Keep project directory browse usable under intercepted pickers

Browser directory picking can be intercepted by embedded automation environments, which raises before the user can choose a folder. The project setup browse flow now treats that specific interception as a signal to use the existing server browse-directory fallback, while preserving normal browser picker behavior and cancellation semantics.

Constraint: In-app browser automation may install Page.setInterceptFileChooserDialog and break showDirectoryPicker
Constraint: Browser File System Access selection should still be preferred when it works
Rejected: Always fall back after any browser picker error | permission and unsupported errors should remain visible instead of silently choosing a server path
Confidence: high
Scope-risk: narrow
Directive: Do not broaden fallback errors without checking browser local-project semantics
Tested: npm run test:run -- src/components/__tests__/ProjectSetupModal.test.tsx --testNamePattern "fall back to browse-directory API"
Tested: npm run test:run -- src/components/__tests__/ProjectSetupModal.test.tsx --testNamePattern "Browse Button"
Tested: npm run test:run -- src/components/__tests__/ProjectSetupModal.test.tsx --testNamePattern "fall back to browse-directory API|should call browse-directory API|should keep selected parent path|should handle cancelled browse dialog"
Tested: npm run build
Not-tested: npm run lint | existing Next 16 next lint script resolves to nonexistent /lint directory
Not-tested: Full ProjectSetupModal test file | existing Provider tab assertions expect API key inputs hidden by current Popi mode

src/components/ProjectSetupModal.tsx

@@ -86,6 +86,20 @@ function getDefaultModelForLLMProvider(provider: LLMProvider): LLMModelType {
   return LLM_MODELS[provider][0].value;
 }
 
+function getBrowseErrorMessage(error: unknown): string {
+  return error instanceof Error ? error.message : String(error);
+}
+
+function isDirectoryPickerCancel(error: unknown): boolean {
+  if (error instanceof DOMException && error.name === "AbortError") return true;
+  const message = getBrowseErrorMessage(error);
+  return message.includes("User canceled") || message.includes("-128");
+}
+
+function shouldFallbackToServerDirectoryPicker(error: unknown): boolean {
+  return getBrowseErrorMessage(error).includes("Page.setInterceptFileChooserDialog");
+}
+
 interface ProjectSetupModalProps {
   isOpen: boolean;
   onClose: () => void;
@@ -258,11 +272,20 @@ export function ProjectSetupModal({
 
     try {
       if (isBrowserDirectoryPickerSupported()) {
-        const browserPath = await pickBrowserWorkflowDirectory();
-        if (browserPath) {
-          setDirectoryPath(browserPath);
+        try {
+          const browserPath = await pickBrowserWorkflowDirectory();
+          if (browserPath) {
+            setDirectoryPath(browserPath);
+          }
+          return;
+        } catch (browserPickerError) {
+          if (isDirectoryPickerCancel(browserPickerError)) {
+            return;
+          }
+          if (!shouldFallbackToServerDirectoryPicker(browserPickerError)) {
+            throw browserPickerError;
+          }
         }
-        return;
       }
 
       const response = await fetch("/api/browse-directory");

src/components/__tests__/ProjectSetupModal.test.tsx

@@ -109,6 +109,7 @@ describe("ProjectSetupModal", () => {
 
   afterEach(() => {
     vi.restoreAllMocks();
+    delete window.showDirectoryPicker;
   });
 
   describe("Visibility", () => {
@@ -692,6 +693,50 @@ describe("ProjectSetupModal", () => {
   });
 
   describe("Browse Button", () => {
+    it("should fall back to browse-directory API when browser directory picker is intercepted", async () => {
+      Object.defineProperty(window, "showDirectoryPicker", {
+        value: vi.fn().mockRejectedValue(
+          new Error("Failed to execute 'showDirectoryPicker' on 'Window': Intercepted by Page.setInterceptFileChooserDialog().")
+        ),
+        configurable: true,
+      });
+
+      mockFetch.mockImplementation((url: string) => {
+        if (url === "/api/env-status") {
+          return Promise.resolve({
+            ok: true,
+            json: () => Promise.resolve({ gemini: false, openai: false, replicate: false, fal: false }),
+          });
+        }
+        if (url === "/api/browse-directory") {
+          return Promise.resolve({
+            ok: true,
+            json: () => Promise.resolve({ success: true, path: "/selected/path" }),
+          });
+        }
+        return Promise.resolve({ ok: true, json: () => Promise.resolve({ success: true }) });
+      });
+
+      render(
+        <ProjectSetupModal
+          isOpen={true}
+          onClose={vi.fn()}
+          onSave={vi.fn()}
+          mode="new"
+        />
+      );
+
+      fireEvent.click(screen.getByText("Browse"));
+
+      await waitFor(() => {
+        expect(mockFetch).toHaveBeenCalledWith("/api/browse-directory");
+        const directoryInput = screen.getByDisplayValue("/selected/path") as HTMLInputElement;
+        expect(directoryInput.value).toBe("/selected/path");
+      });
+
+      expect(screen.queryByText(/Intercepted by Page\.setInterceptFileChooserDialog/)).not.toBeInTheDocument();
+    });
+
     it("should call browse-directory API when Browse is clicked", async () => {
       mockFetch.mockImplementation((url: string) => {
         if (url === "/api/env-status") {