wip

internal/app/cursorshift.go

@@ -67,6 +67,29 @@ func (cs *cursorShifter) clampCol(col int) int {
 	return col
 }
 
+// clampHostRow returns a host-coordinate row clamped to the viewport
+// rows mainTop..mainBottom. A child whose internal row state drifted
+// past the viewport (long-running claude / codex sessions) can issue a
+// CUP / HVP / VPA aimed at row hostRows; after the +rowOffset shift the
+// raw host target sits past the viewport bottom (the status row) or
+// above the viewport top (the tab bar). Without clamping the host
+// cursor lands on the chrome and the next printable wipes it. childRows
+// == 0 (uninitialised shifter, only seen in tests) disables clamping.
+func (cs *cursorShifter) clampHostRow(r int) int {
+	if cs.childRows <= 0 {
+		return r
+	}
+	minR := cs.rowOffset + 1
+	maxR := cs.rowOffset + cs.childRows
+	if r < minR {
+		return minR
+	}
+	if r > maxR {
+		return maxR
+	}
+	return r
+}
+
 // Shift consumes a chunk of PTY-master bytes, applies row offsets to
 // any complete CUP/HVP/VPA/DECSTBM sequences, and returns the rewritten
 // bytes. Partial sequences are buffered across calls so a CSI that
@@ -206,7 +229,7 @@ func (cs *cursorShifter) emitCSI() {
 			cs.pending.Write(cs.buf)
 			return
 		}
-		r += cs.rowOffset
+		r = cs.clampHostRow(r + cs.rowOffset)
 		c = cs.clampCol(c)
 		cs.pending.WriteString("\x1b[")
 		cs.pending.WriteString(strconv.Itoa(r))
@@ -226,13 +249,14 @@ func (cs *cursorShifter) emitCSI() {
 		cs.pending.WriteString(strconv.Itoa(c))
 		cs.pending.WriteByte(final)
 	case 'd':
-		// VPA: row.
+		// VPA: row. Clamp to the viewport so a child that drifted
+		// past its row count can't land the host cursor on the status row.
 		r, ok := parseOneParam(paramsRaw, 1)
 		if !ok {
 			cs.pending.Write(cs.buf)
 			return
 		}
-		r += cs.rowOffset
+		r = cs.clampHostRow(r + cs.rowOffset)
 		cs.pending.WriteString("\x1b[")
 		cs.pending.WriteString(strconv.Itoa(r))
 		cs.pending.WriteByte(final)