feat(verifier): select the candidate label source

Candidates takes the label source as an argument rather than storing it, which
is what keeps the asymmetry structural: the seeded picker selects by index and
never calls Candidates, so the mode cannot reach it. That asymmetry is
load-bearing, because it makes the two seeded cells of the factorial a
manipulation check with identical draw streams.

The identifier ladder deliberately has no text rung. A fallback that reached
for text would silently turn one arm back into the other.

Claude-Session: https://claude.ai/code/session_01A5KmftdEJ49A9z5mF5ESrX

internal/verifier/llm.go

@@ -115,7 +115,8 @@ type ActionCandidate struct {
 	// Description is the rendered action shown to the model and echoed back as
 	// chosen_action, e.g. `Tap "Add credit"`. Dedup keys on it, so it is unique.
 	Description string
-	// Label is the visible-text target label (empty for gestures).
+	// Label is the target label the selected LabelSource named (empty for
+	// gestures).
 	Label string
 	// Weight is the effective selection weight as a percentage (1..100),
 	// meaningful only when Weighted is true (the tree used `weighted`).
@@ -142,6 +143,19 @@ type ActionCandidate struct {
 // enough to render on one numbered line.
 const maxLabelRunes = 40
 
+// The label sources a candidate's target can be named by. This is the
+// observation channel the model reads, and nothing else: the seeded picker
+// selects by index and never asks for a label, so the two seeded cells of a
+// labelling factorial draw the identical stream.
+const (
+	// LabelSourceVisibleText names a control by what a user would read. It is
+	// the default, and the channel every run so far was produced with.
+	LabelSourceVisibleText = "visible-text"
+	// LabelSourceResourceID names a control by the identifier the app assigned
+	// it, which no user ever sees.
+	LabelSourceResourceID = "resource-id"
+)
+
 // Candidates enumerates every action the spec's weighted actionsRoot yields at
 // the current step, each tagged with a plainly-worded description and its
 // effective weight, for the LLM generator to pick one number from. It walks the
@@ -149,7 +163,11 @@ const maxLabelRunes = 40
 // selection probability), authored actions()/whenRoute leaves are called once
 // for their concrete actions, and builtin verbs come straight from the picker's
 // own enumeration. Identical descriptions dedup, summing weight.
-func (v *Verifier) Candidates() []ActionCandidate {
+//
+// labelSource selects the channel each target is named by. An unrecognized
+// value (including the zero value) names targets by visible text; the CLI
+// rejects an unknown mode before a run starts, so only a test reaches that.
+func (v *Verifier) Candidates(labelSource string) []ActionCandidate {
 	if v.lastTree == nil {
 		return nil
 	}
@@ -157,9 +175,9 @@ func (v *Verifier) Candidates() []ActionCandidate {
 	if root == nil || goja.IsUndefined(root) || goja.IsNull(root) {
 		return nil
 	}
-	nodeIndex := buildNodeIndex(v.lastTree)
+	labels := labelContext{nodeIndex: buildNodeIndex(v.lastTree), source: labelSource}
 	var raw []ActionCandidate
-	v.collectNode(root, 1.0, false, nodeIndex, &raw)
+	v.collectNode(root, 1.0, false, labels, &raw)
 	return finalizeCandidates(raw)
 }
 
