feat(verifier): add SetupAction to walk setup without the seeded root

internal/verifier/worker.go

@@ -28,6 +28,11 @@ type Verifier struct {
 	// the shared picker (pick.ts) over the shared Pcg.
 	nextActionFn goja.Callable
 
+	// setupActionFn is the bundle-installed __sanderlingSetupAction__, which
+	// walks ONLY the setup generator. The LLM action generator runs it for setup
+	// precedence (e.g. login) without triggering the seeded action root.
+	setupActionFn goja.Callable
+
 	// sampleInputFn is the bundle-installed __sanderlingSampleInput__, which
 	// draws one value from the shared INPUT_CORPUS. The LLM action backend uses
 	// it to fill InputText values, reusing the exact corpus draw rather than
@@ -158,6 +163,11 @@ func (v *Verifier) Load(source string) error {
 			v.nextActionFn = callable
 		}
 	}
+	if fn := v.runtime.GlobalObject().Get("__sanderlingSetupAction__"); fn != nil {
+		if callable, ok := goja.AssertFunction(fn); ok {
+			v.setupActionFn = callable
+		}
+	}
 
 	// __sanderlingSampleInput__ draws an InputText value from the shared corpus.
 	// The LLM action backend uses it; a raw-JS fixture without the runtime entry
@@ -596,6 +606,28 @@ func (v *Verifier) NextAction() (Action, error) {
 	return DecodeAction(raw)
 }
 
+// SetupAction walks ONLY the setup generator (globalThis.setup), returning its
+// action or ErrNoAction. The LLM action generator runs this for setup
+// precedence (e.g. login) without triggering the seeded action root, which it
+// replaces entirely. Mirrors NextAction's decode.
+func (v *Verifier) SetupAction() (Action, error) {
+	if v.setupActionFn == nil {
+		return Action{}, ErrNoAction
+	}
+	value, err := v.setupActionFn(goja.Undefined())
+	if err != nil {
+		return Action{}, fmt.Errorf("setup action: %w", err)
+	}
+	if value == nil || goja.IsNull(value) || goja.IsUndefined(value) {
+		return Action{}, ErrNoAction
+	}
+	raw, err := json.Marshal(value.Export())
+	if err != nil {
+		return Action{}, fmt.Errorf("marshal action: %w", err)
+	}
+	return DecodeAction(raw)
+}
+
 var ErrNoAction = errors.New("verifier: no action available")
 
 func (v *Verifier) formulaThunk(index int) func() (bool, error) {

pkg/spec/src/runtime-entry.ts

@@ -139,6 +139,16 @@ export function installRuntime(
     () => INPUT_CORPUS[rng.intN(INPUT_CORPUS.length)] ?? "",
   );
   defineLockedGlobal("__sanderlingExtractors__", () => evaluateExtractors());
+  // __sanderlingSetupAction__ walks ONLY the setup generator once, for the LLM
+  // action generator (Go), which drives selection itself and must not run the
+  // seeded action root — but still wants setup's precondition steps (e.g. login)
+  // to run first. Returns null when setup is unset or yields nothing.
+  defineLockedGlobal("__sanderlingSetupAction__", () => {
+    resolveRoot();
+    const setup = resolveSetup();
+    if (!setup) return null;
+    return serializeAction(walk(setup, rng, host));
+  });
   defineLockedGlobal("__sanderlingNextAction__", () => {
     // resolveRoot runs first: on web it also resets the per-tick candidate
     // cache, which setup's walk below must see fresh.