Decode: sync-over-async and the dropped token

This module is different. You’ve learned the idioms; now you decode the actual review comments Rai received on Fusion PRs, so that the next time one lands, you already know what it means and how to write the thing right the first time. We start with the single most-repeated correctness note.

The comment (Mustafa Aleem, on PR #491 and again on #508):

“use await instead of .GetAwaiter().GetResult(); make this method async as well.” “Sync over async again, when it should be awaited.” “‘.GetAwaiter().GetResult()’ was reintroduced and should be removed.” (left twice)

And on the token:

“don’t have = default, cancellationTokens must always be provided.”

What he meant. Two distinct rules, both invisible to a JS developer because JS can’t express the mistake. First, sync-over-async: calling .Result or .GetAwaiter().GetResult() on a Task blocks the current thread until the IO finishes. Under load that starves the thread pool and can deadlock, and it silently discards cancellation. The fix is never to bridge; await the task and let async spread up the call chain (Module 7 covered the mechanism). Second, the required token: a CancellationToken cancellationToken with = default lets every caller quietly drop cancellation, so an abandoned request keeps running a Databricks query for nothing. Making the parameter required forces the token to be threaded from the endpoint all the way down.

// What Mustafa flagged: blocks a thread, discards cancellation.
var summary = _repo.LoadRevertSummary(key).GetAwaiter().GetResult();

// The fix: await, make the caller async, thread a required token down.
public async Task<FlightRevertSummary?> LoadRevertSummary(
    string key, CancellationToken cancellationToken)
{
    return await _repo.LoadRevertSummary(key, cancellationToken);
}