feat: allow multiple meta category ids

backend/prisma/migrations/20260908180621_multi_value_folder_category_ids/migration.sql

@@ -0,0 +1,25 @@
+-- A Folder's site-category matching now accepts several ids per site (e.g. a parent category
+-- plus a couple of its subcategories), not just one. Converts each single-value *CatId column
+-- into a *CatIds int array, preserving any value already set as a one-element array, then swaps
+-- the old scalar indexes for GIN indexes suited to the array-overlap ("hasSome") queries
+-- importService.ts's resolveFolderIdByCategory now runs.
+
+ALTER TABLE "Folder" ADD COLUMN "makerworldCatIds" INTEGER[] NOT NULL DEFAULT '{}';
+ALTER TABLE "Folder" ADD COLUMN "thingiverseCatIds" INTEGER[] NOT NULL DEFAULT '{}';
+ALTER TABLE "Folder" ADD COLUMN "printablesCatIds" INTEGER[] NOT NULL DEFAULT '{}';
+
+UPDATE "Folder" SET "makerworldCatIds" = ARRAY["makerworldCatId"] WHERE "makerworldCatId" IS NOT NULL;
+UPDATE "Folder" SET "thingiverseCatIds" = ARRAY["thingiverseCatId"] WHERE "thingiverseCatId" IS NOT NULL;
+UPDATE "Folder" SET "printablesCatIds" = ARRAY["printablesCatId"] WHERE "printablesCatId" IS NOT NULL;
+
+DROP INDEX "Folder_userId_makerworldCatId_idx";
+DROP INDEX "Folder_userId_thingiverseCatId_idx";
+DROP INDEX "Folder_userId_printablesCatId_idx";
+
+ALTER TABLE "Folder" DROP COLUMN "makerworldCatId";
+ALTER TABLE "Folder" DROP COLUMN "thingiverseCatId";
+ALTER TABLE "Folder" DROP COLUMN "printablesCatId";
+
+CREATE INDEX "Folder_makerworldCatIds_idx" ON "Folder" USING GIN ("makerworldCatIds");
+CREATE INDEX "Folder_thingiverseCatIds_idx" ON "Folder" USING GIN ("thingiverseCatIds");
+CREATE INDEX "Folder_printablesCatIds_idx" ON "Folder" USING GIN ("printablesCatIds");

backend/prisma/schema.prisma

@@ -44,21 +44,25 @@ model Folder {
   position         Int      @default(0)
   metaTitle        String?
   metaDescription  String?
-  // When set, an import from that site whose own category id matches one of these auto-lands
-  // in this folder (see importService.ts's resolveFolderIdByCategory), unless the caller already
-  // picked a folder explicitly. Each site's category ids are independent integer namespaces.
-  makerworldCatId  Int?
-  thingiverseCatId Int?
-  printablesCatId  Int?
-  prints           Print[]
-  createdAt        DateTime @default(now())
-  updatedAt        DateTime @updatedAt
+  // When set, an import from that site whose own category id matches ANY of these auto-lands
+  // in this folder (see importService.ts's resolveFolderIdByCategory -- a Prisma `hasSome`
+  // overlap check), unless the caller already picked a folder explicitly. Each site's category
+  // ids are independent integer namespaces. A folder can list several ids (e.g. a parent
+  // category and a couple of its subcategories) since one folder may reasonably want to catch
+  // more than one upstream category -- entered/edited as a "800;71;1001"-style semicolon-
+  // separated string (see routes/folders.ts's parseCatIdsInput), stored as a real int array.
+  makerworldCatIds  Int[] @default([])
+  thingiverseCatIds Int[] @default([])
+  printablesCatIds  Int[] @default([])
+  prints            Print[]
+  createdAt         DateTime @default(now())
+  updatedAt         DateTime @updatedAt
 
