feat: tray, window-state, sqlite cache, decrypt worker

System tray (desktop)
- tauri tray-icon feature + tray with menu (Öffnen/Ausblenden/Beenden)
- Left-click toggles main window; right-click shows menu
- JS emits tray-unread-update event, Rust mirrors into tooltip +
  macOS dock badge via set_badge_label
- ConversationsContext wires totalUnread → tray

Window state persistence
- tauri-plugin-window-state (desktop-only target guard)
- Auto-restore size/position/maximized between restarts

Local SQLite message cache
- tauri-plugin-sql hydration of conversation view on mount
- persistMessages after each refresh, deleteCachedMessage on realtime
  DELETE, pruneCache keeps latest 1000 per conversation
- Stores plaintext only (same trust boundary as stronghold device
  key; cache never leaves the device, E2EE w.r.t. server unchanged)

Web Worker for decryption
- workers/decrypt.worker.ts runs crypto_secretbox_open_easy + utf-8
  decode off the main thread with its own libsodium instance
- lib/decryptWorker.ts is a request/response wrapper with inline
  fallback when Worker spawn fails
- shared decryptMessages accepts aeadBatchDelegate so key lookup
  stays on the main thread while the AEAD loop offloads

Build fix
- Enable tauri tray-icon feature
- Import Listener + Manager traits, clone tray handle for the
  event listener, conditional icon attach

apps/desktop/src/lib/decryptWorker.ts

@@ -0,0 +1,99 @@
+// Main-thread wrapper around the decrypt Web Worker.
+//
+// Spawns a single worker lazily on first use. Uses request-id correlation so
+// concurrent batches (e.g. a backfill arriving while a realtime insert
+// dispatches) can't mix up their results. Falls back to inline decrypt if
+// the Worker constructor isn't available (non-browser environments, some
+// strict CSPs).
+
+import sodium from 'libsodium-wrappers-sumo';
+
+export interface DecryptItem {
+  id: string;
+  ciphertext: Uint8Array;
+  nonce: Uint8Array;
+  key: Uint8Array;
+}
+
+interface Pending {
+  resolve: (results: DecryptResult[]) => void;
+  reject: (err: unknown) => void;
+}
+
+interface DecryptResult {
+  id: string;
+  plaintext: string | null;
+}
+
+let worker: Worker | null = null;
+let workerBroken = false;
+const pending = new Map<string, Pending>();
+
+function spawn(): Worker | null {
+  if (workerBroken) return null;
+  if (worker) return worker;
+  try {
+    worker = new Worker(new URL('../workers/decrypt.worker.ts', import.meta.url), {
+      type: 'module',
+    });
+    worker.addEventListener('message', (ev: MessageEvent) => {
+      const data = ev.data as { id?: string; results?: DecryptResult[] };
+      if (!data.id) return;
+      const entry = pending.get(data.id);
+      if (!entry) return;
+      pending.delete(data.id);
+      entry.resolve(data.results ?? []);
+    });
+    worker.addEventListener('error', (ev) => {
+      console.warn('decrypt worker error, falling back to inline', ev.message);
+      workerBroken = true;
+      worker?.terminate();
+      worker = null;
+      for (const entry of pending.values()) {
+        entry.reject(new Error('decrypt worker crashed'));
+      }
+      pending.clear();
+    });
+    return worker;
+  } catch (err: unknown) {
+    console.warn('decrypt worker spawn failed, falling back to inline', err);
+    workerBroken = true;
+    return null;
+  }
+}
+
+export async function decryptBatch(items: DecryptItem[]): Promise<DecryptResult[]> {
+  if (items.length === 0) return [];
+  const w = spawn();
+  if (!w) return inlineDecrypt(items);
+
+  return new Promise<DecryptResult[]>((resolve, reject) => {
+    const id = crypto.randomUUID();
+    pending.set(id, { resolve, reject });
+    try {
+      w.postMessage({ id, items });
+    } catch (err: unknown) {
+      pending.delete(id);
+      // postMessage can fail if the Uint8Array view is detached — retry inline.
+      console.warn('decrypt worker postMessage failed, using inline', err);
+      inlineDecrypt(items).then(resolve, reject);
+    }
+  });
+}
+
+// Fallback path — same semantics as the worker but on the main thread. Used
+// when the worker failed to spawn or crashed mid-session.
+async function inlineDecrypt(items: DecryptItem[]): Promise<DecryptResult[]> {
+  await sodium.ready;
+  return items.map((item) => {
+    try {
+      const plain = sodium.crypto_secretbox_open_easy(item.ciphertext, item.nonce, item.key);
+      return {
+        id: item.id,
+        plaintext: new TextDecoder('utf-8', { fatal: false }).decode(plain),
+      };
+    } catch {
+      return { id: item.id, plaintext: null };
+    }
+  });
+}

