diff --git a/backend/apps/agents/core/ws_manager.py b/backend/apps/agents/core/ws_manager.py
index 7d53d64d..efbb1d01 100644
--- a/backend/apps/agents/core/ws_manager.py
+++ b/backend/apps/agents/core/ws_manager.py
@@ -16,6 +16,7 @@ BROWSER_CMD_TIMEOUTS = {
     "wait": 12.0,         # smart-wait already caps itself well under this
     "perform_action": 35.0, # session-borrow shims pack navigate + wait + scrape into ONE command, so it needs more than navigate alone
     "find_composer": 30.0,  # packs trigger + scroll-ladder + retop + open-first into ONE command; on the 15s default the last two tiers were unreachable and heavy pages died mid-ladder (measured: linkedin timed out 2 of 3 runs). The in-page routine self-caps well under this.
+    "import_session": 40.0,  # applies the borrowed cookies AND lets a hidden window sit through the site's bot challenge so the card inherits the clearance; warmBorrowedSession.js self-caps at 15+2.5+5s, and this must outlast that or the warm is killed mid-challenge and we throw away the whole point of it (same trap as find_composer).
 }
 BROWSER_CMD_REBROADCAST_S = 3.0
 # A CPU-starved renderer can briefly drop its WS (a missed heartbeat) and the frontend auto-reconnects a beat later; bridge that gap instead of hard-failing a live run into it. Short enough that a genuinely-closed window still fails quickly (and no LLM turns are ever burned waiting); long enough to ride out a reconnect even on a loaded machine.
diff --git a/backend/tests/test_browser_session_import.py b/backend/tests/test_browser_session_import.py
index 206650bf..b5b3a2dc 100644
--- a/backend/tests/test_browser_session_import.py
+++ b/backend/tests/test_browser_session_import.py
@@ -236,6 +236,23 @@ async def test_wall_handoff_asks_a_human_once_the_door_borrow_did_not_take(monke
         browser_agent.p_signin_borrowed.discard("acme.example")
 
 
+def test_import_timeout_outlasts_the_hidden_window_warm():
+    """INVARIANT, and the second time this exact trap has bitten (see find_composer): the warm sits
+    through the site's bot challenge inside the import command, so the command's timeout has to
+    outlast the warm's own budget. Set them past each other and the window is killed mid-challenge,
+    which throws away the entire reason the warm exists while still looking like a clean import."""
+    from backend.apps.agents.core.ws_manager import BROWSER_CMD_TIMEOUTS, BROWSER_CMD_TIMEOUT_DEFAULT
+
+    with open(os.path.join(P_REPO_ROOT, "electron", "warmBorrowedSession.js"), encoding="utf-8") as fh:
+        src = fh.read()
+    budget_ms = sum(int(m) for m in re.findall(
+        r"^const (?:LOAD_TIMEOUT_MS|SETTLE_MS|DESTROY_GRACE_MS) = (\d+);", src, re.M))
+    assert budget_ms > 0, "warm budget constants not found; did warmBorrowedSession change shape?"
+    timeout_s = BROWSER_CMD_TIMEOUTS.get("import_session", BROWSER_CMD_TIMEOUT_DEFAULT)
+    assert timeout_s * 1000 > budget_ms, (
+        f"import_session timeout {timeout_s}s must outlast the warm budget {budget_ms}ms")
+
+
 def test_agent_checks_the_opt_in_before_reading_anything():
     """INVARIANT: the borrow helper must consult the setting FIRST. Pinned by source because the
     ordering is the whole consent story, and an innocent-looking reorder would start reading the
diff --git a/electron/main.js b/electron/main.js
index 31cb6a56..bedd54c7 100644
--- a/electron/main.js
+++ b/electron/main.js
@@ -16,6 +16,7 @@ const BROWSER_PARTITION = 'persist:openswarm-browser';
 // token because we never borrow for it: its own sign-in is the thing the token exists to satisfy.
 const p_borrowedSessionDomains = new Set();
 const p_uaSwapLogged = new Set();
+const { warmBorrowedSession } = require('./warmBorrowedSession');
 
