feat(39-02): VoiceStep hardware-aware UI with conditional enable/skip

- Add VoiceCapability interface to ui/src/api/hardware.ts
- Export VoiceCapability type from useHardwareInfo.ts
- VoiceStep accepts voiceCapability prop, renders conditionally
- Insufficient hardware: shows capability note with skip-only button
- Binaries present: shows green checkmarks next to STT/TTS labels
- Missing binaries on sufficient hardware: shows install note, dimmed Enable
- NexusOnboardingWizard passes voiceCapability from hardware probe to VoiceStep

ui/src/api/hardware.ts

@@ -3,6 +3,12 @@ import { api } from "./client";
 
 export type HardwareTier = "gpu" | "apple_silicon" | "cpu_only";
 
+export interface VoiceCapability {
+  whisperAvailable: boolean;
+  piperAvailable: boolean;
+  voiceTierSufficient: boolean;
+}
+
 export interface HardwareInfo {
   totalGb: number;
   freeGb: number;
@@ -13,6 +19,7 @@ export interface HardwareInfo {
   unifiedMemory: boolean;
   hardwareTier: HardwareTier;
   cpuModel: string | null;
+  voiceCapability?: VoiceCapability;
 }
 
 export type NexusMode = "personal_ai" | "project_builder" | "both";

ui/src/components/NexusOnboardingWizard.tsx

@@ -430,6 +430,7 @@ export function OnboardingWizard() {
                   setStep(5);
                 }}
                 onSkip={() => setStep(5)}
+                voiceCapability={hardwareInfo?.voiceCapability}
               />
 
               <Button

ui/src/components/onboarding/VoiceStep.tsx

@@ -1,13 +1,15 @@
 import { useEffect, useState } from "react";
-import { Mic, Volume2 } from "lucide-react";
+import { Mic, Volume2, CheckCircle2, AlertTriangle, Info } from "lucide-react";
 import { Button } from "@/components/ui/button";
+import type { VoiceCapability } from "../../hooks/useHardwareInfo";
 
 interface VoiceStepProps {
   onEnable: () => void;
   onSkip: () => void;
+  voiceCapability?: VoiceCapability;
 }
 
-export function VoiceStep({ onEnable, onSkip }: VoiceStepProps) {
+export function VoiceStep({ onEnable, onSkip, voiceCapability }: VoiceStepProps) {
   const [micAvailable, setMicAvailable] = useState<boolean | null>(null);
 
   useEffect(() => {
@@ -16,36 +18,114 @@ export function VoiceStep({ onEnable, onSkip }: VoiceStepProps) {
       .catch(() => setMicAvailable(false));
   }, []);
 
