ui: dedup IME snippet/selection to fix rapid-commit desync

TextField.Draw re-pushed key.SnippetCmd and key.SelectionCmd every frame
while focused. Re-pushing an unchanged snippet resets the IME's composition
and caret, so commits arriving faster than a frame interleaved with those
resets and desynced the cursor (garbled/duplicated text).

Mirror widget.Editor's updateSnippet/selection gating: track the last-pushed
snippet and caret in the main-owned Renderer (keyed by field ID, reset on
focus (re)gain), and only emit the ops when they actually change. A fresh
push is forced whenever the field (re)gains focus so the IME always starts
from a known state. Also drop a leftover per-frame 'Focused:' debug print.

On-device: rapid back-to-back commits (0.08-0.1s cadence, faster than a
frame) now land cleanly - type HELLO, append+backspace, and a
browser->editor navigation round-trip all produce exact content.
go test -race ./... green.

internal/ui/element.go

@@ -7,12 +7,12 @@ import (
 	"strings"
 
 	"gioui.org/font"
+	"gioui.org/io/key"
 	"gioui.org/layout"
 	"gioui.org/op"
 	"gioui.org/op/clip"
 	"gioui.org/op/paint"
 	"gioui.org/unit"
-	"gioui.org/io/key"
 )
 
 // Region defines a screen area in device-independent pixels (Dp).
@@ -209,7 +209,15 @@ func (tf TextField) String() string {
 // and draws display lines inline — one LayoutString call, no double-shaping.
 func (tf TextField) Draw(gtx layout.Context, r *Renderer) {
 	if tf.Focused {
-		fmt.Printf("Focused: tag = %s\n", tf.id)
+		// (Re-)gained focus for this field (or a different field than the one the
+		// dedup state currently tracks): force a fresh snippet/selection push so
+		// the IME starts from a known state.
+		if r.lastIMEField != tf.id || !r.lastWasFocused {
+			r.lastSnippet = key.Snippet{}
+			r.lastSelCaret = -1
+		}
+		r.lastIMEField = tf.id
+		r.lastWasFocused = true
 		gtx.Execute(key.FocusCmd{Tag: tf.id})
 		gtx.Execute(key.SoftKeyboardCmd{Show: true})
 		// IME wiring. The visible window (tf.Value) is pushed as the snippet
@@ -220,16 +228,35 @@ func (tf TextField) Draw(gtx layout.Context, r *Renderer) {
 		// Item 4: tell the IME this is a text field (enables the text keyboard,
 		// autocorrect, and suggestions).
 		key.InputHintOp{Tag: tf.id, Hint: key.HintText}.Add(gtx.Ops)
-		// Item 2: push the snippet (the visible window) for swipe/autocorrect.
+		// Item 2: push the snippet (the visible window) for swipe/autocorrect,
-		gtx.Execute(key.SnippetCmd{Tag: tf.id, Snippet: key.Snippet{
+		// but only when it changed. Re-pushing an unchanged snippet every frame
+		// resets the IME's composition/cursor, which desyncs fast commits (see
+		// widget.Editor's updateSnippet dedup).
+		snippet := key.Snippet{
 			Range: key.Range{Start: 0, End: runeCount(tf.Value, len(tf.Value))},
 			Text:  tf.Value,
-		}})
+		}
+		if snippet != r.lastSnippet {
+			r.lastSnippet = snippet
+			gtx.Execute(key.SnippetCmd{Tag: tf.id, Snippet: snippet})
+		}
 		// Item 1: sync the caret so the IME's selection matches. Window-relative
-		// rune index of the caret (tf.CursorPosition is a byte offset in tf.Value).
+		// rune index of the caret (tf.CursorPosition is a byte offset in
+		// tf.Value). Push only when it moves, so a static caret does not reset
+		// the IME every frame.
 		caret := runeCount(tf.Value, tf.CursorPosition)
+		if caret != r.lastSelCaret {
+			r.lastSelCaret = caret
 			gtx.Execute(key.SelectionCmd{Tag: tf.id, Range: key.Range{Start: caret, End: caret}, Caret: key.Caret{}})
 		}
+	} else if r.lastIMEField == tf.id {
+		// This (previously-focused) field lost focus: forget it so the next focus
+		// pushes a fresh snippet/selection.
+		r.lastIMEField = ""
+		r.lastWasFocused = false
+		r.lastSnippet = key.Snippet{}
+		r.lastSelCaret = -1
+	}
 	r.drawWrappedText(gtx, tf.Value, tf.region, tf.WrapWidth, tf.ScrollOffset, tf.CursorPosition)
 }
 

