Have the draw fence query the read fold, deleting hasRead and its helpers

AGENTS.md

@@ -115,5 +115,4 @@ In [docs/decisions.md](docs/decisions.md):
 - The Swedish ids draw Skatteverket's test series
 - The US given names come from a mirror of the SSA file
 - `List` advertises direct descents only
-- Each entry point to `drawFence.hasRead` says what its caller gets
 - The four path walks are four loops

docs/decisions.md

@@ -834,12 +834,6 @@ import drops them by name rather than by a rank a regeneration would move.
 the set of every descent through a chain of five tables is every subsequence of it, and
 the direct chain is the one a reader can predict from the tables' parents.
 
-## Each entry point to `drawFence.hasRead` says what its caller gets
-
-2026-09-25, larv-review; approved 2026-09-25 by lilleman. Goal 2: a reader lands on
-`readsPath` or `splitsDraws` from its caller, so each doc states where that walk stops,
-though `hasRead` states the same stop rule. Valid while the two differ in where they stop.
-
 ## The four path walks are four loops
 
 2026-09-28, larv-review on systems-architect's finding; approved 2026-09-28 by lilleman.

drawfence.go

@@ -6,26 +6,34 @@ import (
 	"strings"
 )
 
-// drawFence fences each template of a scope as a render of its own, remembering which nodes read a
-// reference path.
+// drawFence fences each template of a scope as a render of its own, over one fold of what every
+// node reads.
 // docs/decisions.md#a-render-shares-one-reference-draw-per-category-per-group
 // docs/decisions.md#the-expansion-hold-and-the-renders-draws-are-two-fences
 type drawFence struct {
-	memo map[hasReadMemo]bool
+	fold *readFold
 }
 
-type hasReadMemo struct {
-	n           node
-	stopAtGroup bool
+func (f *drawFence) reads() *readFold {
+	if f.fold == nil {
+		f.fold = newReadFold()
+	}
+	return f.fold
 }
 
 // checkDrawGroup refuses a draw group that splits nothing: one whose render reads every reference
 // path inside a repeat or a nested draw group, which draw apart from it whatever it names.
 func (f *drawFence) checkDrawGroup(path string, n node) error {
-	if t, ok := n.(*template); ok && t.drawGroup != "" && !f.splitsDraws(t) {
-		return fmt.Errorf("%s: drawGroup %q splits nothing, since nothing it renders reads a reference path outside a repeat or a nested drawGroup; drop it", path, t.drawGroup)
+	t, ok := n.(*template)
+	if !ok || t.drawGroup == "" {
+		return nil
 	}
-	return nil
+	for _, r := range f.reads().rootReads(t) {
+		if r.at.group == "" && r.draws() {
+			return nil
+		}
+	}
+	return fmt.Errorf("%s: drawGroup %q splits nothing, since nothing it renders reads a reference path outside a repeat or a nested drawGroup; drop it", path, t.drawGroup)
 }
 
 func (f *drawFence) checkDraws(path string, n node) error {
@@ -33,10 +41,11 @@ func (f *drawFence) checkDraws(path string, n node) error {
 	if !ok {
 		return nil
 	}
-	if !f.readsPath(t) {
+	reads := f.reads().rootReads(t)
+	if !anyDraws(reads) {
 		return nil
 	}
-	if err := surveyRender(t).check(); err != nil {
+	if err := survey(reads, t.link.drawGroupKey).check(); err != nil {
 		return fmt.Errorf("%s: %w", path, err)
 	}
 	return nil
@@ -50,15 +59,11 @@ func (f *drawFence) checkRecordDraws(path string, n node) error {
 	if !ok || !t.isRecord {
 		return nil
 	}
-	columns := sortedNames(t.fields)
-	reads := false
-	for _, name := range columns {
-		reads = reads || f.readsPath(t.fields[name])
-	}
-	if !reads {
+	reads := f.reads().columnReads(t, sortedNames(t.fields))
+	if !anyDraws(reads) {
 		return nil
 	}
-	if err := surveyColumns(t, columns).check(); err != nil {
+	if err := survey(reads, t.link.drawGroupKey).check(); err != nil {
 		return fmt.Errorf("%s: %w", path, err)
 	}
 	return nil
@@ -100,41 +105,17 @@ func checkOwnFamily(path string, n node) error {
 	return nil
 }
 
-// readsPath reports whether rendering n reads a reference path, short of a repeat, which renders
-// over draws of its own.
-func (f *drawFence) readsPath(n node) bool { return f.hasRead(n, false) }
+// draws reports whether a read's draw is its group's to answer for: a path, or a table read whole,
+// whose row the group draws.
+func (r pathRead) draws() bool { return len(r.a.tail) > 0 || r.tr != nil }
 
-// splitsDraws reports whether rendering n reads a reference path that n's own draw group answers
-// for: one outside a repeat and outside a nested draw group, which hold their own draws.
-func (f *drawFence) splitsDraws(n node) bool { return f.hasRead(n, true) }
-
-// hasRead walks what rendering n renders for a reference path, stopping at a repeat — and at a nested
-// draw group when stopAtGroup — since each holds draws of its own.
-func (f *drawFence) hasRead(n node, stopAtGroup bool) bool {
-	k := hasReadMemo{n, stopAtGroup}
-	if r, done := f.memo[k]; done {
-		return r
-	}
-	r := false
-	for _, e := range renderEdges(n) {
-		if readsOnEdge(n, e) || (walksInto(e.to, stopAtGroup) && f.hasRead(e.to, stopAtGroup)) {
-			r = true
-			break
+func anyDraws(reads []pathRead) bool {
+	for _, r := range reads {
+		if r.draws() {
+			return true
 		}
 	}
-	if f.memo == nil {
-		f.memo = map[hasReadMemo]bool{}
-	}
-	f.memo[k] = r
-	return r
-}
-
-func readsOnEdge(n node, e renderEdge) bool {
-	return e.readsRef() && (len(e.read.tail) > 0 || readsTable(n, e.read))
-}
-
-func walksInto(to node, stopAtGroup bool) bool {
-	return !repeats(to) && !(stopAtGroup && grouped(to))
+	return false
 }
 
 func repeats(n node) bool {
@@ -142,22 +123,6 @@ func repeats(n node) bool {
 	return isTemplate && t.repeat > 1
 }
 
-func grouped(n node) bool {
-	t, isTemplate := n.(*template)
-	return isTemplate && t.link.drawGroupKey != ""
-}
-
-// readsTable reports whether a reference of n names a table, whose draw the render's
-// group answers for even when read whole.
-func readsTable(n node, a arm) bool {
-	t, isTemplate := n.(*template)
-	if !isTemplate {
-		return false
-	}
-	_, isTable := t.head(a.head).(*table)
-	return isTable
-}
-
 // check refuses what one draw per reference path cannot answer for: a read selecting a row its route
 // pinned another of, a read of a level beside a path another read takes into it, and two reads of one
 // table family that select different rows.

todo.md

@@ -36,9 +36,6 @@ on 2026-09-29 a fifth time (Navigation 6.9, Locality 5.2, Shape 6.1, Self-suffic
 
 This round, in order:
 
-- Have `checkDrawGroup`, `checkDraws` and `checkRecordDraws` query the fold, deleting
-  `drawFence.hasRead`, its helpers and the decision "Each entry point to
-  `drawFence.hasRead` says what its caller gets".
 - Move the fold to `reads.go` and the verdicts to `drawfence.go`, deleting
   `readsurvey.go`; name a read's context its `group`, `route` and `branches`, deleting
   `surveyAt`, and let the README's Layout and `doc.go` follow.