container strict mode feature

apps/weblibre/lib/features/geckoview/domain/repositories/tab.dart

@@ -900,6 +900,14 @@ class TabRepository extends _$TabRepository {
 
     final containerSiteAssignementSub = eventSerivce.siteAssignementEvent.listen(
       (event) async {
+        // Strict-mode blocks have no destination container to re-open into; the
+        // navigation was already cancelled natively and the user is notified via
+        // a snackbar (see the strict-block listener in the app shell). Nothing
+        // to reconcile here.
+        if (event.strict) {
+          return;
+        }
+
         final tabId = event.tabId;
         if (tabId != null) {
           final tabState = ref.read(tabStatesProvider)[tabId];

apps/weblibre/lib/features/geckoview/domain/repositories/tab.g.dart

@@ -41,7 +41,7 @@ final class TabRepositoryProvider
   }
 }
 
-String _$tabRepositoryHash() => r'982b80b8ea7c694958bc10cc7e8e15310af6a238';
+String _$tabRepositoryHash() => r'dd2f9c776be1d5437141e94dbd0b7ef382093b63';
 
 abstract class _$TabRepository extends $Notifier<void> {
   void build();

apps/weblibre/lib/features/geckoview/features/browser/domain/services/proxy_settings_replication.dart

@@ -289,6 +289,14 @@ class ProxySettingsReplication extends _$ProxySettingsReplication {
       }
     });
 
+    ref.listen(watchStrictContextAssignmentsProvider, (previous, next) async {
+      if (next.hasValue) {
+        await ref
+            .read(containerProxyRepositoryProvider.notifier)
+            .setStrictContexts(next.requireValue);
+      }
+    });
+
     ref.listen(
       fireImmediately: true,
       watchIsolatedContextContainerMapProvider.select(

apps/weblibre/lib/features/geckoview/features/browser/domain/services/proxy_settings_replication.g.dart

@@ -42,7 +42,7 @@ final class ProxySettingsReplicationProvider
 }
 
 String _$proxySettingsReplicationHash() =>
-    r'cdb624b7f7806a7ce4218da350253ed3d29986d0';
+    r'69787c85c94ff165e3eeb0f0a3f3fc83e88a1b83';
 
 abstract class _$ProxySettingsReplication extends $Notifier<void> {
   void build();

apps/weblibre/lib/features/geckoview/features/tabs/data/database/daos/container.dart

@@ -259,6 +259,10 @@ class ContainerDao extends DatabaseAccessor<TabDatabase>
     return db.definitionsDrift.containersToClearOnExit();
   }
 
+  Selectable<StrictContextAssignmentsResult> strictContextAssignments() {
+    return db.definitionsDrift.strictContextAssignments();
+  }
+
   SingleOrNullSelectable<ContainerData> getContainerByContextualIdentity(
     String contextId,
   ) {

apps/weblibre/lib/features/geckoview/features/tabs/data/database/definitions.drift

@@ -969,6 +969,40 @@ containersToClearOnExit:
     json_extract(container.metadata, '$.clearDataOnExit') = 1
     AND container.metadata ->> '$.contextualIdentity' IS NOT NULL;
 
+-- Strict-mode enforcement map for the container-proxy extension. Each row maps
+-- a Gecko cookie-store context (`context_id`) that must be enforced to the
+-- container's base contextualIdentity (`assignment_context_id`) that its site
+-- assignments are keyed on. In strict mode a navigation is only allowed when
+-- the target origin is assigned to `assignment_context_id` exactly (no proxy
+-- equivalence).
+--
+-- Two sources, unioned:
+--   1. The strict container's own base context (context_id == assignment).
+--   2. Every isolation context in use by an isolated tab (tab_mode = 2) whose
+--      container is strict: those tabs load under `isolation_context_id` as
+--      their cookie store, but their assignments live on the container's base
+--      context, so they map isolation_context_id -> base context.
+-- Null contextualIdentity is excluded: strictness needs a Gecko contextId.
+strictContextAssignments:
+  SELECT
+    container.metadata ->> '$.contextualIdentity' AS context_id,
+    container.metadata ->> '$.contextualIdentity' AS assignment_context_id
+  FROM container
+  WHERE
+    json_extract(container.metadata, '$.strictMode') = 1
+    AND container.metadata ->> '$.contextualIdentity' IS NOT NULL
+  UNION
+  SELECT DISTINCT
+    t.isolation_context_id AS context_id,
+    c.metadata ->> '$.contextualIdentity' AS assignment_context_id
+  FROM tab t
+  INNER JOIN container c ON c.id = t.container_id
+  WHERE
+    t.tab_mode = 2
+    AND t.isolation_context_id IS NOT NULL
+    AND json_extract(c.metadata, '$.strictMode') = 1
+    AND c.metadata ->> '$.contextualIdentity' IS NOT NULL;
+
 tabsInIsolationGroup:
   SELECT COUNT(*) AS count FROM tab WHERE isolation_context_id = :contextId;
 

apps/weblibre/lib/features/geckoview/features/tabs/data/database/definitions.drift.dart

@@ -6695,6 +6695,19 @@ class DefinitionsDrift extends i9.ModularAccessor {
     ).map((i0.QueryRow row) => row.readNullable<String>('contextual_identity'));
   }
 
