feat: show table renders relationships as compact diagrams (ADR-0044)

show table <T> and add/drop relationship echoes now render the focal
structure box plus a Relationships section of compact stacked
connector diagrams (child-left/parent-right, n…1, actions); incidental
DDL echoes keep the prose References:/Referenced by: form. Selected by
command in handle_dsl_success via the "relationship-relevant" reach.

- output_render.rs: render_structure refactored into section helpers
  (box/prose/index/constraint), byte-identical output; new
  render_structure_with_diagrams + compact-box rendering
- app.rs: handle_dsl_success routes ShowTable/Add/DropRelationship to
  the diagram path, others to prose
- fixes: eager widths[1] index on compact (1-col) boxes; body-cell
  padding under title-widening (name wider than columns)

Tests: unit + snapshot + integration; add-relationship echo test
updated to the diagram form. Full suite 2203 pass / 0 fail / 1 ignored;
clippy clean. V1 still [/] (compound routing + self-ref remain).

src/app.rs

@@ -1689,10 +1689,30 @@ impl App {
     fn handle_dsl_success(&mut self, command: &Command, description: Option<TableDescription>) {
         self.note_ok_summary(command);
         if let Some(desc) = description.as_ref() {
+            // ADR-0044 §1 "relationship-relevant" reach: when a
+            // relationship is the subject of the command (`show table`,
+            // `add`/`drop relationship`), render the table's
+            // relationships as compact diagrams; every other DDL echo
+            // keeps the prose `References:` / `Referenced by:` form.
+            if matches!(
+                command,
+                Command::ShowTable { .. }
+                    | Command::AddRelationship { .. }
+                    | Command::DropRelationship { .. }
+            ) {
+                for line in crate::output_render::render_structure_with_diagrams(
+                    desc,
+                    self.last_output_width,
+                    self.mode,
+                ) {
+                    self.push_output(line);
+                }
+            } else {
                 for line in crate::output_render::render_structure(desc) {
                     self.note_system(line);
                 }
             }
+        }
         self.current_table = description;
     }
 

src/output_render.rs

@@ -90,9 +90,18 @@ fn cols_disp(cols: &[String]) -> String {
 
 #[must_use]
 pub fn render_structure(desc: &TableDescription) -> Vec<String> {
-    let mut out: Vec<String> = Vec::new();
-    out.push(desc.name.clone());
+    let mut out = structure_box_lines(desc);
+    out.extend(relationship_prose_lines(desc));
+    out.extend(index_lines(desc));
+    out.extend(constraint_lines(desc));
+    out
+}
 
+/// The table-name header line + the box-drawn column / type /
+/// constraint table. Shared by the prose [`render_structure`] and the
+/// diagram [`render_structure_with_diagrams`] (ADR-0044).
+fn structure_box_lines(desc: &TableDescription) -> Vec<String> {
+    let mut out: Vec<String> = vec![desc.name.clone()];
     let header_cells = vec![
         "Name".to_string(),
         "Type".to_string(),
@@ -101,22 +110,18 @@ pub fn render_structure(desc: &TableDescription) -> Vec<String> {
     let body: Vec<Vec<String>> = desc
         .columns
         .iter()
-        .map(|c| {
-            vec![
-                c.name.clone(),
-                type_display(c),
-                constraints_display(c),
-            ]
-        })
+        .map(|c| vec![c.name.clone(), type_display(c), constraints_display(c)])
         .collect();
-    // Type column gets the same numeric/text rule as data
-    // columns by virtue of consistency, but every entry is
-    // a keyword string ("text", "serial", …) so left-align
-    // is correct in every case. Constraints are similarly
-    // textual.
+    // Every cell is a keyword/text string, so left-align throughout.
     let alignments = vec![Alignment::Left, Alignment::Left, Alignment::Left];
     out.extend(render_table(&header_cells, &body, &alignments));
+    out
+}
 
