fix(gallery): Rescan Output Folder drops the server listing cache and rewalks

The button only re-requested the listing, which the server answers from a
30-second in-memory cache, so a rescan showed exactly what was already on
screen.

- POST /prompt_manager/gallery/rescan invalidates the gallery cache,
  rewalks every output root and returns the file and root counts
- the button calls it, closes the settings modal, reloads the folder tree
  and the first page, and reports what it found

py/api/images.py

@@ -397,6 +397,11 @@ class ImageRoutesMixin:
         async def get_gallery_subfolders_route(request):
             return await self.get_gallery_subfolders(request)
 
+        # POST: drops the server-side listing cache and rewalks the output roots.
+        @routes.post("/prompt_manager/gallery/rescan")
+        async def rescan_gallery_route(request):
+            return await self.rescan_gallery(request)
+
     def _present_images(self, images):
         """Image dicts ready for a response: urls added, server paths hidden."""
         self._enrich_images(images)
@@ -736,6 +741,27 @@ class ImageRoutesMixin:
                 {"success": False, "error": _safe_error(e)}, status=500
             )
 
+    async def rescan_gallery(self, request):
+        """Forget the cached listing and rewalk every output root now.
+
+        The listing is cached for ``_gallery_cache_ttl`` seconds; the gallery's
+        Rescan button needs files added or removed on disk to show up at once.
+        """
+        try:
+            self.invalidate_gallery_cache()
+            output_dirs = list(self._get_all_output_dirs())
+            total = 0
+            for output_path in output_dirs:
+                total += len(await self._get_gallery_files(output_path))
+            return web.json_response(
+                {"success": True, "total": total, "roots": len(output_dirs)}
+            )
+        except Exception:
+            self.logger.exception("Gallery rescan error")
+            return web.json_response(
+                {"success": False, "error": "Failed to rescan the gallery"}, status=500
+            )
+
     async def get_gallery_subfolders(self, request):
         """Get distinct subfolders from gallery output directories."""
         try:

tests/test_api_images.py

@@ -1717,6 +1717,46 @@ if __name__ == "__main__":
     unittest.main()
 
 
+class TestGalleryRescan(ImageAPITestCase):
+    """POST /prompt_manager/gallery/rescan drops the listing cache and rewalks."""
+
+    URL = "/prompt_manager/images/output"
+
+    async def _json(self, method, path, **kwargs):
+        resp = await self.client.request(method, path, **kwargs)
+        return resp.status, await resp.json()
+
+    async def test_rescan_makes_new_files_visible_before_the_cache_expires(self):
+        self.api._gallery_cache_ttl = 3600  # the cache alone would hide the new file
+        make_png(self.output_dir / "a.png")
+        _, first = await self._json("GET", self.URL)
+        self.assertEqual(first["total"], 1)
+
+        make_png(self.output_dir / "b.png")
+        _, stale = await self._json("GET", self.URL)
+        self.assertEqual(stale["total"], 1)
+
+        status, data = await self._json("POST", "/prompt_manager/gallery/rescan")
+        _, fresh = await self._json("GET", self.URL)
+
+        self.assertEqual(status, 200)
+        self.assertTrue(data["success"])
+        self.assertEqual(data["total"], 2)
+        self.assertEqual(data["roots"], 1)
+        self.assertEqual(fresh["total"], 2)
+
+    async def test_rescan_is_post_only(self):
+        resp = await self.client.request("GET", "/prompt_manager/gallery/rescan")
+        self.assertEqual(resp.status, 405)
+
+    async def test_rescan_reports_internal_failure(self):
+        self.api._scan_gallery_files_sync = _raise
+        status, data = await self._json("POST", "/prompt_manager/gallery/rescan")
+        self.assertEqual(status, 500)
+        self.assertFalse(data["success"])
+        self.assertNotIn("boom", json.dumps(data))
+
+
 class TestOutputScanHelpers(ImageAPITestCase):
     """Stable ids for filesystem entries, no symlink reads, stop on disconnect."""
 

web/js/gallery.js

@@ -2123,9 +2123,12 @@ Seed: ${this.currentMetadata.seed || 'Unknown'}`;
                 btn.textContent = 'Scanning...';
                 
                 try {
-                    // Force reload images
-                    await this.loadImages();
-                    this.showNotification('Folder rescanned successfully!', 'success');
+                    // The listing is cached on the server; ask it to rewalk the folders first
+                    const result = await this.api.post('/prompt_manager/gallery/rescan', {});
+                    this.hideSettings();
+                    await Promise.all([this.loadFolderTree(), this.loadImages(1)]);
+                    const where = result.roots === 1 ? 'the output folder' : `${result.roots} folders`;
+                    this.showNotification(`Rescanned ${where}: ${result.total} files`, 'success');
                 } catch (error) {
                     console.error('Rescan error:', error);
                     this.showNotification('Failed to rescan folder', 'error');