MutationRow.op was str despite _MUTATION_OPS existing; Topology.mode/status,
TopologyDecky.state, TopologyMutation.op/state carried valid values only in
comments; deferred json import had no justification.
- Promote _MUTATION_OPS before table classes so table fields can reference it
- Add sa_column=Column(String) on each Literal-annotated table field to satisfy
SQLModel 0.0.38 column-type inference
- Move import json to module top; remove deferred import inside _decode_json_payload
- MutationRow.op: str -> _MUTATION_OPS
anti
3456d3ab45