 0;
 int scan_stops = 0;
 bool scanning_enabled = false;
+int classic_scan_starts = 0;
+int classic_scan_stops = 0;
+bool classic_scanning_enabled = false;
 uni_platform* installed_platform = nullptr;
 bool observed_status_led_on = false;
 int observed_status_led_writes = 0;
+uint32_t now_ms = 0;
+
+bool flash_core_init_result = true;
+int flash_core_init_calls = 0;
+int core1_launch_calls = 0;
+int cyw43_init_calls = 0;
+int uni_init_calls = 0;
+int device_disconnect_calls = 0;
+uni_hid_device_t* last_disconnected_device = nullptr;
+
+struct CoreStopped {};
+
 
 void require(bool condition, const char* message) {
     if (!condition) {
@@ -29,10 +45,14 @@ void play_rumble(uni_hid_device_t* device, uint16_t, uint16_t,
     device->last_low = low;
 }
 
-uni_hid_device_t device(int idx, bool gamepad = true) {
+uni_hid_device_t device(
+    int idx, bool gamepad = true,
+    uni_bt_conn_protocol_t protocol = UNI_BT_CONN_PROTOCOL_NONE) {
     uni_hid_device_t result{};
     result.idx = idx;
     result.gamepad = gamepad;
+    result.conn.protocol = protocol;
+    result.conn.btaddr[5] = static_cast<uint8_t>(idx + 1);
     result.report_parser.play_dual_rumble = play_rumble;
     return result;
 }
@@ -47,29 +67,66 @@ int uni_hid_device_get_idx_for_instance(const uni_hid_device_t* device) {
     return device == nullptr ? -1 : device->idx;
 }
 
+void uni_hid_device_disconnect(uni_hid_device_t* device) {
+    ++device_disconnect_calls;
+    last_disconnected_device = device;
+}
+
 void uni_bt_allow_incoming_connections(bool enabled) {
     incoming_connections = enabled;
 }
 
-void uni_bt_start_scanning_and_autoconnect_unsafe() {
+
+void uni_bt_bredr_scan_start() {
+    ++classic_scan_starts;
+    classic_scanning_enabled = true;
+}
+
+void uni_bt_bredr_scan_stop() {
+    if (classic_scanning_enabled) {
+        ++classic_scan_stops;
+    }
+    classic_scanning_enabled = false;
+}
+
+void uni_bt_le_scan_start() {
     ++scan_starts;
     scanning_enabled = true;
 }
 
-void uni_bt_stop_scanning_unsafe() {
-    ++scan_stops;
+void uni_bt_le_scan_stop() {
+    if (scanning_enabled) {
+        ++scan_stops;
+    }
     scanning_enabled = false;
 }
 
+void uni_bt_start_scanning_and_autoconnect_unsafe() {
+    uni_bt_bredr_scan_start();
+    uni_bt_le_scan_start();
+}
+
+void uni_bt_stop_scanning_unsafe() {
+    uni_bt_bredr_scan_stop();
+    uni_bt_le_scan_stop();
+}
+
 void uni_platform_set_custom(uni_platform* platform) {
     installed_platform = platform;
 }
 
 int uni_init(int, const char**) {
+    ++uni_init_calls;
     return 0;
 }
 
+bool flash_safe_execute_core_init() {
+    ++flash_core_init_calls;
+    return flash_core_init_result;
+}
+
 int cyw43_arch_init() {
+    ++cyw43_init_calls;
     return 0;
 }
 
@@ -78,7 +135,18 @@ void cyw43_arch_gpio_put(int, bool enabled) {
     ++observed_status_led_writes;
 }
 
-void multicore_launch_core1(void (*)()) {}
+void multicore_launch_core1(void (*)()) {
+    ++core1_launch_calls;
+}
+
+void tight_loop_contents() {
+    throw CoreStopped{};
+}
+
+uint32_t btstack_run_loop_get_time_ms() {
+    return now_ms;
+}
+
 
 #include "../bluepad32_input_backend.cpp"
 
@@ -87,9 +155,22 @@ namespace {
 void start_backend() {
     bluepad32_input_backend_init();
     platform_on_init_complete();
-    require(incoming_connections, "initialization must allow connections");
-    require(scan_starts == 1, "initialization must start scanning");
+    require(!incoming_connections,
+            "initialization must keep incoming connections closed");
+    require(scan_starts == 0,
+            "initialization must not scan before a BOOTSEL request");
 }
+void start_pairing_backend() {
+    start_backend();
+    bluepad32_input_backend_open_pairing_window();
+    process_rumble_timer(&g_rumble_timer);
+    require(g_connection_policy_state == ConnectionPolicyState::Open &&
+                scanning_enabled && classic_scanning_enabled &&
+                incoming_connections,
+            "test connection setup requires an open pairing window");
+}
+
+
 
