fix: disable Start Training when eval_steps set without eval split

studio/frontend/src/features/studio/sections/training-section.tsx

@@ -12,6 +12,7 @@ import {
   serializeConfigToYaml,
   useTrainingActions,
   useTrainingConfigStore,
+  validateTrainingConfig,
 } from "@/features/training";
 import {
   Archive04Icon,
@@ -43,7 +44,8 @@ export function TrainingSection() {
   const { isStarting, startError, startTrainingRun } = useTrainingActions();
   const isIncompatible =
     !store.isVisionModel && store.isDatasetImage === true;
-    const fileInputRef = useRef<HTMLInputElement>(null);
+  const configValidation = validateTrainingConfig(store);
+  const fileInputRef = useRef<HTMLInputElement>(null);
 
   const handleFileUpload = (e: React.ChangeEvent<HTMLInputElement>) => {
     const file = e.target.files?.[0];
@@ -150,7 +152,7 @@ export function TrainingSection() {
           data-tour="studio-start"
           className="w-full cursor-pointer bg-gradient-to-r from-emerald-500 to-teal-500 text-white hover:from-emerald-600 hover:to-teal-600"
           onClick={() => void startTrainingRun()}
-          disabled={isStarting || isIncompatible}
+          disabled={isStarting || isIncompatible || !configValidation.ok}
         >
           <HugeiconsIcon icon={Rocket01Icon} className="size-4" />
           {isStarting ? "Starting..." : "Start Training"}
@@ -163,6 +165,9 @@ export function TrainingSection() {
             Text model is not compatible with a multimodal dataset. Switch to a vision model or choose a text-only dataset.
           </p>
         )}
+        {!configValidation.ok && configValidation.message && !isIncompatible && (
+          <p className="text-xs text-red-500 leading-relaxed">{configValidation.message}</p>
+        )}
 
         {/* Upload / Save / Reset */}
         <p className="text-xs text-muted-foreground">Training Config</p>

studio/frontend/src/features/training/index.ts

@@ -11,3 +11,4 @@ export { listLocalModels } from "./api/models-api";
 export type { LocalModelInfo } from "./api/models-api";
 export type { TrainingPhase } from "./types/runtime";
 export { parseYamlConfig, serializeConfigToYaml } from "./lib/yaml-config";
+export { validateTrainingConfig } from "./lib/validation";

studio/frontend/src/features/training/lib/validation.ts

@@ -16,18 +16,22 @@ export function validateTrainingConfig(
     if (!config.dataset) {
       return { ok: false, message: "Select a Hugging Face dataset first." };
     }
-    return { ok: true, message: null };
-  }
-
-  if (config.datasetSource === "upload") {
+  } else if (config.datasetSource === "upload") {
     if (!config.uploadedFile) {
       return { ok: false, message: "Select a local dataset first." };
     }
-    return { ok: true, message: null };
+  } else {
+    return { ok: false, message: "Unsupported dataset source." };
   }
 
-  return {
-    ok: false,
-    message: "Unsupported dataset source.",
-  };
+  // Eval steps requires an eval split to be selected
+  if (config.evalSteps > 0 && !config.datasetEvalSplit) {
+    return {
+      ok: false,
+      message:
+        "Eval Steps is set but no Eval Split is selected. Choose an Eval Split or set Eval Steps to 0.",
+    };
+  }
+
+  return { ok: true, message: null };
 }