🌿 Fern Regeneration -- February 10, 2026

[fern-api]

This PR regenerates code to match the latest API Definition.

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Note

Medium Risk
Modifies core request construction, retries, and auth token handling, which can change runtime behavior and error modes for all API calls.

Overview
Updates the Fern-generated Python SDK to 5.20.5 (new Fern CLI/generator versions) and refreshes dependencies/lockfile, including adding pytest-xdist for dev/testing.

Client behavior changes: instantiating Client/AsyncClient now requires an API token (raises ApiError if neither token nor CO_API_KEY is set), request headers now include runtime/platform metadata, and BaseHttpResponse exposes status_code.

HTTP layer changes: fixes URL construction for base URLs with path prefixes, refines request serialization (omit .../Ellipsis fields; preserve explicit empty bodies; filter None from multipart bodies), changes default retry behavior/backoff (new jitter + x-ratelimit-reset support, default max retries = 2), and adds async header support for async token providers. Also updates generated types/docs (e.g., *ContentItem → *ContentOneItem, error bodies typed as Any, and reference.md now shows explicit return types).

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