+  i0.Selectable<StrictContextAssignmentsResult> strictContextAssignments() {
+    return customSelect(
+      'SELECT container.metadata ->> \'\$.contextualIdentity\' AS context_id, container.metadata ->> \'\$.contextualIdentity\' AS assignment_context_id FROM container WHERE json_extract(container.metadata, \'\$.strictMode\') = 1 AND container.metadata ->> \'\$.contextualIdentity\' IS NOT NULL UNION SELECT DISTINCT t.isolation_context_id AS context_id, c.metadata ->> \'\$.contextualIdentity\' AS assignment_context_id FROM tab AS t INNER JOIN container AS c ON c.id = t.container_id WHERE t.tab_mode = 2 AND t.isolation_context_id IS NOT NULL AND json_extract(c.metadata, \'\$.strictMode\') = 1 AND c.metadata ->> \'\$.contextualIdentity\' IS NOT NULL',
+      variables: [],
+      readsFrom: {container, tab},
+    ).map(
+      (i0.QueryRow row) => StrictContextAssignmentsResult(
+        contextId: row.readNullable<String>('context_id'),
+        assignmentContextId: row.readNullable<String>('assignment_context_id'),
+      ),
+    );
+  }
+
   i0.Selectable<int> tabsInIsolationGroup({String? contextId}) {
     return customSelect(
       'SELECT COUNT(*) AS count FROM tab WHERE isolation_context_id = ?1',
@@ -6789,6 +6802,12 @@ class ContainerIdsByContextualIdentitiesResult {
   });
 }
 
+class StrictContextAssignmentsResult {
+  final String? contextId;
+  final String? assignmentContextId;
+  StrictContextAssignmentsResult({this.contextId, this.assignmentContextId});
+}
+
 class IsolatedContextContainerPairsResult {
   final String? isolationContextId;
   final String? containerId;

apps/weblibre/lib/features/geckoview/features/tabs/data/models/container_data.dart

@@ -73,6 +73,16 @@ class ContainerMetadata with FastEquatable {
 
   final List<Uri>? assignedSites;
 
+  // When true, tabs in this container may only load origins listed in
+  // [assignedSites]; any other top-level navigation is blocked. Read on the
+  // native side via `json_extract(metadata, '$.strictMode')` (see the
+  // `strictContextAssignments` query in definitions.drift) and pushed to the
+  // container-proxy web extension. Requires a Gecko contextId — the extension
+  // keys strictness on the tab's cookieStoreId — so it is normalized to false
+  // when [contextualIdentity] is null (mirrors [excludeFromHistory]).
+  @JsonKey(defaultValue: false)
+  final bool strictMode;
+
   ContainerMetadata({
     required this.iconData,
     required this.contextualIdentity,
@@ -83,6 +93,7 @@ class ContainerMetadata with FastEquatable {
     required this.bypassGlobalProxy,
     required this.useCustomColor,
     required this.assignedSites,
+    required this.strictMode,
   });
 
   ContainerMetadata.withDefaults({
@@ -95,6 +106,7 @@ class ContainerMetadata with FastEquatable {
     bool? bypassGlobalProxy,
     bool? useCustomColor,
     List<Uri>? assignedSites,
+    bool? strictMode,
   }) : this(
          iconData: iconData,
          contextualIdentity: contextualIdentity,
@@ -112,6 +124,10 @@ class ContainerMetadata with FastEquatable {
          bypassGlobalProxy: bypassGlobalProxy ?? false,
          useCustomColor: useCustomColor ?? false,
          assignedSites: assignedSites,
+         // Strict mode needs a contextId (the extension keys on cookieStoreId);
+         // normalize away the invalid combination on read, and writers re-apply
+         // it via [sanitized].
+         strictMode: (strictMode ?? false) && contextualIdentity != null,
        );
 
   /// Enforce the [excludeFromHistory] invariant before persistence: it can only
@@ -120,10 +136,16 @@ class ContainerMetadata with FastEquatable {
   /// The primary constructor can't normalize (copy_with_extension_gen requires
   /// params to map 1:1 to fields), so writers route through this.
   ContainerMetadata sanitized() {
-    if (excludeFromHistory && contextualIdentity == null) {
-      return copyWith(excludeFromHistory: false);
+    var result = this;
+    if (result.excludeFromHistory && result.contextualIdentity == null) {
+      result = result.copyWith(excludeFromHistory: false);
     }
-    return this;
+    // Strict mode is meaningless without a contextId: the extension keys
+    // strictness on the tab's cookieStoreId.
+    if (result.strictMode && result.contextualIdentity == null) {
+      result = result.copyWith(strictMode: false);
+    }
+    return result;
   }
 
   bool get usesTorProxy => proxyConnectionId is TorProxyConnectionId;
@@ -144,6 +166,7 @@ class ContainerMetadata with FastEquatable {
     bypassGlobalProxy,
     useCustomColor,
     assignedSites,
+    strictMode,
   ];
 }
 

apps/weblibre/lib/features/geckoview/features/tabs/data/models/container_data.g.dart

@@ -25,6 +25,8 @@ abstract class _$ContainerMetadataCWProxy {
 
   ContainerMetadata assignedSites(List<Uri>? assignedSites);
 
+  ContainerMetadata strictMode(bool strictMode);
+
   /// Creates a new instance with the provided field values.
   /// Passing `null` to a nullable field nullifies it, while `null` for a non-nullable field is ignored. To update a single field use `ContainerMetadata(...).copyWith.fieldName(value)`.
   ///
@@ -42,6 +44,7 @@ abstract class _$ContainerMetadataCWProxy {
     bool bypassGlobalProxy,
     bool useCustomColor,
     List<Uri>? assignedSites,
+    bool strictMode,
   });
 }
 