@@ -167,7 +185,7 @@ func (v *Verifier) Candidates() []ActionCandidate {
 // accumulated probability the seeded picker reaches this node; weighted records
 // whether any weighted node lies on the path (so weights are shown only when the
 // spec actually declared them).
-func (v *Verifier) collectNode(node goja.Value, prob float64, weighted bool, nodeIndex map[*hierarchy.Element]*hierarchy.Node, out *[]ActionCandidate) {
+func (v *Verifier) collectNode(node goja.Value, prob float64, weighted bool, labels labelContext, out *[]ActionCandidate) {
 	object := node.ToObject(v.runtime)
 	if object == nil {
 		return
@@ -178,13 +196,13 @@ func (v *Verifier) collectNode(node goja.Value, prob float64, weighted bool, nod
 	}
 	switch kind.String() {
 	case "weighted":
-		v.collectWeighted(object, prob, nodeIndex, out)
+		v.collectWeighted(object, prob, labels, out)
 	case "actions":
-		v.collectActions(object, prob, weighted, nodeIndex, out)
+		v.collectActions(object, prob, weighted, labels, out)
 	case "builtin":
 		verb := object.Get("verb")
 		if verb != nil && !goja.IsUndefined(verb) {
-			v.collectBuiltin(verb.String(), prob, weighted, nodeIndex, out)
+			v.collectBuiltin(verb.String(), prob, weighted, labels, out)
 		}
 	case "llm":
 		// The llm marker is the generator, not part of the candidate tree.
@@ -194,7 +212,7 @@ func (v *Verifier) collectNode(node goja.Value, prob float64, weighted bool, nod
 // collectWeighted recurses each branch, splitting the incoming probability by
 // the branch weight over the sibling total (matching the seeded picker's single
 // weighted draw).
-func (v *Verifier) collectWeighted(object *goja.Object, prob float64, nodeIndex map[*hierarchy.Element]*hierarchy.Node, out *[]ActionCandidate) {
+func (v *Verifier) collectWeighted(object *goja.Object, prob float64, labels labelContext, out *[]ActionCandidate) {
 	branches := object.Get("branches")
 	if branches == nil {
 		return
@@ -228,7 +246,7 @@ func (v *Verifier) collectWeighted(object *goja.Object, prob float64, nodeIndex
 		if children[i] == nil {
 			continue
 		}
-		v.collectNode(children[i], prob*weights[i]/total, true, nodeIndex, out)
+		v.collectNode(children[i], prob*weights[i]/total, true, labels, out)
 	}
 }
 
@@ -236,7 +254,7 @@ func (v *Verifier) collectWeighted(object *goja.Object, prob float64, nodeIndex
 // and, off-route, returns []), turning each concrete descriptor into a
 // candidate. It runs OUTSIDE the picker's rng scope, so from(...).generate()
 // draws nothing and no seed advances.
-func (v *Verifier) collectActions(object *goja.Object, prob float64, weighted bool, nodeIndex map[*hierarchy.Element]*hierarchy.Node, out *[]ActionCandidate) {
+func (v *Verifier) collectActions(object *goja.Object, prob float64, weighted bool, labels labelContext, out *[]ActionCandidate) {
 	generate, ok := goja.AssertFunction(object.Get("generate"))
 	if !ok {
 		return
@@ -251,7 +269,7 @@ func (v *Verifier) collectActions(object *goja.Object, prob float64, weighted bo
 	}
 	length := int(array.Get("length").ToInteger())
 	for i := range length {
-		candidate, ok := v.candidateFromDescriptor(array.Get(strconv.Itoa(i)), nodeIndex)
+		candidate, ok := v.candidateFromDescriptor(array.Get(strconv.Itoa(i)), labels)
 		if !ok {
 			continue
 		}
@@ -263,8 +281,8 @@ func (v *Verifier) collectActions(object *goja.Object, prob float64, weighted bo
 
 // candidateFromDescriptor lowers one authored ActionDescriptor (as a goja
 // object) into a ready-to-run candidate, resolving the target's coordinates,
-// selector, and visible-text label. Actions on a disabled control are dropped.
-func (v *Verifier) candidateFromDescriptor(value goja.Value, nodeIndex map[*hierarchy.Element]*hierarchy.Node) (ActionCandidate, bool) {
+// selector, and label. Actions on a disabled control are dropped.
+func (v *Verifier) candidateFromDescriptor(value goja.Value, labels labelContext) (ActionCandidate, bool) {
 	object := value.ToObject(v.runtime)
 	if object == nil {
 		return ActionCandidate{}, false
@@ -276,7 +294,7 @@ func (v *Verifier) candidateFromDescriptor(value goja.Value, nodeIndex map[*hier
 	kind := ActionKind(kindValue.String())
 	switch kind {
 	case ActionKindTap, ActionKindDoubleTap, ActionKindLongPress:
-		target := v.resolveTarget(object.Get("on"), nodeIndex)
+		target := v.resolveTarget(object.Get("on"), labels)
 		if target.disabled {
 			return ActionCandidate{}, false
 		}
@@ -286,7 +304,7 @@ func (v *Verifier) candidateFromDescriptor(value goja.Value, nodeIndex map[*hier
 			Action: Action{Kind: kind, On: target.selector, X: target.x, Y: target.y},
 		}, true
 	case ActionKindInputText:
-		target := v.resolveTarget(object.Get("into"), nodeIndex)
+		target := v.resolveTarget(object.Get("into"), labels)
 		if target.disabled {
 			return ActionCandidate{}, false
 		}
@@ -298,7 +316,7 @@ func (v *Verifier) candidateFromDescriptor(value goja.Value, nodeIndex map[*hier
 			Action:    Action{Kind: kind, On: target.selector, X: target.x, Y: target.y, Text: text},
 		}, true
 	case ActionKindScroll:
-		target := v.resolveTarget(object.Get("in"), nodeIndex)
+		target := v.resolveTarget(object.Get("in"), labels)
 		direction := stringField(object, "direction")
 		if direction == "" {
 			direction = "down"
@@ -309,8 +327,8 @@ func (v *Verifier) candidateFromDescriptor(value goja.Value, nodeIndex map[*hier
 			Action:    Action{Kind: kind, On: target.selector, Direction: direction},
 		}, true
 	case ActionKindSwipe:
-		from := v.resolveTarget(object.Get("from"), nodeIndex)
-		to := v.resolveTarget(object.Get("to"), nodeIndex)
+		from := v.resolveTarget(object.Get("from"), labels)
+		to := v.resolveTarget(object.Get("to"), labels)
 		return ActionCandidate{
 			Kind: kind,
 			Action: Action{
@@ -343,14 +361,14 @@ type resolvedTarget struct {
 }
 
