cli: a delta row wears its block's wash, not one of its own

Selecting a delta broke the band: the adornment row took a segment of its own
and the message it explains went dark, which reads as having left the message.
The wash is asked block by block now, so the block stays lifted whole and the
snake's head is the only thing that moves.

Author: gluck

internal/cli/adornment_pty_test.go

@@ -214,9 +214,16 @@ func adornRowsWalk(t *testing.T, p *adornPane) {
 	if !wash[p.only(t, rows, adornAsk)] {
 		t.Errorf("^P past the first row did not select the parent block\n%s", p.dump())
 	}
+	// THE ADORNMENT IS PART OF THE BLOCK, so the block's wash covers its rows
+	// whether the cursor is on the block or inside its list. What changes is
+	// where the head sits, and nothing else.
 	for _, key := range adornAskKeys {
-		if i := p.only(t, rows, key); wash[i] {
-			t.Errorf("the parent's wash reached delta row %q: %q", key, clean(rows[i]))
+		i := p.only(t, rows, key)
+		if !wash[i] {
+			t.Errorf("the block's wash stopped short of its delta row %q: %q", key, clean(rows[i]))
+		}
+		if strings.Contains(rows[i], deltaGlyph) {
+			t.Errorf("the head stayed on delta row %q with the block selected: %q", key, clean(rows[i]))
 		}
 	}
 }
@@ -305,20 +312,24 @@ func adornBodyAndList(t *testing.T, p *adornPane) {
 
 // adornFocus asserts the cursor stands on the row holding key: washed, with
 // the snake's head in its spine column, and alone in both.
+// adornFocus: the cursor stands on key's row. THE HEAD SAYS WHICH ROW, THE
+// WASH SAYS WHICH BLOCK: a delta row is part of the block it explains, so the
+// block stays lifted whole and only the Δ moves (Gluck, 2026-09-16: "the
+// background highlight of the parent should be retained").
 func adornFocus(t *testing.T, p *adornPane, key, what string) {
 	t.Helper()
 	wash, plain := p.paneWashed(), p.rows()
 	i := p.only(t, plain, key)
 	if !wash[i] {
-		t.Errorf("%s: the row for %q is not the focus\n%s", what, key, p.dump())
+		t.Errorf("%s: the row for %q is not washed with its block\n%s", what, key, p.dump())
 		return
 	}
 	if !strings.Contains(plain[i], deltaGlyph) {
 		t.Errorf("%s: the row for %q carries no head: %q", what, key, plain[i])
 	}
 	for j, row := range plain {
-		if j != i && wash[j] && strings.Contains(row, "->") {
-			t.Errorf("%s: row %d is a washed delta row too: %q", what, j, row)
+		if j != i && strings.Contains(row, "->") && strings.Contains(row, deltaGlyph) {
+			t.Errorf("%s: row %d carries a second head: %q", what, j, row)
 		}
 	}
 }

internal/cli/transcript_index.go

@@ -488,15 +488,22 @@ func (t *transcript) selectionSpan() selectionSpan {
 	return selectionSpan{active: true, lo: lo, hi: hi, focus: t.selection.focus.nodeRef}
 }
 
+// THE WASH IS THE BLOCK'S, NEVER A DELTA ROW'S OWN. An adornment row is part
+// of the block it explains, so selecting one lifts that whole block and the
+// snake's head (the Δ) says which row the cursor stands on. A band that broke
+// to highlight one adornment row told the reader they had left the message,
+// which they had not.
 func (s selectionSpan) mark(ref nodeRef) selectionMark {
 	if !s.active {
 		return selectionMark{}
 	}
-	p := selectionPoint{nodeRef: ref}
-	if pointLess(p, s.lo) || pointLess(s.hi, p) {
+	block := blockOf(ref)
+	p := selectionPoint{nodeRef: block}
+	if pointLess(p, selectionPoint{nodeRef: blockOf(s.lo.nodeRef)}) ||
+		pointLess(selectionPoint{nodeRef: blockOf(s.hi.nodeRef)}, p) {
 		return selectionMark{}
 	}
-	return selectionMark{selected: true, active: ref == s.focus}
+	return selectionMark{selected: true, active: block == blockOf(s.focus)}
 }
 
 // nodeSpanOf reports the line range a node occupies, derived from the index