fix(tests): resolve 4 post-phase test failures

- platformClients.integration: iOS/Android push tests lacked
  setStatus() call before listNodes(), so platform filter excluded
  nodes. Added publishHeartbeat() to set platform on connection state.
- server.test: agent.send now emits run_state events before done (Phase
  1). Added sendAndWaitForDone() helper and updated test to find done
  event rather than assuming index 0.
- handlers.test: updated agent.send/cancel assertions to use find()
  and pass send arg to agent.cancel, consistent with run_state events.
- httpBody: req.destroy() closed socket before 413 response could be
  sent. Removed socket destruction from body reader; 413 responses now
  send Connection: close so Node closes the connection cleanly.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/automation/webhooks.ts

@@ -136,7 +136,7 @@ export class WebhookHandler implements ChannelAdapter {
     } catch (err) {
       if (err instanceof RequestBodyTooLargeError) {
         auditLogger?.webhookDenied(webhookName, `Payload too large (>${this.maxRequestBodyBytes} bytes)`);
-        res.writeHead(413, { 'Content-Type': 'application/json' });
+        res.writeHead(413, { 'Content-Type': 'application/json', 'Connection': 'close' });
         res.end(JSON.stringify({ error: 'Payload too large' }));
         return false;
       }