refactor(event cache): clarify warning when a pinned event couldn't be loaded

[bnjbvr]

The previous warning could trigger with abnormal numbers, since there could be related events applying to a pinned event, the loaded_events list could be bigger than the list of pinned_event_ids, due to the eager flattening. This patch makes it display the correct number, by postponing the flattening after the warning.

• I've documented the public API Changes in the appropriate CHANGELOG.md files.
• This PR was made with the help of AI.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.86%. Comparing base (32e9626) to head (8d2ab5a).
⚠️ Report is 3 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6405      +/-   ##
==========================================
+ Coverage   89.85%   89.86%   +0.01%     
==========================================
  Files         378      378              
  Lines      103384   103389       +5     
  Branches   103384   103389       +5     
==========================================
+ Hits        92893    92911      +18     
+ Misses       6928     6907      -21     
- Partials     3563     3571       +8     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Hywan]

Good finding, thanks. I am suggesting a way to avoid the double allocation, not tested though.

[Hywan]

Good finding. However, we now allocate twice (with collect) instead of once.

We could use StreamExt::inspect() to count the number of pinned events instead of doing this intermediate collect. Something like:

let mut number_of_loaded_events = 0;

let loaded_events: Vec<Event> =
    stream::iter(…)
        .buffer_unordered(max_concurrent_requests)
        .flat_map(stream::iter)
        .inspect(|_| number_of_loaded_events += 1)
        .flat_map(stream::iter)
        .collect();

I think that could work.

Thoughts?

[bnjbvr]

Ah nice, didn't know about that particular StreamExt method, thanks!

[codspeed-hq]

Merging this PR will not alter performance

✅ 50 untouched benchmarks

---

_{Comparing bnjbvr/clarify-warning-pinned-events (8d2ab5a) with main (32e9626)}