Update an existing case. Only the fields included in the request body are modified; omitted fields remain unchanged.

Common updates include changing the status, updating assignees or followers, modifying the description, or linking to an external issue.

Case name and description must be nonempty and cannot contain HTML. Invalid input returns 400. This validation is distinct from comment text.

A supplied assigneeIDs or followerIDs array replaces the complete list; [] clears it and omission retains it. Set externalIssueID to null to unlink the external issue; omission retains the link.

The same complete-replacement, empty-array clearing, and omission-retention rules apply to mutedIDs.