 // resolveTarget reads an authored action's target. Ax element handles carry
-// x/y/__sanderlingSelector plus their own text; a bare selector string resolves
-// against the current tree; a point carries geometry only.
-func (v *Verifier) resolveTarget(value goja.Value, nodeIndex map[*hierarchy.Element]*hierarchy.Node) resolvedTarget {
+// x/y/__sanderlingSelector plus their own text and id; a bare selector string
+// resolves against the current tree; a point carries geometry only.
+func (v *Verifier) resolveTarget(value goja.Value, labels labelContext) resolvedTarget {
 	if value == nil || goja.IsUndefined(value) || goja.IsNull(value) {
 		return resolvedTarget{}
 	}
 	if selector, ok := value.Export().(string); ok {
-		return v.targetFromSelector(selector, nodeIndex)
+		return v.targetFromSelector(selector, labels)
 	}
 	object := value.ToObject(v.runtime)
 	if object == nil {
@@ -366,25 +384,25 @@ func (v *Verifier) resolveTarget(value goja.Value, nodeIndex map[*hierarchy.Elem
 		selector: selector,
 	}
 	if element := v.findBySelector(selector); element != nil {
-		target.label = visibleLabel(element, nodeIndex)
+		target.label = labels.label(element)
 		target.inputType = inputTypeHint(element)
 		target.disabled = !element.Enabled && hasEnabled(element)
 	}
 	if target.label == "" {
-		target.label = truncateLabel(stringField(object, "text"))
+		target.label = truncateLabel(stringField(object, labels.handleField()))
 	}
 	return target
 }
 
 // targetFromSelector resolves a bare selector-string target against the tree.
-func (v *Verifier) targetFromSelector(selector string, nodeIndex map[*hierarchy.Element]*hierarchy.Node) resolvedTarget {
+func (v *Verifier) targetFromSelector(selector string, labels labelContext) resolvedTarget {
 	target := resolvedTarget{selector: selector}
 	element := v.findBySelector(selector)
 	if element == nil {
 		return target
 	}
 	target.x, target.y = element.Bounds.Center()
-	target.label = visibleLabel(element, nodeIndex)
+	target.label = labels.label(element)
 	target.inputType = inputTypeHint(element)
 	target.disabled = !element.Enabled && hasEnabled(element)
 	return target
@@ -403,7 +421,7 @@ func (v *Verifier) findBySelector(selector string) *hierarchy.Element {
 // the two policies select over one action space and cannot drift apart. Each
 // entry's action arrives on the wire contract DecodeAction already reads, so a
 // chosen candidate executes the action the seeded draw would have executed.
-func (v *Verifier) collectBuiltin(verb string, prob float64, weighted bool, nodeIndex map[*hierarchy.Element]*hierarchy.Node, out *[]ActionCandidate) {
+func (v *Verifier) collectBuiltin(verb string, prob float64, weighted bool, labels labelContext, out *[]ActionCandidate) {
 	entries, err := v.enumerateBuiltin(verb)
 	if err != nil {
 		return
@@ -422,7 +440,7 @@ func (v *Verifier) collectBuiltin(verb string, prob float64, weighted bool, node
 		}
 		if entry.targetIndex >= 0 && entry.targetIndex < len(targets) {
 			element := targets[entry.targetIndex].element
-			candidate.Label = visibleLabel(element, nodeIndex)
+			candidate.Label = labels.label(element)
 			candidate.InputType = inputTypeHint(element)
 		}
 		*out = append(*out, candidate)
@@ -558,6 +576,46 @@ func buildNodeIndex(tree *hierarchy.Tree) map[*hierarchy.Element]*hierarchy.Node
 	return index
 }
 
