diff --git a/lib/data/db/database.dart b/lib/data/db/database.dart
index 103df36..93d3939 100644
--- a/lib/data/db/database.dart
+++ b/lib/data/db/database.dart
@@ -7,6 +7,7 @@ import 'package:flutter/services.dart';
 import 'package:path/path.dart' as p;
 import 'package:path_provider/path_provider.dart';
 import 'package:sharedinbox/core/db_schema_version.dart';
+import 'package:sqlite3/sqlite3.dart' show Database;
 
 part 'database.g.dart';
 
@@ -793,18 +794,34 @@ Future<String> resolveDatabasePathForTesting() => _resolveDatabasePath();
 void resetDatabasePathForTesting() => _dbPath = null;
 Future<String?> androidFallbackPathForTesting() => _androidFallbackPath();
 
+/// Configures PRAGMAs on a newly opened SQLite connection.
+///
+/// busy_timeout must come first so subsequent statements retry on SQLITE_BUSY
+/// instead of immediately failing.
+///
+/// journal_mode = WAL is wrapped in a try/catch because a concurrent
+/// WorkManager background task may already have the DB open when the app
+/// starts.  SQLITE_BUSY_SNAPSHOT (extended code 261, primary code 5) is
+/// returned in that situation; it only occurs when the DB is already in WAL
+/// mode, so the pragma would be a no-op anyway and it is safe to continue.
+void _setupPragmas(Database db) {
+  db.execute('PRAGMA busy_timeout = 5000;');
+  try {
+    db.execute('PRAGMA journal_mode = WAL;');
+  } on SqliteException catch (e) {
+    // resultCode strips the extended bits: both SQLITE_BUSY (5) and
+    // SQLITE_BUSY_SNAPSHOT (261) reduce to 5.  Re-throw anything else.
+    if (e.resultCode != 5) rethrow;
+  }
+}
+
 LazyDatabase _openConnection() {
   return LazyDatabase(() async {
     final file = File(await _resolveDatabasePath());
-    return NativeDatabase.createInBackground(
-      file,
-      setup: (db) {
-        // WAL lets readers and writers proceed concurrently (different account
-        // sync loops share the same DB).  busy_timeout makes SQLite retry for
-        // up to 5 s instead of immediately returning SQLITE_BUSY.
-        db.execute('PRAGMA journal_mode = WAL;');
-        db.execute('PRAGMA busy_timeout = 5000;');
-      },
-    );
+    return NativeDatabase.createInBackground(file, setup: _setupPragmas);
   });
 }
+
+// Exposed so tests can run the exact production setup logic on a raw
+// sqlite3 connection (same pattern as resolveDatabasePathForTesting).
+void setupPragmasForTesting(Database db) => _setupPragmas(db);
diff --git a/pubspec.yaml b/pubspec.yaml
index a4b5218..99c9055 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -19,6 +19,7 @@ dependencies:
 
   # Local persistence (offline-first)
   drift: ^2.20.3
+  sqlite3: ^3.1.5  # used directly in lib/data/db/database.dart (_setupPragmas)
   sqlite3_flutter_libs: ^0.6.0+eol
   path_provider: ^2.1.5
   path: ^1.9.1
@@ -78,7 +79,6 @@ dev_dependencies:
   mockito: ^5.4.4
   fake_async: ^1.3.1
   path_provider_platform_interface: ^2.1.2
-  sqlite3: ^3.1.5  # used directly in test/unit/db_test_helper.dart; 3.x required for Database.close()
   url_launcher_platform_interface: ^2.3.2
   plugin_platform_interface: ^2.1.8
   flutter_launcher_icons: ^0.14.0
diff --git a/scripts/setup_dagger_remote.sh b/scripts/setup_dagger_remote.sh
index 0f01768..974e93a 100755
--- a/scripts/setup_dagger_remote.sh
+++ b/scripts/setup_dagger_remote.sh
@@ -76,11 +76,12 @@ if [ "$_elapsed" -gt 10 ]; then
     echo "::warning::ssh-keyscan took ${_elapsed}s — Dagger engine host may be slow to respond"
 fi
 
-# Create a background SSH tunnel to the Dagger engine.
-# We map local port 8080 to remote port 1774 (where our socat bridge is listening).
+# Create a background SSH tunnel to the Dagger engine Unix socket.
+# Forwards local TCP port 8080 directly to /run/dagger/engine.sock on the remote host,
+# eliminating the need for a socat bridge on the server side.
 echo "Establishing SSH tunnel to $DAGGER_ENGINE_HOST..."
 _t0=$SECONDS
-timeout 30 ssh -i ~/.ssh/dagger_key -o StrictHostKeyChecking=no -f -N -L 8080:localhost:1774 "dagger@$DAGGER_ENGINE_HOST"
+timeout 30 ssh -i ~/.ssh/dagger_key -o StrictHostKeyChecking=no -f -N -L 8080:/run/dagger/engine.sock "dagger@$DAGGER_ENGINE_HOST"
 _elapsed=$(( SECONDS - _t0 ))
 if [ "$_elapsed" -gt 10 ]; then
     echo "::warning::SSH tunnel setup took ${_elapsed}s"
diff --git a/test/unit/migration_test.dart b/test/unit/migration_test.dart
index e6e375f..c52cfd6 100644
--- a/test/unit/migration_test.dart
+++ b/test/unit/migration_test.dart
@@ -510,4 +510,40 @@ void main() {
       await db.close();
     });
   });
+
+  // Regression test for https://codeberg.org/guettli/sharedinbox/issues/508:
+  // _openConnection's setup callback must not crash when PRAGMA journal_mode =
+  // WAL fails with SQLITE_BUSY_SNAPSHOT (extended code 261, primary code 5)
+  // because a WorkManager background task already has the DB open in WAL mode.
+  group('WAL setup (#508)', () {
+    test(
+      'setupPragmasForTesting does not throw when WAL is already active and '
+      'another connection holds an open read transaction',
+      () {
+        final dbFile = File('test_wal_busy_508.db');
+        if (dbFile.existsSync()) dbFile.deleteSync();
+        addTearDown(() {
+          if (dbFile.existsSync()) dbFile.deleteSync();
+        });
+
+        // conn1: enable WAL and keep a read transaction open — simulates a
+        // WorkManager background task that opened the DB before the foreground
+        // app starts.
+        final conn1 = sqlite.sqlite3.open(dbFile.path);
+        conn1.execute('PRAGMA journal_mode = WAL;');
+        conn1.execute('BEGIN;');
+        conn1.select('SELECT 1;');
+
+        // conn2: run the exact production setup through setupPragmasForTesting.
+        // This must not throw even though conn1 holds an open transaction and
+        // the DB is already in WAL mode.
+        final conn2 = sqlite.sqlite3.open(dbFile.path);
+        expect(() => setupPragmasForTesting(conn2), returnsNormally);
+
+        conn1.execute('ROLLBACK;');
+        conn1.close();
+        conn2.close();
+      },
+    );
+  });
 }