internal/ui/render.go

@@ -15,6 +15,7 @@ import (
 	"gioui.org/gesture"
 	"gioui.org/io/event" // Import event package
 	"gioui.org/io/input"
+	"gioui.org/io/key"
 	"gioui.org/io/pointer"
 	"gioui.org/layout"
 	"gioui.org/op"
@@ -66,6 +67,16 @@ type Renderer struct {
 	displayLineCount int                       // number of display lines from last drawWrappedText
 	lastLineY        Dp                        // last line baseline offset from text origin, in Dp (derived from GlyphLayout)
 	glyphLayout      GlyphLayout               // captured per-glyph layout from last drawWrappedText
+
+	// IME dedup (main-owned, persistent across frames). Re-pushing an unchanged
+	// snippet or selection every frame resets the IME's composition and caret,
+	// which desyncs fast commits; push only on change, as widget.Editor does in
+	// updateSnippet and its selection gating. Keyed to the focused field's ID so
+	// it stays correct if a second TextField is ever added.
+	lastIMEField   string
+	lastWasFocused bool
+	lastSnippet    key.Snippet
+	lastSelCaret   int // window-relative rune index of last-pushed caret; -1 = none
 }
 
 // New creates a new Renderer.
@@ -228,7 +239,7 @@ func (r *Renderer) CheckGestures(q input.Source, m unit.Metric) []InputEvent {
 		// ScrollY range: Min = -scrollOffset (remaining above), Max = large (content height unknown yet).
 		// With Min==Max==0, clampSplit consumes zero scroll.
 		delta := reg.scroll.Update(m, q, time.Now(), gesture.Vertical,
-			pointer.ScrollRange{}, pointer.ScrollRange{Min: -(1<<30), Max: 1<<30})
+			pointer.ScrollRange{}, pointer.ScrollRange{Min: -(1 << 30), Max: 1 << 30})
 		if delta != 0 {
 			events = append(events, InputEvent{
 				Handler: reg.handler,
@@ -400,7 +411,7 @@ func (r *Renderer) drawText(gtx layout.Context, str string, size unit.Sp, reg Re
 	case AlignStart:
 		drawX = reg.X
 	case AlignCenter:
-		drawX = reg.X + (reg.W - textW) / 2
+		drawX = reg.X + (reg.W-textW)/2
 	case AlignEnd:
 		drawX = reg.X + reg.W - textW
 	}
@@ -515,7 +526,7 @@ func (r *Renderer) drawWrappedText(gtx layout.Context, str string, reg Region, w
 	var layout GlyphLayout
 	layout.LineHeight = Dp(float32(lineHeightSp))
 	byteOffset := 0
-	layout.VisualLineStarts = append(layout.VisualLineStarts,byteOffset)
+	layout.VisualLineStarts = append(layout.VisualLineStarts, byteOffset)
 	for g, ok := r.shp.NextGlyph(); ok; g, ok = r.shp.NextGlyph() {
 		// Record layout data for this glyph.
 		// g.X is in fixed.Int26_6 — shift >> 6 for device pixels, divide by scale for Dp.
@@ -537,7 +548,7 @@ func (r *Renderer) drawWrappedText(gtx layout.Context, str string, reg Region, w
 			line = line[:0]
 			if g.Flags&text.FlagLineBreak != 0 {
 				lineCount++
-				layout.VisualLineStarts = append(layout.VisualLineStarts,byteOffset)
+				layout.VisualLineStarts = append(layout.VisualLineStarts, byteOffset)
 			}
 		}
 	}