+// labelContext carries what naming a candidate's target takes: the node index
+// descendant text is borrowed through, and the channel the name comes from.
+type labelContext struct {
+	nodeIndex map[*hierarchy.Element]*hierarchy.Node
+	source    string
+}
+
+func (l labelContext) label(element *hierarchy.Element) string {
+	if l.source == LabelSourceResourceID {
+		return resourceIdentifierLabel(element)
+	}
+	return visibleLabel(element, l.nodeIndex)
+}
+
+// handleField is the ax-element handle field a label falls back to when the
+// target's selector no longer resolves against the current tree. Reading the
+// handle's text there would leak visible text into an identifier-labelled run,
+// which is the one thing that arm must not see.
+func (l labelContext) handleField() string {
+	if l.source == LabelSourceResourceID {
+		return "id"
+	}
+	return "text"
+}
+
+// resourceIdentifierLabel names a control by the identifier the app assigned it,
+// then by its class, then by a bare word. Every rung a user could read (text,
+// description, hint, descendant text) is deliberately absent: the point of this
+// channel is that the model sees no visible text at all, so a fallback that
+// reached for text would silently turn the arm back into the default one.
+func resourceIdentifierLabel(element *hierarchy.Element) string {
+	if element.ResourceID != "" {
+		return truncateLabel(element.ResourceID)
+	}
+	if element.Class != "" {
+		return element.Class
+	}
+	return "control"
+}
+
 // visibleLabel names a control by what a user would read: its own text, then
 // description, then a field hint, then text borrowed from its descendants (the
 // case that fixes empty-text Compose buttons whose word lives on a child), then

internal/verifier/llm_test.go

@@ -24,6 +24,23 @@ const enumTreeJSON = `{
   ]
 }`
 
+// labelChannelTreeJSON pulls the two label channels apart: every identifier
+// differs from the text a user reads, one control has a class but no identifier,
+// one has neither, and one has an identifier but nothing readable at all.
+const labelChannelTreeJSON = `{
+  "attributes": {"bounds": "[0,0,1080,2400]"},
+  "children": [
+    {"attributes": {"resource-id": "add_credit_button", "class": "android.widget.Button", "bounds": "[0,100,1080,200]"}, "clickable": true, "enabled": true, "children": [
+      {"attributes": {"text": "Add credit", "bounds": "[0,100,540,200]"}, "children": []}
+    ]},
+    {"attributes": {"class": "android.widget.CheckBox", "text": "Remember me", "bounds": "[0,250,1080,300]"}, "clickable": true, "enabled": true, "children": []},
+    {"attributes": {"class": "android.widget.CheckBox", "text": "Stay signed in", "bounds": "[0,300,1080,350]"}, "clickable": true, "enabled": true, "children": []},
+    {"attributes": {"text": "Sign in", "bounds": "[0,400,1080,450]"}, "clickable": true, "enabled": true, "children": []},
+    {"attributes": {"resource-id": "amount_field", "class": "EditText", "hintText": "Amount", "bounds": "[0,500,1080,600]"}, "enabled": true, "children": []},
+    {"attributes": {"resource-id": "silent_row", "bounds": "[0,650,1080,700]"}, "clickable": true, "enabled": true, "children": []}
+  ]
+}`
+
 // enumVerifier loads a spec whose actions root is the given plain-object graph
 // and stages the given tree, so Candidates walks a controlled action tree. The
 // spec is bundled with the goja runtime entry because the model arm reads the
@@ -56,7 +73,7 @@ func hasCandidate(candidates []ActionCandidate, description string) bool {
 
 func TestCandidatesLabelsControlsByVisibleText(t *testing.T) {
 	v := enumVerifier(t, "{kind:'builtin', verb:'taps'}", enumTreeJSON)
-	candidates := v.Candidates()
+	candidates := v.Candidates(LabelSourceVisibleText)
 
