exp/textinput: clear queued states when text field is unfocused

The session's state queue buffers input events that arrive between
a commit-end and the next session start, which is needed when multiple
keys are pressed simultaneously (#3382). However, when a text field
was unfocused, keystroke events continued to be queued by the platform
layer and were replayed when a field was next focused, causing
unexpected text to appear.

Clear the queued states in Field.cleanUp(), which is called when a
field is blurred. This preserves the queue for simultaneous keypresses
within a focused field while discarding stale input from unfocused
periods.

Also refactor textInput to move the session field and theTextInput
variable to the cross-platform textinput.go, with each platform
defining only a textInputImpl with platform-specific fields.

Updates #3382
Closes #3429

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

exp/textinput/field.go

@@ -290,6 +290,8 @@ func (f *Field) cleanUp() {
 		f.end = nil
 		f.state = textInputState{}
 	}
+
+	theTextInput.session.clearQueue()
 }
 
 // Selection returns the current selection range in bytes.

exp/textinput/textinput.go

@@ -117,6 +117,13 @@ func convertByteCountToUTF16Count(text string, c int) int {
 	return -1
 }
 
+type textInput struct {
+	textInputImpl
+	session session
+}
+
+var theTextInput textInput
+
 type session struct {
 	ch   chan textInputState
 	done chan struct{}
@@ -184,6 +191,15 @@ func (s *session) doSend(state textInputState) {
 	}
 }
 
+// clearQueue clears queued states.
+// This should be called when the text field is unfocused
+// so that the queued states are not flushed when the next session starts (#3429).
+func (s *session) clearQueue() {
+	s.m.Lock()
+	defer s.m.Unlock()
+	s.queuedStates = s.queuedStates[:0]
+}
+
 func (s *session) flushStateQueue() {
 	for _, st := range s.queuedStates {
 		s.doSend(st)

exp/textinput/textinput_darwin.go

@@ -25,12 +25,7 @@ import (
 	"github.com/hajimehoshi/ebiten/v2"
 )
 
-type textInput struct {
-	// session must be accessed from the main thread.
-	session session
-}
-
-var theTextInput textInput
+type textInputImpl struct{}
 
 func (t *textInput) Start(bounds image.Rectangle) (<-chan textInputState, func()) {
 	var ch <-chan textInputState

exp/textinput/textinput_js.go

@@ -34,14 +34,10 @@ func init() {
 	theTextInput.init()
 }
 
-type textInput struct {
+type textInputImpl struct {
 	textareaElement js.Value
-
-	session session
 }
 
-var theTextInput textInput
-
 func (t *textInput) init() {
 	t.textareaElement = document.Call("createElement", "textarea")
 	t.textareaElement.Set("id", "ebitengine-textinput")

exp/textinput/textinput_noime.go

@@ -22,14 +22,11 @@ import (
 	"github.com/hajimehoshi/ebiten/v2"
 )
 
-type textInput struct {
-	session  session
+type textInputImpl struct {
 	rs       []rune
 	lastTick int64
 }
 
-var theTextInput textInput
-
 func (t *textInput) Start(bounds image.Rectangle) (<-chan textInputState, func()) {
 	// AppendInputChars is updated only when the tick is updated.
 	// If the tick is not updated, return nil immediately.

exp/textinput/textinput_windows.go

@@ -27,9 +27,7 @@ import (
 	"github.com/hajimehoshi/ebiten/v2/internal/ui"
 )
 
-type textInput struct {
-	session session
-
+type textInputImpl struct {
 	origWndProc     uintptr
 	wndProcCallback uintptr
 	window          windows.HWND
@@ -42,8 +40,6 @@ type textInput struct {
 	err error
 }
 
-var theTextInput textInput
-
 func (t *textInput) Start(bounds image.Rectangle) (<-chan textInputState, func()) {
 	if microsoftgdk.IsXbox() {
 		return nil, nil