fix: Ctrl+Space (ToggleSelection) not working after tcell migration

tcellEventToEvent did not convert Ctrl+Space to KeyCtrlSpace for
CSI u terminals or traditional terminals (tcell emits KeyCtrlSpace
which fell outside the KeyCtrlA..KeyCtrlZ range).

screen.go

@@ -110,8 +110,20 @@ func tcellEventToEvent(tev tcell.Event) Event {
 				}
 			}
 
-			// Special case: space must be sent as KeySpace with Ch=0
-			// to match the convention expected by doAcceptChar
+			// Ctrl+Space via CSI u: tcell delivers KeyRune with
+			// rune=' ' and ModCtrl. Convert to KeyCtrlSpace (0x00).
+			if r == ' ' && mod&keyseq.ModCtrl != 0 {
+				mod &^= keyseq.ModCtrl
+				return Event{
+					Type: EventKey,
+					Key:  keyseq.KeyCtrlSpace,
+					Ch:   0,
+					Mod:  mod,
+				}
+			}
+
+			// Plain space must be sent as KeySpace with Ch=0
+			// to match the convention expected by doAcceptChar.
 			if r == ' ' {
 				return Event{
 					Type: EventKey,
@@ -138,17 +150,17 @@ func tcellEventToEvent(tev tcell.Event) Event {
 			}
 		}
 
-		// Ctrl+letter keys: tcell.KeyCtrlA(65)..KeyCtrlZ(90).
+		// Ctrl keys: tcell.KeyCtrlSpace(64)..KeyCtrlZ(90).
 		// On terminals with enhanced keyboard protocols (CSI u /
 		// fixterms), tcell normalizes Ctrl+letter to these constants
 		// with ModCtrl set. Peco's keyseq system encodes the ctrl
-		// nature in the key value (0x01-0x1A), not in the modifier,
+		// nature in the key value (0x00-0x1A), not in the modifier,
 		// so strip the redundant ModCtrl. (issue #715)
-		if key >= tcell.KeyCtrlA && key <= tcell.KeyCtrlZ {
+		if key >= tcell.KeyCtrlSpace && key <= tcell.KeyCtrlZ {
 			mod &^= keyseq.ModCtrl
 			return Event{
 				Type: EventKey,
-				Key:  keyseq.KeyType(key - tcell.KeyCtrlA + 1),
+				Key:  keyseq.KeyType(key - tcell.KeyCtrlSpace),
 				Ch:   0,
 				Mod:  mod,
 			}

screen_test.go

@@ -538,6 +538,62 @@ func TestTcellEventToEventCtrlKeysStripModCtrl(t *testing.T) {
 	}
 }
 
+// TestTcellEventToEventCtrlSpace verifies that Ctrl+Space is correctly
+// converted to KeyCtrlSpace (0x00) regardless of how the terminal reports it.
+//
+// Traditional terminals send NUL (0x00); tcell's input handler
+// delivers this as KeyCtrlSpace(64) with ModCtrl.
+// The KeyCtrlSpace..KeyCtrlZ path handles this.
+//
+// CSI u / enhanced terminals report Ctrl+Space as KeyRune with rune=' '
+// and ModCtrl. This must also produce Key=KeyCtrlSpace, Mod=ModNone
+// so that the ToggleSelectionAndSelectNext action fires correctly.
+func TestTcellEventToEventCtrlSpace(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name    string
+		tcellEv *tcell.EventKey
+		wantKey keyseq.KeyType
+		wantCh  rune
+		wantMod keyseq.ModifierKey
+	}{
+		{
+			// Traditional terminal: NUL byte (0x00).
+			// tcell's input handler calls
+			//   NewEventKey(KeyCtrlSpace+Key(r), 0, ModCtrl)
+			// which yields key=KeyCtrlSpace(64), mod=ModCtrl.
+			// The KeyCtrlSpace..KeyCtrlZ path strips ModCtrl and
+			// maps to keyseq.KeyCtrlSpace(0x00).
+			name:    "traditional terminal: NUL byte via KeyCtrlSpace+ModCtrl",
+			tcellEv: tcell.NewEventKey(tcell.KeyCtrlSpace, 0, tcell.ModCtrl),
+			wantKey: keyseq.KeyCtrlSpace,
+			wantCh:  0,
+			wantMod: keyseq.ModNone,
+		},
+		{
+			// CSI u / enhanced terminal: Ctrl+Space reported as
+			// KeyRune with rune=' ' and ModCtrl.
+			name:    "CSI u terminal: Ctrl+Space as rune with ModCtrl",
+			tcellEv: tcell.NewEventKey(tcell.KeyRune, ' ', tcell.ModCtrl),
+			wantKey: keyseq.KeyCtrlSpace,
+			wantCh:  0,
+			wantMod: keyseq.ModNone,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+			got := tcellEventToEvent(tt.tcellEv)
+			require.Equal(t, EventKey, got.Type, "event type")
+			require.Equal(t, tt.wantKey, got.Key, "key")
+			require.Equal(t, tt.wantCh, got.Ch, "ch")
+			require.Equal(t, tt.wantMod, got.Mod, "modifier")
+		})
+	}
+}
+
 // TestTcellEventToEventCtrlWithAltPreservesAlt verifies that Ctrl+Alt
 // combinations strip ModCtrl but preserve ModAlt.
 func TestTcellEventToEventCtrlWithAltPreservesAlt(t *testing.T) {