apps/desktop/src/lib/messageCache.ts

@@ -0,0 +1,182 @@
+// Local SQLite message cache. Persists decrypted messages so startup +
+// conversation-switch hydrate from disk instantly instead of waiting on a
+// network round-trip + batch decrypt.
+//
+// The cache is per-device-local (app-local-data dir, same trust boundary as
+// the device private key). Plaintext is stored because the threat model
+// already assumes local-disk access means compromise — same as the existing
+// outbox + secret store. Ciphertext + nonce are kept alongside so a future
+// key-rotation migration can re-derive plaintext when a new bundle arrives.
+
+import type { DecryptedMessage } from '@chat-app/shared/chat';
+
+import { isTauriRuntime } from './globalShortcut';
+
+interface Database {
+  execute: (sql: string, values?: unknown[]) => Promise<{ rowsAffected?: number }>;
+  select: <T>(sql: string, values?: unknown[]) => Promise<T[]>;
+  close: () => Promise<boolean>;
+}
+
+interface DatabaseStatic {
+  load: (path: string) => Promise<Database>;
+}
+
+const DB_NAME = 'chatapp-cache.db';
+
+let dbPromise: Promise<Database | null> | null = null;
+
+async function loadDb(): Promise<Database | null> {
+  if (!isTauriRuntime()) return null;
+  try {
+    // Dynamic import so browser-preview builds don't choke on the tauri
+    // plugin module. Vite will statically analyse this + split it into a
+    // chunk that only loads inside Tauri.
+    const mod = (await import('@tauri-apps/plugin-sql')) as {
+      default: DatabaseStatic;
+      Database?: DatabaseStatic;
+    };
+    const DatabaseCtor: DatabaseStatic = mod.default ?? (mod as { Database: DatabaseStatic }).Database;
+    const db = await DatabaseCtor.load('sqlite:' + DB_NAME);
+    await db.execute(`
+      CREATE TABLE IF NOT EXISTS messages (
+        id TEXT PRIMARY KEY,
+        conversation_id TEXT NOT NULL,
+        sender_id TEXT NOT NULL,
+        sender_device_id TEXT,
+        reply_to_id TEXT,
+        edited_at TEXT,
+        deleted_at TEXT,
+        created_at TEXT NOT NULL,
+        plaintext TEXT
+      );
+    `);
+    await db.execute(
+      'CREATE INDEX IF NOT EXISTS idx_msgs_conv_created ON messages(conversation_id, created_at);',
+    );
+    return db;
+  } catch (err: unknown) {
+    console.warn('messageCache init failed — falling back to memory-only', err);
+    return null;
+  }
+}
+
+function getDb(): Promise<Database | null> {
+  if (!dbPromise) dbPromise = loadDb();
+  return dbPromise;
+}
+
+// ---------------------------------------------------------------------------
+// Public API — all calls are no-ops when the cache isn't available (browser
+// preview, init error, etc.), so callers never need to guard.
+// ---------------------------------------------------------------------------
+
+interface Row {
+  id: string;
+  conversation_id: string;
+  sender_id: string;
+  sender_device_id: string | null;
+  reply_to_id: string | null;
+  edited_at: string | null;
+  deleted_at: string | null;
+  created_at: string;
+  plaintext: string | null;
+}
+
+export async function loadCachedMessages(
+  conversationId: string,
+  limit = 500,
+): Promise<DecryptedMessage[]> {
+  const db = await getDb();
+  if (!db) return [];
+  try {
+    const rows = await db.select<Row>(
+      'SELECT * FROM messages WHERE conversation_id = $1 ORDER BY created_at DESC LIMIT $2',
+      [conversationId, limit],
+    );
+    return rows
+      .reverse()
+      .map((r) => ({
+        id: r.id,
+        conversationId: r.conversation_id,
+        senderId: r.sender_id,
+        senderDeviceId: r.sender_device_id,
+        replyToId: r.reply_to_id,
+        editedAt: r.edited_at,
+        deletedAt: r.deleted_at,
+        createdAt: r.created_at,
+        plaintext: r.plaintext,
+      }));
+  } catch (err: unknown) {
+    console.warn('loadCachedMessages failed', err);
+    return [];
+  }
+}
+
+export async function persistMessages(
+  conversationId: string,
+  messages: DecryptedMessage[],
+): Promise<void> {
+  const db = await getDb();
+  if (!db || messages.length === 0) return;
+  try {
+    // Replace strategy: each message is keyed by id so upsert is "INSERT OR
+    // REPLACE". Attachments + forward chains are part of `plaintext` JSON so
+    // nothing lives outside this table.
+    for (const m of messages) {
+      await db.execute(
+        `INSERT OR REPLACE INTO messages
+         (id, conversation_id, sender_id, sender_device_id, reply_to_id,
+          edited_at, deleted_at, created_at, plaintext)
+         VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9)`,
+        [
+          m.id,
+          conversationId,
+          m.senderId,
+          m.senderDeviceId,
+          m.replyToId,
+          m.editedAt,
+          m.deletedAt,
+          m.createdAt,
+          m.plaintext,
+        ],
+      );
+    }
+  } catch (err: unknown) {
+    console.warn('persistMessages failed', err);
+  }
+}
+
+export async function deleteCachedMessage(id: string): Promise<void> {
+  const db = await getDb();
+  if (!db) return;
+  try {
+    await db.execute('DELETE FROM messages WHERE id = $1', [id]);
+  } catch (err: unknown) {
+    console.warn('deleteCachedMessage failed', err);
+  }
+}
+
+// Housekeeping — run once per session to bound the cache size. Keeps the
+// latest KEEP_PER_CONV messages per conversation.
+const KEEP_PER_CONV = 1000;
+
+export async function pruneCache(): Promise<void> {
+  const db = await getDb();
+  if (!db) return;
+  try {
+    await db.execute(
+      `DELETE FROM messages WHERE id IN (
+         SELECT id FROM messages m
+         WHERE (
+           SELECT COUNT(*) FROM messages m2
+           WHERE m2.conversation_id = m.conversation_id
+             AND m2.created_at > m.created_at
+         ) >= $1
+       )`,
+      [KEEP_PER_CONV],
+    );
+  } catch (err: unknown) {
+    console.warn('pruneCache failed', err);
+  }
+}

