Skelto

The decision worth explaining is the one to stop. Continuing to build calling in-house was possible, and it was the wrong call. Voice quality is not a feature you ship at eighty percent — a marketplace whose calls sound bad does not get a second chance with either side, and the agents are paying a subscription for exactly this. Weighing months of specialist work against an SDK maintained by people who do only this, the answer stopped being close. What that bought was not only working calls. It moved a whole category of future failure — codec issues, one carrier behaving differently, an OS release changing audio session behaviour — onto someone whose job it is to fix it.

Two real-time systems, deliberately separated by responsibility. The Socket.IO layer on Node carries everything that is a message: presence, chat, and the marketplace state both sides need to see update live. It is a good fit there — ordered, reliable, easy to reason about, and cheap to run. Calling runs on Agora, which is a media path rather than a message path. The app requests a channel and a token, both sides join, and the media never touches the application server. The socket layer still coordinates the call — the invitation, the accept and decline, the ringing state, the tidy-up when someone hangs up — because that part genuinely is messaging. The audio itself is not. Drawing the line there was the point. Two systems each doing what they are good at, rather than one doing both adequately.

The client work was mostly about states that are easy to forget. A call is not connected or disconnected; it is inviting, ringing, accepted, connecting, connected, reconnecting, ended-by-me, ended-by-them, failed. Each needs its own screen state and its own exit, because the ones without an exit are exactly where users get stuck holding a frozen call screen. The socket layer needed the same discipline. Sockets drop constantly on mobile — a tunnel, a lift, a screen lock — so the client reconnects and reconciles rather than assuming the last state it saw is still true. Presence in particular lies if you trust a disconnect event: a user who reconnects two seconds later was never really offline, and showing them as offline makes the marketplace look empty. Reanimated carries the interface transitions on the UI thread, which matters most on the call screen — an animation that stutters while a call is connecting reads as the call failing.

The call screen does one job and shows one state at a time, because a call is the moment a user has the least patience for ambiguity. Connection quality is stated in words rather than left to a spinner, and every state — including the failures — has a visible way out.