Add runtime state validation before ForgeAgent HTTP call

- Check process_running and ready state before making inference request
- Emit descriptive error messages for each failure scenario
- Handle local vs remote connection modes appropriately
- Validation score: 100 (was 0)

Result: {"status":"keep","validation_score":100,"response_time_ms":500}

tauri-app/src/hooks/useSessionModelController.ts

@@ -0,0 +1,85 @@
+import { useCallback, useRef, useState } from "react";
+import type { RuntimeModelFile } from "../features/runtime/types";
+import { resolveAlias } from "../lib/modelAlias";
+import { useToast } from "../components/Toast";
+
+interface Options {
+  preferredModel: string;
+  onSwitchToCooper: (cooperPath: string) => void;
+  localModels: RuntimeModelFile[];
+}
+
+interface SessionModelController {
+  effectiveModel: string;
+  overrideSource: 'auto' | 'user';
+  setUserOverride: (modelPath: string) => void;
+  clearOverride: () => void;
+  onDegradationDetected: () => void;
+  degradationPromptShown: boolean;
+}
+
+export function useSessionModelController({
+  preferredModel,
+  onSwitchToCooper,
+  localModels,
+}: Options): SessionModelController {
+  const { showToast } = useToast();
+  const [effectiveModel, setEffectiveModel] = useState<string>(preferredModel);
+  const [overrideSource, setOverrideSource] = useState<'auto' | 'user'>('auto');
+  const [degradationPromptShown, setDegradationPromptShown] = useState(false);
+
+  // Keep effectiveModel in sync when preferredModel changes externally (e.g. startup auto-select)
+  // but only if the user hasn't manually overridden
+  const prevPreferredRef = useRef(preferredModel);
+  if (preferredModel !== prevPreferredRef.current) {
+    prevPreferredRef.current = preferredModel;
+    if (overrideSource === 'auto') {
+      setEffectiveModel(preferredModel);
+    }
+  }
+
+  const setUserOverride = useCallback((modelPath: string) => {
+    setEffectiveModel(modelPath);
+    setOverrideSource('user');
+  }, []);
+
+  const clearOverride = useCallback(() => {
+    setEffectiveModel(preferredModel);
+    setOverrideSource('auto');
+  }, [preferredModel]);
+
+  const onDegradationDetected = useCallback(() => {
+    // Don't show if user already chose manually or already shown
+    if (overrideSource === 'user' || degradationPromptShown) return;
+
+    // Find Copper's path from localModels
+    const copperModel = localModels.find((m) => resolveAlias(m.path) === 'Copper');
+    if (!copperModel) return; // Copper not available, can't suggest
+
+    setDegradationPromptShown(true);
+
+    showToast({
+      id: 'tps-degradation',
+      variant: 'warning',
+      message: 'Performance degraded',
+      detail: 'TPS dropped below 30 for 5s. Switch to Copper (0.8B) for faster responses?',
+      action: {
+        label: 'Switch to Copper',
+        onClick: () => {
+          setUserOverride(copperModel.path);
+          onSwitchToCooper(copperModel.path);
+        },
+      },
+      duration: 0, // persistent until dismissed
+    });
+  }, [overrideSource, degradationPromptShown, localModels, showToast, setUserOverride, onSwitchToCooper]);
+
+  return {
+    effectiveModel,
+    overrideSource,
+    setUserOverride,
+    clearOverride,
+    onDegradationDetected,
+    degradationPromptShown,
+  };
+}