fix(documents): tighten cross-port test + refine paths + signing-details coverage

Three follow-ups from Task 9 code review:
1. Cross-port isolation test now explicitly asserts the other-port
   file's id is absent from the aggregated result (previously only
   checked .length > 0, which would pass even with leakage).
2. Refine errors now carry path fields so frontend field-level error
   display can target the right form input (matches createDocumentSchema
   pattern in the same validators module).
3. Add a service-composition test for the signing-details route's
   workflow+signers+events shape — closes the coverage gap for the
   thin Promise.all combinator.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/validators/documents.ts

@@ -106,10 +106,14 @@ export const listDocumentsSchema = baseListQuerySchema
   })
   .refine(
     (q) => !(q.folderId !== undefined && (q.entityType !== undefined || q.entityId !== undefined)),
-    { message: 'folderId is mutually exclusive with entityType/entityId' },
+    {
+      message: 'folderId is mutually exclusive with entityType/entityId',
+      path: ['folderId'],
+    },
   )
   .refine((q) => Boolean(q.entityType) === Boolean(q.entityId), {
     message: 'entityType and entityId must be provided together',
+    path: ['entityType'],
   });
 
 export const uploadSignedSchema = z.object({

src/lib/validators/files.ts

@@ -31,10 +31,14 @@ export const listFilesSchema = baseListQuerySchema
   })
   .refine(
     (q) => !(q.folderId !== undefined && (q.entityType !== undefined || q.entityId !== undefined)),
-    { message: 'folderId is mutually exclusive with entityType/entityId' },
+    {
+      message: 'folderId is mutually exclusive with entityType/entityId',
+      path: ['folderId'],
+    },
   )
   .refine((q) => Boolean(q.entityType) === Boolean(q.entityId), {
     message: 'entityType and entityId must be provided together',
+    path: ['entityType'],
   });
 
 export type UploadFileInput = z.infer<typeof uploadFileSchema>;