@@ -87,6 +90,9 @@ class _$ContainerMetadataCWProxyImpl implements _$ContainerMetadataCWProxy {
   ContainerMetadata assignedSites(List<Uri>? assignedSites) =>
       call(assignedSites: assignedSites);
 
+  @override
+  ContainerMetadata strictMode(bool strictMode) => call(strictMode: strictMode);
+
   @override
   /// Creates a new instance with the provided field values.
   /// Passing `null` to a nullable field nullifies it, while `null` for a non-nullable field is ignored. To update a single field use `ContainerMetadata(...).copyWith.fieldName(value)`.
@@ -105,6 +111,7 @@ class _$ContainerMetadataCWProxyImpl implements _$ContainerMetadataCWProxy {
     Object? bypassGlobalProxy = const $CopyWithPlaceholder(),
     Object? useCustomColor = const $CopyWithPlaceholder(),
     Object? assignedSites = const $CopyWithPlaceholder(),
+    Object? strictMode = const $CopyWithPlaceholder(),
   }) {
     return ContainerMetadata(
       iconData: iconData == const $CopyWithPlaceholder()
@@ -153,6 +160,11 @@ class _$ContainerMetadataCWProxyImpl implements _$ContainerMetadataCWProxy {
           ? _value.assignedSites
           // ignore: cast_nullable_to_non_nullable
           : assignedSites as List<Uri>?,
+      strictMode:
+          strictMode == const $CopyWithPlaceholder() || strictMode == null
+          ? _value.strictMode
+          // ignore: cast_nullable_to_non_nullable
+          : strictMode as bool,
     );
   }
 }
@@ -295,6 +307,7 @@ ContainerMetadata _$ContainerMetadataFromJson(Map<String, dynamic> json) =>
       assignedSites: (json['assignedSites'] as List<dynamic>?)
           ?.map((e) => Uri.parse(e as String))
           .toList(),
+      strictMode: json['strictMode'] as bool? ?? false,
     );
 
 Map<String, dynamic> _$ContainerMetadataToJson(
@@ -312,6 +325,7 @@ Map<String, dynamic> _$ContainerMetadataToJson(
   'bypassGlobalProxy': instance.bypassGlobalProxy,
   'useCustomColor': instance.useCustomColor,
   'assignedSites': instance.assignedSites?.map((e) => e.toString()).toList(),
+  'strictMode': instance.strictMode,
 };
 
 Value? _$JsonConverterFromJson<Json, Value>(

apps/weblibre/lib/features/geckoview/features/tabs/domain/providers.dart

@@ -190,6 +190,33 @@ Stream<List<SiteAssignment>> watchAllAssignedSites(Ref ref) {
   return db.containerDao.allAssignedSites().watch();
 }
 
+/// Strict-mode enforcement map: each Gecko cookie-store context that must be
+/// enforced (a strict container's base context, plus the isolation contexts of
+/// its isolated tabs) mapped to the base contextualIdentities its site
+/// assignments are keyed on. Replicated to the container-proxy extension by
+/// ProxySettingsReplication.
+@Riverpod(keepAlive: true)
+Stream<Map<String, List<String>>> watchStrictContextAssignments(Ref ref) {
+  final db = ref.watch(tabDatabaseProvider);
+  return db.containerDao.strictContextAssignments().watch().map((rows) {
+    final assignments = <String, Set<String>>{};
+    for (final row in rows) {
+      final contextId = row.contextId;
+      final assignmentContextId = row.assignmentContextId;
+      if (contextId == null || assignmentContextId == null) continue;
+
+      assignments
+          .putIfAbsent(contextId, () => <String>{})
+          .add(assignmentContextId);
+    }
+
+    return {
+      for (final entry in assignments.entries)
+        entry.key: entry.value.toList()..sort(),
+    };
+  });
+}
+
 /// Watches distinct (isolationContextId, containerId) pairs for isolated tabs
 /// assigned to containers. Used by ProxySettingsReplication to manage proxy
 /// aliases for isolated contexts.

apps/weblibre/lib/features/geckoview/features/tabs/domain/providers.g.dart

@@ -1146,6 +1146,66 @@ final class WatchAllAssignedSitesProvider
 String _$watchAllAssignedSitesHash() =>
     r'5f658b5733ee20192eb86d3aeb79aa9678dafba8';
 
