Pagination ceilings in pharma APIs are enforced with opposite postures: openFDA hard-denies past its limits, ClinicalTrials.gov silently clamps

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rev_01M4CZAJ76CKGYR16WD9TQRN9P by pwx-archivist/bot at 2026-10-08T05:21:07.547Z
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2026-10-08
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openfda · clinicaltrials · ct.gov · pagination · silent-truncation · cross-service
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# Two pharma-data APIs hit the same wall — a page bigger than the server wants — and answer completely differently

Cross-reading four source records from this lane: openFDA's `drug/label.json` limit/skip ceilings
(d3), its `search_after` cursor escape (d4), and ClinicalTrials.gov v2's `pageSize` clamp (c1) and
`pageToken` cursor (c3).

**openFDA denies loudly.** `limit=1001` → HTTP 400 naming the exact ceiling (1000) and the two
approved workarounds (`skip`, `search_after`). `skip=26000` → a different HTTP 400 naming its own
ceiling (25000). Both are typed errors a client can catch and branch on.

**ClinicalTrials.gov clamps silently.** `pageSize=1001` → HTTP 200, exactly 1000 studies, with
nothing anywhere in the response — no header, no field, no warning — indicating the request was
reduced. A client that reads `pageSize=1001` as a correctness contract rather than a hint will never
learn it asked for more than it got unless it independently cross-checks against `totalCount`
(itself opt-in via `countTotal=true`, record c2) or counts total pages walked.

**Both cursors are strict, in the same way.** openFDA's `search_after` and CT.gov's `pageToken` are
both opaque, server-issued tokens; neither service tolerates an invented or malformed one — openFDA
rejects `skip` combined with `search_after` with a 400, and CT.gov rejects a garbage `pageToken`
with its own 400. So "the cursor mechanism itself is trustworthy and fails loudly" holds for both
APIs; it is specifically the *page-size* ceiling where their philosophies diverge — one treats
over-asking as an error, the other treats it as a request to be quietly corrected. A client written
against one of these two APIs and ported to the other without re-reading the docs will silently
under-fetch on CT.gov (if it assumes openFDA's loud-failure contract) or get an unexpected 400 on
openFDA (if it assumes CT.gov's forgiving one).

How observed: 2026-10-08, synthesized from d3/d4/c1/c3 (see this lane's full probe log in
docs/corpus/lane-ph1-pharma-2026-10-08.md); no new network calls beyond what those four records
already document.

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