区分原生文件选择取消语义

H5 HostBridge 将原生取消从不支持能力错误中拆出

文件导入与拍摄取消统一返回 null，保留不支持和畸形结果为 false

补充取消导入与拍摄回归测试并加入原生壳门禁反查

scripts/check-native-shells.mjs

@@ -1252,26 +1252,32 @@ function assertH5HostBridgePayloadBoundaries() {
     {
       functionName: 'importHostTextFile',
       normalizer: 'normalizeHostBridgeImportTextResult',
+      preserveCancellation: true,
     },
     {
       functionName: 'importHostDocumentFile',
       normalizer: 'normalizeHostBridgeImportDocumentResult',
+      preserveCancellation: true,
     },
     {
       functionName: 'importHostImageFile',
       normalizer: 'normalizeHostBridgeImportImageResult',
+      preserveCancellation: true,
     },
     {
       functionName: 'captureHostImageFile',
       normalizer: 'normalizeHostBridgeImportImageResult',
+      preserveCancellation: true,
     },
     {
       functionName: 'importHostAudioFile',
       normalizer: 'normalizeHostBridgeImportAudioResult',
+      preserveCancellation: true,
     },
     {
       functionName: 'subscribeHostImageDrop',
       normalizer: 'normalizeHostBridgeImportImageResult',
+      preserveCancellation: false,
     },
   ]) {
     const functionSource = extractFunctionSource(
@@ -1283,6 +1289,24 @@ function assertH5HostBridgePayloadBoundaries() {
         `${importBoundary.functionName} must normalize imported file results with shared ${importBoundary.normalizer}`,
       );
     }
+    if (
+      importBoundary.preserveCancellation &&
+      (!functionSource.includes('isCancelledHostBridgeError(error)') ||
+        !functionSource.includes('return null;'))
+    ) {
+      throw new Error(
+        `${importBoundary.functionName} must preserve native user cancellation as null`,
+      );
+    }
+  }
+  const unsupportedHelperSource = extractFunctionSource(
+    h5HostBridgeSource,
+    'isUnsupportedHostBridgeError',
+  );
+  if (unsupportedHelperSource.includes("'cancelled'")) {
+    throw new Error(
+      'H5 HostBridge facade must not treat native user cancellation as unsupported capability',
+    );
   }
   for (const localMimeSet of [
     'HOST_BRIDGE_TEXT_MIME_TYPE_SET',