 function bareChromeUserAgent(ua) {
   return String(ua || '').replace(/\s*(?:openswarm|Electron)\/\S+/gi, '').replace(/\s{2,}/g, ' ').trim();
@@ -2897,7 +2898,15 @@ async function writePartitionCookies(domain, cookies) {
   // Borrowing the session and presenting as the browser that earned it are one decision, not two:
   // apply the cookies without the matching UA and the site refuses them.
   if (set > 0) p_borrowedSessionDomains.add(d);
-  return { ok: set > 0, set, total: list.length };
+  // Let a plain hidden window take the site's challenge before the card does. It shares this
+  // partition, so whatever clearance it earns is already waiting when the card loads.
+  let warmed = false;
+  if (set > 0) {
+    const ua = bareChromeUserAgent(session.fromPartition(BROWSER_PARTITION).getUserAgent());
+    warmed = await warmBorrowedSession(BROWSER_PARTITION, `https://${d}/`, ua);
+    console.log(`[borrowed-warm] ${d} warmed=${warmed}`);
+  }
+  return { ok: set > 0, set, total: list.length, warmed };
 }
 ipcMain.handle('set-partition-cookies', (_e, domain, cookies) => writePartitionCookies(domain, cookies));
 
diff --git a/electron/warmBorrowedSession.js b/electron/warmBorrowedSession.js
new file mode 100644
index 00000000..80aa541a
--- /dev/null
+++ b/electron/warmBorrowedSession.js
@@ -0,0 +1,71 @@
+// Warm a borrowed sign-in in a hidden window before the visible card loads the site.
+//
+// Measured 2026-07-27: transplanting the user's own Chrome session into the browser partition works
+// (claude.ai accepted it and showed the real account name and plan), but sites behind a serious
+// anti-bot edge refuse it in a browser CARD: chatgpt.com, medium.com and instagram.com all had the
+// cookies applied and the user agent matched and still reported signed-out. The decisive clue is
+// that onboarding's harvest beats Cloudflare on chatgpt.com with those SAME cookies, and the only
+// thing it does differently is load them in a plain hidden BrowserWindow instead of a <webview>
+// guest. A guest carries a preload and the automation tells that come with being embedded; a hidden
+// window is just a browser.
+//
+// So we let the context that passes do the handshake. The hidden window shares the card's partition,
+// which means any clearance it earns lands in the same cookie jar the card is about to use. The
+// card then arrives already cleared instead of being challenged on its first request.
+//
+// Main-process only (an offscreen BrowserWindow is not a renderer webview). Always destroys its
+// window in a finally, so a failure can never leak one, and never throws: a warm that does not work
+// just leaves the card exactly as it would have been.
+const { BrowserWindow } = require('electron');
+
+const LOAD_TIMEOUT_MS = 15000;
+// Anti-bot edges run a JS challenge after the document lands; the clearance cookie is only written
+// once that finishes, so returning at load time would throw away the entire point of doing this.
+const SETTLE_MS = 2500;
+const DESTROY_GRACE_MS = 5000;
+
+async function warmBorrowedSession(partition, url, userAgent) {
+  let win = null;
+  try {
+    win = new BrowserWindow({
+      show: false,
+      width: 1280,
+      height: 900,
+      webPreferences: {
+        partition,
+        sandbox: true,
+        contextIsolation: true,
+        nodeIntegration: false,
+        backgroundThrottling: false,
+      },
+    });
+  } catch {
+    return false;
+  }
+
+  const killer = setTimeout(() => {
+    try { if (win && !win.isDestroyed()) win.destroy(); } catch { /* already gone */ }
+  }, LOAD_TIMEOUT_MS + SETTLE_MS + DESTROY_GRACE_MS);
+
+  try {
+    // Passed to loadURL, not just setUserAgent: the popup-UA spoofer in main.js rewrites any
+    // contents of type 'window' during construction, and the per-load option is what wins.
+    if (userAgent) {
+      try { win.webContents.setUserAgent(userAgent); } catch { /* the load option still carries it */ }
+    }
+    const opts = userAgent ? { userAgent } : undefined;
+    // loadURL rejects when any sub-resource aborts even though the main frame is fine, so a
+    // rejection here is noise; what matters is that the challenge got time to run.
+    const load = win.loadURL(url, opts).catch(() => {});
+    await Promise.race([load, new Promise((r) => setTimeout(r, LOAD_TIMEOUT_MS))]);
+    await new Promise((r) => setTimeout(r, SETTLE_MS));
+    return true;
+  } catch {
+    return false;
+  } finally {
+    clearTimeout(killer);
+    try { if (win && !win.isDestroyed()) win.destroy(); } catch { /* already gone */ }
+  }
+}
+
+module.exports = { warmBorrowedSession, LOAD_TIMEOUT_MS, SETTLE_MS, DESTROY_GRACE_MS };