diff --git a/src/runtime/guest-error.test.ts b/src/runtime/guest-error.test.ts
new file mode 100644
index 0000000..e970203
--- /dev/null
+++ b/src/runtime/guest-error.test.ts
@@ -0,0 +1,77 @@
+import { describe, expect, test } from "bun:test";
+import { describeGuestError, isGuestOriginError } from "./guest-error.js";
+
+/** The exact stack from the field crash report (v4.5.5, TUI mode). */
+function fieldCrash(): Error {
+  const err = new ReferenceError("moveBy is not defined");
+  err.stack =
+    "ReferenceError: moveBy is not defined\n" +
+    "    at tE (https://g.alicdn.com/captcha-frontend/FeiLin/1.5.1/" +
+    "feilin008.489f1fe42772a97d510f162902b33c35c004ce7746ca3f4696c42f8d1f677670.js:1:169658)";
+  return err;
+}
+
+function withStack(message: string, stack: string): Error {
+  const err = new Error(message);
+  err.stack = stack;
+  return err;
+}
+
+describe("guest-origin classification", () => {
+  test("the captcha SDK crash that killed the TUI is attributed to the guest", () => {
+    expect(isGuestOriginError(fieldCrash())).toBe(true);
+  });
+
+  test("host faults stay fatal", () => {
+    // The v4.5.2 crash shape: a Bun-internal timer stripped of `.unref()`.
+    // It is a real proxy defect and must never be swallowed as guest noise.
+    const unref = withStack(
+      "setTimeout(() => {}, 0).unref is not a function",
+      "TypeError: …unref is not a function\n    at node:_http_server:512:9",
+    );
+    expect(isGuestOriginError(unref)).toBe(false);
+    expect(
+      isGuestOriginError(withStack("boom", "Error: boom\n    at buildFrame (/app/src/tui/frame.ts:88:3)")),
+    ).toBe(false);
+  });
+
+  test("an unattributable error is treated as a host fault", () => {
+    // No evidence must never mean "assume guest": that would silently mask
+    // genuine crashes behind a log line.
+    expect(isGuestOriginError(new Error("no stack recorded"))).toBe(false);
+    expect(isGuestOriginError({ message: "not even an Error" })).toBe(false);
+    expect(isGuestOriginError(undefined)).toBe(false);
+  });
+
+  test("lookalike hosts are not guest evidence", () => {
+    expect(
+      isGuestOriginError(withStack("x", "at f (https://evil-alicdn.com.attacker.net/x.js:1:1)")),
+    ).toBe(false);
+    expect(
+      isGuestOriginError(withStack("x", "at f (https://cdn.example.com/p?ref=alicdn.com)")),
+    ).toBe(false);
+  });
+
+  test("every host serving the SDK counts, including subdomains and cause chains", () => {
+    expect(isGuestOriginError(withStack("x", "at https://o.alicdn.com/captcha-frontend/a.js:1:1"))).toBe(true);
+    expect(isGuestOriginError(withStack("x", "at https://captcha.ap-southeast-1.aliyuncs.com/x.js:1:1"))).toBe(true);
+    const wrapped = withStack("wrapper", "Error: wrapper\n    at host (/app/x.ts:1:1)");
+    (wrapped as { cause?: unknown }).cause = fieldCrash();
+    expect(isGuestOriginError(wrapped)).toBe(true);
+  });
+
+  test("a self-referential cause chain terminates", () => {
+    const a = withStack("a", "at /app/a.ts:1:1");
+    const b = withStack("b", "at /app/b.ts:1:1");
+    (a as { cause?: unknown }).cause = b;
+    (b as { cause?: unknown }).cause = a;
+    expect(isGuestOriginError(a)).toBe(false);
+  });
+
+  test("the log line names the error and the bundle, without the content hash", () => {
+    const line = describeGuestError(fieldCrash());
+    expect(line).toContain("ReferenceError: moveBy is not defined");
+    expect(line).toContain("feilin008");
+    expect(line).not.toContain("https://");
+  });
+});
diff --git a/src/runtime/guest-error.ts b/src/runtime/guest-error.ts
new file mode 100644
index 0000000..145ee1e
--- /dev/null
+++ b/src/runtime/guest-error.ts
@@ -0,0 +1,73 @@
+/**
+ * guest-error.ts — provenance test for errors thrown by third-party captcha
+ * SDK code ("guest" scripts) running inside the in-process happy-dom solver.
+ *
+ * Under Bun the guest scripts execute in the HOST realm (happy-dom's VM
+ * isolation is a no-op there), so an error escaping a guest callback reaches
+ * process-level `uncaughtException` exactly like an error from our own code.
+ * The two must not share a fate: a rotated pe/FeiLin bundle tripping over an
+ * emulation gap must fail that one solve — the pool retries — while a genuine
+ * fault in the proxy still terminates loudly.
+ *
+ * `serve` mode already draws that line (captcha-happy.ts logs and continues).
