Avoid large exponents in `BackoffMachine`

[PIG208]

  Future<void> wait() async {
    final bound = _minDuration(maxBound,
                               firstBound * pow(base, _waitsCompleted));

[ERROR:flutter/runtime/dart_vm_initializer.cc(40)] Unhandled Exception: Unsupported operation: Infinity or NaN toInt
#0      double.round (dart:core-patch/double.dart)
#1      Duration.* (dart:core/duration.dart:213:56)
#2      BackoffMachine.wait (package:zulip/api/backoff.dart:87:43)
#3      UpdateMachine._registerQueueWithRetry (package:zulip/model/store.dart:930:53)
<asynchronous suspension>
#4      UpdateMachine.load (package:zulip/model/store.dart:875:29)
<asynchronous suspension>
#5      LiveGlobalStore.doLoadPerAccount (package:zulip/model/store.dart:816:27)

What might have happened here is that _waitsCompleted gets to a large enough value that pow(base, _waitsCompleted) becomes either infinity or NaN.

Proposed fix by Greg:

• Instead of only _waitsCompleted, have also a (private) field equivalent to that bound local.
• Then at each iteration, multiply that by base and apply _minDuration.
• That way there's no pow (especially none with a potentially-large argument), and no giant numbers as intermediates in the calculation.

CZO discussion

[ajayrajsaini]

hi @PIG208,
i will love contribute to this issue, if it is still open

[suraj-aayush]

Hi @PIG208
I would like to work on this issue. Can you please assign it to me?
I have set up and corrected the code.

My Code:
Fixes incorrect backoff logic – Now, _currentBound correctly increases exponentially.
Prevents exceeding maxBound – Ensures we don’t wait longer than necessary.
Improves reliability – Makes sure backoff logic works consistently across retries.

[gnprice]

Saw this today in real life: I opened the app in the morning, and it was apparently still alive from the night before. It was showing the loading indicator at top (normal), but also an error snackbar at bottom. Hitting "Details" on the error showed a dialog with the same error message as in the console-log quote above.