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Code changes was requested by @mihow.

• Endpoint for stats about verified occurrences #1307 (comment)

The following files were modified:

• ami/base/serializers.py
• ami/main/api/views.py

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[mihow]

Claude says: Closing this — it's superseded by #1307, which merged on 2026-05-29 (the same day this PR was opened). The endpoint, ModelAgreementSerializer, model_agreement_for_project, and the filter backends this diff would add are all already on main, and the branch is now conflicting against it.

The one genuinely new idea here is the EnumChoiceField helper in ami/base/serializers.py — a reusable enum-backed ChoiceField that accepts member names case-insensitively and supports excluding sentinel values like UNKNOWN. That abstraction didn't land with #1307.

For reference, the rank param is currently validated inline in model_agreement (ami/main/api/views.py, around line 1463):

valid_ranks = [r.name for r in TaxonRank if r != TaxonRank.UNKNOWN]
raw_rank = request.query_params.get("agreement_coarsest_rank")
# Build a plain dict (not the QueryDict) so a blank value is validated as a real "".
# DRF treats blank fields in HTML/QueryDict input as absent, which would let
# ?agreement_coarsest_rank= silently no-op. Uppercase to stay case-insensitive.
rank_data = {} if raw_rank is None else {"agreement_coarsest_rank": raw_rank.upper()}
coarsest_rank_param = SingleParamSerializer[str].clean(
    param_name="agreement_coarsest_rank",
    field=serializers.ChoiceField(choices=valid_ranks, required=False, allow_blank=False),
    data=rank_data,
)
coarsest_rank = TaxonRank[coarsest_rank_param] if coarsest_rank_param else None

This works and gives strict 400s for blank, unknown, and UNKNOWN ranks, plus drf-spectacular reads the choices into the OpenAPI schema. EnumChoiceField would just DRY this up — worth doing once a second enum-backed query param appears.

Potential follow-up (good first issue): extract EnumChoiceField into ami/base/serializers.py as a fresh PR off current main, swap this call site to use it, and add a couple of unit tests covering the case-insensitive name match, the exclude rejection, and the blank-value 400.