 void tick_backend_timer(int ticks) {
     for (int tick = 0; tick < ticks; ++tick) {
@@ -98,7 +179,7 @@ void tick_backend_timer(int ticks) {
 }
 
 void test_ready_order(bool reverse) {
-    start_backend();
+    start_pairing_backend();
     uni_hid_device_t devices[kSlotCount] = {
         device(0), device(1), device(2), device(3)};
     uni_hid_device_t replacements[kSlotCount] = {
@@ -107,23 +188,7 @@ void test_ready_order(bool reverse) {
     const int backward[kSlotCount] = {3, 2, 1, 0};
     const int* order = reverse ? backward : forward;
 
-    tick_backend_timer(99);
-    require(observed_status_led_on,
-            "scanning LED must stay on for the first slow-blink half-cycle");
-    tick_backend_timer(1);
-    require(!observed_status_led_on,
-            "scanning LED must turn off at the slow-blink half-cycle");
-
     platform_on_device_connected(&devices[order[0]]);
-    tick_backend_timer(19);
-    require(observed_status_led_on,
-            "connecting LED must stay on for the first fast-blink half-cycle");
-    tick_backend_timer(1);
-    require(!observed_status_led_on,
-            "connecting LED must turn off at the fast-blink half-cycle");
-    tick_backend_timer(20);
-    require(observed_status_led_on,
-            "connecting LED must turn on for the next fast-blink cycle");
 
     for (int position = 0; position < kSlotCount; ++position) {
         const int slot = order[position];
@@ -146,14 +211,6 @@ void test_ready_order(bool reverse) {
                     "scanning must continue while any slot remains free");
             require(incoming_connections,
                     "incoming connections must remain enabled before all slots are ready");
-            if (position == 0) {
-                tick_backend_timer(99);
-                require(observed_status_led_on,
-                        "a partially full backend must use the scanning LED on half-cycle");
-                tick_backend_timer(1);
-                require(!observed_status_led_on,
-                        "a partially full backend must use the scanning LED off half-cycle");
-            }
         }
     }
 
@@ -161,14 +218,6 @@ void test_ready_order(bool reverse) {
             "scanning must stop exactly when all four slots are ready");
     require(!incoming_connections,
             "incoming connections must be disabled only when all slots are full");
-    tick_backend_timer(1);
-    require(observed_status_led_on,
-            "four ready slots must turn the status LED on");
-    const int ready_led_writes = observed_status_led_writes;
-    tick_backend_timer(200);
-    require(observed_status_led_on &&
-                observed_status_led_writes == ready_led_writes,
-            "four ready slots must keep the status LED solid");
 
     for (int slot = 0; slot < kSlotCount; ++slot) {
         const int starts_before_disconnect = scan_starts;
@@ -245,19 +294,13 @@ void test_rejections() {
 }
 
 void test_independent_lifecycle() {
-    start_backend();
+    start_pairing_backend();
 
     uni_hid_device_t aborted = device(0);
     const uint32_t aborted_generation = g_slots[0].connection_generation;
     platform_on_device_connected(&aborted);
     require(g_slots[0].device == &aborted && !g_slots[0].active,
             "connected device must remain identifiable while becoming ready");
-    tick_backend_timer(19);
-    require(observed_status_led_on,
-            "a lone pending connection must use the fast LED on half-cycle");
-    tick_backend_timer(1);
-    require(!observed_status_led_on,
-            "a lone pending connection must use the fast LED off half-cycle");
 
     const int starts_before_aborted_disconnect = scan_starts;
     platform_on_device_disconnected(&aborted);
@@ -266,15 +309,10 @@ void test_independent_lifecycle() {
     require(g_slots[0].connection_generation == aborted_generation + 1,
             "pre-ready disconnect must invalidate its connection generation");
     require(g_connection_status == ConnectionStatus::Scanning &&
-                scanning_enabled && incoming_connections &&
-                scan_starts == starts_before_aborted_disconnect + 1,
-            "pre-ready disconnect with no peer must resume scanning");
-    tick_backend_timer(99);
-    require(observed_status_led_on,
-            "pre-ready disconnect must restore the slow LED on half-cycle");
-    tick_backend_timer(1);
-    require(!observed_status_led_on,
-            "pre-ready disconnect must restore the slow LED off half-cycle");
+                scanning_enabled && classic_scanning_enabled &&
+                incoming_connections &&
+                scan_starts == starts_before_aborted_disconnect,
+            "pre-ready disconnect must preserve the open pairing scan");
 