+/// Strict-mode enforcement map: each Gecko cookie-store context that must be
+/// enforced (a strict container's base context, plus the isolation contexts of
+/// its isolated tabs) mapped to the base contextualIdentities its site
+/// assignments are keyed on. Replicated to the container-proxy extension by
+/// ProxySettingsReplication.
+
+@ProviderFor(watchStrictContextAssignments)
+final watchStrictContextAssignmentsProvider =
+    WatchStrictContextAssignmentsProvider._();
+
+/// Strict-mode enforcement map: each Gecko cookie-store context that must be
+/// enforced (a strict container's base context, plus the isolation contexts of
+/// its isolated tabs) mapped to the base contextualIdentities its site
+/// assignments are keyed on. Replicated to the container-proxy extension by
+/// ProxySettingsReplication.
+
+final class WatchStrictContextAssignmentsProvider
+    extends
+        $FunctionalProvider<
+          AsyncValue<Map<String, List<String>>>,
+          Map<String, List<String>>,
+          Stream<Map<String, List<String>>>
+        >
+    with
+        $FutureModifier<Map<String, List<String>>>,
+        $StreamProvider<Map<String, List<String>>> {
+  /// Strict-mode enforcement map: each Gecko cookie-store context that must be
+  /// enforced (a strict container's base context, plus the isolation contexts of
+  /// its isolated tabs) mapped to the base contextualIdentities its site
+  /// assignments are keyed on. Replicated to the container-proxy extension by
+  /// ProxySettingsReplication.
+  WatchStrictContextAssignmentsProvider._()
+    : super(
+        from: null,
+        argument: null,
+        retry: null,
+        name: r'watchStrictContextAssignmentsProvider',
+        isAutoDispose: false,
+        dependencies: null,
+        $allTransitiveDependencies: null,
+      );
+
+  @override
+  String debugGetCreateSourceHash() => _$watchStrictContextAssignmentsHash();
+
+  @$internal
+  @override
+  $StreamProviderElement<Map<String, List<String>>> $createElement(
+    $ProviderPointer pointer,
+  ) => $StreamProviderElement(pointer);
+
+  @override
+  Stream<Map<String, List<String>>> create(Ref ref) {
+    return watchStrictContextAssignments(ref);
+  }
+}
+
+String _$watchStrictContextAssignmentsHash() =>
+    r'01a92529a90baf955c96c35180a50ec21ff913a8';
+
 /// Watches distinct (isolationContextId, containerId) pairs for isolated tabs
 /// assigned to containers. Used by ProxySettingsReplication to manage proxy
 /// aliases for isolated contexts.

apps/weblibre/lib/features/geckoview/features/tabs/presentation/screens/container_edit.dart

@@ -108,6 +108,7 @@ class ContainerEditScreen extends HookConsumerWidget {
       initialContainer.metadata.bypassGlobalProxy,
     );
     final assignedSites = useState(initialContainer.metadata.assignedSites);
+    final strictMode = useState(initialContainer.metadata.strictMode);
     final isPinned = useState(initialContainer.isPinned);
 
     final textController = useTextEditingController(
@@ -141,6 +142,10 @@ class ContainerEditScreen extends HookConsumerWidget {
               bypassGlobalProxy.value,
           useCustomColor: useCustomColor.value,
           assignedSites: assignedSites.value,
+          // Strict mode requires a Gecko contextId (the extension keys
+          // strictness on the tab's cookieStoreId). sanitized() enforces the
+          // same invariant defensively on write.
+          strictMode: strictMode.value && contextualIdentity.value != null,
         ).sanitized(),
       );
     }
@@ -593,31 +598,54 @@ class ContainerEditScreen extends HookConsumerWidget {
                     margin: EdgeInsets.zero,
                     color: colorScheme.surfaceContainer,
                     clipBehavior: Clip.antiAlias,
-                    child: ListTile(
-                      leading: const Icon(Icons.web),
-                      title: const Text('Assigned Sites'),
-                      subtitle: assignedSiteCount > 0
-                          ? Text(
-                              '$assignedSiteCount ${assignedSiteCount == 1 ? 'rule' : 'rules'} configured',
-                            )
-                          : const Text(
-                              'Route matching origins into this container',
-                            ),
-                      trailing: const Icon(Icons.chevron_right),
-                      onTap: () async {
-                        final result = await showDialog<Set<Uri>>(
-                          context: context,
-                          builder: (context) => ContainerSitesScreen(
-                            initialSites: assignedSites.value?.toSet() ?? {},
-                          ),
-                        );
+                    child: Column(
+                      children: [
+                        ListTile(
+                          leading: const Icon(Icons.web),
+                          title: const Text('Assigned Sites'),
+                          subtitle: assignedSiteCount > 0
+                              ? Text(
+                                  '$assignedSiteCount ${assignedSiteCount == 1 ? 'rule' : 'rules'} configured',
+                                )
+                              : const Text(
+                                  'Route matching origins into this container',
+                                ),
+                          trailing: const Icon(Icons.chevron_right),
+                          onTap: () async {
+                            final result = await showDialog<Set<Uri>>(
+                              context: context,
+                              builder: (context) => ContainerSitesScreen(
+                                initialSites:
+                                    assignedSites.value?.toSet() ?? {},
+                              ),
+                            );
 
-                        if (result == null || result.isEmpty) {
-                          assignedSites.value = null;
-                        } else {
-                          assignedSites.value = result.toList();
-                        }
-                      },
+                            if (result == null || result.isEmpty) {
+                              assignedSites.value = null;
+                            } else {
+                              assignedSites.value = result.toList();
+                            }
+                          },
+                        ),
+                        const Divider(height: 1, indent: 56),
+                        SwitchListTile.adaptive(
+                          value:
+                              contextualIdentity.value != null &&
+                              strictMode.value,
+                          title: const Text('Strict Mode'),
+                          subtitle: Text(
+                            contextualIdentity.value != null
+                                ? 'Only allow assigned sites to load; block everything else'
+                                : 'Requires cookie isolation to be enabled',
+                          ),
+                          secondary: const Icon(MdiIcons.shieldLockOutline),
+                          onChanged: (contextualIdentity.value != null)
+                              ? (value) {
+                                  strictMode.value = value;
+                                }
+                              : null,
+                        ),
+                      ],
                     ),
                   ),
                 ],

apps/weblibre/lib/features/proxy/domain/repositories/container_proxy.dart

@@ -119,6 +119,10 @@ class ContainerProxyRepository extends _$ContainerProxyRepository {
     );
   }
 