+  // Determine STT status label
+  function whisperStatusLabel(): string {
+    if (!voiceCapability) {
+      // Fall back to mic-only check
+      if (micAvailable === false) return "No microphone detected — unavailable";
+      if (micAvailable === true) return "Microphone detected — speak to your assistant";
+      return "Checking microphone...";
+    }
+    if (voiceCapability.whisperAvailable) return "Whisper detected — speech recognition ready";
+    return "Whisper not found — install whisper-cpp for voice input";
+  }
+
+  function whisperStatusIcon() {
+    if (!voiceCapability) return null;
+    if (voiceCapability.whisperAvailable) {
+      return <CheckCircle2 className="h-4 w-4 text-green-500 shrink-0" />;
+    }
+    return <AlertTriangle className="h-4 w-4 text-amber-500 shrink-0" />;
+  }
+
+  // Determine TTS status label
+  function piperStatusLabel(): string {
+    if (!voiceCapability) {
+      return "Hear responses read aloud. Runs entirely on your device — no server needed.";
+    }
+    if (voiceCapability.piperAvailable) return "Piper detected — text-to-speech ready";
+    return "Piper not found — install piper for voice output";
+  }
+
+  function piperStatusIcon() {
+    if (!voiceCapability) return null;
+    if (voiceCapability.piperAvailable) {
+      return <CheckCircle2 className="h-4 w-4 text-green-500 shrink-0" />;
+    }
+    return <AlertTriangle className="h-4 w-4 text-amber-500 shrink-0" />;
+  }
+
+  // Insufficient hardware: show note + skip only
+  if (voiceCapability && !voiceCapability.voiceTierSufficient) {
+    return (
+      <div className="flex flex-col gap-4">
+        <div className="flex items-start gap-3 rounded-lg border border-amber-200 bg-amber-50 dark:border-amber-800 dark:bg-amber-950/20 p-3">
+          <Info className="h-5 w-5 text-amber-500 shrink-0 mt-0.5" />
+          <div>
+            <p className="text-sm font-medium text-amber-800 dark:text-amber-300">Hardware may not support voice</p>
+            <p className="text-xs text-amber-700 dark:text-amber-400 mt-1">
+              Voice features require at least 4GB free RAM. Your system currently has insufficient free memory for local voice processing.
+            </p>
+          </div>
+        </div>
+
+        <div className="flex flex-col gap-2">
+          <Button variant="ghost" onClick={onSkip} className="w-full">
+            Skip voice setup
+          </Button>
+        </div>
+      </div>
+    );
+  }
+
+  // Sufficient hardware or unknown — show full UI
+  const neitherBinaryFound =
+    voiceCapability &&
+    !voiceCapability.whisperAvailable &&
+    !voiceCapability.piperAvailable;
+
   return (
     <div className="flex flex-col gap-4">
+      {/* Install note when tier is sufficient but binaries are missing */}
+      {neitherBinaryFound && (
+        <div className="flex items-start gap-3 rounded-lg border border-blue-200 bg-blue-50 dark:border-blue-800 dark:bg-blue-950/20 p-3">
+          <Info className="h-5 w-5 text-blue-500 shrink-0 mt-0.5" />
+          <p className="text-xs text-blue-700 dark:text-blue-400">
+            Install whisper-cpp and piper for local voice features. You can enable voice now and configure binaries later.
+          </p>
+        </div>
+      )}
+
       <div className="flex flex-col gap-3">
         <div className="flex items-center gap-3 rounded-lg border p-3">
           <Mic className="h-5 w-5 text-primary shrink-0" />
-          <div>
+          <div className="flex-1">
             <p className="text-sm font-medium">Speech-to-Text (Whisper)</p>
             <p className="text-xs text-muted-foreground">
-              {micAvailable === false
-                ? "No microphone detected — unavailable"
-                : micAvailable === true
-                  ? "Microphone detected — speak to your assistant"
-                  : "Checking microphone..."}
+              {whisperStatusLabel()}
             </p>
           </div>
+          {whisperStatusIcon()}
         </div>
 
         <div className="flex items-center gap-3 rounded-lg border p-3">
           <Volume2 className="h-5 w-5 text-primary shrink-0" />
-          <div>
+          <div className="flex-1">
             <p className="text-sm font-medium">Text-to-Speech (Piper)</p>
             <p className="text-xs text-muted-foreground">
-              Hear responses read aloud. Runs entirely on your device — no server needed.
+              {piperStatusLabel()}
             </p>
           </div>
+          {piperStatusIcon()}
         </div>
       </div>
 
       <div className="flex flex-col gap-2">
-        <Button onClick={onEnable} className="w-full">
+        <Button
+          onClick={onEnable}
+          className="w-full"
+          variant={neitherBinaryFound ? "outline" : "default"}
+        >
           Enable voice
         </Button>
         <Button variant="ghost" onClick={onSkip} className="w-full">

ui/src/hooks/useHardwareInfo.ts

@@ -1,8 +1,10 @@
 // [nexus] React Query hook for hardware detection data
 import { useQuery } from "@tanstack/react-query";
-import { fetchHardwareInfo, type HardwareInfo } from "../api/hardware";
+import { fetchHardwareInfo, type HardwareInfo, type VoiceCapability } from "../api/hardware";
 import { queryKeys } from "../lib/queryKeys";
 
+export type { VoiceCapability };
+
 export function useHardwareInfo(enabled = true) {
   return useQuery<HardwareInfo>({
     queryKey: queryKeys.hardware.info,