Update

ArtifactServiceUpdateRequest changes only selected audience-visible metadata. Consumers must require a nonempty unique mask relative to Artifact, drawn exactly from display_name, description and tags. Wildcards, nested paths, unknown paths and output-only fields (including the publication pointer) are rejected; only selected fields are applied. Recursive Artifact validation is skipped so description-only or tags-only updates do not require a name. Consumers must manually validate artifact.id and selected fields after normal hooks: ID shape, field byte bounds, tag grammar, count and uniqueness, and a nonempty, non-Unicode-whitespace-only display_name when selected. Names must not be automatically trimmed. Generated validation checks only artifact and update_mask message presence; it does not enforce mask semantics or selected-field validation.

ArtifactServiceUpdateResponse contains the updated catalog metadata.