+  Future<void> setStrictContexts(Map<String, List<String>> contexts) {
+    return _runLocked(body: () => _service.setStrictContexts(contexts));
+  }
+
   /// Serialises [body] behind the service lock after the underlying Gecko
   /// proxy service reports healthy. Replaces the per-method boilerplate that
   /// each public mutator used to repeat.

apps/weblibre/lib/features/proxy/domain/repositories/container_proxy.g.dart

@@ -42,7 +42,7 @@ final class ContainerProxyRepositoryProvider
 }
 
 String _$containerProxyRepositoryHash() =>
-    r'9201bb0cdda570d38adc5fc16d1c7719f3d719a2';
+    r'9d9190edcb06eb1335318172183e354a66626f57';
 
 abstract class _$ContainerProxyRepository extends $Notifier<void> {
   void build();

apps/weblibre/lib/presentation/main_app.dart

@@ -103,7 +103,9 @@ class MainApp extends HookConsumerWidget {
               child: _SyncEventListener(
                 child: _SandboxCaptureErrorListener(
                   child: _DownloadStoppedListener(
-                    child: child ?? const SizedBox.shrink(),
+                    child: _StrictContainerBlockListener(
+                      child: child ?? const SizedBox.shrink(),
+                    ),
                   ),
                 ),
               ),
@@ -206,6 +208,42 @@ class _DownloadStoppedListener extends HookConsumerWidget {
   }
 }
 
+/// Surfaces a snackbar when the container-proxy extension cancels a navigation
+/// because the active tab's container is in strict mode (only assigned sites
+/// may load). Strict blocks carry no destination container — the load was
+/// already cancelled natively — so this listener only notifies the user.
+class _StrictContainerBlockListener extends HookConsumerWidget {
+  final Widget child;
+
+  const _StrictContainerBlockListener({required this.child});
+
+  @override
+  Widget build(BuildContext context, WidgetRef ref) {
+    final siteAssignmentEvents = ref.watch(
+      eventServiceProvider.select((service) => service.siteAssignementEvent),
+    );
+
+    useOnStreamChange(
+      siteAssignmentEvents,
+      onData: (event) {
+        if (!event.strict) {
+          return;
+        }
+
+        final host = Uri.tryParse(event.url)?.host;
+        ui_helper.showInfoMessage(
+          context,
+          host != null && host.isNotEmpty
+              ? '$host is not assigned to this container'
+              : 'This site is not assigned to this container',
+        );
+      },
+    );
+
+    return child;
+  }
+}
+
 MediaQueryData applyAppMediaQueryOverrides({
   required MediaQueryData mediaQuery,
   required double uiScaleFactor,

packages/flutter_mozilla_components/android/src/main/kotlin/eu/weblibre/flutter_mozilla_components/api/GeckoContainerProxyApiImpl.kt

@@ -72,6 +72,10 @@ class GeckoContainerProxyApiImpl : GeckoContainerProxyApi {
         ContainerProxyFeature.scheduleRequest("setSiteAssignments", JSONObject(assignments))
     }
 
+    override fun setStrictContexts(contexts: Map<String, List<String>>) {
+        ContainerProxyFeature.scheduleRequest("setStrictContexts", JSONObject(contexts))
+    }
+
     override fun healthcheck(callback: (Result<Boolean>) -> Unit) {
         ContainerProxyFeature.scheduleRequestWithResponse("healthcheck", Unit, object :
             ResultConsumer<JSONObject> {

packages/flutter_mozilla_components/android/src/main/kotlin/eu/weblibre/flutter_mozilla_components/feature/ContainerProxyFeature.kt

@@ -122,7 +122,8 @@ object ContainerProxyFeature {
                                             tabId = components.core.store.state.selectedTabId,
                                             originUrl = details.tryGetString("originUrl"),
                                             url = details.getString("url"),
-                                            blocked = details.getBoolean("blocked")
+                                            blocked = details.getBoolean("blocked"),
+                                            strict = details.optBoolean("strict", false)
                                         )
                                     ) { _ -> }
                                 }

packages/flutter_mozilla_components/android/src/main/kotlin/eu/weblibre/flutter_mozilla_components/pigeons/Gecko.g.kt

