fix(runtime): bound resources and quarantine stalled extensions

lib/utils/ttl_cache.dart

@@ -1,22 +1,56 @@
-/// Simple in-memory cache where each entry expires after [ttl].
+import 'dart:collection';
+
+/// Bounded in-memory LRU cache where each entry expires after [ttl].
 class TtlCache<T> {
   final Duration ttl;
-  final Map<String, _TtlEntry<T>> _entries = {};
+  final int maxEntries;
+  final LinkedHashMap<String, _TtlEntry<T>> _entries =
+      LinkedHashMap<String, _TtlEntry<T>>();
 
-  TtlCache(this.ttl);
+  TtlCache(this.ttl, {this.maxEntries = 100}) {
+    if (maxEntries <= 0) {
+      throw ArgumentError.value(
+        maxEntries,
+        'maxEntries',
+        'must be greater than zero',
+      );
+    }
+  }
 
   T? get(String key) {
+    _removeExpired();
     final entry = _entries[key];
     if (entry == null) return null;
-    if (DateTime.now().isAfter(entry.expiresAt)) {
-      _entries.remove(key);
-      return null;
-    }
+    // LinkedHashMap preserves insertion order, so reinserting makes this the
+    // most recently used entry.
+    _entries
+      ..remove(key)
+      ..[key] = entry;
     return entry.value;
   }
 
   void set(String key, T value) {
+    _removeExpired();
+    _entries.remove(key);
     _entries[key] = _TtlEntry(value, DateTime.now().add(ttl));
+    while (_entries.length > maxEntries) {
+      _entries.remove(_entries.keys.first);
+    }
+  }
+
+  void remove(String key) => _entries.remove(key);
+
+  void clear() => _entries.clear();
+
+  int get length {
+    _removeExpired();
+    return _entries.length;
+  }
+
+  void _removeExpired() {
+    if (_entries.isEmpty) return;
+    final now = DateTime.now();
+    _entries.removeWhere((_, entry) => !now.isBefore(entry.expiresAt));
   }
 }