 	// The empty-text clickable wrapper is labeled by its child Text, NOT its
 	// resource-id.
@@ -79,9 +96,110 @@ func TestCandidatesLabelsControlsByVisibleText(t *testing.T) {
 	}
 }
 
+func TestCandidatesLabelsControlsByResourceIdentifier(t *testing.T) {
+	candidates := enumVerifier(t, "{kind:'builtin', verb:'taps'}", labelChannelTreeJSON).
+		Candidates(LabelSourceResourceID)
+
+	if !hasCandidate(candidates, `Tap "add_credit_button"`) {
+		t.Errorf("want the control named by its identifier, got %v", descriptions(candidates))
+	}
+	// Nothing a user could read may reach this channel, including through a
+	// fallback rung: an arm that sees the text is the other arm.
+	for _, readable := range []string{`Tap "Add credit"`, `Tap "Remember me"`, `Tap "Sign in"`} {
+		if hasCandidate(candidates, readable) {
+			t.Errorf("visible text leaked in as %s: %v", readable, descriptions(candidates))
+		}
+	}
+}
+
+func TestCandidatesIdentifierChannelFallsBackToClassThenBareControl(t *testing.T) {
+	candidates := enumVerifier(t, "{kind:'builtin', verb:'taps'}", labelChannelTreeJSON).
+		Candidates(LabelSourceResourceID)
+
+	if !hasCandidate(candidates, `Tap "android.widget.CheckBox"`) {
+		t.Errorf("a control with no identifier falls back to its class, got %v", descriptions(candidates))
+	}
+	if !hasCandidate(candidates, `Tap "control"`) {
+		t.Errorf("a control with neither identifier nor class falls back to a bare word, got %v",
+			descriptions(candidates))
+	}
+}
+
+// TestCandidatesIdentifierChannelMergesControlsItCannotTellApart pins the cost
+// of the channel rather than a defect in it: dedup keys on the rendered line, so
+// two identifier-less controls of one class arrive as ONE numbered entry and the
+// model can only reach the first. The list the identifier arm picks from is
+// therefore shorter than the text arm's on the same screen.
+func TestCandidatesIdentifierChannelMergesControlsItCannotTellApart(t *testing.T) {
+	text := enumVerifier(t, "{kind:'builtin', verb:'taps'}", labelChannelTreeJSON).
+		Candidates(LabelSourceVisibleText)
+	identifier := enumVerifier(t, "{kind:'builtin', verb:'taps'}", labelChannelTreeJSON).
+		Candidates(LabelSourceResourceID)
+
+	if count(text, `Tap "Remember me"`) != 1 || count(text, `Tap "Stay signed in"`) != 1 {
+		t.Fatalf("the text channel should address both checkboxes, got %v", descriptions(text))
+	}
+	if got := count(identifier, `Tap "android.widget.CheckBox"`); got != 1 {
+		t.Errorf("the two checkboxes should merge into one line, got %d: %v", got, descriptions(identifier))
+	}
+	if len(identifier) >= len(text) {
+		t.Errorf("identifier list (%d) should be shorter than the text list (%d): %v vs %v",
+			len(identifier), len(text), descriptions(identifier), descriptions(text))
+	}
+}
+
+// TestCandidatesVisibleTextFallsBackToTheIdentifier is where the two channels
+// agree: a control carrying nothing readable is named by its identifier in both,
+// so a screen built entirely from such controls is one cell, not two.
+func TestCandidatesVisibleTextFallsBackToTheIdentifier(t *testing.T) {
+	candidates := enumVerifier(t, "{kind:'builtin', verb:'taps'}", labelChannelTreeJSON).
+		Candidates(LabelSourceVisibleText)
+
+	if !hasCandidate(candidates, `Tap "silent_row"`) {
+		t.Errorf("a control with no readable text falls back to its identifier, got %v",
+			descriptions(candidates))
+	}
+}
+
+func TestCandidatesTypingLabelFollowsTheLabelSource(t *testing.T) {
+	text := enumVerifier(t, "{kind:'builtin', verb:'typing'}", labelChannelTreeJSON).
+		Candidates(LabelSourceVisibleText)
+	if !hasCandidate(text, `Type into "Amount" (number)`) {
+		t.Errorf("want the field named by its hint, got %v", descriptions(text))
+	}
+
+	identifier := enumVerifier(t, "{kind:'builtin', verb:'typing'}", labelChannelTreeJSON).
+		Candidates(LabelSourceResourceID)
+	if !hasCandidate(identifier, `Type into "amount_field" (number)`) {
+		t.Errorf("want the field named by its identifier, got %v", descriptions(identifier))
+	}
+}
+
+// TestLabelSourceChangesOnlyTheDescription is the claim the factorial rests on:
+// the channel renames the target and does nothing else, so a difference in
+// defect yield cannot come from the two arms executing different actions.
+func TestLabelSourceChangesOnlyTheDescription(t *testing.T) {
+	text := enumVerifier(t, "{kind:'builtin', verb:'taps'}", labelChannelTreeJSON).
+		Candidates(LabelSourceVisibleText)
+	identifier := enumVerifier(t, "{kind:'builtin', verb:'taps'}", labelChannelTreeJSON).
+		Candidates(LabelSourceResourceID)
+
+	readable, ok := findCandidate(text, `Tap "Add credit"`)
+	if !ok {
+		t.Fatalf("missing the text-labelled tap: %v", descriptions(text))
+	}
+	named, ok := findCandidate(identifier, `Tap "add_credit_button"`)
+	if !ok {
+		t.Fatalf("missing the identifier-labelled tap: %v", descriptions(identifier))
+	}
+	if readable.Action != named.Action {
+		t.Errorf("same control, different action:\n text=%+v\n   id=%+v", readable.Action, named.Action)
+	}
+}
+
 func TestCandidatesDropsDisabledControls(t *testing.T) {
 	v := enumVerifier(t, "{kind:'builtin', verb:'taps'}", enumTreeJSON)
-	for _, candidate := range v.Candidates() {
+	for _, candidate := range v.Candidates(LabelSourceVisibleText) {
 		if strings.Contains(candidate.Description, "Off") {
 			t.Errorf("disabled control surfaced as %q", candidate.Description)
 		}
@@ -90,7 +208,7 @@ func TestCandidatesDropsDisabledControls(t *testing.T) {
 