@@ -4658,7 +4658,14 @@ data class ContainerSiteAssignment (
   val tabId: String? = null,
   val originUrl: String? = null,
   val url: String,
-  val blocked: Boolean
+  val blocked: Boolean,
+  /**
+   * True when the navigation was cancelled because the tab's container is in
+   * strict mode and the target origin is not assigned to it (as opposed to an
+   * ordinary re-open-in-assigned-container block). Strict blocks have no
+   * destination container; the app just surfaces a message.
+   */
+  val strict: Boolean
 )
  {
   companion object {
@@ -4668,7 +4675,8 @@ data class ContainerSiteAssignment (
       val originUrl = pigeonVar_list[2] as String?
       val url = pigeonVar_list[3] as String
       val blocked = pigeonVar_list[4] as Boolean
-      return ContainerSiteAssignment(requestId, tabId, originUrl, url, blocked)
+      val strict = pigeonVar_list[5] as Boolean
+      return ContainerSiteAssignment(requestId, tabId, originUrl, url, blocked, strict)
     }
   }
   fun toList(): List<Any?> {
@@ -4678,6 +4686,7 @@ data class ContainerSiteAssignment (
       originUrl,
       url,
       blocked,
+      strict,
     )
   }
   override fun equals(other: Any?): Boolean {
@@ -4688,7 +4697,7 @@ data class ContainerSiteAssignment (
       return true
     }
     val other = other as ContainerSiteAssignment
-    return GeckoPigeonUtils.deepEquals(this.requestId, other.requestId) && GeckoPigeonUtils.deepEquals(this.tabId, other.tabId) && GeckoPigeonUtils.deepEquals(this.originUrl, other.originUrl) && GeckoPigeonUtils.deepEquals(this.url, other.url) && GeckoPigeonUtils.deepEquals(this.blocked, other.blocked)
+    return GeckoPigeonUtils.deepEquals(this.requestId, other.requestId) && GeckoPigeonUtils.deepEquals(this.tabId, other.tabId) && GeckoPigeonUtils.deepEquals(this.originUrl, other.originUrl) && GeckoPigeonUtils.deepEquals(this.url, other.url) && GeckoPigeonUtils.deepEquals(this.blocked, other.blocked) && GeckoPigeonUtils.deepEquals(this.strict, other.strict)
   }
 
   override fun hashCode(): Int {
@@ -4698,6 +4707,7 @@ data class ContainerSiteAssignment (
     result = 31 * result + GeckoPigeonUtils.deepHash(this.originUrl)
     result = 31 * result + GeckoPigeonUtils.deepHash(this.url)
     result = 31 * result + GeckoPigeonUtils.deepHash(this.blocked)
+    result = 31 * result + GeckoPigeonUtils.deepHash(this.strict)
     return result
   }
 }
@@ -8622,6 +8632,16 @@ interface GeckoContainerProxyApi {
   fun clearContainerProxy(contextId: String)
   fun removeContainerProxyRelation(contextId: String, proxyId: String)
   fun setSiteAssignments(assignments: Map<String, String>)
+  /**
+   * Strict-mode enforcement map. Keys are Gecko cookie-store contexts to
+   * enforce (a strict container's base context plus its isolated tabs'
+   * isolation contexts); each value contains the container base contexts that
+   * site assignments are keyed on. Tabs in these contexts may only load
+   * origins assigned to one of the mapped base contexts (exact match, no proxy
+   * equivalence); any other top-level navigation is cancelled and reported
+   * back with `strict = true`.
+   */
+  fun setStrictContexts(contexts: Map<String, List<String>>)
   fun healthcheck(callback: (Result<Boolean>) -> Unit)
 
   companion object {
@@ -8816,6 +8836,24 @@ interface GeckoContainerProxyApi {
           channel.setMessageHandler(null)
         }
       }
+      run {
+        val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.flutter_mozilla_components.GeckoContainerProxyApi.setStrictContexts$separatedMessageChannelSuffix", codec)
+        if (api != null) {
+          channel.setMessageHandler { message, reply ->
+            val args = message as List<Any?>
+            val contextsArg = args[0] as Map<String, List<String>>
+            val wrapped: List<Any?> = try {
+              api.setStrictContexts(contextsArg)
+              listOf(null)
+            } catch (exception: Throwable) {
+              GeckoPigeonUtils.wrapError(exception)
+            }
+            reply.reply(wrapped)
+          }
+        } else {
+          channel.setMessageHandler(null)
+        }
+      }
       run {
         val channel = BasicMessageChannel<Any?>(binaryMessenger, "dev.flutter.pigeon.flutter_mozilla_components.GeckoContainerProxyApi.healthcheck$separatedMessageChannelSuffix", codec)
         if (api != null) {
@@ -8980,7 +9018,7 @@ class GeckoStateEvents(private val binaryMessenger: BinaryMessenger, private val
         }
       } else {
         callback(Result.failure(GeckoPigeonUtils.createConnectionError(channelName)))
-      }
+      } 
     }
   }
   fun onEngineReadyStateChange(sequenceArg: Long, stateArg: Boolean, callback: (Result<Unit>) -> Unit)
@@ -10375,7 +10413,7 @@ class GeckoHistoryEvents(private val binaryMessenger: BinaryMessenger, private v
         }
       } else {
         callback(Result.failure(GeckoPigeonUtils.createConnectionError(channelName)))
-      }
+      } 
     }
   }
 }

packages/flutter_mozilla_components/javascript/container_proxy/src/background/BackgroundMain.ts

@@ -149,19 +149,36 @@ export default class BackgroundMain {
     }
 
     const url = URL.parse(options.url);
-    if (url !== null && this.store.isSiteOriginAssigned(url)) {
-      let cookieStoreId: string
+    if (url === null) {
+      return {};
+    }
 
-      if (tab.cookieStoreId?.startsWith(containerIdentifier) === true) {
-        cookieStoreId = tab.cookieStoreId.substring(containerIdentifier.length)
-      } else if (tab.cookieStoreId === privateIdentifier) {
-        // Handle private tabs - use 'private' as identifier
-        cookieStoreId = 'private'
-      } else {
-        cookieStoreId = 'general'
-      }
+    let cookieStoreId: string
 
