Add more tests; make fall back more resilient and visible

src/memory/index.ts

@@ -1,3 +1,7 @@
 export { MemoryIndexManager } from "./manager.js";
-export type { MemorySearchResult, MemorySearchManager } from "./types.js";
+export type {
+  MemoryEmbeddingProbeResult,
+  MemorySearchManager,
+  MemorySearchResult,
+} from "./types.js";
 export { getMemorySearchManager, type MemorySearchManagerResult } from "./search-manager.js";