[TexasCoding]

Closes #531

Upstream perps OpenAPI now lists require_category_cap (boolean) as a required property of CreateMarginFCMSubtraderRequest (POST /margin/fcm/subtraders).

Changes

• CreateMarginFCMSubtraderRequest.require_category_cap: bool (required; False is serialized, not omitted).
• Sync + async FcmResource.create_subtrader accept require_category_cap and require it alongside subtrader_suffix when no request= is passed.
• Re-vendored specs: specs/perps_openapi.yaml (new field + description-only tweak on MarginMarket.market_version), specs/openapi.yaml info.version 3.32.0 → 3.33.0 (no schema change; generate.py produced no _generated/ diff).
• Tests: happy path, False-is-sent, missing-arg error, wrong-type validation, sync + async.
• Docs: CHANGELOG 20.0.0, docs/migration.md, docs/perps.md. Version bump to 20.0.0 (new required request field = breaking).

Blast radius (GitNexus unavailable on the maintainer box; assessed manually)

Only kalshi/perps/models/fcm.py::CreateMarginFCMSubtraderRequest, kalshi/perps/resources/fcm.py::_build_create_subtrader_body, and the sync/async create_subtrader methods. No other callers in the package.

Gate

• uv run ruff check . pass
• uv run mypy kalshi/ pass
• uv run pytest tests/ --ignore=tests/integration -q pass (4635 passed, 3 skipped)
• uv run pytest tests/test_contracts.py -v -W error::UserWarning (nightly strict) pass