feat(bundler): BundleWeb + V8-side runtime shim

web-runtime.ts installs globalThis.__sanderling__ with extractor / action
registries, plus __sanderlingExtractors__ + __sanderlingNextAction__
globals. BundleWeb composes user spec + runtime under esbuild's
PlatformBrowser into one IIFE.

internal/bundler/web_bundle_test.go

@@ -0,0 +1,91 @@
+package bundler
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const fakeRuntime = `
+(globalThis as Record<string, unknown>).__sanderling__ = {
+  extract: (g: () => unknown) => ({ current: g(), previous: undefined }),
+  always: () => ({ __sanderlingFormula: true }),
+  now: () => ({ __sanderlingFormula: true }),
+  next: () => ({ __sanderlingFormula: true }),
+  eventually: () => ({ __sanderlingFormula: true }),
+  actions: (g: () => unknown) => ({ __sanderlingActionGenerator: true, generate: g }),
+  weighted: () => ({ __sanderlingActionGenerator: true }),
+  from: () => ({ generate: () => null }),
+  tap: () => null,
+  inputText: () => null,
+  swipe: () => null,
+  pressKey: () => null,
+  wait: () => null,
+  taps: {},
+  swipes: {},
+  waitOnce: {},
+  pressKeys: {},
+};
+(globalThis as Record<string, unknown>).__sanderlingExtractors__ = () => ({});
+(globalThis as Record<string, unknown>).__sanderlingNextAction__ = () => null;
+export {};
+`
+
+const fakeSpec = `
+const handle = (globalThis as { __sanderling__: { extract: (g: () => unknown) => unknown } }).__sanderling__.extract(() => 42);
+(globalThis as { actions?: unknown }).actions = handle;
+export {};
+`
+
+func TestBundleWeb_RegistersExpectedGlobals(t *testing.T) {
+	directory := t.TempDir()
+	runtimePath := filepath.Join(directory, "web-runtime.ts")
+	specPath := filepath.Join(directory, "spec.ts")
+	if err := os.WriteFile(runtimePath, []byte(fakeRuntime), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(specPath, []byte(fakeSpec), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	result, err := BundleWeb(WebOptions{
+		EntryFile:      specPath,
+		WebRuntimeFile: runtimePath,
+	})
+	if err != nil {
+		t.Fatalf("BundleWeb: %v", err)
+	}
+	source := string(result.JavaScript)
+	for _, expected := range []string{
+		"__sanderlingExtractors__",
+		"__sanderlingNextAction__",
+		"__sanderling__",
+	} {
+		if !strings.Contains(source, expected) {
+			t.Errorf("bundle missing %q\nsource head:\n%s", expected, head(source, 500))
+		}
+	}
+	if !strings.HasPrefix(strings.TrimSpace(source), "(()") {
+		t.Errorf("expected IIFE format, head:\n%s", head(source, 200))
+	}
+	if result.SHA256 == "" {
+		t.Errorf("expected non-empty sha256")
+	}
+}
+
+func TestBundleWeb_RejectsMissingEntry(t *testing.T) {
+	if _, err := BundleWeb(WebOptions{}); err == nil {
+		t.Error("expected error for empty options")
+	}
+	if _, err := BundleWeb(WebOptions{EntryFile: "x.ts"}); err == nil {
+		t.Error("expected error for missing runtime")
+	}
+}
+
+func head(text string, max int) string {
+	if len(text) <= max {
+		return text
+	}
+	return text[:max] + "..."
+}