0644 — Public type names state semantic roles

Superseded in part by [0653].

Context. [0625] made handles bare nouns and materialized resources *Data; the later handle split added Handle without revisiting the values. The result mixed representation names (TopicData, MessageData) with role names (TopicSnapshot, GroupStatus, VersionHealth), while unqualified projection names collided as the facade aliased more roots. WorkerData also made it unclear whether Worker or Work named the domain resource.

Decision. An exported type suffix names its semantic role. A lazy identity plus client is <Noun>Handle; the materialized resource or payload is the bare <Noun>. Plural resource reads return materialized values in the existing list query; singular selectors return no-I/O handles. The remaining roles are Config, verb-led Options / Item / Result, Snapshot, Status, Summary, Health, Declaration, Row, and Instance. Data and Info are not roles and are banned exported suffixes. A projection adds its subject when needed to avoid collisions.

The value renames are Topic, Group, Worker, Schedule, System, and Message[T]. The qualified projections are ScheduleGroupSummary, ScheduleMessageStatus, TopicVersionHealth, TopicSchemaVersionSnapshot, ConsumerGroupSchemaVersionLag, and ConsumerGroupLag. Worker stays the noun: it is Vulkan’s maintenance actor and row; Work would name an action or unit. Alert, Measurement, ProduceItem, ProduceResult, BindingDeclaration, TopicSnapshot, and ConsumerGroupSnapshot already follow the rule.

Supersedes [0625]‘s bare-handle / *Data / List<Child> naming clauses and amends [0643]: vulkan declares nine handles and three instance wrappers, no Producer or Consumer interfaces; aliases keep each declaration’s new name.

Consequences. The migration is compile-time breaking and JSON is unchanged. Client.Topics, Client.Schedulers, TopicHandle.Groups, SystemHandle.Alerts, and SystemHandle.Measurements delegate to their one existing list read; the matching singular noun selects a handle. Convention tests reject exported names ending in Data or Info anywhere under pkg.

Rejected: keeping Data as a generic read-model suffix; Info; returning handles from plural reads and issuing one Get per handle; Work for maintenance rows.