   @@index([userId, parentId, position])
   @@index([tags], type: Gin)
-  @@index([userId, makerworldCatId])
-  @@index([userId, thingiverseCatId])
-  @@index([userId, printablesCatId])
+  @@index([makerworldCatIds], type: Gin)
+  @@index([thingiverseCatIds], type: Gin)
+  @@index([printablesCatIds], type: Gin)
 }
 
 model Print {

backend/src/dto.ts

@@ -119,9 +119,12 @@ export type FolderOut = {
   position: number;
   meta_title: string | null;
   meta_description: string | null;
-  makerworld_cat_id: number | null;
-  thingiverse_cat_id: number | null;
-  printables_cat_id: number | null;
+  // Semicolon-separated, e.g. "800;71;1001" -- same format the category manager dialog reads
+  // and writes (see routes/folders.ts's parseCatIdsInput), so the frontend can bind the field
+  // straight to a text input with no extra parsing. Empty string when none are set.
+  makerworld_cat_ids: string;
+  thingiverse_cat_ids: string;
+  printables_cat_ids: string;
 };
 
 function plateThumbUrl(plateId: string): string | null {
@@ -315,6 +318,10 @@ export function toSystemCollectionOut(
   };
 }
 
+function formatCatIds(ids: number[]): string {
+  return ids.join(";");
+}
+
 export function toFolderOut(folder: Folder): FolderOut {
   return {
     id: folder.id,
@@ -324,9 +331,9 @@ export function toFolderOut(folder: Folder): FolderOut {
     position: folder.position,
     meta_title: folder.metaTitle,
     meta_description: folder.metaDescription,
-    makerworld_cat_id: folder.makerworldCatId,
-    thingiverse_cat_id: folder.thingiverseCatId,
-    printables_cat_id: folder.printablesCatId,
+    makerworld_cat_ids: formatCatIds(folder.makerworldCatIds),
+    thingiverse_cat_ids: formatCatIds(folder.thingiverseCatIds),
+    printables_cat_ids: formatCatIds(folder.printablesCatIds),
   };
 }
 

backend/src/routes/folders.ts

@@ -87,13 +87,48 @@ router.patch(
   }),
 );
 
-const catIdField = z.number().int().positive().nullable().optional();
+const MAX_CAT_IDS = 50;
+
+/** Parses the category manager's "800;71;1001"-style text field into the int array actually
+ * stored on Folder.*CatIds -- a folder can list several ids per site (e.g. a parent category
+ * plus a couple of its subcategories), matched by overlap at import time (see importService.ts's
+ * resolveFolderIdByCategory). Blank/whitespace-only input clears the field. Stray/duplicate
+ * separators are tolerated (e.g. "800;;71;" or "800;800;71") since that's an easy typo to make
+ * in a free-text field and there's nothing genuinely ambiguous about it; anything that isn't a
+ * positive whole number is rejected with a message naming the exact bad token, so a typo doesn't
+ * silently vanish instead of erroring. */
+function parseCatIdsInput(raw: string | null | undefined): number[] {
+  const trimmed = (raw ?? "").trim();
+  if (!trimmed) return [];
+  const tokens = trimmed.split(";").map((t) => t.trim()).filter(Boolean);
+  const ids: number[] = [];
+  const seen = new Set<number>();
+  for (const token of tokens) {
+    if (!/^\d+$/.test(token) || token.length > 15) {
+      throw new HttpError(400, `Invalid category id "${token}" -- use numbers separated by ";", e.g. 800;71;1001`);
+    }
+    const id = Number(token);
+    if (!Number.isSafeInteger(id) || id <= 0) {
+      throw new HttpError(400, `Invalid category id "${token}" -- must be a positive whole number`);
+    }
+    if (!seen.has(id)) {
+      seen.add(id);
+      ids.push(id);
+    }
+  }
+  if (ids.length > MAX_CAT_IDS) {
+    throw new HttpError(400, `Too many category ids -- at most ${MAX_CAT_IDS} allowed`);
+  }
+  return ids;
+}
+
+const catIdsField = z.string().trim().max(1000).nullable().optional();
 const folderMetaSchema = z.object({
   meta_title: z.string().trim().max(200).nullable().optional(),
   meta_description: z.string().trim().max(2000).nullable().optional(),
-  makerworld_cat_id: catIdField,
-  thingiverse_cat_id: catIdField,
-  printables_cat_id: catIdField,
+  makerworld_cat_ids: catIdsField,
+  thingiverse_cat_ids: catIdsField,
+  printables_cat_ids: catIdsField,
 });
 
