diff --git a/bcnr-preload.js b/bcnr-preload.js
index 699b1257..4b433356 100644
--- a/bcnr-preload.js
+++ b/bcnr-preload.js
@@ -35,7 +35,11 @@ contextBridge.exposeInMainWorld("bcnr", {
   // verifies the publisher signature against the name's owner and installs.
   // Resolves `{ ok, version, publisher }` or `{ ok:false, error }` (also
   // "cancelled"). Pages can feature-detect it: absent on older builds.
-  installExtension: (id)   => ipcRenderer.invoke("bcnr:installExtension", String(id || "")),
+  // Needs a real click: the isolated world reads the page's user activation,
+  // which page script cannot fake.
+  installExtension: (id)   => (navigator.userActivation && !navigator.userActivation.isActive
+    ? Promise.resolve({ ok: false, error: "installing needs a click on the page" })
+    : ipcRenderer.invoke("bcnr:installExtension", String(id || ""))),
 });
 
 // Install-as-app relay. Theseus fires a synthetic `beforeinstallprompt` in
diff --git a/js-dialog.html b/js-dialog.html
index f8cea12e..584eeb9a 100644
--- a/js-dialog.html
+++ b/js-dialog.html
@@ -118,7 +118,20 @@
           ${order.map((i) => `<button class="pbtn ${i === req.defaultId ? "primary" : "quiet"}" type="button" data-i="${i}">${esc(req.buttons[i])}</button>`).join("")}
         </div>
       </div></div>`;
-    document.querySelectorAll("button[data-i]").forEach((b) => b.addEventListener("click", () => finishApp(Number(b.dataset.i))));
+    // Armed like the approval overlay: for the first moments only the
+    // cancel choice works, so a click aimed at whatever was under the
+    // pointer when the sheet appeared (a page timing a double-click) cannot
+    // land on Install or another affirmative button.
+    const ARM_MS = 800;
+    const armAt = Date.now() + ARM_MS;
+    req.armAt = armAt;
+    const acts = Array.from(document.querySelectorAll("button[data-i]")).filter((b) => Number(b.dataset.i) !== req.cancelId);
+    acts.forEach((b) => { b.disabled = true; b.style.opacity = "0.45"; });
+    setTimeout(() => { if (current === req) acts.forEach((b) => { b.disabled = false; b.style.opacity = ""; }); }, ARM_MS);
+    document.querySelectorAll("button[data-i]").forEach((b) => b.addEventListener("click", () => {
+      if (Number(b.dataset.i) !== req.cancelId && Date.now() < armAt) return;
+      finishApp(Number(b.dataset.i));
+    }));
     document.getElementById("close").addEventListener("click", () => finishApp(req.cancelId));
     const mask = document.querySelector(".promptmask");
     mask.addEventListener("mousedown", (e) => { if (e.target === mask) finishApp(req.cancelId); });
@@ -159,7 +172,11 @@
     if (!current) return;
     if (current.kind === "app") {
       if (e.key === "Escape") { e.preventDefault(); finishApp(current.cancelId); }
-      else if (e.key === "Enter" && !(e.target && e.target.matches("button.quiet, #close"))) { e.preventDefault(); finishApp(current.defaultId); }
+      else if (e.key === "Enter" && !(e.target && e.target.matches("button.quiet, #close"))) {
+        e.preventDefault();
+        if (current.defaultId !== current.cancelId && Date.now() < (current.armAt || 0)) return;
+        finishApp(current.defaultId);
+      }
       return;
     }
     if (e.key === "Escape") { e.preventDefault(); finish(current.kind === "alert"); }
diff --git a/main.js b/main.js
index 837eac38..1b1b1b89 100644
--- a/main.js
+++ b/main.js
@@ -4009,7 +4009,12 @@ function createTab(initial, opts = {}) {
       const installId = installLinkId(u);
       if (installId) {
         e.preventDefault();
-        let requester = null; try { requester = new URL(wc.getURL()).host || null; } catch {}
+        let requester = null; try { requester = new URL(String(wc.getURL()).replace(/^bns:\/\//i, "https://")).host || null; } catch {}
+        const init = e.initiator;
+        if (!installRequesterOk(requester) || (init && init.frameTreeNodeId !== wc.mainFrame.frameTreeNodeId)) {
+          console.log("[addons] install link ignored: not from theseus.x's top frame");
+          return;
+        }
         installExtensionWithConsent(installId, requester);
         return;
       }
@@ -4123,8 +4128,11 @@ function createTab(initial, opts = {}) {
     }
     const installId = installLinkId(url);
     if (installId) {
-      let requester = null; try { requester = new URL(wc.getURL()).host || null; } catch {}
-      installExtensionWithConsent(installId, requester);
+      let requester = null; try { requester = new URL(String(wc.getURL()).replace(/^bns:\/\//i, "https://")).host || null; } catch {}
+      let refHost = null; try { refHost = details.referrer && details.referrer.url ? new URL(String(details.referrer.url).replace(/^bns:\/\//i, "https://")).host : null; } catch {}
+      // Same rule as the bcnr call: the catalog site's own top frame only.
+      if (installRequesterOk(requester) && refHost === requester) installExtensionWithConsent(installId, requester);
+      else console.log("[addons] install window ignored: not from theseus.x's top frame");
     } else if (url && url !== "about:blank") {
       // Chromium won't let a web page navigate to file://, chrome:// or
       // theseus://, but createTab → loadURL runs from main and would. Web
@@ -5647,9 +5655,17 @@ ipcMain.handle("webapp-prompt", async (e) => {
 ipcMain.handle("webapps-list", () => webapps.list().map((a) => ({ key: a.key, name: a.name, host: a.host, startUrl: a.startUrl, installedAt: a.installedAt })));
 ipcMain.handle("webapps-open", (_e, key) => { const a = webapps.find(String(key || "")); if (a) webapps.open(a); return !!a; });
 ipcMain.handle("webapps-remove", (_e, key) => webapps.uninstall(String(key || ""), true).then((ok) => { emitTabs(); return ok; }));
+// Only the catalog site may ask, and only from its top frame. Any page used
+// to be able to raise the install sheet without a click (bcnr is in every
+// page's main world), timed so a double-click landed on Install — and an
+// installed extension runs in the main process at once.
+const INSTALL_REQUESTERS = new Set(["theseus.x"]);
+function installRequesterOk(host) { return !!host && INSTALL_REQUESTERS.has(String(host).toLowerCase()); }
 ipcMain.handle("bcnr:installExtension", (e, id) => {
+  if (!e.senderFrame || e.senderFrame !== e.sender.mainFrame) return { ok: false, error: "only the top frame may install" };
   let requester = null;
-  try { requester = new URL(e.sender.getURL()).host || null; } catch {}
+  try { requester = new URL(String(e.sender.getURL()).replace(/^bns:\/\//i, "https://")).host || null; } catch {}
+  if (!installRequesterOk(requester)) return { ok: false, error: "extensions can only be installed from theseus.x" };
   return installExtensionWithConsent(id, requester);
 });
 // Background / manual add-on update check. Whatever gets staged is pushed to