feat(spec): goja runtime entry wires the shared picker over the Go host

pkg/spec/src/goja-runtime.ts

@@ -0,0 +1,23 @@
+// Goja-side runtime entry for the native verifier (internal/verifier).
+//
+// Go installs globalThis.__sanderlingHost__ (platform/seed/queryCandidates/
+// reportUnsupported, implemented over the hierarchy tree in bindings.go) before
+// the spec evaluates. This module bundles AFTER the spec, reads that host, and
+// wires the shared picker via installRuntime so the goja verifier and the V8 web
+// runtime run the SAME pick.ts over the SAME Pcg.
+//
+// Extractors are driven by Go (bindExtract + PushSnapshot advance current/
+// previous against the Go-built `state`), so the extractor callback is a no-op
+// here; Go never invokes __sanderlingExtractors__ on native.
+
+import { installRuntime } from "./runtime-entry.ts";
+import type { GeneratorNode, Host } from "./action-tree.ts";
+
+const host = (globalThis as { __sanderlingHost__?: Host }).__sanderlingHost__;
+if (!host) throw new Error("goja runtime: __sanderlingHost__ not installed");
+
+installRuntime(
+  host,
+  () => (globalThis as { actions?: GeneratorNode }).actions ?? null,
+  () => ({}),
+);