paging hard-capped at offset 1000 (dev only)

[jmandel]

Bug

For large value sets, requesting offset >= 1000 triggers a "too costly" error even with a small count. This prevents clients from paging through the full expansion. Offset 990 works fine; offset 1000 fails.

Repro

# offset=990 works
curl -s -o /dev/null -w '%{http_code}' \
  'https://tx-dev.fhir.org/r4/ValueSet/$expand?url=http://loinc.org/vs&offset=990&count=10' \
  -H 'Accept: application/fhir+json'
# Returns: 200

# offset=1000 fails
curl -s -o /dev/null -w '%{http_code}' \
  'https://tx-dev.fhir.org/r4/ValueSet/$expand?url=http://loinc.org/vs&offset=1000&count=10' \
  -H 'Accept: application/fhir+json'
# Returns: 400 — "The value set expansion has too many codes to display (>1000)"

[grahamegrieve]

this is not a bug, it's by design