 func TestCandidatesTypingExposesInputType(t *testing.T) {
 	v := enumVerifier(t, "{kind:'builtin', verb:'typing'}", enumTreeJSON)
-	candidates := v.Candidates()
+	candidates := v.Candidates(LabelSourceVisibleText)
 	candidate, ok := findCandidate(candidates, `Type into "Amount" (number)`)
 	if !ok {
 		t.Fatalf("want typing candidate with input type, got %v", descriptions(candidates))
@@ -113,7 +231,7 @@ func TestCandidatesLabelsEditableFieldByHintNotTypedValue(t *testing.T) {
       ]
     }`
 	v := enumVerifier(t, "{kind:'builtin', verb:'typing'}", tree)
-	candidates := v.Candidates()
+	candidates := v.Candidates(LabelSourceVisibleText)
 	if hasCandidate(candidates, `Type into "99" (number)`) || hasCandidate(candidates, `Type into "99"`) {
 		t.Errorf("editable field labeled by its typed value: %v", descriptions(candidates))
 	}
@@ -126,7 +244,7 @@ func TestCandidatesKeepsGestureVerbsDistinct(t *testing.T) {
 	v := enumVerifier(t,
 		"{kind:'weighted', branches:[[1,{kind:'builtin',verb:'scrolls'}],[1,{kind:'builtin',verb:'swipes'}]]}",
 		enumTreeJSON)
-	candidates := v.Candidates()
+	candidates := v.Candidates(LabelSourceVisibleText)
 
 	// `scrolls` folds to one directional pair over the single scrollable
 	// container, which is what keeps the list short.
@@ -168,7 +286,7 @@ func TestCandidatesWeightsCombineAcrossPaths(t *testing.T) {
 	v := enumVerifier(t,
 		"{kind:'weighted', branches:[[1,{kind:'builtin',verb:'taps'}],[1,{kind:'builtin',verb:'taps'}]]}",
 		oneClickable)
-	candidates := v.Candidates()
+	candidates := v.Candidates(LabelSourceVisibleText)
 	if len(candidates) != 1 {
 		t.Fatalf("want one deduped candidate, got %v", descriptions(candidates))
 	}
@@ -185,7 +303,7 @@ func TestCandidatesWeightReflectsBranchShare(t *testing.T) {
 	v := enumVerifier(t,
 		"{kind:'weighted', branches:[[1,{kind:'builtin',verb:'taps'}],[3,{kind:'builtin',verb:'typing'}]]}",
 		enumTreeJSON)
-	candidates := v.Candidates()
+	candidates := v.Candidates(LabelSourceVisibleText)
 	tap, ok := findCandidate(candidates, `Tap "Sign in"`)
 	if !ok {
 		t.Fatalf("missing tap candidate: %v", descriptions(candidates))
@@ -204,7 +322,7 @@ func TestCandidatesWeightReflectsBranchShare(t *testing.T) {
 
