refactor(spec): picker emits native selector + scroll endpoints, setup precedence

pkg/spec/src/action-tree.ts

@@ -44,7 +44,10 @@ export type ActionDescriptor =
   | { kind: "Tap"; on: Target }
   | { kind: "DoubleTap"; on: Target }
   | { kind: "LongPress"; on: Target }
-  | { kind: "Scroll"; direction: Direction; in?: Target }
+  // Scroll carries the author target (in) for spec-written scrolls; the builtin
+  // generator additionally pre-computes the swipe from/to so the wire contract
+  // carries a real gesture rather than a zero-length one.
+  | { kind: "Scroll"; direction: Direction; in?: Target; from?: Target; to?: Target }
   | { kind: "InputText"; into: Target; text: string }
   | { kind: "Swipe"; from: Target; to: Target; durationMillis?: number }
   | { kind: "PressKey"; key: string }

pkg/spec/src/pick.ts

@@ -142,24 +142,76 @@ function walkBuiltin(
 
   switch (verb) {
     case "taps":
-      return { kind: "Tap", on: point };
+      return tapDescriptor("Tap", point, picked.selector);
     case "doubleTaps":
-      return { kind: "DoubleTap", on: point };
+      return tapDescriptor("DoubleTap", point, picked.selector);
     case "longPresses":
-      return { kind: "LongPress", on: point };
+      return tapDescriptor("LongPress", point, picked.selector);
     case "typing": {
       const text = INPUT_CORPUS[rng.intN(INPUT_CORPUS.length)] ?? "";
-      return { kind: "InputText", into: point, text };
+      return { kind: "InputText", into: withSelector(point, picked.selector), text };
     }
     case "swipes":
       return buildSwipe(point, rng);
     case "scrolls": {
       const direction = DIRECTIONS[rng.intN(DIRECTIONS.length)] ?? "down";
-      return { kind: "Scroll", direction, in: point };
+      return buildScroll(point, direction, picked, rng);
     }
   }
 }
 
+// withSelector attaches a native selector to a resolved Point so the runner can
+// re-resolve the target by id/text. The web host omits it (point-only).
+function withSelector(point: Point, selector?: string): Point {
+  if (selector === undefined) return point;
+  return { ...point, selector } as Point;
+}
+
+function tapDescriptor(
+  kind: "Tap" | "DoubleTap" | "LongPress",
+  point: Point,
+  selector?: string,
+): ActionDescriptor {
+  return { kind, on: withSelector(point, selector) } as ActionDescriptor;
+}
+
+// buildScroll lowers a scroll to a swipe over the container, matching
+// worker.go's geometry: the gesture drags opposite the named content motion,
+// magnitude 40% of the container extent. Missing width/height (web root) yields
+// a zero-length endpoint, which the runner re-derives from container bounds.
+function buildScroll(
+  from: Point,
+  direction: Direction,
+  candidate: { width?: number; height?: number },
+  _rng: Pcg,
+): ActionDescriptor {
+  const width = candidate.width ?? 0;
+  const height = candidate.height ?? 0;
+  let toX = from.x;
+  let toY = from.y;
+  switch (direction) {
+    case "down":
+      toY = from.y - Math.trunc((4 * height) / 10);
+      break;
+    case "up":
+      toY = from.y + Math.trunc((4 * height) / 10);
+      break;
+    case "left":
+      toX = from.x + Math.trunc((4 * width) / 10);
+      break;
+    case "right":
+      toX = from.x - Math.trunc((4 * width) / 10);
+      break;
+  }
+  return {
+    kind: "Scroll",
+    direction,
+    in: from,
+    from,
+    to: { x: Math.max(0, toX), y: Math.max(0, toY) },
+  } as ActionDescriptor;
+}
+
 function walkPressKey(rng: Pcg, host: Host): ActionDescriptor | null {
   const keys = host.platform() === "web" ? WEB_PRESS_KEYS : NATIVE_PRESS_KEYS;
   if (keys.length === 0) return null;

pkg/spec/src/runtime-entry.ts

@@ -8,7 +8,7 @@
 // identical action stream by construction.
 
 import { Pcg } from "./pcg.ts";
-import { nextAction } from "./pick.ts";
+import { nextAction, walk } from "./pick.ts";
 import type { ActionDescriptor, GeneratorNode, Host } from "./action-tree.ts";
 import type { Point } from "./types.ts";
 
@@ -82,15 +82,18 @@ export function serializeAction(action: ActionDescriptor | null): SerializedActi
       };
     }
     case "Scroll": {
-      const from = pointOf(action.in);
+      const from = pointOf(action.from) ?? pointOf(action.in);
       if (!from) return null;
+      // The builtin generator pre-computes `to`; an author Scroll without it
+      // collapses to a zero-length gesture the runner re-derives from bounds.
+      const to = pointOf(action.to) ?? from;
       return {
         kind: "Scroll",
         direction: action.direction,
         fromX: from.x,
         fromY: from.y,
-        toX: from.x,
-        toY: from.y,
+        toX: to.x,
+        toY: to.y,
         durationMillis: DEFAULT_SWIPE_DURATION,
       };
     }
@@ -106,6 +109,11 @@ export function serializeAction(action: ActionDescriptor | null): SerializedActi
 // AFTER this call (the web bundle imports the runtime before the spec, so the
 // root only exists on globalThis.actions once the spec has evaluated).
 // evaluateExtractors is the engine's snapshot of the spec's extract() handles.
+//
+// Setup precedence: when the spec assigned globalThis.setup, it is walked ONCE
+// per tick first; if it yields an action that wins, otherwise the call falls
+// through to the action root's 16-attempt retry. This matches the native
+// verifier's prior NextAction precedence and applies on both engines.
 export function installRuntime(
   host: Host,
   root: GeneratorNode | null | (() => GeneratorNode | null),
@@ -113,9 +121,18 @@ export function installRuntime(
 ): void {
   const rng = new Pcg(host.seedHi(), host.seedLo());
   const resolveRoot = typeof root === "function" ? root : () => root;
+  const resolveSetup = () =>
+    (globalThis as { setup?: GeneratorNode }).setup ?? null;
   defineLockedGlobal("__sanderlingExtractors__", () => evaluateExtractors());
   defineLockedGlobal("__sanderlingNextAction__", () => {
+    // resolveRoot runs first: on web it also resets the per-tick candidate
+    // cache, which setup's walk below must see fresh.
     const current = resolveRoot();
+    const setup = resolveSetup();
+    if (setup) {
+      const setupAction = walk(setup, rng, host);
+      if (setupAction) return serializeAction(setupAction);
+    }
     if (!current) return null;
     return serializeAction(nextAction(current, rng, host));
   });