     uni_hid_device_t devices[kSlotCount] = {
         device(0), device(1), device(2), device(3)};
@@ -284,12 +322,6 @@ void test_independent_lifecycle() {
                     !g_slots[slot].active,
                 "each pending device must retain its indexed identity");
     }
-    tick_backend_timer(19);
-    require(observed_status_led_on,
-            "concurrent pending devices must use the fast LED on half-cycle");
-    tick_backend_timer(1);
-    require(!observed_status_led_on,
-            "concurrent pending devices must use the fast LED off half-cycle");
 
     const uint32_t first_pending_generation =
         g_slots[0].connection_generation;
@@ -306,15 +338,10 @@ void test_independent_lifecycle() {
                 first_pending_generation + 1,
             "pending disconnect beside peers must invalidate its generation");
     require(g_connection_status == ConnectionStatus::Connecting &&
-                scanning_enabled && incoming_connections &&
+                scanning_enabled && classic_scanning_enabled &&
+                incoming_connections &&
                 scan_starts == starts_before_first_pending_disconnect + 1,
-            "open slot must scan while other slots remain connecting");
-    tick_backend_timer(19);
-    require(observed_status_led_on,
-            "surviving pending devices must retain the fast LED on half-cycle");
-    tick_backend_timer(1);
-    require(!observed_status_led_on,
-            "surviving pending devices must retain the fast LED off half-cycle");
+            "open pairing slot must preserve pending peers and resume scanning");
 
     for (int slot = 1; slot < kSlotCount; ++slot) {
         require(platform_on_device_ready(&devices[slot]) == UNI_ERROR_SUCCESS,
@@ -412,11 +439,6 @@ void test_independent_lifecycle() {
                 devices[0].last_low == 115 &&
                 devices[0].last_high == 116,
             "slot 0 rumble must continue while slot 3 is disconnected");
-    require(observed_status_led_on,
-            "disconnect scanning must use the slow LED on half-cycle");
-    tick_backend_timer(1);
-    require(!observed_status_led_on,
-            "disconnect scanning must reach the slow LED off half-cycle");
 
     uni_hid_device_t slot_three_replacement = device(3);
     require(platform_on_device_ready(&slot_three_replacement) ==
@@ -425,13 +447,6 @@ void test_independent_lifecycle() {
     process_rumble_timer(&g_rumble_timer);
     require(slot_three_replacement.rumble_calls == 0,
             "slot 3 replacement must not receive disconnected device rumble");
-    require(observed_status_led_on,
-            "slot 3 replacement must restore the solid ready LED");
-    const int replacement_ready_led_writes = observed_status_led_writes;
-    tick_backend_timer(100);
-    require(observed_status_led_on &&
-                observed_status_led_writes == replacement_ready_led_writes,
-            "replacement quartet must keep the ready LED solid");
 
     g_slots[3].pending_rumble = {
         3, disconnected_generation, SwitchRumbleOutput{77, 88}};
@@ -536,6 +551,128 @@ void test_independent_lifecycle() {
             "slot 0 activity must not evict the slot 3 mailbox");
 }
 
