[vikramlc-cognite]

Summary

Adds the extractor self-registration/heartbeat protocol (startup, checkin) now that cognitedata/service-contracts PR #3378 removed their ifdef: internal marking, plus the retry-idempotency registration and codespell config needed to support the "checkin" identifier. Builds on the Actions sub-resource from #2831 — this is the final PR in the stack; once merged, the IntegrationsAPI surface is complete.

Type of change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that changes existing behavior)
• Refactor (no functional change)
• Documentation update
• Chore / tooling / CI

What changed

• New cognite/client/data_classes/integrations/checkin.py: TaskUpdate, ErrorWithTask, StartupRequest, CheckinRequest, CheckinResponse.
• New IntegrationsAPI.startup() and IntegrationsAPI.checkin() methods, POST-ing to /integrations/startup and /integrations/checkin respectively with the same beta header as the rest of the module.
• Added integrations/checkin and integrations/startup to the non-idempotent POST pattern list in utils/_url.py, with matching cases in test_api_client.py.
• .pre-commit-config.yaml: added --ignore-words-list=checkin to the codespell hook args, since "checkin" is the API's real operationId/URL segment and can't be reworded to "check-in" without diverging from the actual wire contract. Passed as a hook arg rather than pyproject.toml's [tool.codespell] because reading TOML config requires tomli/tomllib, which isn't guaranteed available in the hook's isolated environment on Python <3.11.
• New tests: test_startup/test_checkin in test_api/test_integrations/test_integrations.py, and round-trip tests for all 5 new data classes in test_data_classes/test_integrations.py.

Why it changed

• Related issue: EDG-827
• Related docs / discussion: cognitedata/service-contracts PR #3378 (removed the ifdef: internal tag from these two endpoints) — https://github.com/cognitedata/service-contracts/pull/3378#discussion_r3932420851

What to focus on during review

• startup()/checkin() are explicitly documented (Note: in the docstring) as normally only called by extractor implementations as part of the integrations protocol, not typical SDK consumers.
• The codespell hook fix: an earlier attempt via pyproject.toml's [tool.codespell] worked locally but silently failed in CI (Python 3.10 in the hook's isolated venv couldn't parse the TOML without tomli) — this PR's .pre-commit-config.yaml args-based fix is the one that's CI-verified.

Test evidence

• pytest tests/tests_unit/ -q → 6,708 passed, 8 failed (pre-existing, unrelated: missing geopandas/sympy in the local dev environment — confirmed via git stash/pop A-B testing that these fail identically on master), 6 skipped
• python scripts/sync_client_codegen/main.py verify → sync mirrors up to date
• ruff check / ruff format --check → clean (550 files)
• mypy → no issues (550 source files)
• Confirmed this branch reconstructs the original unsplit branch byte-for-byte (git diff against it is empty)

Risks and unknowns

• startup/checkin are part of an extractor-facing heartbeat protocol rather than typical end-user SDK surface — low usage risk for most SDK consumers, but worth a sanity check from someone on the extractors side that the request/response shapes match what real extractors send.

Rollout and rollback

• Same beta FeaturePreviewWarning gating as the rest of the module. No migrations. Revert is a straight revert of this commit.

Checklist

• Self-reviewed the diff
• Tests added or updated (or N/A with reason)
• Docs updated (or N/A) — N/A, no public docs page exists yet for this beta API
• No secrets, credentials, or PII committed
• Breaking changes called out above and communicated to affected teams — N/A, no breaking changes