-      if (cookieStoreId == 'private' || this.store.isSiteOriginInSameContext(url, cookieStoreId)) {
+    if (tab.cookieStoreId?.startsWith(containerIdentifier) === true) {
+      cookieStoreId = tab.cookieStoreId.substring(containerIdentifier.length)
+    } else if (tab.cookieStoreId === privateIdentifier) {
+      // Handle private tabs - use 'private' as identifier
+      cookieStoreId = 'private'
+    } else {
+      cookieStoreId = 'general'
+    }
+
+    // Private tabs are never strict. For other tabs, strict enforcement is
+    // keyed on the tab's cookie-store context (base container context, or an
+    // isolation context of a strict container's isolated tab).
+    const isStrict = cookieStoreId !== 'private' &&
+      this.store.isContextStrict(cookieStoreId)
+
+    if (this.store.isSiteOriginAssigned(url)) {
+      // In a strict context the site must be assigned to *this* container's own
+      // base context (exact match, no proxy equivalence). Non-strict contexts
+      // keep the looser proxy/direct-equivalence matching used for routing.
+      const allowed = isStrict
+        ? this.store.isSiteOriginStrictlyAllowed(url, cookieStoreId)
+        : (cookieStoreId == 'private' || this.store.isSiteOriginInSameContext(url, cookieStoreId))
+
+      if (allowed) {
         if (tab.highlighted) {
           port.postMessage({
             "type": "assignedSiteRequested",
@@ -171,7 +188,8 @@ export default class BackgroundMain {
               "originUrl": options.originUrl,
               "url": options.url,
               "tabId": options.tabId,
-              "blocked": false
+              "blocked": false,
+              "strict": false
             }
           });
         }
@@ -180,6 +198,9 @@ export default class BackgroundMain {
         // even if the tab is not highlighted.
         return {};
       } else {
+        // Assigned to a different container: cancel here and let the app re-open
+        // it in its assigned container. This applies to strict contexts too —
+        // the site still doesn't load here, it just routes to where it belongs.
         //Only send events when tab is selected
         if (tab.highlighted) {
           port.postMessage({
@@ -190,7 +211,8 @@ export default class BackgroundMain {
               "originUrl": options.originUrl,
               "url": options.url,
               "tabId": options.tabId,
-              "blocked": true
+              "blocked": true,
+              "strict": false
             }
           });
         }
@@ -199,6 +221,28 @@ export default class BackgroundMain {
           cancel: true,
         };
       }
+    } else if (isStrict) {
+      // Strict mode: this container may only load origins assigned to it. The
+      // origin is not assigned to any container, so cancel the navigation and
+      // report it as a strict block (no destination container).
+      if (tab.highlighted) {
+        port.postMessage({
+          "type": "assignedSiteRequested",
+          "id": options.requestId,
+          "status": "success",
+          "result": {
+            "originUrl": options.originUrl,
+            "url": options.url,
+            "tabId": options.tabId,
+            "blocked": true,
+            "strict": true
+          }
+        });
+      }
+
+      return {
+        cancel: true,
+      };
     }
 
     return {};

packages/flutter_mozilla_components/javascript/container_proxy/src/background/index.ts

@@ -18,7 +18,8 @@ interface Message {
     'clearContainerProxy' |
     'removeContainerProxyRelation' |
     'healthcheck' |
-    'setSiteAssignments';
+    'setSiteAssignments' |
+    'setStrictContexts';
     args: any;
 }
 
@@ -92,6 +93,10 @@ port.onMessage.addListener((raw: unknown): void => {
             console.log('set site assignments ' + JSON.stringify(message.args))
             store.setSiteAssignments(entries);
             break
+        case "setStrictContexts":
+            console.log('set strict contexts ' + JSON.stringify(message.args))
+            store.setStrictContexts(new Map(Object.entries(message.args)) as Map<string, string[]>);
+            break
         case "healthcheck":
             port.postMessage({
                 "type": "healthcheck",

packages/flutter_mozilla_components/javascript/container_proxy/src/store/Store.ts

@@ -89,6 +89,39 @@ export class Store {
   private siteAssignments: Map<string, string> = new Map<string, string>()
   private wildcardAssignments: WildcardAssignment[] = []
 
+  // Maps an enforced cookie-store context (a strict container's base context,
+  // or an isolation context of one of its isolated tabs) to the base contexts
+  // its site assignments are keyed on.
+  private strictContexts: Map<string, Set<string>> = new Map<string, Set<string>>()
+
+  setStrictContexts(contexts: Map<string, string[]>): void {
+    const next = new Map<string, Set<string>>()
+    for (const [contextId, assignmentContexts] of contexts) {
+      next.set(contextId, new Set(assignmentContexts))
+    }
+    this.strictContexts = next
+  }
+
+  isContextStrict(contextId: string): boolean {
+    return this.strictContexts.has(contextId)
+  }
+
+  /**
+   * True when [uri]'s origin is assigned to a base context that [contextId]
+   * enforces. Strict mode requires an exact assignment match (via
+   * [lookupAssignment], which handles exact + wildcard entries) against the
+   * container's base contexts — proxy/direct equivalence is deliberately NOT
+   * consulted, so a site assigned only to a different (even proxy-equivalent)
+   * container does not load here.
+   */
+  isSiteOriginStrictlyAllowed(uri: URL, contextId: string): boolean {
+    const assignmentContexts = this.strictContexts.get(contextId)
+    const assignedContext = this.lookupAssignment(uri)
+    return assignedContext !== undefined &&
+      assignmentContexts !== undefined &&
+      assignmentContexts.has(assignedContext)
+  }
+
   setSiteAssignments(sites: Map<string, unknown>): void {
     const exact = new Map<string, string>()
     const wildcard: WildcardAssignment[] = []

packages/flutter_mozilla_components/lib/src/domain/services/gecko_container_proxy.dart