 func TestCandidatesUnweightedTreeShowsNoWeight(t *testing.T) {
 	v := enumVerifier(t, "{kind:'builtin', verb:'taps'}", enumTreeJSON)
-	for _, candidate := range v.Candidates() {
+	for _, candidate := range v.Candidates(LabelSourceVisibleText) {
 		if candidate.Weighted || candidate.Weight != 0 {
 			t.Errorf("%q carries a weight despite no weighted node", candidate.Description)
 		}
@@ -218,7 +336,7 @@ func TestCandidatesCallsAuthoredLeafOnce(t *testing.T) {
       {kind:'InputText', into:'id:Amount', text:'42'}
     ]}`
 	v := enumVerifier(t, actions, enumTreeJSON)
-	candidates := v.Candidates()
+	candidates := v.Candidates(LabelSourceVisibleText)
 
 	// Authored Tap resolves its selector to the visible-text label.
 	if !hasCandidate(candidates, `Tap "Sign in"`) {
@@ -252,7 +370,7 @@ func TestCandidatesSurfaceAuthoredUntargetedActions(t *testing.T) {
       {kind:'PressKey', key:'back'},
       {kind:'Wait'}
     ]}`
-	candidates := enumVerifier(t, actions, enumTreeJSON).Candidates()
+	candidates := enumVerifier(t, actions, enumTreeJSON).Candidates(LabelSourceVisibleText)
 	for _, want := range []string{"Swipe from (10,600) to (10,100)", "Press back", "Wait"} {
 		if !hasCandidate(candidates, want) {
 			t.Errorf("authored %q missing: %v", want, descriptions(candidates))
@@ -262,7 +380,7 @@ func TestCandidatesSurfaceAuthoredUntargetedActions(t *testing.T) {
 
 func TestCandidatesOffRouteLeafYieldsNothing(t *testing.T) {
 	v := enumVerifier(t, "{kind:'actions', generate: () => []}", enumTreeJSON)
-	if got := v.Candidates(); len(got) != 0 {
+	if got := v.Candidates(LabelSourceVisibleText); len(got) != 0 {
 		t.Errorf("off-route leaf should yield no candidates, got %v", descriptions(got))
 	}
 }
@@ -280,7 +398,7 @@ func TestCandidatesSkipsCrossFadeFrames(t *testing.T) {
       ]
     }`
 	v := enumVerifier(t, "{kind:'builtin', verb:'taps'}", crossFade)
-	if got := v.Candidates(); len(got) != 0 {
+	if got := v.Candidates(LabelSourceVisibleText); len(got) != 0 {
 		t.Errorf("cross-fade frame should yield no candidates, got %v", descriptions(got))
 	}
 	// The seeded policy is skipped by the SAME guard, in the shared producer,
@@ -292,13 +410,13 @@ func TestCandidatesSkipsCrossFadeFrames(t *testing.T) {
 
 func TestCandidatesNilWithoutTreeOrActions(t *testing.T) {
 	withActions := newLoadedVerifier(t, "globalThis.actions = {kind:'builtin', verb:'taps'};")
-	if got := withActions.Candidates(); got != nil {
+	if got := withActions.Candidates(LabelSourceVisibleText); got != nil {
 		t.Errorf("Candidates with no tree = %v, want nil", got)
 	}
 	noActions := newLoadedVerifier(t, "globalThis.properties = {};")
 	tree, _ := hierarchy.Parse(enumTreeJSON)
 	noActions.lastTree = tree
-	if got := noActions.Candidates(); got != nil {
+	if got := noActions.Candidates(LabelSourceVisibleText); got != nil {
 		t.Errorf("Candidates with no actions root = %v, want nil", got)
 	}
 }