+void test_pairing_window_policy() {
+    bd_addr_t address = {1, 2, 3, 4, 5, 6};
+
+    bluepad32_input_backend_init();
+    require(platform_on_device_discovered(address, "controller", 0, 0) ==
+                    UNI_ERROR_IGNORE_DEVICE,
+            "discovery must remain closed before backend initialization");
+
+    start_backend();
+    require(g_connection_policy_state == ConnectionPolicyState::Locked &&
+                !classic_scanning_enabled && !scanning_enabled &&
+                !incoming_connections,
+            "boot must disable all discovery and incoming connections");
+    require(platform_on_device_discovered(address, "controller", 0, 0) ==
+                    UNI_ERROR_IGNORE_DEVICE,
+            "locked policy must reject every discovery");
+
+    uni_hid_device_t rejected = device(0);
+    platform_on_device_connected(&rejected);
+    require(device_disconnect_calls == 1 &&
+                last_disconnected_device == &rejected &&
+                g_slots[0].device == nullptr,
+            "locked policy must disconnect every incoming controller");
+
+    bluepad32_input_backend_open_pairing_window();
+    require(!g_pairing_window_open,
+            "Core0 request must wait for Core1 consumption");
+    process_rumble_timer(&g_rumble_timer);
+    require(g_pairing_window_open &&
+                g_pairing_window_deadline_ms == 60000 &&
+                g_connection_policy_state == ConnectionPolicyState::Open &&
+                classic_scanning_enabled && scanning_enabled &&
+                incoming_connections,
+            "BOOTSEL window must run Bluepad32's normal pairing scan");
+    require(platform_on_device_discovered(address, "controller", 0, 0) ==
+                    UNI_ERROR_SUCCESS,
+            "open pairing window must accept a discovered controller");
+
+    uni_hid_device_t paired = device(0);
+    platform_on_device_connected(&paired);
+    require(device_disconnect_calls == 1 &&
+                g_slots[0].device == &paired,
+            "open pairing window must retain a connected controller");
+    platform_on_device_disconnected(&paired);
+
+    tick_backend_timer(20);
+    require(!observed_status_led_on,
+            "pairing double blink must finish its first pulse");
+    tick_backend_timer(20);
+    require(observed_status_led_on,
+            "pairing double blink must start its second pulse");
+    tick_backend_timer(20);
+    require(!observed_status_led_on,
+            "pairing double blink must finish its second pulse");
+
+    now_ms = 30000;
+    bluepad32_input_backend_open_pairing_window();
+    process_rumble_timer(&g_rumble_timer);
+    require(g_pairing_window_deadline_ms == 90000,
+            "pairing request must extend deadline from current Core1 time");
+
+    uni_hid_device_t devices[kSlotCount] = {
+        device(0), device(1), device(2), device(3)};
+    for (int slot = 0; slot < kSlotCount; ++slot) {
+        require(platform_on_device_ready(&devices[slot]) == UNI_ERROR_SUCCESS,
+                "policy test devices must fill all slots");
+    }
+    require(g_connection_policy_state == ConnectionPolicyState::Paused &&
+                g_pairing_window_open && !scanning_enabled &&
+                !classic_scanning_enabled && !incoming_connections,
+            "full slots must pause pairing without closing the deadline");
+
+    now_ms = 90000;
+    process_rumble_timer(&g_rumble_timer);
+    require(!g_pairing_window_open &&
+                g_connection_policy_state == ConnectionPolicyState::Paused,
+            "deadline must expire while slots remain full");
+    platform_on_device_disconnected(&devices[3]);
+    require(g_connection_policy_state == ConnectionPolicyState::Locked &&
+                !classic_scanning_enabled && !scanning_enabled &&
+                !incoming_connections,
+            "a freed slot after expiry must remain closed");
+    require(platform_on_device_discovered(address, "controller", 0, 0) ==
+                    UNI_ERROR_IGNORE_DEVICE,
+            "expired pairing policy must reject discovery");
+}
+
+
+void test_flash_core_start_contract() {
+    bluepad32_input_backend_init();
+    flash_core_init_result = false;
+    bluepad32_input_backend_start();
+    require(flash_core_init_calls == 1 && core1_launch_calls == 0 &&
+                g_connection_policy_state ==
+                    ConnectionPolicyState::FailedClosed,
+            "Core0 flash-safe init failure must prevent Core1 launch");
+
+    flash_core_init_result = true;
+    bluepad32_input_backend_start();
+    require(flash_core_init_calls == 2 && core1_launch_calls == 1,
+            "Core0 must register as a flash-safe victim before Core1 launch");
+    bluepad32_input_backend_start();
+    require(flash_core_init_calls == 2 && core1_launch_calls == 1,
+            "backend start must remain idempotent");
+}
+
+void test_flash_core_init_fatal() {
+    bluepad32_input_backend_init();
+    flash_core_init_result = false;
+    bool stopped = false;
+    try {
+        core1_main();
+    } catch (const CoreStopped&) {
+        stopped = true;
+    }
+    require(stopped && flash_core_init_calls == 1 &&
+                cyw43_init_calls == 0 && uni_init_calls == 0 &&
+                g_connection_policy_state ==
+                    ConnectionPolicyState::FailedClosed,
+            "flash-safe Core1 init failure must halt before CYW43 init");
+}
+
 }  // namespace
 
 int main(int argc, char** argv) {
@@ -549,6 +686,12 @@ int main(int argc, char** argv) {
         test_rejections();
     } else if (scenario == "lifecycle") {
         test_independent_lifecycle();
+    } else if (scenario == "pairing-policy") {
+        test_pairing_window_policy();
+    } else if (scenario == "flash-core-start") {
+        test_flash_core_start_contract();
+    } else if (scenario == "flash-core-failure") {
+        test_flash_core_init_fatal();
     } else {
         require(false, "unknown scenario");
     }
diff --git a/tests/bluepad32_native_stubs/btstack_run_loop.h b/tests/bluepad32_native_stubs/btstack_run_loop.h
index 2d422d6..5487f88 100644
--- a/tests/bluepad32_native_stubs/btstack_run_loop.h
+++ b/tests/bluepad32_native_stubs/btstack_run_loop.h
@@ -19,4 +19,5 @@ inline void btstack_run_loop_set_timer(btstack_timer_source_t* timer,
 }
 
