Use MutableHashMap for collection manager

ts/EFFECT_NATIVE_REWRITE_AUDIT.md

@@ -2234,6 +2234,26 @@ Notes:
   - `cd ts && bun run lint`
   - `git diff --check`
 
+### 2026-06-04: Librarian Collection Manager MutableHashMap Slice
+
+- Status: migrated and package-verified.
+- Completed:
+  - `ts/packages/flow/src/librarian/collection-manager.ts` now stores
+    in-memory collection entries in `MutableHashMap` instead of native `Map`.
+  - Public `listCollections`, `getCollection`, `updateCollection`,
+    `deleteCollection`, `ensureCollectionExists`, `toJSON`, and `loadFromJSON`
+    behavior stays array/boolean/undefined based at the API and persistence
+    boundaries.
+  - New focused coverage verifies create/update/list/get/delete and JSON
+    restore behavior through the migrated collection state.
+- Verification:
+  - `cd ts/packages/flow && bunx --bun vitest run src/__tests__/collection-manager.test.ts src/__tests__/librarian-service.test.ts`
+  - `cd ts && bun run check:tsgo`
+  - `cd ts && bun run build`
+  - `cd ts && bun run test`
+  - `cd ts && bun run lint`
+  - `git diff --check`
+
 ## Subagent Findings To Preserve
 
 - MCP/workbench:
@@ -2420,9 +2440,9 @@ Notes:
     The workbench random id helper is complete; the remaining workbench
     `Effect.gen` match is a local one-shot command effect value.
   - Remaining real long-lived native collection targets include base processor
-    registries, Librarian service / collection manager state, prompt template
+    registries, Librarian service state, prompt template cache, and a workbench
-    cache, and a workbench module cache. Local traversal sets and test fakes
+    module cache. The standalone Librarian collection manager is complete.
-    remain no-op boundaries.
+    Local traversal sets and test fakes remain no-op boundaries.
 
 ## Ranked Findings
 

ts/packages/flow/src/__tests__/collection-manager.test.ts

@@ -0,0 +1,44 @@
+import { describe, expect, it } from "vitest";
+import { makeCollectionManager } from "../librarian/collection-manager.js";
+
+describe("CollectionManager", () => {
+  it("manages collection entries through Effect MutableHashMap state", () => {
+    const manager = makeCollectionManager();
+
+    const created = manager.ensureCollectionExists("alice", "papers");
+    expect(created).toEqual({
+      user: "alice",
+      collection: "papers",
+      name: "papers",
+      description: "",
+      tags: [],
+    });
+
+    const updated = manager.updateCollection(
+      "alice",
+      "papers",
+      "Research Papers",
+      "Curated PDFs",
+      ["research", "pdf"],
+    );
+    manager.updateCollection("bob", "notes", "Notes", "", []);
+
+    expect(manager.getCollection("alice", "papers")).toEqual(updated);
+    expect(manager.listCollections("alice")).toEqual([updated]);
+    expect(manager.toJSON()).toEqual([updated, {
+      user: "bob",
+      collection: "notes",
+      name: "Notes",
+      description: "",
+      tags: [],
+    }]);
+
+    expect(manager.deleteCollection("alice", "papers")).toBe(true);
+    expect(manager.deleteCollection("alice", "papers")).toBe(false);
+    expect(manager.getCollection("alice", "papers")).toBeUndefined();
+
+    manager.loadFromJSON([updated]);
+    expect(manager.listCollections("alice")).toEqual([updated]);
+    expect(manager.listCollections("bob")).toEqual([]);
+  });
+});

ts/packages/flow/src/librarian/collection-manager.ts

@@ -6,6 +6,9 @@
  * via the parent LibrarianService JSON snapshot).
  */
 
+import * as MutableHashMap from "effect/MutableHashMap";
+import * as O from "effect/Option";
+
 export interface CollectionEntry {
   user: string;
   collection: string;
@@ -32,7 +35,7 @@ export interface CollectionManager {
 
 export function makeCollectionManager(): CollectionManager {
   /** keyed by `${user}:${collection}` */
-  const collections = new Map<string, CollectionEntry>();
+  const collections = MutableHashMap.empty<string, CollectionEntry>();
 
   const key = (user: string, collection: string): string => `${user}:${collection}`;
 
@@ -44,35 +47,41 @@ export function makeCollectionManager(): CollectionManager {
     tags: string[],
   ): CollectionEntry => {
     const entry: CollectionEntry = { user, collection, name, description, tags };
-    collections.set(key(user, collection), entry);
+    MutableHashMap.set(collections, key(user, collection), entry);
     return entry;
   };
 
   return {
     listCollections: (user) => {
       const result: CollectionEntry[] = [];
-      for (const entry of collections.values()) {
+      for (const entry of MutableHashMap.values(collections)) {
         if (entry.user === user) {
           result.push(entry);
         }
       }
       return result;
     },
-    getCollection: (user, collection) => collections.get(key(user, collection)),
+    getCollection: (user, collection) =>
+      O.getOrUndefined(MutableHashMap.get(collections, key(user, collection))),
     updateCollection,
-    deleteCollection: (user, collection) => collections.delete(key(user, collection)),
+    deleteCollection: (user, collection) => {
+      const collectionKey = key(user, collection);
+      const exists = MutableHashMap.has(collections, collectionKey);
+      MutableHashMap.remove(collections, collectionKey);
+      return exists;
+    },
     ensureCollectionExists: (user, collection) => {
-      const existing = collections.get(key(user, collection));
+      const existing = O.getOrUndefined(MutableHashMap.get(collections, key(user, collection)));
       if (existing !== undefined) return existing;
       return updateCollection(user, collection, collection, "", []);
     },
     /** Serialize to a plain array for JSON persistence. */
-    toJSON: () => [...collections.values()],
+    toJSON: () => Array.from(MutableHashMap.values(collections)),
     /** Restore from a serialized array. */
     loadFromJSON: (entries) => {
-      collections.clear();
+      MutableHashMap.clear(collections);
       for (const entry of entries) {
-        collections.set(key(entry.user, entry.collection), entry);
+        MutableHashMap.set(collections, key(entry.user, entry.collection), entry);
       }
     },
   };