Answer architecture round 3: walk a table's row node in the cycle check, record where the read-once spelling meets an inline refusal, and cite goal 5.2 for a path tag drawing afresh

docs/decisions.md

@@ -298,8 +298,8 @@ not agree on one among themselves; each must only hold that type.
 
 The fields an embedded struct promotes are the struct's own — `e.First`, as
 `encoding/json` and SQL mappers read them — so they are columns of its record and share
-its names: one tag may bind `{/person as p}{p.first}` and another read `{p.sex}`, while a
-path tag draws afresh as `{/path}` does (goal 4.1); a tagged field that another field hides is refused, not dropped. A named
+its names: one tag may bind `{/person as p}{p.first}` and another read `{p.sex}` (goal 4.1),
+while a path tag draws afresh as `{/path}` does (goal 5.2); a tagged field that another field hides is refused, not dropped. A named
 struct field is another entity and a record of its own. `fake:"-"` leaves a struct
 field, embedded or named, unfilled, so no name may be `-`; a pointer back to a struct
 already being filled is left alone, since filling it would never end. `New` cannot see a

graph.go

@@ -174,6 +174,9 @@ func checkNoCycles(s nodeScope) error {
 	inScope := map[node]bool{}
 	_ = s(func(_ string, n node) error {
 		inScope[n] = true
+		if t, isTable := n.(*table); isTable {
+			inScope[t.rowNode] = true // a selector lands on it, and contained lists it nowhere
+		}
 		return nil
 	})
 	color := map[node]int{}

namefence.go

@@ -58,7 +58,9 @@ func rendersInside(nodes []node, t *template) bool {
 }
 
 // checkUses refuses a binding read once at a spot the bound spelling can stand: that spelling
-// draws the same way without the name. A field stands only beside its binding.
+// draws the same way without the name. A field stands only beside its binding. Where the spelling
+// would be a CLI argument or tag of one reference alone, that entry point's own refusal then
+// names the bare path.
 func (b *nameBinding) checkUses() error {
 	r := b.uses[0]
 	if len(b.uses) > 1 || r.nested || b.bindsField() && r.in != b.binder {

reference_test.go

@@ -339,3 +339,14 @@ func TestSlashAfterAReferenceSigilIsRejected(t *testing.T) {
 		}
 	}
 }
+
+func TestACycleThroughASelectedRowIsRefused(t *testing.T) {
+	_, err := New(WithoutShippedData(), WithDataPath(writeFiles(t, map[string]string{
+		"x.json": `{"format":"{v} {/y}","rows":"x.tsv","key":"code"}`,
+		"x.tsv":  "code\tv\n1\ta\n2\tb\n",
+		"y.json": `"{/x[1]}"`,
+	})))
+	if err == nil || !strings.Contains(err.Error(), "cycle") {
+		t.Fatalf("New = %v, want the cycle through x[1] refused", err)
+	}
+}