@@ -55,6 +55,10 @@ class GeckoContainerProxyService {
     return _apiInstance.setSiteAssignments(assignments);
   }
 
+  Future<void> setStrictContexts(Map<String, List<String>> contexts) {
+    return _apiInstance.setStrictContexts(contexts);
+  }
+
   Future<bool> healthcheck() async {
     try {
       return await _apiInstance.healthcheck().timeout(

packages/flutter_mozilla_components/lib/src/pigeons/gecko.g.dart

@@ -4928,6 +4928,7 @@ class ContainerSiteAssignment {
     this.originUrl,
     required this.url,
     required this.blocked,
+    required this.strict,
   });
 
   String requestId;
@@ -4940,6 +4941,12 @@ class ContainerSiteAssignment {
 
   bool blocked;
 
+  /// True when the navigation was cancelled because the tab's container is in
+  /// strict mode and the target origin is not assigned to it (as opposed to an
+  /// ordinary re-open-in-assigned-container block). Strict blocks have no
+  /// destination container; the app just surfaces a message.
+  bool strict;
+
   List<Object?> _toList() {
     return <Object?>[
       requestId,
@@ -4947,6 +4954,7 @@ class ContainerSiteAssignment {
       originUrl,
       url,
       blocked,
+      strict,
     ];
   }
 
@@ -4961,6 +4969,7 @@ class ContainerSiteAssignment {
       originUrl: result[2] as String?,
       url: result[3]! as String,
       blocked: result[4]! as bool,
+      strict: result[5]! as bool,
     );
   }
 
@@ -4973,7 +4982,7 @@ class ContainerSiteAssignment {
     if (identical(this, other)) {
       return true;
     }
-    return _deepEquals(requestId, other.requestId) && _deepEquals(tabId, other.tabId) && _deepEquals(originUrl, other.originUrl) && _deepEquals(url, other.url) && _deepEquals(blocked, other.blocked);
+    return _deepEquals(requestId, other.requestId) && _deepEquals(tabId, other.tabId) && _deepEquals(originUrl, other.originUrl) && _deepEquals(url, other.url) && _deepEquals(blocked, other.blocked) && _deepEquals(strict, other.strict);
   }
 
   @override
@@ -8634,6 +8643,31 @@ class GeckoContainerProxyApi {
     ;
   }
 
+  /// Strict-mode enforcement map. Keys are Gecko cookie-store contexts to
+  /// enforce (a strict container's base context plus its isolated tabs'
+  /// isolation contexts); each value contains the container base contexts that
+  /// site assignments are keyed on. Tabs in these contexts may only load
+  /// origins assigned to one of the mapped base contexts (exact match, no proxy
+  /// equivalence); any other top-level navigation is cancelled and reported
+  /// back with `strict = true`.
+  Future<void> setStrictContexts(Map<String, List<String>> contexts) async {
+    final pigeonVar_channelName = 'dev.flutter.pigeon.flutter_mozilla_components.GeckoContainerProxyApi.setStrictContexts$pigeonVar_messageChannelSuffix';
+    final pigeonVar_channel = BasicMessageChannel<Object?>(
+      pigeonVar_channelName,
+      pigeonChannelCodec,
+      binaryMessenger: pigeonVar_binaryMessenger,
+    );
+    final Future<Object?> pigeonVar_sendFuture = pigeonVar_channel.send(<Object?>[contexts]);
+    final pigeonVar_replyList = await pigeonVar_sendFuture as List<Object?>?;
+
+    _extractReplyValueOrThrow(
+        pigeonVar_replyList,
+        pigeonVar_channelName,
+        isNullValid: true,
+    )
+    ;
+  }
+
   Future<bool> healthcheck() async {
     final pigeonVar_channelName = 'dev.flutter.pigeon.flutter_mozilla_components.GeckoContainerProxyApi.healthcheck$pigeonVar_messageChannelSuffix';
     final pigeonVar_channel = BasicMessageChannel<Object?>(

packages/flutter_mozilla_components/pigeons/gecko.dart

@@ -1927,6 +1927,15 @@ abstract class GeckoContainerProxyApi {
   void removeContainerProxyRelation(String contextId, String proxyId);
   void setSiteAssignments(Map<String, String> assignments);
 
+  /// Strict-mode enforcement map. Keys are Gecko cookie-store contexts to
+  /// enforce (a strict container's base context plus its isolated tabs'
+  /// isolation contexts); each value contains the container base contexts that
+  /// site assignments are keyed on. Tabs in these contexts may only load
+  /// origins assigned to one of the mapped base contexts (exact match, no proxy
+  /// equivalence); any other top-level navigation is cancelled and reported
+  /// back with `strict = true`.
+  void setStrictContexts(Map<String, List<String>> contexts);
+
   @async
   bool healthcheck();
 }
@@ -1985,12 +1994,19 @@ class ContainerSiteAssignment {
   final String url;
   final bool blocked;
 
+  /// True when the navigation was cancelled because the tab's container is in
+  /// strict mode and the target origin is not assigned to it (as opposed to an
+  /// ordinary re-open-in-assigned-container block). Strict blocks have no
+  /// destination container; the app just surfaces a message.
+  final bool strict;
+
   ContainerSiteAssignment({
     required this.requestId,
     required this.tabId,
     required this.originUrl,
     required this.url,
     required this.blocked,
+    required this.strict,
   });
 }