 router.patch(
@@ -107,9 +142,9 @@ router.patch(
       data: {
         metaTitle: body.meta_title || null,
         metaDescription: body.meta_description || null,
-        makerworldCatId: body.makerworld_cat_id ?? null,
-        thingiverseCatId: body.thingiverse_cat_id ?? null,
-        printablesCatId: body.printables_cat_id ?? null,
+        makerworldCatIds: parseCatIdsInput(body.makerworld_cat_ids),
+        thingiverseCatIds: parseCatIdsInput(body.thingiverse_cat_ids),
+        printablesCatIds: parseCatIdsInput(body.printables_cat_ids),
       },
     });
     res.json(toFolderOut(updated));

backend/src/services/importService.ts

@@ -393,16 +393,19 @@ export async function attachImportedPreviewImages(
 }
 
 const CATEGORY_SITE_FOLDER_FIELD = {
-  makerworld: "makerworldCatId",
-  thingiverse: "thingiverseCatId",
-  printables: "printablesCatId",
+  makerworld: "makerworldCatIds",
+  thingiverse: "thingiverseCatIds",
+  printables: "printablesCatIds",
 } as const;
 
 /** When the caller didn't pick a folder explicitly, checks whether any of the user's folders
- * declared a `*CatId` for this source site matching one of the model's own category ids -- if
- * so, the import auto-lands there instead of staying uncategorized. Site-scoped (each site's
- * category ids are an independent namespace) and best-effort: a lookup failure just leaves the
- * print uncategorized rather than failing the import. */
+ * declared a `*CatIds` list for this source site overlapping the model's own category ids -- if
+ * so, the import auto-lands there instead of staying uncategorized. A folder can list several
+ * ids per site (e.g. a parent category plus a couple of its subcategories -- see
+ * routes/folders.ts's parseCatIdsInput), so this is a set-overlap ("hasSome") check, not an
+ * equality one. Site-scoped (each site's category ids are an independent namespace) and
+ * best-effort: a lookup failure just leaves the print uncategorized rather than failing the
+ * import. */
 async function resolveFolderIdByCategory(
   userId: string,
   categorySite: ImportedPageMetadata["categorySite"],
@@ -411,7 +414,7 @@ async function resolveFolderIdByCategory(
   if (!categorySite || !siteCategoryIds.length) return null;
   const field = CATEGORY_SITE_FOLDER_FIELD[categorySite];
   const folder = await prisma.folder.findFirst({
-    where: { userId, [field]: { in: siteCategoryIds } },
+    where: { userId, [field]: { hasSome: siteCategoryIds } },
     orderBy: { position: "asc" },
   });
   return folder?.id ?? null;

backend/src/services/makerworldCloudApi.ts

@@ -255,7 +255,7 @@ function extractGalleryImages(design: Record<string, unknown>): MakerworldGaller
 
 /** design.categories -- a flat array of `{id, name, ...}` objects, most-specific first (e.g.
  * "Cosplay Weapons" then its parent "Props & Cosplays"). Used to auto-land the import into a
- * Folder whose makerworldCatId matches one of these (see importService.ts's
+ * Folder whose makerworldCatIds overlaps one of these (see importService.ts's
  * resolveFolderIdByCategory); every id is kept, not just the first, so a folder configured for
  * either the specific or the parent category still matches. */
 function extractCategoryIds(design: Record<string, unknown>): number[] {