+ * The TUI's own uncaughtException handler used to exit(1) for everything,
+ * which turned a recoverable guest error into a dead proxy:
+ *
+ *     zcode-proxy: tui crashed: ReferenceError: moveBy is not defined
+ *         at tE (https://g.alicdn.com/captcha-frontend/FeiLin/1.5.1/feilin008…js)
+ *
+ * Evidence is the source URL of the throwing frame: guest bundles are served
+ * from Aliyun CDN/API hosts and carry those URLs in their stack frames (and,
+ * for generated code, in the `//# sourceURL` we preserve when evaluating).
+ */
+
+// CDN/API hosts serving the Aliyun captcha SDK bundles. Anchored at the URL
+// authority (`scheme://`, optional userinfo) and terminated by a port/path/
+// delimiter, so the domain must be the real host — `evil-alicdn.com.bad.net`
+// and `…?ref=alicdn.com` are not guest evidence.
+const GUEST_SCRIPT_HOST =
+  /https?:\/\/(?:[^/\s@]*@)?(?:[a-z0-9-]+\.)*(?:alicdn\.com|aliyuncs\.com)(?=[:/?#]|\s|$)/i;
+
+/** Follows `cause` chains without looping on self-referential errors. */
+function* errorChain(err: unknown, depth = 4): Generator<object> {
+  const seen = new Set<unknown>();
+  let current = err;
+  for (let i = 0; i < depth; i++) {
+    if (!current || typeof current !== "object" || seen.has(current)) return;
+    seen.add(current);
+    yield current as object;
+    current = (current as { cause?: unknown }).cause;
+  }
+}
+
+/**
+ * True when `err` originates in third-party captcha SDK code.
+ *
+ * Deliberately conservative: only a guest source URL counts as evidence. A
+ * missing/truncated stack yields `false`, so an unattributable error keeps the
+ * strict (fatal) treatment.
+ */
+export function isGuestOriginError(err: unknown): boolean {
+  for (const link of errorChain(err)) {
+    const e = link as { stack?: unknown; sourceURL?: unknown; message?: unknown };
+    if (typeof e.stack === "string" && GUEST_SCRIPT_HOST.test(e.stack)) return true;
+    // Bun/JSC attach the throwing script's URL directly on the error.
+    if (typeof e.sourceURL === "string" && GUEST_SCRIPT_HOST.test(e.sourceURL)) return true;
+    if (typeof e.message === "string" && GUEST_SCRIPT_HOST.test(e.message)) return true;
+  }
+  return false;
+}
+
+/** One-line render of a guest error for the log pane / stderr. */
+export function describeGuestError(err: unknown): string {
+  const e = err as { name?: unknown; message?: unknown; stack?: unknown } | null;
+  const name = typeof e?.name === "string" ? e.name : "Error";
+  const message = typeof e?.message === "string" ? e.message : String(err);
+  const frame =
+    typeof e?.stack === "string"
+      ? (e.stack.split("\n").find((line) => GUEST_SCRIPT_HOST.test(line)) ?? "").trim()
+      : "";
+  // Bundle URLs carry a 64-char content hash — keep the readable filename only.
+  const source = frame.replace(/^at\s+/, "").replace(/https?:\/\/[^\s)]*\/([^/\s)]+)/, "$1");
+  return source ? `${name}: ${message} (${source})` : `${name}: ${message}`;
+}
diff --git a/src/tui/app.ts b/src/tui/app.ts
index e479b1b..c72f38c 100644
--- a/src/tui/app.ts
+++ b/src/tui/app.ts
@@ -23,6 +23,7 @@ import { ZaiOAuthClient, BigmodelOAuthClient, LOGIN_TIMEOUT_MS, parsePastedCallb
 import { KeyResolver } from "../auth/resolver.js";
 import { openBrowser } from "../runtime/open-browser.js";
 import { pasteLoginInstructions, readPastedLine, boldIfTTY } from "../runtime/paste-login.js";
+import { isGuestOriginError, describeGuestError } from "../runtime/guest-error.js";
 import { ensureDeviceMidInConfig, VERSION, type ServeArgs } from "../index.js";
 import { writeFileSync, existsSync, appendFileSync } from "node:fs";
 import type { ProxyConfig } from "../config/types.js";
@@ -636,7 +637,18 @@ export async function runTui(args: ServeArgs): Promise<void> {
   process.on("SIGTERM", quit);
   process.on("exit", restore);
   stdout.on("resize", scheduleRender);
+  // Guest captcha-SDK errors must NOT kill the TUI. Under Bun the Aliyun/
+  // FeiLin bundles run in the HOST realm, so an error escaping one of their
+  // stray callbacks arrives here exactly like an internal fault. `serve` mode
+  // already logs-and-continues (captcha-happy.ts); the TUI used to exit(1) for
+  // everything, turning a retryable solve failure into a dead proxy (field
+  // report: "tui crashed: ReferenceError: moveBy is not defined" from
+  // feilin008.js). The pool retries the solve; the proxy keeps serving.
   process.on("uncaughtException", (err: Error) => {
+    if (isGuestOriginError(err)) {
+      emit(`[warn] captcha SDK error (ignored): ${describeGuestError(err)}`, "warn");
+      return;
+    }
     cleanup();
     origError(`zcode-proxy: tui crashed: ${err.stack ?? String(err)}`);
     process.exit(1);