The first wired slice of relationship visualization (V1). `show
relationship <name>` now renders the relationship as two full
structure boxes joined by a width-jogging connector (child-left /
parent-right, n…1 cardinality, on delete/update actions), styled
App-side, with a vertical-stack fallback for narrow terminals.
- db.rs: RelationshipDiagramData + show_relationship worker path
(structured data: the relationship + both endpoint TableDescriptions)
- runtime.rs: named relationships route to the structured outcome
(boxed); other show <kind> forms stay prose
- app.rs/event.rs/ui.rs: DslShowRelationshipSucceeded rendered App-side;
new diagram OutputStyleClass variants; App::last_output_width from ui.rs
- output_render.rs: styled Seg layout engine (boxes, connector routing,
side-by-side + vertical), composing the ADR-0016 box primitives
Tests: 4 unit + 4 integration; full suite 2201 pass / 0 fail / 1 ignored;
clippy nursery clean. requirements.md V1 stays [/] (show table diagrams,
compound routing, DDL-echo wiring remain).
claude@clouddev1
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