+/// The `References:` / `Referenced by:` prose blocks (ADR-0016 §5),
+/// retained for the incidental DDL echoes (ADR-0044 §1).
+fn relationship_prose_lines(desc: &TableDescription) -> Vec<String> {
+    let mut out: Vec<String> = Vec::new();
     if !desc.outbound_relationships.is_empty() {
         out.push("References:".to_string());
         for r in &desc.outbound_relationships {
@@ -145,11 +150,14 @@ pub fn render_structure(desc: &TableDescription) -> Vec<String> {
             ));
         }
     }
+    out
+}
 
-    // Indexes section (ADR-0025), shown only when the table
-    // carries at least one user-created index. A UNIQUE index is
-    // marked `[unique]` so a learner can tell a uniqueness-enforcing
-    // index from a performance-only one (ADR-0035 §4d).
+/// Indexes section (ADR-0025), only when the table carries a
+/// user-created index. A UNIQUE index is marked `[unique]` (ADR-0035
+/// §4d).
+fn index_lines(desc: &TableDescription) -> Vec<String> {
+    let mut out: Vec<String> = Vec::new();
     if !desc.indexes.is_empty() {
         out.push("Indexes:".to_string());
         for index in &desc.indexes {
@@ -161,17 +169,18 @@ pub fn render_structure(desc: &TableDescription) -> Vec<String> {
             ));
         }
     }
+    out
+}
 
-    // Table-level constraints (ADR-0035 §4i b): composite `UNIQUE (a, b)`
-    // and table `CHECK (…)` constraints. Single-column UNIQUE / NOT NULL /
-    // PK / column-level CHECK already show in the per-column "Constraints"
-    // column above; this section is the table-level constraints that span
-    // columns or stand alone. A named CHECK shows its name.
+/// Table-level constraints (ADR-0035 §4i b): composite `UNIQUE (a, b)`
+/// and table `CHECK (…)`. Column-level constraints already show in the
+/// per-column "Constraints" column; this is the multi-column / named
+/// set, each with its addressable name where it has one.
+fn constraint_lines(desc: &TableDescription) -> Vec<String> {
+    let mut out: Vec<String> = Vec::new();
     if !desc.unique_constraints.is_empty() || !desc.check_constraints.is_empty() {
         out.push("Table constraints:".to_string());
         for cols in &desc.unique_constraints {
-            // Annotate with the derived, addressable name (ADR-0035
-            // Amendment 1) so the user can `drop constraint <name>`.
             out.push(format!(
                 "  {}: unique ({})",
                 crate::db::unique_constraint_name(cols),
@@ -185,7 +194,6 @@ pub fn render_structure(desc: &TableDescription) -> Vec<String> {
             }
         }
     }
-
     out
 }
 
@@ -701,7 +709,9 @@ fn render_box(t: &DiagramTable) -> BoxLayout {
     segs.push(title_seg(&t.name, inner));
     segs.push(conn_line(border_row(&widths, BorderRow::TitleUnderline)));
     for c in &t.cols {
-        segs.push(body_seg(c, label_w, has_types.then_some(widths[1])));
+        // Use the (possibly title-widened) label column width so the
+        // body cells pad to the box width even when the name is wider.
+        segs.push(body_seg(c, widths[0], has_types.then(|| widths[1])));
     }
     segs.push(conn_line(border_row(&widths, BorderRow::Bottom)));
 
@@ -940,6 +950,101 @@ pub(crate) fn render_relationship_diagram(
         .collect()
 }
 
