diff --git a/extension/src/popup/styles.css b/extension/src/popup/styles.css
index 4d26e57..362e3ae 100644
--- a/extension/src/popup/styles.css
+++ b/extension/src/popup/styles.css
@@ -1256,3 +1256,23 @@ textarea {
 .mode-card.active { border-color: #58a6ff; background: rgba(88,166,255,0.08); }
 .mode-card-title { font-weight: 600; margin-bottom: 4px; font-size: 14px; }
 .mode-card-blurb { color: #8b949e; font-size: 12px; margin: 0; line-height: 1.5; }
+
+/* --- Setup wizard probe banners (Step 2) --- */
+.banner { padding: 12px; border-radius: 6px; margin: 12px 0; font-size: 13px; }
+.banner-ok {
+  background: rgba(46,160,67,0.10);
+  border: 1px solid rgba(46,160,67,0.4);
+}
+.banner-warn {
+  background: rgba(218,54,51,0.08);
+  border: 1px solid rgba(218,54,51,0.4);
+}
+.banner strong { display: block; margin-bottom: 4px; }
+.banner p { margin: 6px 0; line-height: 1.5; color: #c9d1d9; }
+.banner code {
+  font-family: ui-monospace, SFMono-Regular, monospace;
+  font-size: 12px;
+  background: #21262d;
+  padding: 1px 5px;
+  border-radius: 3px;
+}
diff --git a/extension/src/setup/setup.ts b/extension/src/setup/setup.ts
index c32d626..fd3b076 100644
--- a/extension/src/setup/setup.ts
+++ b/extension/src/setup/setup.ts
@@ -7,6 +7,7 @@
 /// Step 5: Finish (download reference image, push config to extension or copy JSON)
 
 import { createGitHost, uint8ArrayToBase64 } from '../service-worker/git-host';
+import { probeVault } from './probe';
 import type { VaultConfig } from '../shared/types';
 
 // --- WASM module (loaded dynamically) ---
@@ -400,7 +401,55 @@ function attachStep1(): void {
 
 // --- Step 2: Configure Connection ---
 
+function renderProbeBanner(): string {
+  const probe = state.vaultProbe;
+  if (!state.connectionTested || !probe) return '';
+  const meta = probe.lastCommit
+    ? `Last commit: <code>${escapeHtml(probe.lastCommit.sha)}</code> by ${escapeHtml(probe.lastCommit.author)} on ${escapeHtml(probe.lastCommit.date.slice(0, 10))}.`
+    : '';
+  if (state.mode === 'new' && probe.exists) {
+    return `
+      <div class="banner banner-warn">
+        <strong>⚠ This repository already contains a relicario vault.</strong>
+        <p>${meta}</p>
+        <p>Creating a new vault here would overwrite the existing one and <strong>destroy all data inside</strong>.
+           To use this vault on this device, switch to <em>attach</em> mode instead.
+           If you really mean to start over, delete the repository via your git host's web UI and come back here.</p>
+        <div class="form-actions">
+          <button class="btn" id="switch-mode-btn" data-target="attach">switch to attach mode</button>
+        </div>
+      </div>`;
+  }
+  if (state.mode === 'attach' && !probe.exists) {
+    return `
+      <div class="banner banner-warn">
+        <strong>No vault found in this repo.</strong>
+        <p>Did you mean to create a new vault?</p>
+        <div class="form-actions">
+          <button class="btn" id="switch-mode-btn" data-target="new">switch to new-vault mode</button>
+        </div>
+      </div>`;
+  }
+  if (state.mode === 'attach' && probe.exists) {
+    return `
+      <div class="banner banner-ok">
+        <strong>✓ Existing vault found.</strong>
+        <p>${meta}</p>
+        <p>Continue to attach this device.</p>
+      </div>`;
+  }
+  // mode = new, !exists
+  return `
+    <div class="banner banner-ok">
+      <strong>✓ Repo is empty — ready to create a new vault.</strong>
+    </div>`;
+}
+
 function renderStep2(): string {
+  const probe = state.vaultProbe;
+  const modeMismatch =
+    !!probe && ((state.mode === 'new' && probe.exists) || (state.mode === 'attach' && !probe.exists));
+  const nextDisabled = !state.connectionTested || !probe || modeMismatch;
   return `
     <div class="wizard-step">
       <h3>configure connection</h3>
@@ -420,9 +469,10 @@ function renderStep2(): string {
         <button class="btn" id="test-btn">test connection</button>
         ${state.connectionTested ? '<span class="test-result pass">connected</span>' : ''}
       </div>
+      ${renderProbeBanner()}
       <div class="form-actions" style="margin-top:12px;">
         <button class="btn" id="back-btn">back</button>
-        <button class="btn btn-primary" id="next-btn" ${!state.connectionTested ? 'disabled' : ''}>next</button>
+        <button class="btn btn-primary" id="next-btn" ${nextDisabled ? 'disabled' : ''}>next</button>
       </div>
     </div>
   `;
@@ -430,6 +480,8 @@ function renderStep2(): string {
 
 function attachStep2(): void {
   document.getElementById('test-btn')?.addEventListener('click', async () => {
+    state.connectionTested = false;
+    state.vaultProbe = null;
     const hostUrl = state.hostType === 'github'
       ? 'https://api.github.com'
       : (document.getElementById('host-url') as HTMLInputElement).value.trim();
@@ -456,8 +508,15 @@ function attachStep2(): void {
       await host.listDir('');
       state.connectionTested = true;
       state.error = null;
+      try {
+        state.vaultProbe = await probeVault(host);
+      } catch (probeErr) {
+        state.vaultProbe = null;
+        state.error = `Could not check repo state: ${probeErr instanceof Error ? probeErr.message : String(probeErr)}`;
+      }
     } catch (err: unknown) {
       state.connectionTested = false;
+      state.vaultProbe = null;
       state.error = `Connection failed: ${err instanceof Error ? err.message : String(err)}`;
     }
     render();
@@ -475,6 +534,13 @@ function attachStep2(): void {
     state.error = null;
     render();
   });
+
+  document.getElementById('switch-mode-btn')?.addEventListener('click', (e) => {
+    const target = (e.currentTarget as HTMLElement).dataset.target as 'new' | 'attach';
+    state.mode = target;
+    state.error = null;
+    render();
+  });
 }
 
 // --- Step 3 (new-vault variant): Create Vault ---