fix: keep Push connections consistent across concurrent subscribes and credential changes

[ArnabChatterjee20k]

Stacked on #1947. Fixes the MQTT Push issues reported on appwrite/sdk-for-console#114 in the Web SDK, and the same issues in the other SDKs that have them. React Native got these fixes in #1947.

What was wrong

	Web	Android	Flutter (io / web)	Unity	Apple
A subscribe during a pending connect used an unaccepted client	yes	yes (and two threads could build two clients)	no	yes (a second client replaced the first)	no
A failed connect cleared other callers' subscriptions	yes	yes (and stopped background delivery)	yes	yes	no
A credential or project change kept the old connection	yes	yes (in-process)	yes (in-process)	yes (reconnects also reused the old options)	yes
Two tabs of one user shared a client id	yes	no (per install)	n/a	n/a	n/a

Fixes

Connects

• Web waits on the pending open.
• Android serializes connect() under a lock.
• Unity shares one in-flight connect task.
• Flutter and Apple already shared one connect.

Failed connects

• A failed connect now only drops its own client. The failing subscribe rolls back only its own registrations.

Credential changes

• Every SDK keys the connection on endpoint, project, client id, auth method and credential.
• When a subscribe finds the key changed, it supersedes the open (or opening) connection, bumps a connection epoch and connects with the current credential. The subscriptions it had are re-subscribed on the new connection.
• A connect superseded while in flight gives up, instead of tearing down its replacement or hanging.
• A subscribe that was waiting on it, or on its SUBACK, retries on the new connection. A plain close() never retries.

Web client id

• The default is now <userId>-<tabId>, with the tab id kept in sessionStorage. It stays stable across reloads, so replay resumes, and differs per tab. An explicit setPushClientId() still wins.

Tests

PUSH_CREDENTIAL_SWITCH_RESPONSES is added to Web, Android (16 and 5), Flutter (stable, beta, web), Unity and Apple:

• Switch: the same Push subscribes, the client's JWT changes to one the mock refuses, and the next subscribe must fail with the broker's reason, which proves it reconnected.
• Pending switch: the switch lands while the first subscribe is still connecting. The second subscribe must fail. The first must fail the same way, or succeed only if it had already connected; it must never hang.
• Apple: checks only that an error arrives, since MQTTNIO does not expose the reason string.

Not changed

Session expiry interval. Appwrite's broker does not use MQTT sessions for offline replay. It keeps a ledger and a cursor per project, user and client id, replays from the cursor on SUBSCRIBE, and purges the cursor only on clean start. So clean: false with a stable client id keeps the replay window; no session expiry is needed.

Cleartext credentials over ws:// or mqtt://. The push endpoint follows the API endpoint's scheme, the same way Realtime sends the session over ws:// for an http:// endpoint. A plain-text endpoint is a local-development setup the app chooses explicitly.

Empty default client ids. Apple, Flutter iOS/desktop/web and Unity send an empty client id and let the broker derive one. Whether two devices of one user then collide depends on how the broker derives it.

[greptile-apps]

Confidence Score: 5/5

[Medium risk] Push service connection handling for concurrent subscribes and credential changes.

The PR appears safe to merge based on the reviewed changes.

Summary

The PR coordinates Push connections across concurrent subscribes and credential changes in Web, Android, Flutter, Unity, and Apple SDKs. It also gives Web connections distinct default client IDs and adds broker-backed tests. Since the previous review, it removed a shared MQTT test diagnostic and added an Android test delay.

_{Reviews (12) · Last reviewed commit: "test(android): let the mock's delayed pu..."}