internal/verifier/policy_parity_test.go

@@ -62,7 +62,7 @@ func TestModelCandidateDescriptionsAreUniqueAndNamed(t *testing.T) {
 		t.Run(verb, func(t *testing.T) {
 			verifier := loadVerbSpec(t, verb)
 			seen := map[string]bool{}
-			for _, candidate := range verifier.Candidates() {
+			for _, candidate := range verifier.Candidates(LabelSourceVisibleText) {
 				if candidate.Description == "" {
 					t.Fatalf("%s produced a candidate with no description: %+v", verb, candidate.Action)
 				}
@@ -81,17 +81,64 @@ func TestModelCandidateDescriptionsAreUniqueAndNamed(t *testing.T) {
 // dropped, so the model could never navigate back or let the app settle.
 func TestModelIsOfferedTheUntargetedVerbs(t *testing.T) {
 	verifier := loadVerbSpec(t, "pressKeys")
-	if !hasCandidate(verifier.Candidates(), "Press back") {
+	if !hasCandidate(verifier.Candidates(LabelSourceVisibleText), "Press back") {
 		t.Errorf("pressKeys missing from the model's candidates: %v",
-			descriptions(verifier.Candidates()))
+			descriptions(verifier.Candidates(LabelSourceVisibleText)))
 	}
 	verifier = loadVerbSpec(t, "waitOnce")
-	if !hasCandidate(verifier.Candidates(), "Wait") {
+	if !hasCandidate(verifier.Candidates(LabelSourceVisibleText), "Wait") {
 		t.Errorf("waitOnce missing from the model's candidates: %v",
-			descriptions(verifier.Candidates()))
+			descriptions(verifier.Candidates(LabelSourceVisibleText)))
 	}
 }
 
+// TestSeededDrawStreamIgnoresLabelSource is the manipulation check the
+// labelling factorial needs: the seeded picker selects by index and never asks
+// for a label, so its draw stream must be bit-identical whichever channel the
+// model policy would have been given, and identical again to a run where the
+// candidate list was never enumerated at all. Any difference between two seeded
+// cells is then the application and the harness, not the factor.
+func TestSeededDrawStreamIgnoresLabelSource(t *testing.T) {
+	for _, verb := range policyVerbs {
+		t.Run(verb, func(t *testing.T) {
+			never := seededDrawStream(t, verb, "")
+			text := seededDrawStream(t, verb, LabelSourceVisibleText)
+			identifier := seededDrawStream(t, verb, LabelSourceResourceID)
+			if !slices.Equal(never, text) {
+				t.Errorf("enumerating visible-text candidates moved the seeded stream for %s", verb)
+			}
+			if !slices.Equal(never, identifier) {
+				t.Errorf("enumerating identifier candidates moved the seeded stream for %s", verb)
+			}
+		})
+	}
+}
+
+// seededDrawStream drives the seeded picker for the draw budget and returns
+// every action in order. An empty labelSource enumerates nothing; otherwise the
+// model's candidate list is built under that channel before each draw, which is
+// the only way the two could ever touch.
+func seededDrawStream(t *testing.T, verb, labelSource string) []string {
+	t.Helper()
+	verifier := loadVerbSpec(t, verb)
+	stream := make([]string, 0, seededDrawBudget)
+	for range seededDrawBudget {
+		if labelSource != "" {
+			verifier.Candidates(labelSource)
+		}
+		action, err := verifier.NextAction()
+		if errors.Is(err, ErrNoAction) {
+			stream = append(stream, "no action")
+			continue
+		}
+		if err != nil {
+			t.Fatalf("%s next action: %v", verb, err)
+		}
+		stream = append(stream, fmt.Sprintf("%+v", action))
+	}
+	return stream
+}
+
 // loadVerbSpec builds a verifier whose whole action tree is one builtin verb,
 // with policyTreeJSON pushed as the current state.
 func loadVerbSpec(t *testing.T, verb string) *Verifier {
@@ -128,7 +175,7 @@ func modelOfferedActions(t *testing.T, verb string) map[string]Action {
 	t.Helper()
 	verifier := loadVerbSpec(t, verb)
 	offered := map[string]Action{}
-	for _, candidate := range verifier.Candidates() {
+	for _, candidate := range verifier.Candidates(LabelSourceVisibleText) {
 		offered[actionIdentity(candidate.Action)] = candidate.Action
 	}
 	return offered