 inline void btstack_run_loop_add_timer(btstack_timer_source_t*) {}
+uint32_t btstack_run_loop_get_time_ms();
 inline void btstack_run_loop_execute() {}
diff --git a/tests/bluepad32_native_stubs/pico/flash.h b/tests/bluepad32_native_stubs/pico/flash.h
new file mode 100644
index 0000000..fd6a2c8
--- /dev/null
+++ b/tests/bluepad32_native_stubs/pico/flash.h
@@ -0,0 +1,3 @@
+#pragma once
+
+bool flash_safe_execute_core_init();
diff --git a/tests/bluepad32_native_stubs/pico/stdlib.h b/tests/bluepad32_native_stubs/pico/stdlib.h
index d5ce0cb..510d071 100644
--- a/tests/bluepad32_native_stubs/pico/stdlib.h
+++ b/tests/bluepad32_native_stubs/pico/stdlib.h
@@ -1,3 +1,3 @@
 #pragma once
 
-inline void tight_loop_contents() {}
+void tight_loop_contents();
diff --git a/tests/bluepad32_native_stubs/uni.h b/tests/bluepad32_native_stubs/uni.h
index 2de0fa7..b229a86 100644
--- a/tests/bluepad32_native_stubs/uni.h
+++ b/tests/bluepad32_native_stubs/uni.h
@@ -3,6 +3,30 @@
 #include <stdint.h>
 
 typedef uint8_t bd_addr_t[6];
+typedef uint8_t link_key_t[16];
+typedef uint8_t sm_key_t[16];
+typedef int link_key_type_t;
+
+enum bd_addr_type_t {
+    BD_ADDR_TYPE_LE_PUBLIC = 0,
+    BD_ADDR_TYPE_LE_RANDOM = 1,
+    BD_ADDR_TYPE_LE_PUBLIC_IDENTITY = 2,
+    BD_ADDR_TYPE_LE_RANDOM_IDENTITY = 3,
+    BD_ADDR_TYPE_UNKNOWN = 0xfe,
+};
+
+enum hci_link_type_t {
+    HCI_LINK_TYPE_SCO = 0,
+    HCI_LINK_TYPE_ACL = 1,
+};
+
+struct btstack_link_key_iterator_t {
+    int index;
+};
+
+enum {
+    ERROR_CODE_SUCCESS = 0,
+};
 typedef int uni_property_idx_t;
 typedef int uni_platform_oob_event_t;
 struct uni_property_t {};
@@ -63,7 +87,20 @@ struct uni_report_parser_t {
     uni_play_dual_rumble_t play_dual_rumble;
 };
 
+enum uni_bt_conn_protocol_t {
+    UNI_BT_CONN_PROTOCOL_NONE,
+    UNI_BT_CONN_PROTOCOL_BR_EDR,
+    UNI_BT_CONN_PROTOCOL_BLE,
+};
+
+
+struct uni_bt_conn_t {
+    bd_addr_t btaddr;
+    uni_bt_conn_protocol_t protocol;
+};
+
 struct uni_hid_device_t {
+    uni_bt_conn_t conn;
     int idx;
     bool gamepad;
     uni_report_parser_t report_parser;
@@ -91,8 +128,14 @@ struct uni_platform {
 
