fix(dependencies): send feature_states when creating the change request

Also show the API's message when creation is refused, instead of a generic one.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: talissoncosta

frontend/common/services/useChangeRequest.ts

@@ -25,6 +25,9 @@ export const changeRequestService = service
             ...rest,
             // The modal hands back users and groups in one list.
             approvals: approvals.filter((approval) => !!approval.user),
+            // Required by the API even where the changes live in change sets,
+            // as the feature modal's own flow sends.
+            feature_states: [],
             group_assignments: approvals.filter((approval) => !!approval.group),
           },
           method: 'POST',

frontend/web/components/modals/create-feature/tabs/FeatureDependenciesTab/hooks/useStagedPrerequisites.tsx

@@ -22,6 +22,17 @@ export type StagedChange = {
 
 export type StagingError = { message: string; prerequisiteId?: number }
 
+// DRF answers with { detail } or { field: [messages] }.
+const describeApiError = (e: unknown): string | undefined => {
+  const data = (e as { data?: Record<string, unknown> })?.data
+  if (!data || typeof data !== 'object') return
+  if (typeof data.detail === 'string') return data.detail
+  const [field, messages] = Object.entries(data)[0] ?? []
+  return field
+    ? `${field}: ${([] as unknown[]).concat(messages).join(' ')}`
+    : undefined
+}
+
 type UseStagedPrerequisitesArgs = {
   environmentId: string
   projectId: number
@@ -127,7 +138,10 @@ export const useStagedPrerequisites = ({
       setError(
         (e as StagingError)?.message
           ? (e as StagingError)
-          : { message: 'Could not create the change request.' },
+          : {
+              message:
+                describeApiError(e) ?? 'Could not create the change request.',
+            },
       )
     } finally {
       setIsSubmitting(false)