backend/tests/folderCategoryIds.test.ts

@@ -0,0 +1,117 @@
+import { beforeAll, describe, expect, it } from "vitest";
+import request from "supertest";
+import { createApp } from "../src/app";
+import { prisma } from "../src/db";
+
+// PATCH /folder/:id/meta's makerworld_cat_ids/thingiverse_cat_ids/printables_cat_ids fields:
+// free-text "800;71;1001"-style input, parsed and validated by routes/folders.ts's
+// parseCatIdsInput into the real Folder.*CatIds int array that importService.ts's
+// resolveFolderIdByCategory matches against (see thingiverseImport.test.ts for that side of it).
+
+const app = createApp();
+let token: string;
+
+beforeAll(async () => {
+  const email = `folder-category-ids-test-${Date.now()}@example.com`;
+  const res = await request(app)
+    .post("/api/register")
+    .send({ displayName: "Category Ids Test", email, password: "password123" });
+  if (res.status !== 200) {
+    throw new Error(`Failed to register during test setup: ${res.status} ${JSON.stringify(res.body)}`);
+  }
+  token = res.body.token;
+});
+
+function auth() {
+  return { Authorization: `Bearer ${token}` };
+}
+
+async function createFolder(name: string): Promise<string> {
+  const res = await request(app).post("/api/folders").set(auth()).send({ name, tags: [] });
+  expect(res.status).toBe(200);
+  return res.body.id;
+}
+
+describe("PATCH /folder/:id/meta -- multi-value category ids", () => {
+  it("parses a semicolon-separated string into multiple ids, and round-trips it back the same way", async () => {
+    const folderId = await createFolder("Multi Cat Folder");
+    const res = await request(app)
+      .patch(`/api/folder/${folderId}/meta`)
+      .set(auth())
+      .send({ thingiverse_cat_ids: "800;71;1001" });
+
+    expect(res.status).toBe(200);
+    expect(res.body.thingiverse_cat_ids).toBe("800;71;1001");
+
+    const stored = await prisma.folder.findUnique({ where: { id: folderId } });
+    expect(stored?.thingiverseCatIds).toEqual([800, 71, 1001]);
+  });
+
+  it("tolerates stray/duplicate separators and whitespace, deduping the result", async () => {
+    const folderId = await createFolder("Messy Input Folder");
+    const res = await request(app)
+      .patch(`/api/folder/${folderId}/meta`)
+      .set(auth())
+      .send({ makerworld_cat_ids: " 800 ;;71; 800 ;1001;" });
+
+    expect(res.status).toBe(200);
+    expect(res.body.makerworld_cat_ids).toBe("800;71;1001");
+  });
+
+  it("clears the field on an empty or whitespace-only string", async () => {
+    const folderId = await createFolder("Clearable Folder");
+    await request(app).patch(`/api/folder/${folderId}/meta`).set(auth()).send({ printables_cat_ids: "42" });
+
+    const res = await request(app).patch(`/api/folder/${folderId}/meta`).set(auth()).send({ printables_cat_ids: "   " });
+    expect(res.status).toBe(200);
+    expect(res.body.printables_cat_ids).toBe("");
+
+    const stored = await prisma.folder.findUnique({ where: { id: folderId } });
+    expect(stored?.printablesCatIds).toEqual([]);
+  });
+
+  it("rejects a non-numeric token, naming it in the error", async () => {
+    const folderId = await createFolder("Bad Input Folder");
+    const res = await request(app)
+      .patch(`/api/folder/${folderId}/meta`)
+      .set(auth())
+      .send({ thingiverse_cat_ids: "800;abc;71" });
+
+    expect(res.status).toBe(400);
+    expect(res.body.detail).toContain("abc");
+  });
+
+  it("rejects zero, negative, and decimal ids", async () => {
+    const folderId = await createFolder("Invalid Numbers Folder");
+    for (const bad of ["0", "-5", "1.5"]) {
+      const res = await request(app)
+        .patch(`/api/folder/${folderId}/meta`)
+        .set(auth())
+        .send({ thingiverse_cat_ids: bad });
+      expect(res.status).toBe(400);
+    }
+  });
+
+  it("rejects an excessive number of ids", async () => {
+    const folderId = await createFolder("Too Many Ids Folder");
+    const manyIds = Array.from({ length: 51 }, (_, i) => i + 1).join(";");
+    const res = await request(app)
+      .patch(`/api/folder/${folderId}/meta`)
+      .set(auth())
+      .send({ thingiverse_cat_ids: manyIds });
+    expect(res.status).toBe(400);
+  });
+
+  it("keeps each site's ids independent of the others", async () => {
+    const folderId = await createFolder("Independent Sites Folder");
+    const res = await request(app)
+      .patch(`/api/folder/${folderId}/meta`)
+      .set(auth())
+      .send({ makerworld_cat_ids: "1;2", thingiverse_cat_ids: "3;4", printables_cat_ids: "5;6" });
+
+    expect(res.status).toBe(200);
+    expect(res.body.makerworld_cat_ids).toBe("1;2");
+    expect(res.body.thingiverse_cat_ids).toBe("3;4");
+    expect(res.body.printables_cat_ids).toBe("5;6");
+  });
+});

