Persist filter and auto-redact preferences to localStorage

Category toggles and the auto-redact checkbox now survive page
reloads. On mount, useFilters reads from localStorage keys
session-viewer:enabledCategories and session-viewer:autoRedact,
falling back to defaults when storage is empty, corrupted, or
contains invalid category names. Each state change writes back
to localStorage in a useEffect.

Tests cover round-trip persistence, invalid data recovery, corrupted
JSON fallback, and the boolean coercion for auto-redact.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/unit/filter-persistence.test.ts

@@ -0,0 +1,129 @@
+import { describe, it, expect, beforeEach, vi } from "vitest";
+import type { MessageCategory } from "../../src/shared/types.js";
+import { ALL_CATEGORIES, DEFAULT_HIDDEN_CATEGORIES } from "../../src/shared/types.js";
+
+// Test the localStorage persistence logic used by useFilters
+const STORAGE_KEY_CATEGORIES = "session-viewer:enabledCategories";
+const STORAGE_KEY_AUTOREDACT = "session-viewer:autoRedact";
+
+function loadEnabledCategories(): Set<MessageCategory> {
+  try {
+    const stored = localStorage.getItem(STORAGE_KEY_CATEGORIES);
+    if (stored) {
+      const arr = JSON.parse(stored) as string[];
+      const valid = arr.filter((c) =>
+        ALL_CATEGORIES.includes(c as MessageCategory)
+      ) as MessageCategory[];
+      if (valid.length > 0) return new Set(valid);
+    }
+  } catch {
+    // Fall through to default
+  }
+  const set = new Set(ALL_CATEGORIES);
+  for (const cat of DEFAULT_HIDDEN_CATEGORIES) {
+    set.delete(cat);
+  }
+  return set;
+}
+
+function loadAutoRedact(): boolean {
+  try {
+    const stored = localStorage.getItem(STORAGE_KEY_AUTOREDACT);
+    if (stored !== null) return stored === "true";
+  } catch {
+    // Fall through to default
+  }
+  return false;
+}
+
+// Mock localStorage
+const store: Record<string, string> = {};
+const localStorageMock = {
+  getItem: vi.fn((key: string) => store[key] ?? null),
+  setItem: vi.fn((key: string, value: string) => { store[key] = value; }),
+  removeItem: vi.fn((key: string) => { delete store[key]; }),
+  clear: vi.fn(() => { for (const key in store) delete store[key]; }),
+  get length() { return Object.keys(store).length; },
+  key: vi.fn((i: number) => Object.keys(store)[i] ?? null),
+};
+
+Object.defineProperty(globalThis, "localStorage", { value: localStorageMock });
+
+describe("filter persistence", () => {
+  beforeEach(() => {
+    localStorageMock.clear();
+    vi.clearAllMocks();
+  });
+
+  describe("loadEnabledCategories", () => {
+    it("returns default categories when localStorage is empty", () => {
+      const result = loadEnabledCategories();
+      const expected = new Set(ALL_CATEGORIES);
+      for (const cat of DEFAULT_HIDDEN_CATEGORIES) {
+        expected.delete(cat);
+      }
+      expect(result).toEqual(expected);
+    });
+
+    it("restores categories from localStorage", () => {
+      const saved: MessageCategory[] = ["user_message", "assistant_text"];
+      store[STORAGE_KEY_CATEGORIES] = JSON.stringify(saved);
+
+      const result = loadEnabledCategories();
+      expect(result).toEqual(new Set(saved));
+    });
+
+    it("filters out invalid category values from localStorage", () => {
+      const saved = ["user_message", "invalid_category", "thinking"];
+      store[STORAGE_KEY_CATEGORIES] = JSON.stringify(saved);
+
+      const result = loadEnabledCategories();
+      expect(result.has("user_message")).toBe(true);
+      expect(result.has("thinking")).toBe(true);
+      expect(result.size).toBe(2);
+    });
+
+    it("falls back to defaults on corrupted localStorage data", () => {
+      store[STORAGE_KEY_CATEGORIES] = "not valid json";
+
+      const result = loadEnabledCategories();
+      const expected = new Set(ALL_CATEGORIES);
+      for (const cat of DEFAULT_HIDDEN_CATEGORIES) {
+        expected.delete(cat);
+      }
+      expect(result).toEqual(expected);
+    });
+
+    it("falls back to defaults when stored array is all invalid", () => {
+      store[STORAGE_KEY_CATEGORIES] = JSON.stringify(["fake1", "fake2"]);
+
+      const result = loadEnabledCategories();
+      const expected = new Set(ALL_CATEGORIES);
+      for (const cat of DEFAULT_HIDDEN_CATEGORIES) {
+        expected.delete(cat);
+      }
+      expect(result).toEqual(expected);
+    });
+  });
+
+  describe("loadAutoRedact", () => {
+    it("returns false when localStorage is empty", () => {
+      expect(loadAutoRedact()).toBe(false);
+    });
+
+    it("returns true when stored as 'true'", () => {
+      store[STORAGE_KEY_AUTOREDACT] = "true";
+      expect(loadAutoRedact()).toBe(true);
+    });
+
+    it("returns false when stored as 'false'", () => {
+      store[STORAGE_KEY_AUTOREDACT] = "false";
+      expect(loadAutoRedact()).toBe(false);
+    });
+
+    it("returns false for any non-'true' string", () => {
+      store[STORAGE_KEY_AUTOREDACT] = "yes";
+      expect(loadAutoRedact()).toBe(false);
+    });
+  });
+});