diff --git a/packages/core/src/__tests__/builtin-workflows.test.ts b/packages/core/src/__tests__/builtin-workflows.test.ts
index 491314877f..01c1e04c25 100644
--- a/packages/core/src/__tests__/builtin-workflows.test.ts
+++ b/packages/core/src/__tests__/builtin-workflows.test.ts
@@ -549,6 +549,12 @@ describe("built-in workflows", () => {
       expect(await store.getWorkflowDefinition("builtin:compound-engineering")).toBeUndefined();
     });
 
+    it("opens the plugin store before the shared harness resets globalDir", async () => {
+      const pluginStore = store.getPluginStore();
+      await pluginStore.init();
+      expect(await pluginStore.listPlugins()).toEqual([]);
+    });
+
     it("shows the compound-engineering built-in when its plugin is installed", async () => {
       await store.getPluginStore().registerPlugin({
         manifest: {
diff --git a/packages/core/src/__tests__/store-test-helpers.ts b/packages/core/src/__tests__/store-test-helpers.ts
index 503beb21dd..d9855dc7bd 100644
--- a/packages/core/src/__tests__/store-test-helpers.ts
+++ b/packages/core/src/__tests__/store-test-helpers.ts
@@ -94,6 +94,14 @@ function resetMockPassThroughs() {
 }
 
 async function resetStoreFilesystem(rootDir: string, globalDir: string, store: TaskStore): Promise<void> {
+  /*
+   * FNXC:CoreTests 2026-06-25-03:32:
+   * The shared harness reuses a TaskStore while clearing globalDir between tests.
+   * Close and null the lazy PluginStore first so its file-backed central DB never survives after fusion-central.db is removed.
+   */
+  (store as any).pluginStore?.close?.();
+  (store as any).pluginStore = null;
+
   const fusionDir = store.getFusionDir();
   await clearDirectoryContents(join(fusionDir, "tasks"));
   await clearDirectoryContents(join(fusionDir, "task-documents"));
diff --git a/packages/core/src/__tests__/test-project.test.ts b/packages/core/src/__tests__/test-project.test.ts
index 8c21af2a2b..0e7d101f04 100644
--- a/packages/core/src/__tests__/test-project.test.ts
+++ b/packages/core/src/__tests__/test-project.test.ts
@@ -44,8 +44,12 @@ describe("test-project fixture", () => {
     const configRaw = await readFile(join(fixture.rootDir, ".fusion", "config.json"), "utf-8");
     const config = JSON.parse(configRaw);
     expect(config.nextId).toBeUndefined();
-    // FNXC:Workspace 2026-06-24-23:50: taskPrefix defaults to undefined (derived from project name at runtime, see commit 800f845e1). The "FN" fallback is applied in store.ts createTask, not persisted in config.json.
+    /*
+     * FNXC:Workspace 2026-06-24-23:50: taskPrefix defaults to undefined (derived from project name at runtime, see commit 800f845e1). The "FN" fallback is applied in store.ts createTask, not persisted in config.json.
+     * FNXC:Settings 2026-06-25-03:36: Also assert the effective prefix so the fixture matches production config serialization without weakening explicit overrides.
+     */
     expect(config.settings.taskPrefix).toBeUndefined();
+    expect(config.settings.taskPrefix ?? "FN").toBe("FN");
 
     const tasks = await fixture.store.listTasks();
     expect(tasks).toHaveLength(0);
diff --git a/packages/core/src/plugin-store.ts b/packages/core/src/plugin-store.ts
index 7f7f399a92..62b568cee4 100644
--- a/packages/core/src/plugin-store.ts
+++ b/packages/core/src/plugin-store.ts
@@ -129,6 +129,18 @@ export class PluginStore extends EventEmitter<PluginStoreEvents> {
     return this._centralDb;
   }
 
+  /**
+   * FNXC:Plugins 2026-06-25-03:31:
+   * Shared test harnesses clear the file-backed global settings directory between tests while reusing one TaskStore.
+   * Dispose both plugin database handles first so future plugin access reopens a fresh central DB instead of writing through a connection whose backing file was removed.
+   */
+  close(): void {
+    this._localDb?.close();
+    this._localDb = null;
+    this._centralDb?.close();
+    this._centralDb = null;
+  }
+
   async init(): Promise<void> {
     const _ = this.localDb;
     const __ = this.centralDb;