pkg/spec/test/pick.test.ts

@@ -53,7 +53,11 @@ test("taps draws one candidate index and targets its point", () => {
   const action = walk(builtin("taps"), rng, host);
   assert.deepEqual(action, {
     kind: "Tap",
-    on: { x: POINTS[expectedIndex]!.x, y: POINTS[expectedIndex]!.y },
+    on: {
+      x: POINTS[expectedIndex]!.x,
+      y: POINTS[expectedIndex]!.y,
+      selector: POINTS[expectedIndex]!.selector,
+    },
   });
 });
 
@@ -72,6 +76,7 @@ test("typing draws candidate index then corpus index, in that order", () => {
   assert.deepEqual(action.into, {
     x: POINTS[candidateIndex]!.x,
     y: POINTS[candidateIndex]!.y,
+    selector: POINTS[candidateIndex]!.selector,
   });
   assert.equal(action.text, INPUT_CORPUS[corpusIndex]);
 });
@@ -142,7 +147,11 @@ test("doubleTaps and longPresses draw exactly one candidate index", () => {
     const kind = verb === "doubleTaps" ? "DoubleTap" : "LongPress";
     assert.deepEqual(action, {
       kind,
-      on: { x: POINTS[index]!.x, y: POINTS[index]!.y },
+      on: {
+        x: POINTS[index]!.x,
+        y: POINTS[index]!.y,
+        selector: POINTS[index]!.selector,
+      },
     });
   }
 });

pkg/spec/test/runtime-entry.test.ts

@@ -98,7 +98,75 @@ test("PressKey and Wait pass through their fields", () => {
   });
 });
 
+test("builtin Scroll carries the pre-computed to endpoint", () => {
+  assert.deepEqual(
+    serializeAction({
+      kind: "Scroll",
+      direction: "down",
+      in: { x: 100, y: 200 },
+      from: { x: 100, y: 200 },
+      to: { x: 100, y: 120 },
+    }),
+    {
+      kind: "Scroll",
+      direction: "down",
+      fromX: 100,
+      fromY: 200,
+      toX: 100,
+      toY: 120,
+      durationMillis: 250,
+    },
+  );
+});
+
 test("an unresolved (string) target drops the action", () => {
   assert.equal(serializeAction({ kind: "Tap", on: "id:never-resolved" }), null);
   assert.equal(serializeAction(null), null);
 });
+
+// Wire round-trip: serialize -> JSON -> parse asserts every field the Go
+// decodeAction reads survives by its exact camelCase name. A rename (fromX vs
+// from_x) would silently turn web/native actions into no-ops; this catches it.
+test("serialized actions JSON round-trip with the decoder's field names", () => {
+  const cases: ActionDescriptor[] = [
+    { kind: "Tap", on: { x: 1, y: 2, selector: "id:a" } as never },
+    { kind: "InputText", into: { x: 3, y: 4 } as never, text: "x" },
+    { kind: "Swipe", from: { x: 5, y: 6 }, to: { x: 7, y: 8 }, durationMillis: 9 },
+    { kind: "Scroll", direction: "up", in: { x: 1, y: 1 } as never },
+    { kind: "PressKey", key: "enter" },
+    { kind: "Wait", durationMillis: 10 },
+  ];
+  for (const descriptor of cases) {
+    const wire = serializeAction(descriptor);
+    assert.ok(wire, `expected ${descriptor.kind} to serialize`);
+    const decoded = JSON.parse(JSON.stringify(wire)) as Record<string, unknown>;
+    assert.equal(decoded.kind, wire!.kind);
+    switch (wire!.kind) {
+      case "Tap":
+        assert.equal(typeof decoded.x, "number");
+        assert.equal(typeof decoded.y, "number");
+        assert.equal(decoded.selector, "id:a");
+        break;
+      case "InputText":
+        assert.equal(typeof decoded.x, "number");
+        assert.equal(decoded.text, "x");
+        break;
+      case "Swipe":
+        assert.equal(decoded.fromX, 5);
+        assert.equal(decoded.toY, 8);
+        assert.equal(decoded.durationMillis, 9);
+        break;
+      case "Scroll":
+        assert.equal(decoded.direction, "up");
+        assert.equal(typeof decoded.fromX, "number");
+        assert.equal(typeof decoded.toX, "number");
+        break;
+      case "PressKey":
+        assert.equal(decoded.key, "enter");
+        break;
+      case "Wait":
+        assert.equal(decoded.durationMillis, 10);
+        break;
+    }
+  }
+});