feat: ADR-0035 4i(a,b) — CREATE TABLE help/usage + describe table constraints; Phase 4 complete

(b) describe shows table-level constraints: TableDescription gains
unique_constraints + check_constraints (populated by do_describe_table
from read_schema), rendered in a new "Table constraints:" section —
composite UNIQUE and table-level CHECK (named + unnamed). The per-column
Constraints column already covered single-column NOT NULL/UNIQUE/PK/CHECK.

(a) CREATE TABLE help/usage skeleton refreshed for the column DEFAULT/
CHECK/REFERENCES, table-level composite UNIQUE, table CHECK, and
table-level FOREIGN KEY forms (4a.2/4a.3/4b) — engine-neutral,
vocab-audit clean.

With 4i's (c)/(d)/(e) already shipped, this completes sub-phase 4i — the
verification sweep — and therefore ADR-0035 Phase 4 (4a–4i). ADR-0035
Status, §13 4i, the ADR index, and requirements.md Q1 updated to
"Phase 4 complete".

Tests: render_structure table-level-constraints unit test +
e2e_describe_shows_table_level_constraints. Full suite 1917 passing /
0 failing / 1 ignored; clippy clean.

src/output_render.rs

@@ -152,6 +152,24 @@ pub fn render_structure(desc: &TableDescription) -> Vec<String> {
         }
     }
 
+    // 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.
+    if !desc.unique_constraints.is_empty() || !desc.check_constraints.is_empty() {
+        out.push("Table constraints:".to_string());
+        for cols in &desc.unique_constraints {
+            out.push(format!("  unique ({})", cols.join(", ")));
+        }
+        for chk in &desc.check_constraints {
+            match &chk.name {
+                Some(name) => out.push(format!("  check {name} ({})", chk.expr)),
+                None => out.push(format!("  check ({})", chk.expr)),
+            }
+        }
+    }
+
     out
 }
 
@@ -730,6 +748,8 @@ mod tests {
             outbound_relationships: Vec::new(),
             inbound_relationships: Vec::new(),
             indexes: Vec::new(),
+            unique_constraints: Vec::new(),
+            check_constraints: Vec::new(),
         };
         assert_snapshot!(render_structure(&desc).join("\n"));
     }
@@ -749,6 +769,8 @@ mod tests {
                 on_update: ReferentialAction::NoAction,
             }],
             indexes: Vec::new(),
+            unique_constraints: Vec::new(),
+            check_constraints: Vec::new(),
         };
         let out = render_structure(&desc).join("\n");
         assert!(
@@ -774,6 +796,8 @@ mod tests {
             outbound_relationships: Vec::new(),
             inbound_relationships: Vec::new(),
             indexes: Vec::new(),
+            unique_constraints: Vec::new(),
+            check_constraints: Vec::new(),
         };
         let out = render_structure(&desc).join("\n");
         // PK appears for id, NOT NULL for name, blank for nick.
@@ -796,6 +820,8 @@ mod tests {
                 columns: vec!["Email".to_string()],
                 unique: false,
             }],
+            unique_constraints: Vec::new(),
+            check_constraints: Vec::new(),
         };
         let out = render_structure(&desc).join("\n");
         assert!(out.contains("Indexes:"), "got:\n{out}");
@@ -821,11 +847,43 @@ mod tests {
                 columns: vec!["Email".to_string()],
                 unique: true,
             }],
+            unique_constraints: Vec::new(),
+            check_constraints: Vec::new(),
         };
         let out = render_structure(&desc).join("\n");
         assert!(out.contains("uidx_email (Email) [unique]"), "got:\n{out}");
     }
 
+    #[test]
+    fn render_structure_shows_table_level_constraints() {
+        // ADR-0035 §4i (b): composite UNIQUE and table-level CHECK
+        // (named + unnamed) render in a "Table constraints:" section,
+        // distinct from the per-column "Constraints" column.
+        let desc = TableDescription {
+            name: "T".to_string(),
+            columns: vec![
+                col("a", Type::Int, true, false),
+                col("b", Type::Int, false, false),
+            ],
+            outbound_relationships: Vec::new(),
+            inbound_relationships: Vec::new(),
+            indexes: Vec::new(),
+            unique_constraints: vec![vec!["a".to_string(), "b".to_string()]],
+            check_constraints: vec![
+                crate::persistence::TableCheck { name: None, expr: "a < b".to_string() },
+                crate::persistence::TableCheck {
+                    name: Some("a_lt_b".to_string()),
+                    expr: "a <> b".to_string(),
+                },
+            ],
+        };
+        let out = render_structure(&desc).join("\n");
+        assert!(out.contains("Table constraints:"), "got:\n{out}");
+        assert!(out.contains("unique (a, b)"), "got:\n{out}");
+        assert!(out.contains("check (a < b)"), "unnamed check; got:\n{out}");
+        assert!(out.contains("check a_lt_b (a <> b)"), "named check shows its name; got:\n{out}");
+    }
+
     #[test]
     fn render_structure_omits_indexes_section_when_none() {
         let desc = TableDescription {
@@ -834,6 +892,8 @@ mod tests {
             outbound_relationships: Vec::new(),
             inbound_relationships: Vec::new(),
             indexes: Vec::new(),
+            unique_constraints: Vec::new(),
+            check_constraints: Vec::new(),
         };
         let out = render_structure(&desc).join("\n");
         assert!(!out.contains("Indexes:"), "got:\n{out}");
@@ -1026,6 +1086,8 @@ mod tests {
             outbound_relationships: Vec::new(),
             inbound_relationships: Vec::new(),
             indexes: Vec::new(),
+            unique_constraints: Vec::new(),
+            check_constraints: Vec::new(),
         };
         let out = render_structure(&desc).join("\n");
         // The lowercase form of the SQLite type should appear.