test(verifier): cross-runtime goja/node parity gate on the shared picker

internal/verifier/parity_test.go

@@ -0,0 +1,120 @@
+package verifier
+
+import (
+	"encoding/json"
+	"os/exec"
+	"path/filepath"
+	"strconv"
+	"testing"
+
+	"github.com/priyanshujain/sanderling/internal/hierarchy"
+)
+
+// TestCrossRuntimeParity is the W2 acceptance gate: given the SAME seed and the
+// SAME candidate state, the goja verifier and the node/web picker must emit a
+// BYTE-IDENTICAL action stream. Both engines run the SHARED pick.ts over the
+// SHARED Pcg, so this test fails the moment one runtime's JS number/bigint
+// behavior diverges from the other's.
+//
+// The goja side drives the real verifier.NextAction over a fixed hierarchy. The
+// candidate list that hierarchy yields is then handed verbatim to the node
+// harness so both engines index the same targets; the only variable left is the
+// JS engine.
+func TestCrossRuntimeParity(t *testing.T) {
+	const seed uint64 = 0x9e3779b97f4a7c15
+	const steps = 32
+
+	const treeJSON = `{
+	  "attributes": {"resource-id": "root", "bounds": "[0,0,400,800]"},
+	  "children": [
+	    {"attributes": {"resource-id": "alpha", "bounds": "[0,0,400,100]"}, "clickable": true, "enabled": true, "children": []},
+	    {"attributes": {"resource-id": "beta", "bounds": "[0,100,400,200]"}, "clickable": true, "enabled": true, "children": []},
+	    {"attributes": {"resource-id": "gamma", "bounds": "[0,200,400,300]"}, "clickable": true, "enabled": true, "children": []},
+	    {"attributes": {"resource-id": "delta", "bounds": "[0,300,400,400]"}, "clickable": true, "enabled": true, "children": []},
+	    {"attributes": {"resource-id": "epsilon", "bounds": "[0,400,400,500]"}, "clickable": true, "enabled": true, "children": []}
+	  ]
+	}`
+	tree, err := hierarchy.Parse(treeJSON)
+	if err != nil {
+		t.Fatalf("parse tree: %v", err)
+	}
+
+	verifier := newVerifier(t, WithSeed(seed))
+	loadActionSpec(t, verifier, `
+		import { taps } from "@sanderling/spec";
+		globalThis.actions = taps;
+	`)
+	if err := verifier.PushSnapshot(SnapshotInput{Tree: tree}); err != nil {
+		t.Fatalf("push snapshot: %v", err)
+	}
+
+	gojaStream := make([]Action, 0, steps)
+	for range steps {
+		action, err := verifier.NextAction()
+		if err != nil {
+			t.Fatalf("goja next action: %v", err)
+		}
+		gojaStream = append(gojaStream, action)
+	}
+
+	// Hand node the exact candidate list goja drew from, so both engines index
+	// the same targets and only the JS engine differs.
+	nodeStream := runNodeParity(t, seed, steps, verifier.candidatesForVerb("taps"))
+	if len(nodeStream) != len(gojaStream) {
+		t.Fatalf("stream length: goja=%d node=%d", len(gojaStream), len(nodeStream))
+	}
+	for i := range gojaStream {
+		if gojaStream[i] != nodeStream[i] {
+			t.Fatalf("step %d diverged:\n goja=%+v\n node=%+v", i, gojaStream[i], nodeStream[i])
+		}
+	}
+}
+
+// runNodeParity runs the shared picker under node (tsx) with the given seed and
+// candidate list, decoding its serialized stream with the SAME DecodeAction the
+// runner uses so the comparison is apples-to-apples.
+func runNodeParity(t *testing.T, seed uint64, steps int, candidates []candidate) []Action {
+	t.Helper()
+	wire := make([]map[string]any, len(candidates))
+	for i, candidate := range candidates {
+		wire[i] = map[string]any{
+			"x": candidate.x, "y": candidate.y,
+			"width": candidate.width, "height": candidate.height,
+			"selector": candidate.selector,
+		}
+	}
+	candidatesJSON, err := json.Marshal(wire)
+	if err != nil {
+		t.Fatal(err)
+	}
+	specDir, err := filepath.Abs("../../pkg/spec")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	command := exec.Command("node", "--import", "tsx", "test/parity-harness.ts")
+	command.Dir = specDir
+	command.Env = append(command.Environ(),
+		"SANDERLING_PARITY_SEED="+strconv.FormatUint(seed, 10),
+		"SANDERLING_PARITY_STEPS="+strconv.Itoa(steps),
+		"SANDERLING_PARITY_CANDIDATES="+string(candidatesJSON),
+	)
+	output, err := command.Output()
+	if err != nil {
+		t.Fatalf("node parity harness: %v\noutput: %s", err, output)
+	}
+
+	var raw []json.RawMessage
+	if err := json.Unmarshal(output, &raw); err != nil {
+		t.Fatalf("decode node output %q: %v", output, err)
+	}
+	stream := make([]Action, len(raw))
+	for i, message := range raw {
+		action, err := DecodeAction(message)
+		if err != nil {
+			t.Fatalf("decode node action %d: %v", i, err)
+		}
+		stream[i] = action
+	}
+	return stream
+}