 bool uni_hid_device_is_gamepad(const uni_hid_device_t* device);
 int uni_hid_device_get_idx_for_instance(const uni_hid_device_t* device);
+void uni_hid_device_disconnect(uni_hid_device_t* device);
 void uni_bt_allow_incoming_connections(bool enabled);
 void uni_bt_start_scanning_and_autoconnect_unsafe();
 void uni_bt_stop_scanning_unsafe();
+void uni_bt_bredr_scan_start();
+void uni_bt_bredr_scan_stop();
+void uni_bt_le_scan_start();
+void uni_bt_le_scan_stop();
 void uni_platform_set_custom(uni_platform* platform);
 int uni_init(int argc, const char** argv);
+
diff --git a/tests/bootsel_native_stubs/hardware/gpio.h b/tests/bootsel_native_stubs/hardware/gpio.h
new file mode 100644
index 0000000..32af518
--- /dev/null
+++ b/tests/bootsel_native_stubs/hardware/gpio.h
@@ -0,0 +1,27 @@
+#pragma once
+
+#include <cstdint>
+
+using io_rw_32 = volatile uint32_t;
+
+enum gpio_override {
+    GPIO_OVERRIDE_NORMAL = 0,
+    GPIO_OVERRIDE_LOW = 2,
+};
+
+void bootsel_test_masked_write(io_rw_32* address, uint32_t values,
+                               uint32_t mask);
+
+inline void hw_write_masked(io_rw_32* address, uint32_t values,
+                            uint32_t mask) {
+    *address = (*address & ~mask) | (values & mask);
+    bootsel_test_masked_write(address, values, mask);
+}
+
+#if PICO_RP2350
+#define IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_LSB 14u
+#define IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_BITS 0x0000c000u
+#else
+#define IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_LSB 12u
+#define IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_BITS 0x00003000u
+#endif
diff --git a/tests/bootsel_native_stubs/hardware/regs/sio.h b/tests/bootsel_native_stubs/hardware/regs/sio.h
new file mode 100644
index 0000000..6b0f9eb
--- /dev/null
+++ b/tests/bootsel_native_stubs/hardware/regs/sio.h
@@ -0,0 +1,3 @@
+#pragma once
+
+#define SIO_GPIO_HI_IN_QSPI_CSN_BITS 0x08000000u
diff --git a/tests/bootsel_native_stubs/hardware/structs/ioqspi.h b/tests/bootsel_native_stubs/hardware/structs/ioqspi.h
new file mode 100644
index 0000000..9a7e80b
--- /dev/null
+++ b/tests/bootsel_native_stubs/hardware/structs/ioqspi.h
@@ -0,0 +1,14 @@
+#pragma once
+
+#include "hardware/gpio.h"
+
+struct ioqspi_status_ctrl_hw_t {
+    io_rw_32 status;
+    io_rw_32 ctrl;
+};
+
+struct ioqspi_hw_t {
+    ioqspi_status_ctrl_hw_t io[6];
+};
+
+extern ioqspi_hw_t* ioqspi_hw;
diff --git a/tests/bootsel_native_stubs/hardware/structs/sio.h b/tests/bootsel_native_stubs/hardware/structs/sio.h
new file mode 100644
index 0000000..9564835
--- /dev/null
+++ b/tests/bootsel_native_stubs/hardware/structs/sio.h
@@ -0,0 +1,10 @@
+#pragma once
+
+#include <cstdint>
+
+struct sio_hw_t {
+    volatile uint32_t gpio_in;
+    volatile uint32_t gpio_hi_in;
+};
+
+extern sio_hw_t* sio_hw;
diff --git a/tests/bootsel_native_stubs/pico/flash.h b/tests/bootsel_native_stubs/pico/flash.h
new file mode 100644
index 0000000..e33f7f3
--- /dev/null
+++ b/tests/bootsel_native_stubs/pico/flash.h
@@ -0,0 +1,10 @@
+#pragma once
+
+#include <cstdint>
+
+#define __no_inline_not_in_flash_func(function_name) function_name
+
+constexpr int PICO_OK = 0;
+
+int flash_safe_execute(void (*function)(void*), void* parameter,
+                       uint32_t enter_exit_timeout_ms);
diff --git a/tests/bootsel_native_stubs/pico/time.h b/tests/bootsel_native_stubs/pico/time.h
new file mode 100644
index 0000000..c3921f1
--- /dev/null
+++ b/tests/bootsel_native_stubs/pico/time.h
@@ -0,0 +1,8 @@
+#pragma once
+
+#include <cstdint>
+
+using absolute_time_t = uint64_t;
+
+absolute_time_t get_absolute_time();
+uint64_t to_ms_since_boot(absolute_time_t time);
diff --git a/tests/bootsel_pairing_button_test.cpp b/tests/bootsel_pairing_button_test.cpp
new file mode 100644
index 0000000..1d30ff6
--- /dev/null
+++ b/tests/bootsel_pairing_button_test.cpp
@@ -0,0 +1,224 @@
+#include "bootsel_pairing_button.h"
+
+#include <cstdlib>
+#include <cstdint>
+#include <iostream>
+#include <vector>
+
+#include "hardware/gpio.h"
+#include "hardware/regs/sio.h"
+#include "hardware/structs/ioqspi.h"
+#include "hardware/structs/sio.h"
+#include "pico/flash.h"
+#include "pico/time.h"
+
+namespace {
+
+#if PICO_RP2350
+constexpr uint32_t kBootselInputMask = SIO_GPIO_HI_IN_QSPI_CSN_BITS;
+#else
+constexpr uint32_t kBootselInputMask = 1u << 1u;
+#endif
+
+struct FlashResponse {
+    int result;
+    bool pressed;
+};
+
+ioqspi_hw_t qspi_registers{};
+sio_hw_t sio_registers{};
+uint64_t now_ms = 0;
+std::vector<FlashResponse> flash_responses;
+std::size_t next_flash_response = 0;
+std::vector<uint32_t> qspi_override_writes;
+int flash_safe_calls = 0;
+bool inside_flash_safe_callback = false;
+
+void require(bool condition, const char* message) {
