refactor: stop persisting workspace state in the browser

frontend/src/workspaces/preferences.test.ts

@@ -1,15 +1,39 @@
-import { expect, test } from "vitest";
+import { beforeEach, expect, test } from "vitest";
 import { workspacePreferences } from "./preferences";
 
-test("migrates legacy selections once and keeps later browser choices", () => {
+beforeEach(() => {
   localStorage.clear();
+  workspacePreferences.reset();
+});
 
+test("keeps selections only in current application memory", () => {
+  localStorage.setItem("unrelated", "keep-me");
+  workspacePreferences.save({
+    workspaceId: "research",
+    provider: "deepseek",
+    model: "deepseek-v4-pro",
+    thinking: "high",
+  });
+
+  expect(workspacePreferences.load()).toEqual({
+    workspaceId: "research",
+    provider: "deepseek",
+    model: "deepseek-v4-pro",
+    thinking: "high",
+  });
+  expect(localStorage.length).toBe(1);
+  expect(localStorage.getItem("unrelated")).toBe("keep-me");
+  expect(localStorage.getItem("thothii.workspace-registry.v1.preferences")).toBeNull();
+});
+
+test("seeds memory from backend settings once and returns defensive copies", () => {
   expect(workspacePreferences.migrate({
     workspaceId: "psd-clinical", provider: "zai", model: "glm-5.2", thinking: "medium",
   })).toMatchObject({ workspaceId: "psd-clinical", model: "glm-5.2" });
-  workspacePreferences.save({ workspaceId: "research", provider: "deepseek", model: "deepseek-v4-pro", thinking: "high" });
+  const snapshot = workspacePreferences.load();
+  snapshot.workspaceId = "mutated-copy";
 
   expect(workspacePreferences.migrate({ workspaceId: "legacy" })).toMatchObject({
-    workspaceId: "research", provider: "deepseek", model: "deepseek-v4-pro", thinking: "high",
+    workspaceId: "psd-clinical", provider: "zai", model: "glm-5.2", thinking: "medium",
   });
 });