+/// A plain (unstyled) system output line — falls back to whole-line
+/// `System` styling, exactly like `note_system`.
+const fn plain_system(text: String, mode: Mode) -> OutputLine {
+    OutputLine {
+        text,
+        kind: OutputKind::System,
+        mode_at_submission: mode,
+        styled_runs: None,
+        status: None,
+    }
+}
+
+/// A compact (name-only) box for one endpoint of a `show table`
+/// relationship diagram (ADR-0044 §4): the table name + just the
+/// participating column(s), all marked as endpoints.
+fn compact_table(name: &str, cols: &[String]) -> DiagramTable {
+    DiagramTable {
+        name: name.to_string(),
+        cols: cols
+            .iter()
+            .map(|c| DiagramCol {
+                name: c.clone(),
+                type_text: None,
+                pk: false,
+                endpoint: true,
+            })
+            .collect(),
+    }
+}
+
+/// One relationship of the focal table as a compact connector diagram
+/// (ADR-0044 §4). `outbound` = the focal table is the child (FK
+/// holder, drawn left); otherwise it is the parent (drawn right).
+fn render_compact_relationship(
+    focal: &str,
+    rel: &crate::db::RelationshipEnd,
+    outbound: bool,
+    width: usize,
+) -> Vec<Seg> {
+    let focal_box = compact_table(focal, &rel.local_columns);
+    let other_box = compact_table(&rel.other_table, &rel.other_columns);
+    let (child, parent) = if outbound {
+        (focal_box, other_box)
+    } else {
+        (other_box, focal_box)
+    };
+    render_relationship_layout(
+        &child,
+        &parent,
+        &rel.on_delete.to_string(),
+        &rel.on_update.to_string(),
+        width,
+    )
+}
+
+/// `show table <T>` and relationship-DDL echoes (ADR-0044 §1, Diagram
+/// mode): the focal structure box, then a **Relationships** section of
+/// compact stacked diagrams, then indexes / table constraints. Box,
+/// index and constraint sections are plain system lines; the diagrams
+/// are styled.
+pub(crate) fn render_structure_with_diagrams(
+    desc: &TableDescription,
+    width: u16,
+    mode: Mode,
+) -> Vec<OutputLine> {
+    let mut out: Vec<OutputLine> = structure_box_lines(desc)
+        .into_iter()
+        .map(|s| plain_system(s, mode))
+        .collect();
+
+    if !desc.outbound_relationships.is_empty() || !desc.inbound_relationships.is_empty() {
+        out.push(plain_system("Relationships".to_string(), mode));
+        // Outbound (this table is the child) first, then inbound, each
+        // a compact connector diagram stacked vertically (ADR-0044 §4).
+        for rel in &desc.outbound_relationships {
+            for seg in render_compact_relationship(&desc.name, rel, true, width as usize) {
+                out.push(seg.into_line(mode));
+            }
+        }
+        for rel in &desc.inbound_relationships {
+            for seg in render_compact_relationship(&desc.name, rel, false, width as usize) {
+                out.push(seg.into_line(mode));
+            }
+        }
+    }
+
+    for s in index_lines(desc) {
+        out.push(plain_system(s, mode));
+    }
+    for s in constraint_lines(desc) {
+        out.push(plain_system(s, mode));
+    }
+    out
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -1042,6 +1147,49 @@ mod tests {
         assert!(pi > ci, "parent stacked below child:\n{out}");
     }
 
+    #[test]
+    fn render_structure_with_diagrams_replaces_prose_with_compact_diagrams() {
+        let desc = TableDescription {
+            name: "Customers".to_string(),
+            columns: vec![col("id", Type::Serial, true, false)],
+            outbound_relationships: Vec::new(),
+            inbound_relationships: vec![RelationshipEnd {
+                name: "cust_orders".to_string(),
+                other_table: "Orders".to_string(),
+                other_columns: vec!["cust_id".to_string()],
+                local_columns: vec!["id".to_string()],
+                on_delete: ReferentialAction::Cascade,
+                on_update: ReferentialAction::NoAction,
+            }],
+            indexes: Vec::new(),
+            unique_constraints: Vec::new(),
+            check_constraints: Vec::new(),
+        };
+        let lines = render_structure_with_diagrams(&desc, 200, Mode::Simple);
+        let text = lines
+            .iter()
+            .map(|l| l.text.as_str())
+            .collect::<Vec<_>>()
+            .join("\n");
+        // Diagram form: a Relationships heading + a connector, NOT the
+        // prose `Referenced by:` block.
+        assert!(text.contains("Relationships"), "heading:\n{text}");
+        assert!(!text.contains("Referenced by:"), "no prose block:\n{text}");
+        assert!(text.contains("Customers"), "focal box:\n{text}");
+        assert!(text.contains("Orders"), "neighbour box:\n{text}");
+        assert!(text.contains('▶'), "connector arrow:\n{text}");
+        // Box lines plain; diagram lines styled.
+        assert!(
+            lines.iter().any(|l| l.styled_runs.is_some()),
+            "styled diagram lines",
+        );
+        assert!(
+            lines.iter().any(|l| l.styled_runs.is_none()),
+            "plain box lines",
+        );
+        assert_snapshot!(text);
+    }
+
     fn col(name: &str, ty: Type, pk: bool, notnull: bool) -> ColumnDescription {
         ColumnDescription {
             name: name.to_string(),

