🤖 Repo Assist — automated bug fix (Task 3: Issue Investigation and Fix)

Summary

Fixes the bug in #310: lazy series .Between(ds, de).Sample(interval) loads data from the full original range instead of just the restricted window.

The maintainer @dsyme requested this fix in #310 (comment).

Root Cause

DelayedSource.With always forwarded the original rangeMin/rangeMax to the new source, regardless of the range restriction passed in ranges. This had two effects:

1. KeyRange returned the wrong bounds. DelayedIndex.KeyRange is backed by source.RangeMin/source.RangeMax, so after .Between(ds, de), series.KeyRange still returned (original_min, original_max). The generateKeys function in Series.Sample/resampleUniform calls series.KeyRange to determine the window for which to generate sample keys — so it generated keys across the entire original range.

2. flattenRanges used the original bounds as overallMin/overallMax. This added spurious boundary segments outside the restriction window into the loader call.

Fix

Added optional rangeMin and rangeMax parameters to DelayedSource.With, and updated DelayedIndexBuilder.GetRange to pass the effective lower/upper bound (fst lo / fst hi) when creating the restricted source.

// Before
member x.With(?loader, ?ranges) =
  DelayedSource<'K, 'V>(scheme, rangeMin, rangeMax, ...)

// After
member x.With(?loader, ?ranges, ?rangeMin, ?rangeMax) =
  DelayedSource<'K, 'V>(scheme, defaultArg rangeMin x.RangeMin, defaultArg rangeMax x.RangeMax, ...)

And in GetRange:

// After
let restrictSource otherRange loader =
  let ranges = Intersect(range, otherRange)
  index.Source.With(ranges=ranges, loader=loader, rangeMin=fst lo, rangeMax=fst hi)

Trade-offs

• Minimal, surgical change — only 4 lines of production code changed.
• No behaviour change for the non-restricted case (default args preserve old values).
• The fix is correct even for nested restrictions (e.g., .Before(40).After(10)): each GetRange call narrows rangeMin/rangeMax further.

Test Status

• ✅ Added 2 regression tests in LazySeries.fs:
  • KeyRange reflects Between restriction on a lazy series (regression #310)
  • Loader is only called with restricted range after Between (regression #310)
• ✅ All 573 tests pass
• ✅ Build succeeded with 0 errors

Generated by Repo Assist · ◷

To install this agentic workflow, run

gh aw add githubnext/agentics/workflows/repo-assist.md@30f2254f2a7a944da1224df45d181a3f8faefd0d