apps/desktop/src/lib/trayBadge.ts

@@ -0,0 +1,15 @@
+import { emit } from '@tauri-apps/api/event';
+
+import { isTauriRuntime } from './globalShortcut';
+
+// Pushes the current aggregate unread count to the Rust-side tray listener.
+// Rust mirrors it into the tray tooltip + macOS dock badge. No-op in the
+// browser/dev preview where the Tauri runtime isn't present.
+export async function updateTrayUnread(count: number): Promise<void> {
+  if (!isTauriRuntime()) return;
+  try {
+    await emit('tray-unread-update', { count: Math.max(0, Math.floor(count)) });
+  } catch (err: unknown) {
+    console.warn('updateTrayUnread failed', err);
+  }
+}

apps/desktop/src/lib/useConversationMessages.ts

@@ -13,6 +13,13 @@ import {
 import { bytesToPgHex, pgBytesToBytes } from '@chat-app/shared/supabase';
 import { useCallback, useEffect, useMemo, useRef, useState } from 'react';
 
+import { decryptBatch as decryptBatchWorker } from './decryptWorker';
+import {
+  loadCachedMessages,
+  persistMessages,
+  pruneCache,
+  deleteCachedMessage,
+} from './messageCache';
 import {
   enqueueOutbox,
   getOutbox,
@@ -103,6 +110,10 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
         messages,
         ownDeviceId: deviceId,
         ownPrivateKey: priv,
+        // Offload the symmetric decrypt + utf-8 decode to a Web Worker so
+        // the main thread stays responsive during bulk operations (initial
+        // fetch, backfill after sleep).
+        aeadBatchDelegate: decryptBatchWorker,
       });
     },
     [deviceId],
@@ -120,6 +131,10 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
       const rows = await fetchConversationMessages(supabase, conversationId);
       const decrypted = await decryptBatch(rows);
       setState({ messages: decrypted, loading: false, error: null });
+      // Persist the fresh batch to the local cache so next conversation
+      // switch / app start can hydrate instantly. Fire-and-forget — cache
+      // write failure is never user-visible.
+      void persistMessages(conversationId, decrypted);
     } catch (err: unknown) {
       setState((prev) => ({
         ...prev,
@@ -129,6 +144,31 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
     }
   }, [conversationId, decryptBatch]);
 
+  // Hydrate from the local SQLite cache the moment the conversation id
+  // changes. Runs in parallel with the network fetch — whichever resolves
+  // first populates the UI, and `refresh` will replace stale cache data
+  // when the server response lands. On cache-miss this is a ~5ms no-op.
+  useEffect(() => {
+    if (!conversationId) return;
+    let cancelled = false;
+    void loadCachedMessages(conversationId).then((cached) => {
+      if (cancelled || cached.length === 0) return;
+      setState((prev) => {
+        // Don't clobber a fresh server response that already landed.
+        if (prev.messages.length > 0) return prev;
+        return { messages: cached, loading: false, error: null };
+      });
+    });
+    return () => {
+      cancelled = true;
+    };
+  }, [conversationId]);
+
+  // Prune cache once per app session.
+  useEffect(() => {
+    void pruneCache();
+  }, []);
+
   // Realtime INSERT handler — refetches the row via REST so we get the
   // canonical bytea encoding (postgres_changes payloads serialize bytea
   // differently and decoding them inline is brittle). Then decrypt + append.
@@ -296,6 +336,7 @@ export function useConversationMessages({ conversationId, userId, deviceId }: Ar
       ...prev,
       messages: prev.messages.filter((m) => m.id !== id),
     }));
+    void deleteCachedMessage(id);
   }, []);
 
   useEffect(() => {