feat(tui): composer soft-wrap, alt+backspace, bracketed paste, borderless input

- editorLines now soft-wraps long logical lines at the box width (caret tracked
  across wrapped rows) instead of overflowing/truncating
- alt+backspace deletes the word before the cursor (deleteWordBack)
- handle tea.PasteMsg so bracketed paste (Ctrl+V / Ctrl+Shift+V / right-click)
  drops clipboard text into the focused composer; was silently dropped
- render the composer (in-session + launcher) borderless: top rule + flush text,
  no side borders or trailing padding, so a terminal drag-copy yields just the
  typed text instead of box chrome and whitespace

apps/tui-go/internal/app/view.go

@@ -446,16 +446,18 @@ func (m Model) renderLauncher(w, h int) string {
 // box scrolls to keep the cursor's tail in view.
 const maxInputLines = 6
 
-// editorLines renders the input buffer as styled display lines with the caret at the cursor,
-// so multi-line input (Ctrl+J / Alt+Enter) shows across rows. Tabs are flattened to a space.
-func (m Model) editorLines() []string {
+// editorLines renders the input buffer as styled display lines with the caret at the cursor.
+// Explicit newlines (Ctrl+J / Alt+Enter) break rows; a logical line wider than wrapW soft-wraps
+// onto continuation rows so long input never overflows the box. Tabs are flattened to a space.
+func (m Model) editorLines(wrapW int) []string {
 	t := m.theme
-	caret := ""
+	if wrapW < 1 {
+		wrapW = 1
+	}
 	// Only the focused composer (no modal over it) owns the live cursor; an open
 	// overlay keeps editMode==Insert but draws its own filter caret instead.
-	if m.editMode == ModeInsert && m.overlay == OverlayNone {
-		caret = lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Render(cursorMarker)
-	}
+	showCaret := m.editMode == ModeInsert && m.overlay == OverlayNone
+
 	buf := m.inputBuffer
 	cur := m.inputCursor
 	if cur > len(buf) {
@@ -464,16 +466,46 @@ func (m Model) editorLines() []string {
 	if cur < 0 {
 		cur = 0
 	}
-	style := func(s string) string { return t.span(strings.ReplaceAll(s, "\t", " "), t.P.FgStrong) }
-	before := strings.Split(buf[:cur], "\n")
-	after := strings.Split(buf[cur:], "\n")
-	var lines []string
-	for _, ln := range before[:len(before)-1] {
-		lines = append(lines, style(ln))
+	curRune := len([]rune(buf[:cur]))
+
+	// First pass: fold the buffer into plain display rows (rune-count wrap), tracking which
+	// row/column the cursor lands on so the caret marker can be slotted back in afterwards.
+	runes := []rune(buf)
+	var rowsRunes [][]rune
+	var row []rune
+	caretRow, caretCol := 0, 0
+	push := func() { rowsRunes = append(rowsRunes, row); row = nil }
+	for i := 0; i <= len(runes); i++ {
+		if i == curRune {
+			caretRow, caretCol = len(rowsRunes), len(row)
+		}
+		if i == len(runes) {
+			break
+		}
+		if runes[i] == '\n' {
+			push()
+			continue
+		}
+		row = append(row, runes[i])
+		if len(row) >= wrapW {
+			push()
+		}
 	}
-	lines = append(lines, style(before[len(before)-1])+caret+style(after[0]))
-	for _, ln := range after[1:] {
-		lines = append(lines, style(ln))
+	push()
+
+	style := func(s []rune) string { return t.span(strings.ReplaceAll(string(s), "\t", " "), t.P.FgStrong) }
+	caret := ""
+	if showCaret {
+		caret = lipgloss.NewStyle().Foreground(t.P.Accent).Background(t.P.Bg).Render(cursorMarker)
+	}
+	lines := make([]string, len(rowsRunes))
+	for i, r := range rowsRunes {
+		if showCaret && i == caretRow {
+			c := min(caretCol, len(r))
+			lines[i] = style(r[:c]) + caret + style(r[c:])
+		} else {
+			lines[i] = style(r)
+		}
 	}
 	if len(lines) > maxInputLines {
 		lines = lines[len(lines)-maxInputLines:]
@@ -492,7 +524,7 @@ func (m Model) launcherInput(w int) string {
 	if m.inputBuffer == "" && !insert {
 		content = []string{prompt + t.span("Ask anything…", t.P.Faint)}
 	} else {
-		for i, ln := range m.editorLines() {
+		for i, ln := range m.editorLines(w - 2) {
 			if i == 0 {
 				content = append(content, prompt+ln)
 			} else {
@@ -500,7 +532,17 @@ func (m Model) launcherInput(w int) string {
 			}
 		}
 	}
-	box := t.box("", content, w, len(content)+2, insert)
+	// Borderless (see renderInput): top rule + flush text, so a terminal copy is just the prompt.
+	ruleColor := t.P.Border
+	if insert {
+		ruleColor = t.P.BorderHi
+	}
+	rule := lipgloss.NewStyle().Foreground(ruleColor).Background(t.P.Bg).Render(strings.Repeat("─", w))
+	boxLines := append([]string{rule}, content...)
+	for i, ln := range boxLines {
+		boxLines[i] = ansi.Truncate(ln, w, "")
+	}
+	box := strings.Join(boxLines, "\n")
 
 	wf := lipgloss.NewStyle().Foreground(t.P.Accent2).Background(t.P.Bg).Render(m.launcherWfName())
 	leftSub := "  " + wf + t.span(" · ", t.P.Faint) + t.span(m.currentModel, t.P.Faint)
@@ -611,7 +653,7 @@ func (m Model) renderInput() string {
 	case m.inputBuffer == "":
 		content = []string{caret + t.span(placeholder, t.P.Faint)}
 	default:
-		content = m.editorLines()
+		content = m.editorLines(m.width)
 	}
 
 	// status sub-line: <session/none> · <uuid> · <mode>
@@ -637,18 +679,30 @@ func (m Model) renderInput() string {
 	sub += t.span(" · ", t.P.Faint) +
 		t.span(mode, t.P.Dim)
 
-	body := append(content, sub)
-	return t.box("", body, m.width, len(body)+2, insert)
+	// Borderless composer: a faint top rule for separation, then the text lines flush-left with
+	// no side borders and no right-padding. A bordered/filled box copies its `│` chrome and
+	// trailing whitespace when terminal-selected; this keeps a drag-copy to just the typed text.
+	ruleColor := t.P.Border
+	if insert {
+		ruleColor = t.P.BorderHi
+	}
+	rule := lipgloss.NewStyle().Foreground(ruleColor).Background(t.P.Bg).Render(strings.Repeat("─", m.width))
+	lines := append([]string{rule}, content...)
+	lines = append(lines, sub)
+	for i, ln := range lines {
+		lines[i] = ansi.Truncate(ln, m.width, "")
+	}
+	return strings.Join(lines, "\n")
 }
 
 // inputBarHeight is the bottom input bar's current height (it grows with multi-line input):
-// content lines (capped at maxInputLines) + the status sub-line + 2 borders.
+// top rule + content lines (capped at maxInputLines) + the status sub-line.
 func (m Model) inputBarHeight() int {
 	n := 1
 	if m.inputBuffer != "" {
-		n = len(m.editorLines())
+		n = len(m.editorLines(m.width))
 	}
-	return n + 1 + 2
+	return n + 2
 }
 
 // --- body row builders ---