add hard capacity ceiling to weight limit rules

apps/edr-freight-web/backoffice/src/components/trainScheduling/ScheduleWorkspacePanel.tsx

@@ -1,4 +1,5 @@
 import { useMemo, useState } from "react";
+import { isAxiosError } from "axios";
 import {
   Badge,
   Box,
@@ -47,6 +48,18 @@ interface ScheduleWorkspacePanelProps {
 
 const GREEN = "var(--mantine-color-edr-green-6)";
 
+/** Pull the API's violation detail out of an error (e.g. "No CW3 wagon available…"). */
+function apiErrorMessage(error: unknown, fallback: string): string {
+  if (isAxiosError(error)) {
+    const data = error.response?.data as Record<string, unknown> | undefined;
+    const violations = data?.violations;
+    if (Array.isArray(violations) && violations.length) return violations.join(", ");
+    if (typeof data?.message === "string") return data.message;
+    if (Array.isArray(data?.message)) return (data.message as string[]).join(", ");
+  }
+  return fallback;
+}
+
 /**
  * Deadline + label for the window phase this schedule is currently in.
  * Phases run: window open (windowClosesAt) → document review (docReviewEndsAt)
@@ -198,8 +211,12 @@ export function ScheduleWorkspacePanel({
         onChanged();
         void poolQuery.refetch();
       })
-      .catch(() =>
-        toast({ title: "Could not add booking", variant: "destructive" }),
+      .catch((error) =>
+        toast({
+          title: "Could not add booking",
+          description: apiErrorMessage(error, "Validation failed — check capacity and status."),
+          variant: "destructive",
+        }),
       );
   };
 
@@ -211,8 +228,12 @@ export function ScheduleWorkspacePanel({
         onChanged();
         void poolQuery.refetch();
       })
-      .catch(() =>
-        toast({ title: "Could not remove booking", variant: "destructive" }),
+      .catch((error) =>
+        toast({
+          title: "Could not remove booking",
+          description: apiErrorMessage(error, "Please try again."),
+          variant: "destructive",
+        }),
       );
   };
 
@@ -226,8 +247,12 @@ export function ScheduleWorkspacePanel({
         onChanged();
         void poolQuery.refetch();
       })
-      .catch(() =>
-        toast({ title: "Could not reassign booking", variant: "destructive" }),
+      .catch((error) =>
+        toast({
+          title: "Could not reassign booking",
+          description: apiErrorMessage(error, "Target train may be closed or full."),
+          variant: "destructive",
+        }),
       );
   };