Give arm its head as written, and spell readRow's selector from it

format.go

@@ -308,6 +308,7 @@ func checkNoRepeatedArm(body string, names []string) error {
 type arm struct {
 	spelling    string // as written, for messages
 	head        string
+	writtenHead string // head as written, sigil included
 	tail        []string
 	levels      []string // the path at each level the tail passes through, the head first
 	path        string   // head and tail, the one path every way of writing this read shares
@@ -325,21 +326,23 @@ func splitArm(name string, refs map[string]refBinding) arm {
 			}
 			return arm{spelling: name, head: head, path: head}
 		}
-		return pathArm(name, b.head, b.tail)
+		sigil, rest, _ := refShape(name) // linkRefs proved it
+		written, _ := splitPath(rest)
+		return pathArm(name, b.head, sigil+joinSegments(written[:len(written)-len(b.tail)]), b.tail)
 	}
 	segs, err := splitPath(name)
 	if err != nil || len(segs) == 1 {
 		return arm{spelling: name, head: name, path: name}
 	}
-	return pathArm(name, segs[0], segs[1:])
+	return pathArm(name, segs[0], segs[0], segs[1:])
 }
 
-func pathArm(name, head string, segs []string) arm {
+func pathArm(name, head, writtenHead string, segs []string) arm {
 	levels := []string{head}
 	for i := 0; i < len(segs)-1; i++ {
 		levels = append(levels, head+"."+strings.Join(segs[:i+1], "."))
 	}
-	return arm{spelling: name, head: head, tail: segs, levels: levels, path: head + "." + strings.Join(segs, ".")}
+	return arm{spelling: name, head: head, writtenHead: writtenHead, tail: segs, levels: levels, path: head + "." + strings.Join(segs, ".")}
 }
 
 // checkSegments rejects an unfinished path: "{a.}" and "{a..b}" each have a

path.go

@@ -333,8 +333,7 @@ func (w *pathProbe) readRow(t *table, tail []string, r tableRoute) error {
 	case r.sel != "":
 		if w.a != nil {
 			walked := len(w.a.tail) - len(tail) + 1
-			written := w.a.spelling[:len(w.a.spelling)-len(joinSegments(w.a.tail))]
-			w.sels = append(w.sels, tableSel{t, written + joinSegments(w.a.tail[:walked])})
+			w.sels = append(w.sels, tableSel{t, joinSegments(append([]string{w.a.writtenHead}, w.a.tail[:walked]...))})
 		}
 		return w.pins.selectRow(t, r.sel)
 	case r.draw && w.a != nil:

todo.md

@@ -31,9 +31,6 @@ on 2026-09-29 a third time (Navigation 7.0, Locality 5.6, Shape 6.3, Self-suffic
 
 This round, in order:
 
-- Give `arm` its head as written, set where `splitArm` splits, and build
-  `pathProbe.readRow`'s selector spelling from it: six seats found the slice of
-  `arm.spelling` by `len(joinSegments(tail))` resting on an invariant nothing states.
 - Pick `disagreement`'s fix through a named `itemKind` comparison: six seats could not
   see that the kinds' declaration order is the rule.
 - Give `tableSite` one test for a cell, and have `traceRead` report no row outside a