internal(coin-app): Harden StreamManager reconnect and subscriptions

[ntucker]

Requested by Nathaniel · project thread

Follow-up to #4103.

Motivation

The coin app's StreamManager had several pre-existing problems:

• cleanup() didn't cancel a pending reconnect() timer, so it could open a new socket after unmount.
• Reconnects received no data: the subscribe flush only listened for open on the first socket.
• One component unsubscribing a product killed the feed for any other component still showing it.
• After cleanup → init, the old socket's onerror called this.evtSource.close(), closing the new socket.
• tsc error in send() (ArrayBufferView<ArrayBufferLike> vs ArrayBufferView<ArrayBuffer>), plus an unused ctrl param and a msgQueue that was never drained.

Solution

Before:

reconnect() {
  setTimeout(() => { this.attempts++; this.connect(); }, backoff);
}
cleanup() {
  this.evtSource.onclose = null;
  this.evtSource.close();
  clearTimeout(this.flushTimeout);
}

After:

reconnect() {
  this.reconnectTimeout = setTimeout(() => {
    this.reconnectTimeout = undefined;
    this.attempts++;
    this.connect();
  }, backoff);
}
cleanup() {
  // detach handlers so the closing socket can't reconnect or touch a new one
  this.evtSource.onopen = null;
  this.evtSource.onmessage = null;
  this.evtSource.onclose = null;
  this.evtSource.onerror = null;
  this.evtSource.close();
  clearTimeout(this.reconnectTimeout);
  // ...
}

• Subscriptions are ref-counted per product. useSubscription dispatches SUBSCRIBE/UNSUBSCRIBE per hook mount, so a count is the right model.
• A debounced sync() sends the difference between active subscriptions and what the current socket was sent, so subscribes and unsubscribes are batched. onopen resets the sent set and syncs, so every reconnect re-subscribes. This replaces the never-drained msgQueue and the send() with the type error.
• handleMessage(msg) drops the unused controller.

The docs snippet in docs/core/concepts/managers.md has no reconnect, send() or handleMessage, so it needs no change. This is a private example, so there's no changeset.

Validated with tsc --noEmit in examples/coin-app (the send() error reproduced before the change and is gone after), eslint, prettier, and a mock-WebSocket simulation of subscribe/unsubscribe batching, reconnect re-subscription and cleanup.

🤖 Generated with Claude Code

https://claude.ai/code/session_01MhCkU7NpfSuvJiu4NyRNB6

---

Note

Low Risk
Changes are confined to the coin-app example’s WebSocket manager; no auth, data persistence, or shared library API surface.

Overview
Hardens the coin-app StreamManager WebSocket lifecycle and subscription handling so reconnects, multi-component usage, and teardown behave correctly.

Subscription state moves from a flat product_ids list and never-drained msgQueue/send() to ref-counted products plus a debounced sync() that batches subscribe/unsubscribe deltas against what the current socket already has; onopen clears sent and re-syncs so every reconnect restores active feeds. UNSUBSCRIBE goes through unsubscribe() instead of a one-off wire message, so one hook unmounting no longer drops a product other components still use.

cleanup() now nulls all socket handlers (avoiding a stale socket closing a replacement after init), cancels pending reconnect and sync timers, and reconnect() stores its timeout id for that cancellation. handleMessage drops the unused controller argument; unused ActionTypes import is removed.

^{Reviewed by Cursor Bugbot for commit b9e3d22. Bugbot is set up for automated code reviews on this repo. Configure here.}

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Latest commit: b9e3d22

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.93%. Comparing base (f03332e) to head (b9e3d22).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4123   +/-   ##
=======================================
  Coverage   97.93%   97.93%           
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  Files         158      158           
  Lines        3095     3095           
  Branches      619      619           
=======================================
  Hits         3031     3031           
  Misses         18       18           
  Partials       46       46           

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