diff --git a/frontend/packages/swarm-ui/src/agent/claude-login/ClaudeLoginDialog.tsx b/frontend/packages/swarm-ui/src/agent/claude-login/ClaudeLoginDialog.tsx
index fa91a72e..135bad83 100644
--- a/frontend/packages/swarm-ui/src/agent/claude-login/ClaudeLoginDialog.tsx
+++ b/frontend/packages/swarm-ui/src/agent/claude-login/ClaudeLoginDialog.tsx
@@ -2,7 +2,8 @@
 // login minter. Opening it starts the login (`POST …/claude-login`), which
 // answers with the URL claude printed; the operator opens it and pastes the
 // code back (`POST …/claude-login/code`). Closing it while the code is
-// still awaited stops the login (`DELETE …/claude-login`).
+// still awaited stops the login (`DELETE …/claude-login`). Closing while the
+// start is still in flight stops it once the start answers.
 //
 // Mounted only while open, so each open is a fresh login.
 import { useEffect, useState } from "preact/hooks";
@@ -15,9 +16,12 @@ import { TextField } from "../../ui/text-field/TextField.js";
 import {
   afterCode,
   afterStart,
+  beginStart,
   claudeLoginPath,
+  isLatestStart,
   leavesLoginRunning,
   pastedCode,
+  startOutlivedDialog,
   type LoginStep,
 } from "./ClaudeLoginSteps.js";
 import "./ClaudeLoginDialog.css";
@@ -38,10 +42,15 @@ export function ClaudeLoginDialog({
 
   useEffect(() => {
     let live = true;
+    const mine = beginStart(agent);
     void (async () => {
       try {
         const r = await fetch(claudeLoginPath(agent), { method: "POST" });
         const problem = await problemOf(r);
+        if (startOutlivedDialog(live, problem, isLatestStart(agent, mine))) {
+          void fetch(claudeLoginPath(agent), { method: "DELETE" });
+          return;
+        }
         const next = afterStart(
           problem ? { problem } : ((await r.json()) as { url: string }),
         );
diff --git a/frontend/packages/swarm-ui/src/agent/claude-login/ClaudeLoginSteps.ts b/frontend/packages/swarm-ui/src/agent/claude-login/ClaudeLoginSteps.ts
index 5366130b..59a849f6 100644
--- a/frontend/packages/swarm-ui/src/agent/claude-login/ClaudeLoginSteps.ts
+++ b/frontend/packages/swarm-ui/src/agent/claude-login/ClaudeLoginSteps.ts
@@ -34,6 +34,35 @@ export function leavesLoginRunning(s: LoginStep): boolean {
   return s.step === "code";
 }
 
+// The newest start per agent. The minter keeps one login per agent and a
+// new start replaces it, so a late stop from an older start would end the
+// newer dialog's login.
+const latestStart = new Map<string, number>();
+
+// Marks a start as the agent's newest and returns its number.
+export function beginStart(agent: string): number {
+  const n = (latestStart.get(agent) ?? 0) + 1;
+  latestStart.set(agent, n);
+  return n;
+}
+
+// Whether `n` is still the agent's newest start.
+export function isLatestStart(agent: string, n: number): boolean {
+  return latestStart.get(agent) === n;
+}
+
+// Whether a start that answered after the dialog went away left a login
+// running that nothing else owns: it did unless the start itself failed or a
+// newer start has replaced it. The dialog stops it then, since nothing is
+// left to.
+export function startOutlivedDialog(
+  dialogLive: boolean,
+  problem: ProblemDetails | null,
+  latest: boolean,
+): boolean {
+  return !dialogLive && problem === null && latest;
+}
+
 // What the code form may submit: the pasted code without surrounding
 // whitespace, or nothing.
 export function pastedCode(raw: string): string | null {
diff --git a/frontend/packages/swarm-ui/test/claude-login.test.mjs b/frontend/packages/swarm-ui/test/claude-login.test.mjs
index e61e05ff..8ba401ce 100644
--- a/frontend/packages/swarm-ui/test/claude-login.test.mjs
+++ b/frontend/packages/swarm-ui/test/claude-login.test.mjs
@@ -6,9 +6,12 @@ import { test } from "node:test";
 import {
   afterCode,
   afterStart,
+  beginStart,
   claudeLoginPath,
+  isLatestStart,
   leavesLoginRunning,
   pastedCode,
+  startOutlivedDialog,
 } from "../src/agent/claude-login/ClaudeLoginSteps.ts";
 
 test("the routes name the agent, escaped", () => {
@@ -48,6 +51,28 @@ test("only a login waiting for its code is stopped on close", () => {
   assert.equal(leavesLoginRunning({ step: "stored" }), false);
 });
 
+test("a start that answers after the dialog closed is stopped, unless it failed or was replaced", () => {
+  assert.equal(startOutlivedDialog(false, null, true), true);
+  assert.equal(startOutlivedDialog(true, null, true), false);
+  assert.equal(
+    startOutlivedDialog(false, { detail: "no minter" }, true),
+    false,
+  );
+  assert.equal(startOutlivedDialog(false, null, false), false);
+});
+
+test("only an agent's newest start counts as the latest", () => {
+  const first = beginStart("login-test-a");
+  assert.equal(isLatestStart("login-test-a", first), true);
+  const second = beginStart("login-test-a");
+  assert.equal(isLatestStart("login-test-a", first), false);
+  assert.equal(isLatestStart("login-test-a", second), true);
+  // Another agent's starts are counted on their own.
+  const other = beginStart("login-test-b");
+  assert.equal(isLatestStart("login-test-a", second), true);
+  assert.equal(isLatestStart("login-test-b", other), true);
+});
+
 test("a pasted code is trimmed, and a blank one is nothing", () => {
   assert.equal(pastedCode("  abc-def \n"), "abc-def");
   assert.equal(pastedCode(" \n "), null);