+    if (!condition) {
+        std::cerr << message << '\n';
+        std::exit(1);
+    }
+}
+
+int apply_pressed(BootselPairingButtonHoldFsm& fsm, int count) {
+    int events = 0;
+    for (int sample = 0; sample < count; ++sample) {
+        if (fsm.update(BootselPairingButtonSample::kPressed)) {
+            ++events;
+        }
+    }
+    return events;
+}
+
+void test_short_press() {
+    BootselPairingButtonHoldFsm fsm;
+    require(apply_pressed(fsm, 19) == 0,
+            "a 19-sample press must not complete the hold");
+    require(!fsm.update(BootselPairingButtonSample::kReleased),
+            "a short-press release must not report a hold");
+    require(apply_pressed(fsm, 19) == 0,
+            "a release must discard the previous short press");
+}
+
+void test_exact_and_long_hold_once() {
+    BootselPairingButtonHoldFsm fsm;
+    require(apply_pressed(fsm, 19) == 0,
+            "the hold must not fire before sample 20");
+    require(fsm.update(BootselPairingButtonSample::kPressed),
+            "the hold must fire on exactly sample 20");
+    require(apply_pressed(fsm, 100) == 0,
+            "a continuously held button must not repeat");
+}
+
+void test_release_and_rearm() {
+    BootselPairingButtonHoldFsm fsm;
+    require(apply_pressed(fsm, 20) == 1,
+            "the initial hold must fire once");
+    require(!fsm.update(BootselPairingButtonSample::kReleased),
+            "release must rearm without reporting an event");
+    require(apply_pressed(fsm, 20) == 1,
+            "a valid release must permit one later hold");
+}
+
+void test_unread_samples_do_not_transition() {
+    BootselPairingButtonHoldFsm fsm;
+    require(apply_pressed(fsm, 10) == 0,
+            "the first half of a hold must not fire");
+    for (int sample = 0; sample < 8; ++sample) {
+        require(!fsm.update(BootselPairingButtonSample::kUnread),
+                "unread press samples must not report or reset a hold");
+    }
+    require(apply_pressed(fsm, 9) == 0,
+            "valid pressed samples must resume after unread samples");
+    require(fsm.update(BootselPairingButtonSample::kPressed),
+            "20 valid pressed samples must fire despite unread samples");
+
+    require(!fsm.update(BootselPairingButtonSample::kUnread),
+            "an unread release must not rearm a completed hold");
+    require(apply_pressed(fsm, 20) == 0,
+            "the held state must persist until a valid release");
+    require(!fsm.update(BootselPairingButtonSample::kReleased),
+            "a valid release must only rearm");
+    require(apply_pressed(fsm, 20) == 1,
+            "the FSM must fire after the eventual valid release");
+}
+
+bool run_sample(uint64_t sample_time_ms, int result, bool pressed) {
+    flash_responses.push_back({result, pressed});
+    now_ms = sample_time_ms;
+    const std::size_t expected_consumed = flash_responses.size();
+    const bool event = bootsel_pairing_button_task();
+    require(next_flash_response == expected_consumed,
+            "a due poll must invoke flash_safe_execute exactly once");
+    return event;
+}
+
+void test_sampler_cadence_and_callback_failure() {
+    now_ms = 0;
+    require(!bootsel_pairing_button_task(),
+            "the sampler must wait for its first 100 ms cadence");
+    now_ms = 99;
+    require(!bootsel_pairing_button_task(),
+            "the sampler must not poll before 100 ms");
+    require(flash_safe_calls == 0,
+            "sub-cadence task calls must not enter flash-safe execution");
+
+    require(!run_sample(100, PICO_OK, true),
+            "the first valid pressed sample must only start the hold");
+    require(flash_safe_calls == 1 && qspi_override_writes.size() == 2,
+            "a successful sample must float and restore QSPI CSn once");
+    const uint32_t disabled =
+        GPIO_OVERRIDE_LOW << IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_LSB;
+    require(qspi_override_writes[0] == disabled,
+            "the callback must float QSPI CSn before reading BOOTSEL");
+    require(qspi_override_writes[1] == 0,
+            "the callback must restore normal QSPI CSn control");
+
+    now_ms = 199;
+    require(!bootsel_pairing_button_task(),
+            "the sampler must remain gated between 10 Hz polls");
+    require(flash_safe_calls == 1,
+            "an early task call must not sample BOOTSEL");
+
+    const std::size_t writes_before_failure = qspi_override_writes.size();
+    require(!run_sample(200, -1, true),
+            "flash-safe failure must be treated as unread");
+    require(qspi_override_writes.size() == writes_before_failure,
+            "a failed flash-safe entry must not invoke the callback");
+
