feat: coalesce: single flight async call deduplication - #1921
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Closes toss#1608. Add coalesce(key, fn): if a call with `key` is already in flight, return its promise; otherwise run `fn()` and store the promise so concurrent callers await the same result. The entry is removed once the promise settles (later calls re run fn). fn is invoked on a microtask AFTER the entry is stored, so a re entrant coalesce(key, …) inside fn returns the stored promise instead of re running fn and racing: the robustness the issue asks for.
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Closes #1608.
Add coalesce(key, fn): if a call with
keyis already in flight, return its promise; otherwise runfn()and store the promise so concurrent callers await the same result. The entry is removed once the promise settles (later calls re run fn). fn is invoked on a microtask AFTER the entry is stored, so a re entrant coalesce(key, …) inside fn returns the stored promise instead of re running fn and racing: the robustness the issue asks for.