test(e2b): satisfy the steer() receipt signature in Agent stubs

Master's steering-receipt API (agent.steer returns SteeringReceipt) reached
this branch through the parent sync; the two E2B live-fixture Agent stubs
return the same rejected-outcome receipt the pty test stubs use.

examples/headless-agent/tests/fixtures/e2b/e2b/bin.ts

@@ -22,7 +22,7 @@ const owner: Agent = {
   acceptsNextStep: false,
   ctx: ownerFiber.ctx,
   followup() {},
-  steer() {},
+  steer: () => ({ outcome: Promise.resolve({ status: 'rejected' as const }) }),
   inject() {},
   send() {},
   cancel() {},

packages/e2b/e2b/tests/composition.e2e.ts

@@ -86,7 +86,7 @@ describe.skipIf(!process.env.E2B_API_KEY)('E2B live Loader composition', () => {
         acceptsNextStep: false,
         ctx,
         followup() {},
-        steer() {},
+        steer: () => ({ outcome: Promise.resolve({ status: 'rejected' as const }) }),
         inject() {},
         send() {},
         cancel() {},