src/snapshots/rdbms_playground__output_render__tests__render_structure_with_diagrams_replaces_prose_with_compact_diagrams.snap

@@ -0,0 +1,17 @@
+---
+source: src/output_render.rs
+expression: text
+---
+Customers
+┌──────┬────────┬─────────────┐
+│ Name │ Type   │ Constraints │
+├──────┼────────┼─────────────┤
+│ id   │ serial │ PK          │
+└──────┴────────┴─────────────┘
+Relationships
+┌───────────┐                  ┌───────────┐
+│ Orders    │                  │ Customers │
+├───────────┤                  ├───────────┤
+│ cust_id ● │n───────────────1▶│ id ●      │
+└───────────┘                  └───────────┘
+  on delete cascade · on update no action

tests/it/show_list.rs

@@ -454,3 +454,38 @@ fn app_show_relationship_not_found_shows_friendly_line() {
         "friendly not-found line",
     );
 }
+
+#[test]
+fn app_show_table_renders_relationships_as_compact_diagrams() {
+    let (_p, db, _dir) = open_project_db();
+    let rt = rt();
+    rt.block_on(seed_schema(&db));
+    // Orders holds the FK to Customers — an outbound relationship.
+    let desc = rt
+        .block_on(db.describe_table("Orders".to_string(), None))
+        .expect("describe Orders");
+
+    let mut app = App::new();
+    app.output.push_back(rdbms_playground::app::OutputLine::echo(
+        "show table Orders",
+        Mode::Simple,
+    ));
+    app.update(AppEvent::DslSucceeded {
+        command: Command::ShowTable {
+            name: "Orders".to_string(),
+        },
+        description: Some(desc),
+        echo: None,
+    });
+    let text: String = app
+        .output
+        .iter()
+        .map(|l| l.text.as_str())
+        .collect::<Vec<_>>()
+        .join("\n");
+    // The focal structure box, then a diagram (not the prose block).
+    assert!(text.contains("Relationships"), "diagram heading: {text}");
+    assert!(!text.contains("References:"), "prose suppressed: {text}");
+    assert!(text.contains("Customers"), "neighbour box: {text}");
+    assert!(text.contains('▶'), "connector arrow: {text}");
+}

tests/it/walking_skeleton.rs

@@ -473,9 +473,15 @@ fn add_relationship_flow_shows_parent_side_with_inbound_section() {
         echo: None,
     });
 
-    let rendered = rendered_text(&mut app, &Theme::dark(), 80, 24);
-    assert!(rendered.contains("Referenced by:"), "{rendered}");
-    assert!(rendered.contains("Orders.CustId"), "{rendered}");
+    // Tall viewport so the [ok] echo line stays visible above the
+    // (taller-than-prose) diagram for the endpoint-subject assertion.
+    let rendered = rendered_text(&mut app, &Theme::dark(), 80, 40);
+    // ADR-0044: `add relationship` is relationship-relevant, so its echo
+    // renders the relationship as a compact diagram, not the prose block.
+    assert!(rendered.contains("Relationships"), "heading: {rendered}");
+    assert!(rendered.contains("Orders"), "neighbour box: {rendered}");
+    assert!(rendered.contains("CustId"), "FK column: {rendered}");
+    assert!(rendered.contains('▶'), "connector: {rendered}");
     assert!(rendered.contains("on delete cascade"), "{rendered}");
     // The [ok] subject lists the endpoints. Long lines wrap in
     // the panel, so we check the first half of the phrase only.