+    for (uint64_t time = 300; time < 2100; time += 100) {
+        require(!run_sample(time, PICO_OK, true),
+                "the sampler must wait for 20 valid pressed samples");
+    }
+    require(run_sample(2100, PICO_OK, true),
+            "a failed sample must not reset the valid pressed count");
+    require(!run_sample(2200, PICO_OK, true),
+            "a held button must not repeat after firing");
+
+    require(!run_sample(2300, -1, false),
+            "a failed release sample must remain unread");
+    require(!run_sample(2400, PICO_OK, true),
+            "an unread release must not rearm the sampler FSM");
+    require(!run_sample(2500, PICO_OK, false),
+            "a valid release must rearm without firing");
+
+    for (uint64_t time = 2600; time < 4500; time += 100) {
+        require(!run_sample(time, PICO_OK, true),
+                "the rearmed sampler must count a fresh hold");
+    }
+    require(run_sample(4500, PICO_OK, true),
+            "a valid release must permit a second completed hold");
+}
+
+}  // namespace
+
+ioqspi_hw_t* ioqspi_hw = &qspi_registers;
+sio_hw_t* sio_hw = &sio_registers;
+
+absolute_time_t get_absolute_time() {
+    return now_ms;
+}
+
+uint64_t to_ms_since_boot(absolute_time_t time) {
+    return time;
+}
+
+void bootsel_test_masked_write(io_rw_32* address, uint32_t, uint32_t mask) {
+    require(inside_flash_safe_callback,
+            "QSPI override writes must occur inside flash_safe_execute");
+    require(address == &ioqspi_hw->io[1].ctrl,
+            "the callback must only override QSPI CSn");
+    qspi_override_writes.push_back(*address & mask);
+}
+
+int flash_safe_execute(void (*function)(void*), void* parameter,
+                       uint32_t enter_exit_timeout_ms) {
+    require(enter_exit_timeout_ms == 100,
+            "BOOTSEL sampling must use the 100 ms flash-safe timeout");
+    require(next_flash_response < flash_responses.size(),
+            "flash-safe execution requires a queued test response");
+    ++flash_safe_calls;
+    const FlashResponse response = flash_responses[next_flash_response++];
+    if (response.result != PICO_OK) {
+        return response.result;
+    }
+
+    sio_hw->gpio_hi_in = response.pressed ? 0 : kBootselInputMask;
+    inside_flash_safe_callback = true;
+    function(parameter);
+    inside_flash_safe_callback = false;
+    require((ioqspi_hw->io[1].ctrl &
+             IO_QSPI_GPIO_QSPI_SS_CTRL_OEOVER_BITS) == 0,
+            "the callback must restore QSPI CSn before returning");
+    return PICO_OK;
+}
+
+int main() {
+    test_short_press();
+    test_exact_and_long_hold_once();
+    test_release_and_rearm();
+    test_unread_samples_do_not_transition();
+    test_sampler_cadence_and_callback_failure();
+    return 0;
+}
diff --git a/tests/test_bluepad32_backend_lifecycle_native.py b/tests/test_bluepad32_backend_lifecycle_native.py
index dedb67b..b9fdb8d 100644
--- a/tests/test_bluepad32_backend_lifecycle_native.py
+++ b/tests/test_bluepad32_backend_lifecycle_native.py
@@ -35,5 +35,8 @@ def test_bluepad32_backend_lifecycle_native(tmp_path: Path) -> None:
         "ready-reverse",
         "rejections",
         "lifecycle",
+        "pairing-policy",
+        "flash-core-start",
+        "flash-core-failure",
     ):
         subprocess.run([str(executable), scenario], check=True, cwd=root)
diff --git a/tests/test_bootsel_pairing_button_native.py b/tests/test_bootsel_pairing_button_native.py
new file mode 100644
index 0000000..b05f1b7
--- /dev/null
+++ b/tests/test_bootsel_pairing_button_native.py
@@ -0,0 +1,34 @@
+from __future__ import annotations
+
+import shutil
+import subprocess
+from pathlib import Path
+
+
+def test_bootsel_pairing_button_native(tmp_path: Path) -> None:
+    root = Path(__file__).resolve().parents[1]
+    compiler = shutil.which("c++") or shutil.which("g++")
+    assert compiler is not None, "a host C++ compiler is required"
+
+    for platform, rp2350 in (("rp2350", 1), ("rp2040", 0)):
+        executable = tmp_path / f"bootsel_pairing_button_test_{platform}"
+        subprocess.run(
+            [
+                compiler,
+                "-std=c++17",
+                "-Wall",
+                "-Wextra",
+                "-Werror",
+                "-pedantic",
+                f"-DPICO_RP2350={rp2350}",
+                f"-I{root / 'tests' / 'bootsel_native_stubs'}",
+                f"-I{root}",
+                str(root / "bootsel_pairing_button.cpp"),
+                str(root / "tests" / "bootsel_pairing_button_test.cpp"),
+                "-o",
+                str(executable),
+            ],
+            check=True,
+            cwd=root,
+        )
+        subprocess.run([str(executable)], check=True, cwd=root)