The last hop
is the hard part.

The problem

Every realtime feature has two halves. Only one of them is solved.

Capabilities

Six things, and then it stops.

The surface area is the product. Everything below fits in one sitting, the client SDK is nine kilobytes, and there is no seventh item waiting behind a feature flag.

1. 01

   Ordered per topic, per subscriber

   Every message carries a monotonic cursor. A subscriber sees a topic in publish order, and a client that reconnects with a cursor cannot receive an older message after a newer one.

2. 02

   Replay from the last cursor

   Acknowledge a cursor, disconnect, come back ninety seconds later and present it again. The mesh replays the gap from the topic's retention buffer, then resumes live. Tunnels stop generating bug reports.

3. 03

   Namespaces are the tenancy wall

   Topics, tokens, quota, retention and regional placement all scope to a single namespace. A token minted for one namespace cannot read another, and there is no cross-namespace API surface to misconfigure.

4. 04

   Fan-out you don't pay per socket

   One publish to fifty thousand subscribers is one billable message. Connection-hours meter separately and generously. Adding viewers does not multiply the invoice.

5. 05

   Backpressure that names the subscriber

   A subscriber that stops reading is buffered to its topic's limit, then disconnected with slow_consumer. It appears in the namespace log by connection ID — not as an aggregate you have to go correlate.

6. 06

   Regional placement, one topic name

   Pin a namespace to a set of regions. Subscribers attach at the nearest edge, the topic name is identical everywhere, and the ordering guarantee holds across regions at 95 ms p99.

The shape of it

Two calls. That's the integration.

Publish over HTTP from anything that can make a request. Subscribe over WebSocket from anything that can hold one open. Examples use namespace q2m9r1 — substitute your own.

# Publish once. The mesh handles every attached subscriber.
curl -X POST https://bus.topcmesh.com/bus/namespace/q2m9r1/topic/orders.status \
  -H "Authorization: Bearer $TOPCMESH_PUBLISH_TOKEN" \
  -H "Content-Type: application/json" \
  -d '{"order_id":"ord_8f2a","state":"picked","at":"2026-07-26T14:02:11Z"}'

# 202 Accepted
# { "cursor": "84f21c", "topic": "orders.status", "fanout": 1284 }

import { connect } from '@topcmesh/client';      // 9 KB gzipped

const mesh = connect({
  namespace: 'q2m9r1',
  token: await mintSubscriberToken(),        // scoped, short-lived
  cursor: localStorage.getItem('cursor') ?? 'latest',
});

mesh.topic('orders.status').on('message', (msg) => {
  render(msg.data);
  localStorage.setItem('cursor', msg.cursor);   // acknowledge
});

mesh.on('replay', ({ from, count }) =>
  console.log(`replayed ${count} from ${from}`));  // after a reconnect

Full reference, auth model and error codes →