backend/tests/thingiverseImport.test.ts

@@ -120,11 +120,13 @@ describe("importPrintFromUrl -- Thingiverse", () => {
 
   it("imports a Thing's model files as plates, matches category, and attaches metadata + images", async () => {
     await setThingiverseAccessToken(ACCESS_TOKEN);
-    // A folder configured to auto-match this Thing's Thingiverse category (129, "3D Printing
-    // Tests") -- proves category matching, previously believed infeasible against the internal
-    // v2 API, actually works against the official API's separate categories_url.
+    // A folder configured with several category ids, only one of which (129, "3D Printing
+    // Tests") actually matches this Thing -- proves both that category matching works against
+    // the official API's separate categories_url (previously believed infeasible against the
+    // internal v2 API), and that a folder listing multiple ids matches on ANY overlap, not just
+    // an exact single-id equality.
     const folder = await prisma.folder.create({
-      data: { userId, name: "Thingiverse Tests", tags: [], thingiverseCatId: CATEGORY_ID },
+      data: { userId, name: "Thingiverse Tests", tags: [], thingiverseCatIds: [999001, CATEGORY_ID, 999002] },
     });
 
     global.fetch = mockThingiverseFetch();

frontend/src/api/folders.ts

@@ -1,5 +1,5 @@
 import { authHeaders } from "../utils/auth";
-import { apiBase, assertOk } from "./client";
+import { apiBase, assertOk, readErrorMessage, UnauthorizedError } from "./client";
 
 export type Folder = {
   id: string;
@@ -9,17 +9,20 @@ export type Folder = {
   position: number;
   meta_title: string | null;
   meta_description: string | null;
-  makerworld_cat_id: number | null;
-  thingiverse_cat_id: number | null;
-  printables_cat_id: number | null;
+  // Semicolon-separated, e.g. "800;71;1001" -- a folder can match more than one upstream
+  // category id per site (see backend's routes/folders.ts parseCatIdsInput). Empty string when
+  // none are set.
+  makerworld_cat_ids: string;
+  thingiverse_cat_ids: string;
+  printables_cat_ids: string;
 };
 
 export type FolderMetaInput = {
   metaTitle: string | null;
   metaDescription: string | null;
-  makerworldCatId: number | null;
-  thingiverseCatId: number | null;
-  printablesCatId: number | null;
+  makerworldCatIds: string;
+  thingiverseCatIds: string;
+  printablesCatIds: string;
 };
 
 export const foldersApi = {
@@ -62,12 +65,17 @@ export const foldersApi = {
       body: JSON.stringify({
         meta_title: meta.metaTitle,
         meta_description: meta.metaDescription,
-        makerworld_cat_id: meta.makerworldCatId,
-        thingiverse_cat_id: meta.thingiverseCatId,
-        printables_cat_id: meta.printablesCatId,
+        makerworld_cat_ids: meta.makerworldCatIds,
+        thingiverse_cat_ids: meta.thingiverseCatIds,
+        printables_cat_ids: meta.printablesCatIds,
       }),
     });
-    assertOk(res, "Update category details failed");
+    if (res.status === 401) throw new UnauthorizedError();
+    if (!res.ok) {
+      // A bad category-id string (e.g. a typo) gets a specific message from the backend --
+      // assertOk's fixed fallback text would swallow that, leaving the user without a reason.
+      throw new Error(await readErrorMessage(res, "Update category details failed"));
+    }
     return res.json();
   },
 

