[Repo Assist] perf: optimize windowed ring-buffer and toResizeArrayAsync

[github-actions]

🤖 This is an automated pull request from Repo Assist.

Summary

Two focused performance improvements to hot-path internal functions.

1. windowed — replace integer modulo with circular-buffer pointer arithmetic

The old implementation computed count % windowSize twice per element in the inner loop:

arr.[count % windowSize]<- item
count <- count +1letstart= count % windowSize // second modulo

Integer division/modulo is typically 5–10× slower than a simple increment + equality check on modern CPUs. The new implementation tracks the write position explicitly:

arr.[writePos]<- item
writePos <- writePos +1if writePos = windowSize then writePos <-0
count <- count +1// writePos is now directly the 'start' index — no second computation needed

This also removes the need to compute start separately for the blit step.

2. toResizeArrayAsync — direct loop instead of iter (SimpleAction(...))

The old implementation:

do! source |> iter (SimpleAction(fun item -> res.Add item))

This allocates a closure capturing res, wraps it in a struct-DU case, and dispatches through a pattern-match inside iter. The new implementation:

use e = source.GetAsyncEnumerator CancellationToken.None
while! e.MoveNextAsync()do
res.Add e.Current

No closure allocation, no DU dispatch, one fewer level of task composition. toResizeArrayAsync is called by every toArrayAsync, toListAsync, and toSeqAsync operation, making this a broadly beneficial change.

Test Status

Build: ✅ succeeded (0 warnings, 0 errors)
Tests: ✅ 5013 passed, 2 skipped (infrastructure), 0 failed

Branch: repo-assist/perf-windowed-toarray-20260317

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[dsyme]

/repo-assist please update AGENTS.md to make ti very, very clear that, for suggested performance improvements, before/after benchmarking MUST be done to PROVE the performance improvement is real.

Also do this benchmarking for this change. If the changes are not significant, remove the existing code changes and just include the AGENTS.md changes.

[dsyme]

/repo-assist please update AGENTS.md to make ti very, very clear that, for suggested performance improvements, before/after benchmarking MUST be done to PROVE the performance improvement is real.

Also do this benchmarking for this change. If the changes are not significant, remove the existing code changes and just include the AGENTS.md changes.