A subscription reconnects in its handle, by a fixed backoff

Status: accepted, 2026-10-11; amended 2026-10-07, an environment failure ends the stream as a request error does. Answers #12's reconnection, parking and gap handling. Serves The store is the UI's state and What earns a concept. Reopen the constants when a server is shown for which they are wrong; reopen the single-connection mode of graphql-sse for a gateway that cannot do HTTP/2.

Context#

A subscription's stream that failed set error and isActive false, and nothing reconnected. A socket stayed open in the background until the system closed it, and the stream died with the socket. The issue asked for reconnection with a configurable backoff, a lifecycle observer, sharing of equal subscriptions and a callback for a gap. Sharing already existed; the owner's review proposed the rest as values on the handle and one input on the environment.

Decision#

• Reconnection is the handle's, so every transport gets it. A stream that ends by a failure while the handle is retained and the environment active is a wait, not an end: the handle opens it again after a backoff. The server's completion ends the stream, and so does a request error, the server's refusal of the operation as written, which a retry would only repeat every half minute for as long as the handle lived. An environment failure ends the stream likewise: an environment with no subscription transport cannot gain one after its creation, so the backoff would repeat the failure forever. retry() opens an ended or waiting stream again at once, and meets the same failure if nothing changed. A stream that fails while the environment is inactive, or a handle retained while it is, parks rather than waits, so activity opens it.
• The backoff is fixed and documented: a step doubling from one second to a cap of thirty, jittered to between half and the whole of the step, reset by an event. No policy object: five numbers on the environment are a settings bag, and no server has shown the constants wrong.
• The stream's states are values: idle, connecting, open, waiting to reconnect until an instant, ended. A count of resumptions on the handle, raised each time the stream is opened again after a wait or a parking, is the gap's signal: an owner observes it and refetches its baseline. No callback: an observable value already is the hook.
• Parking is one input, Environment.isActive, set by the app from its scene phase and by hand in tests. False closes every retained subscription's stream and keeps the retention; true opens them again. Queries read nothing of it.
• The transport's element stays a payload. The handle knows a resumption because it made it, so the stream's element need not say "connected".

Evidence#

• The runtime as built before this change: a failed stream stayed ended (Operation.swift, the handle's start), and nothing observed the app's lifecycle.
• The owner's review of #12 (2026-10-04): sharing exists; reconnect in the handle with fixed constants; state and gaps as values; one input for parking; graphql-sse in its distinct-connections mode first.

Not chosen#

• Environment.subscriptionPolicy with five numbers: a settings bag for constants no server has contradicted.
• An onResume callback: a second channel beside the observable count.
• A transport element that says "connected": the handle makes every reconnection itself and needs no word from the stream.
• Reconnecting an unretained handle, or past the environment's end: there is no view to serve.