frontend/src/i18n/locales/en.json

@@ -607,9 +607,11 @@
         "metaDialogTitle": "Details — {{name}}",
         "metaTitleLabel": "Meta title",
         "metaDescriptionLabel": "Meta description",
-        "makerworldCatIdLabel": "MakerWorld category ID",
-        "thingiverseCatIdLabel": "Thingiverse category ID",
-        "printablesCatIdLabel": "Printables category ID"
+        "makerworldCatIdLabel": "MakerWorld category IDs",
+        "thingiverseCatIdLabel": "Thingiverse category IDs",
+        "printablesCatIdLabel": "Printables category IDs",
+        "catIdsPlaceholder": "e.g. 800;71;1001",
+        "catIdsHelp": "Separate multiple IDs with \";\" -- matches if an import's category is any of these"
       }
     }
   }

frontend/src/i18n/locales/lt.json

@@ -608,9 +608,11 @@
         "metaDialogTitle": "Informacija — {{name}}",
         "metaTitleLabel": "Meta pavadinimas",
         "metaDescriptionLabel": "Meta aprašymas",
-        "makerworldCatIdLabel": "MakerWorld kategorijos ID",
-        "thingiverseCatIdLabel": "Thingiverse kategorijos ID",
-        "printablesCatIdLabel": "Printables kategorijos ID"
+        "makerworldCatIdLabel": "MakerWorld kategorijų ID",
+        "thingiverseCatIdLabel": "Thingiverse kategorijų ID",
+        "printablesCatIdLabel": "Printables kategorijų ID",
+        "catIdsPlaceholder": "pvz. 800;71;1001",
+        "catIdsHelp": "Kelis ID atskirkite „;“ -- atitiks, jei importo kategorija sutampa su bet kuriuo iš jų"
       }
     }
   }

frontend/src/pages/ModelsPage/CategoryManagerModal.tsx

@@ -41,9 +41,9 @@ function hasMeta(folder: Folder): boolean {
   return Boolean(
     folder.meta_title ||
       folder.meta_description ||
-      folder.makerworld_cat_id ||
-      folder.thingiverse_cat_id ||
-      folder.printables_cat_id,
+      folder.makerworld_cat_ids ||
+      folder.thingiverse_cat_ids ||
+      folder.printables_cat_ids,
   );
 }
 

frontend/src/pages/ModelsPage/CategoryMetaDialog.tsx

@@ -7,6 +7,7 @@ import DialogActions from "@mui/material/DialogActions";
 import Stack from "@mui/material/Stack";
 import TextField from "@mui/material/TextField";
 import Button from "@mui/material/Button";
+import Alert from "@mui/material/Alert";
 import CircularProgress from "@mui/material/CircularProgress";
 import type { Folder, FolderMetaInput } from "../../api/folders";
 
@@ -16,41 +17,40 @@ type Props = {
   onSave: (meta: FolderMetaInput) => Promise<void>;
 };
 
-/** Parses a category-id field: blank stays null, anything else must be a positive integer (kept
- *  as free text while typing so "12" isn't clobbered mid-edit; validated only on save). */
-function parseCatId(raw: string): number | null {
-  const trimmed = raw.trim();
-  if (!trimmed) return null;
-  const value = Number(trimmed);
-  return Number.isInteger(value) && value > 0 ? value : null;
-}
-
-/** Meta title/description/site-category-id editor for one category, opened from its "details"
+/** Meta title/description/site-category-ids editor for one category, opened from its "details"
  *  icon in the manager. Saving with all fields blank clears the category's metadata entirely.
- *  The three `*CatId` fields drive auto-categorization on import (see importService.ts's
+ *  The three `*CatIds` fields drive auto-categorization on import (see importService.ts's
  *  resolveFolderIdByCategory on the backend): when an imported model's own site category id
- *  matches one set here, it lands in this category automatically. */
+ *  matches ANY id listed here, it lands in this category automatically -- a folder can list
+ *  several ids per site (e.g. a parent category plus a couple of its subcategories), entered as
+ *  plain numbers separated by ";" (parsed and validated server-side by routes/folders.ts's
+ *  parseCatIdsInput). A validation failure (a typo, say) is shown inline here and keeps the
+ *  dialog open with the edits intact, rather than closing and discarding them. */
 export default function CategoryMetaDialog({ folder, onClose, onSave }: Props) {
   const { t } = useTranslation(["models", "common"]);
   const untitledLabel = t("models:categories.untitled");
   const [title, setTitle] = useState(folder.meta_title ?? "");
   const [description, setDescription] = useState(folder.meta_description ?? "");
-  const [makerworldCatId, setMakerworldCatId] = useState(folder.makerworld_cat_id?.toString() ?? "");
-  const [thingiverseCatId, setThingiverseCatId] = useState(folder.thingiverse_cat_id?.toString() ?? "");
-  const [printablesCatId, setPrintablesCatId] = useState(folder.printables_cat_id?.toString() ?? "");
+  const [makerworldCatIds, setMakerworldCatIds] = useState(folder.makerworld_cat_ids);
+  const [thingiverseCatIds, setThingiverseCatIds] = useState(folder.thingiverse_cat_ids);
+  const [printablesCatIds, setPrintablesCatIds] = useState(folder.printables_cat_ids);
   const [saving, setSaving] = useState(false);
+  const [error, setError] = useState<string | null>(null);
 
