Author and manage test cases in TestRail via REST API v2 - create cases, organise into suites + sections, update steps + expected results, bulk import from CSV/JSON, set automation status, link to references (Jira / requirements). Covers the Steps / Text / Exploratory templates, custom-field discovery (`get_case_fields`), and pagination on `get_cases`. Use for pre-execution case authoring and repository management. Do NOT use for submitting test-run results (pass/fail, status updates): posting results via add_results_for_cases is a separate post-execution concern.