diff --git a/services/agents-login/src/worker/session.ts b/services/agents-login/src/worker/session.ts
index c81d89d2..eceffb16 100644
--- a/services/agents-login/src/worker/session.ts
+++ b/services/agents-login/src/worker/session.ts
@@ -165,9 +165,14 @@ export class LoginSession {
     this.proc = this.deps.spawner(cmd.file, cmd.args, {
       cwd: this.deps.paths.home,
       env,
-      // Wide enough that the ~350-char authorize URL is emitted on one line;
-      // the default 80 cols wraps it and breaks URL extraction.
-      cols: 400,
+      // Wide enough that the authorize URL is emitted on ONE line. If the URL
+      // wraps, the `&state=...` tail lands on the next line and the parser's
+      // [^\s]+ stops at the break — the captured URL then lacks `state` and
+      // claude.ai rejects it ("Missing state parameter"). The Claude subscription
+      // authorize URL is ~450 chars (client_id + redirect_uri + the full scope
+      // set + code_challenge + state); 400 cols was too narrow and dropped state.
+      // 2000 leaves ample headroom.
+      cols: 2000,
       rows: 50,
     })
     this.proc.onData((chunk) => this.onData(chunk, updatedBy))
diff --git a/services/agents-login/test/helpers/fakePty.ts b/services/agents-login/test/helpers/fakePty.ts
index d3be0ec1..073cf1b9 100644
--- a/services/agents-login/test/helpers/fakePty.ts
+++ b/services/agents-login/test/helpers/fakePty.ts
@@ -1,4 +1,4 @@
-import type { PtyProcess, PtySpawner } from '../../src/worker/pty.js'
+import type { PtyProcess, PtySpawner, PtySpawnOptions } from '../../src/worker/pty.js'
 
 /**
  * Fake PTY whose script is a list of programmed actions: emit output, or wait
@@ -69,13 +69,16 @@ export class FakePty implements PtyProcess {
 export function fakeSpawner(scriptFor: (file: string, args: string[]) => Action[]): {
   spawner: PtySpawner
   instances: FakePty[]
+  spawns: Array<{ file: string; args: string[]; options: PtySpawnOptions }>
 } {
   const instances: FakePty[] = []
-  const spawner: PtySpawner = (file, args) => {
+  const spawns: Array<{ file: string; args: string[]; options: PtySpawnOptions }> = []
+  const spawner: PtySpawner = (file, args, options) => {
+    spawns.push({ file, args, options })
     const pty = new FakePty(scriptFor(file, args))
     instances.push(pty)
     pty.run()
     return pty
   }
-  return { spawner, instances }
+  return { spawner, instances, spawns }
 }
diff --git a/services/agents-login/test/session.test.ts b/services/agents-login/test/session.test.ts
index e48c5e40..16f9e8f8 100644
--- a/services/agents-login/test/session.test.ts
+++ b/services/agents-login/test/session.test.ts
@@ -145,8 +145,9 @@ describe('LoginSession state machine', () => {
   ): {
     deps: SessionDeps
     instances: ReturnType<typeof fakeSpawner>['instances']
+    spawns: ReturnType<typeof fakeSpawner>['spawns']
   } {
-    const { spawner, instances } = fakeSpawner(scriptFor)
+    const { spawner, instances, spawns } = fakeSpawner(scriptFor)
     return {
       deps: {
         spawner,
@@ -157,9 +158,22 @@ describe('LoginSession state machine', () => {
         ttlMs: 60_000,
       },
       instances,
+      spawns,
     }
   }
 
+  it('spawns the Claude login PTY wide enough that the authorize URL + state never wraps', () => {
+    // The subscription authorize URL is ~450 chars (scopes + code_challenge +
+    // state). A narrow PTY wraps it and the `&state=...` tail is dropped, so
+    // claude.ai rejects the URL with "Missing state parameter". Guard the width.
+    const { deps: d, spawns } = deps(() => [{ type: 'emit', data: '' }])
+    const mgr = new SessionManager(d)
+    mgr.start('claude', 'alice')
+    const claudeSpawn = spawns.find((s) => s.file === 'claude')
+    expect(claudeSpawn).toBeDefined()
+    expect(claudeSpawn!.options.cols ?? 0).toBeGreaterThanOrEqual(1000)
+  })
+
   it('seeds Claude subscription login settings and drives bounded onboarding Enter-through', async () => {
     vi.useFakeTimers()
     try {