   const handleSave = async () => {
     setSaving(true);
+    setError(null);
     try {
       await onSave({
         metaTitle: title.trim() || null,
         metaDescription: description.trim() || null,
-        makerworldCatId: parseCatId(makerworldCatId),
-        thingiverseCatId: parseCatId(thingiverseCatId),
-        printablesCatId: parseCatId(printablesCatId),
+        makerworldCatIds,
+        thingiverseCatIds,
+        printablesCatIds,
       });
       onClose();
+    } catch (err) {
+      setError(err instanceof Error ? err.message : t("models:errors.updateCategoryMetaFailed"));
     } finally {
       setSaving(false);
     }
@@ -85,29 +85,33 @@ export default function CategoryMetaDialog({ folder, onClose, onSave }: Props) {
           <Stack direction="row" spacing={2}>
             <TextField
               label={t("models:categories.manager.makerworldCatIdLabel")}
-              type="number"
+              placeholder={t("models:categories.manager.catIdsPlaceholder") ?? undefined}
+              helperText={t("models:categories.manager.catIdsHelp")}
               fullWidth
-              value={makerworldCatId}
-              onChange={e => setMakerworldCatId(e.target.value)}
+              value={makerworldCatIds}
+              onChange={e => setMakerworldCatIds(e.target.value)}
               disabled={saving}
             />
             <TextField
               label={t("models:categories.manager.thingiverseCatIdLabel")}
-              type="number"
+              placeholder={t("models:categories.manager.catIdsPlaceholder") ?? undefined}
+              helperText={t("models:categories.manager.catIdsHelp")}
               fullWidth
-              value={thingiverseCatId}
-              onChange={e => setThingiverseCatId(e.target.value)}
+              value={thingiverseCatIds}
+              onChange={e => setThingiverseCatIds(e.target.value)}
               disabled={saving}
             />
             <TextField
               label={t("models:categories.manager.printablesCatIdLabel")}
-              type="number"
+              placeholder={t("models:categories.manager.catIdsPlaceholder") ?? undefined}
+              helperText={t("models:categories.manager.catIdsHelp")}
               fullWidth
-              value={printablesCatId}
-              onChange={e => setPrintablesCatId(e.target.value)}
+              value={printablesCatIds}
+              onChange={e => setPrintablesCatIds(e.target.value)}
               disabled={saving}
             />
           </Stack>
+          {error && <Alert severity="error">{error}</Alert>}
         </Stack>
       </DialogContent>
       <DialogActions>

frontend/src/pages/ModelsPage/index.tsx

@@ -159,7 +159,12 @@ export default function ModelsPage({ folderId, onSelectFolder, foldersVersion, o
       await foldersApi.updateMeta(id, meta);
       onFoldersChanged();
     } catch (err) {
-      handleError(err, t("models:errors.updateCategoryMetaFailed"));
+      // Unlike the other handlers here, this one rethrows anything but the auth-redirect case:
+      // CategoryMetaDialog shows the specific message (e.g. a bad category-id string naming the
+      // exact typo) inline and keeps the dialog open with the user's edits intact, instead of a
+      // generic alert() that closes the dialog and discards what they typed either way.
+      if (handleError(err)) return;
+      throw err;
     }
   };