diff --git a/armsrc/appmain.c b/armsrc/appmain.c
index 1678a10cb..b67974745 100644
--- a/armsrc/appmain.c
+++ b/armsrc/appmain.c
@@ -4859,7 +4859,18 @@ void __attribute__((noreturn)) AppMain(void) {
         }
 
 #ifdef PM5
-        pm5_power_idle();
+        // WFI sleep adds ~40-50ms of latency before the main loop notices a
+        // fresh byte on CEP's SPI1 - fine at idle, but it's what made the
+        // original attach handshake miss bytes (see cep_attach_poll()'s own
+        // comment on the attach-edge bug this caused, GH #3667). Skip the
+        // sleep entirely while a Flipper is attached so the loop polls as
+        // fast as the hardware allows; cep_is_attached() drops back to false
+        // within CEP_ACTIVITY_TIMEOUT_MS of the FAP going away, so this
+        // isn't a permanent always-on cost.
+#ifdef WITH_CEP
+        if (!cep_is_attached())
+#endif
+            pm5_power_idle();
 #endif
     }
 }
diff --git a/armsrc/pm5_cep.c b/armsrc/pm5_cep.c
index ac9f425dc..cd5648fec 100644
--- a/armsrc/pm5_cep.c
+++ b/armsrc/pm5_cep.c
@@ -55,12 +55,23 @@
 #define CEP_SYNC_BYTE            0x55
 #define CEP_SYNC_MAX_DISCARD     600
 
+// How long cep_attach_poll() will go without seeing a real SPI poll from the
+// Flipper before deciding the FAP has quit (see the comment at its one use
+// below) and letting AppMain() go back to sleeping between iterations.
+#define CEP_ACTIVITY_TIMEOUT_MS      3000
+
 static bool s_cep_active = false;   // handshake completed, SPI transport live
+static bool s_cep_attached = false; // CC controller reports a physical attach
+static uint32_t s_last_spi_activity_tick = 0; // last time a real SPI poll was seen
 
 bool cep_is_active(void) {
     return s_cep_active;
 }
 
+bool cep_is_attached(void) {
+    return s_cep_attached;
+}
+
 // ---------------------------------------------------------------------------
 // One-time peripheral bring-up
 // ---------------------------------------------------------------------------
@@ -279,6 +290,7 @@ void cep_attach_poll(void) {
     }
 
     bool attached = ((cc_ctrl_data >> 6 & 0x03) != 0);
+    s_cep_attached = attached;
 
     if (!attached) {
         s_cep_active = false;
@@ -294,6 +306,18 @@ void cep_attach_poll(void) {
         // can't hang the main loop.
         if (usart_flag_get(USART1, USART_RDBF_FLAG) != RESET) {
             s_cep_active = cep_do_handshake();
+            if (s_cep_active) {
+                s_last_spi_activity_tick = GetTickCount();
+            }
+        }
+
+        // The FAP quitting doesn't touch the CC controller's attach bit - the
+        // cable stays connected, so `attached` alone can't tell us it's gone.
+        // Losing its SPI poll cadence (normally every 20-120ms) is what
+        // actually means it has - fall back to the slower/idle main loop
+        // once that cadence has been missing this long.
+        if (s_cep_active && (GetTickCountDelta(s_last_spi_activity_tick) > CEP_ACTIVITY_TIMEOUT_MS)) {
+            s_cep_active = false;
         }
     }
 
@@ -336,6 +360,7 @@ bool cep_spi_data_available(void) {
     if (!cep_spi_read_byte(&len_header[1])) {
         return false;
     }
+    s_last_spi_activity_tick = GetTickCount(); // FAP is still polling, valid frame or not
     uint16_t data_len = (len_header[1] << 8) | len_header[0];
     if (data_len > PM3_CMD_DATA_SIZE * 2) {
         return false;
diff --git a/armsrc/pm5_cep.h b/armsrc/pm5_cep.h
index d040bd1ef..28d7bb0d9 100644
--- a/armsrc/pm5_cep.h
+++ b/armsrc/pm5_cep.h
@@ -39,6 +39,13 @@ void cep_init(void);
 // Flipper is attached.
 bool cep_is_active(void);
 
+// True once the CC controller reports a Flipper physically attached,
+// independent of whether the handshake/SPI transport is up yet. Gate for
+// AppMain()'s WFI-skip (see appmain.c) - a Flipper merely being plugged in
+// is reason enough to stop sleeping between main-loop iterations, before
+// any handshake has even started.
+bool cep_is_attached(void);
+
 // Rate-limited (see PM5_CEP_ATTACH_POLL_MS), non-blocking. Call once per
 // AppMain() main-loop iteration, alongside bwm_autooff_check(). Detects the
 // Flipper attach/detach transition via the CC controller and, on a fresh