diff --git a/lib/api-client-react/src/generated/api.schemas.ts b/lib/api-client-react/src/generated/api.schemas.ts
index d1dc49fb..e34b53c2 100644
--- a/lib/api-client-react/src/generated/api.schemas.ts
+++ b/lib/api-client-react/src/generated/api.schemas.ts
@@ -802,6 +802,11 @@ export interface RequestUploadUrlBody {
 }
 
 export interface RequestUploadUrlResponse {
+  /**
+   * Presigned upload destination. May be either an absolute URL (S3 driver) or a same-origin path starting with `/` (local driver) — the browser resolves the latter against `window.location.origin` so uploads always target the host serving the SPA.
+
+   * @minLength 1
+   */
   uploadURL: string;
   objectPath: string;
   metadata?: RequestUploadUrlBody;
diff --git a/lib/api-spec/openapi.yaml b/lib/api-spec/openapi.yaml
index 9c1a4de9..0ab1b7c1 100644
--- a/lib/api-spec/openapi.yaml
+++ b/lib/api-spec/openapi.yaml
@@ -4283,7 +4283,13 @@ components:
       properties:
         uploadURL:
           type: string
-          format: uri
+          minLength: 1
+          description: >
+            Presigned upload destination. May be either an absolute URL
+            (S3 driver) or a same-origin path starting with `/` (local
+            driver) — the browser resolves the latter against
+            `window.location.origin` so uploads always target the host
+            serving the SPA.
         objectPath:
           type: string
         metadata:
diff --git a/lib/api-zod/src/generated/api.ts b/lib/api-zod/src/generated/api.ts
index e84bd146..ceb34993 100644
--- a/lib/api-zod/src/generated/api.ts
+++ b/lib/api-zod/src/generated/api.ts
@@ -1061,7 +1061,12 @@ export const RequestUploadUrlBody = zod.object({
 });
 
 export const RequestUploadUrlResponse = zod.object({
-  uploadURL: zod.string().url(),
+  uploadURL: zod
+    .string()
+    .min(1)
+    .describe(
+      "Presigned upload destination. May be either an absolute URL (S3 driver) or a same-origin path starting with `\/` (local driver) — the browser resolves the latter against `window.location.origin` so uploads always target the host serving the SPA.\n",
+    ),
   objectPath: zod.string(),
   metadata: zod
     .object({