diff --git a/crates/jerrycan/src/platform/migrate/entities.rs b/crates/jerrycan/src/platform/migrate/entities.rs
index 7ba120a..77d4efb 100644
--- a/crates/jerrycan/src/platform/migrate/entities.rs
+++ b/crates/jerrycan/src/platform/migrate/entities.rs
@@ -229,6 +229,41 @@ fn build_one(
         return None;
     }
 
+    // Table-level composite `UNIQUE(a, b, …)` (#115): translate each group whose
+    // columns all survive as a declared field or a belongs_to fk column — the same
+    // shape JC0559 accepts, so the round-trip is validation-clean. A column that
+    // dropped out (e.g. an unmappable-type column) can't be indexed, so raise a
+    // gap for that constraint rather than silently dropping it (never guess).
+    let mut unique = Vec::new();
+    for group in &table.composite_uniques {
+        let missing: Vec<&str> = group
+            .iter()
+            .filter(|col| {
+                !fields.iter().any(|f| &f.name == *col)
+                    && !belongs_to.iter().any(|b| &b.fk_column() == *col)
+            })
+            .map(String::as_str)
+            .collect();
+        if missing.is_empty() {
+            unique.push(group.clone());
+        } else {
+            gaps.push(GapItem {
+                kind: GapKind::UnmappedType,
+                source: format!("{key} unique({})", group.join(", ")),
+                location: format!("schema.sql:{}", table.line),
+                reason: format!(
+                    "composite UNIQUE column(s) `{}` did not survive translation (dropped/unmapped), so the constraint can't be reproduced as a composite `unique` index",
+                    missing.join(", ")
+                ),
+                original: format!("unique ({})", group.join(", ")),
+                suggested:
+                    "map the missing column(s) to a field, then add the group to the entity's `unique`, or enforce the invariant in a handler"
+                        .into(),
+                severity: Severity::Blocking,
+            });
+        }
+    }
+
     // Preserve the source table name losslessly: pin `table` only when the
     // default (snake_case + pluralization) would NOT reproduce it, so a clean
     // name stays override-free while an irregular one round-trips exactly.
@@ -239,7 +274,7 @@ fn build_one(
         table,
         belongs_to,
         public_read: false,
-        unique: vec![],
+        unique,
         fields,
     })
 }
@@ -345,6 +380,68 @@ create table public.order_items (
         assert!(!item.fields.iter().any(|f| f.name == "location"));
     }
 
+    #[test]
+    fn composite_unique_survives_translation_and_an_unrepresentable_one_gaps() {
+        // WHY: docs/ai/19 promises the migrator never silently drops what it can't
+        // translate. A multi-column UNIQUE(a, b) IS translatable — jerrycan carries
+        // it as the entity's composite `unique` (#115). It must survive; a group over
+        // a dropped (unmappable-type) column must gap, not vanish.
+        let schema = r#"
+create table public.memberships (
+    id uuid primary key,
+    org_id uuid not null,
+    user_id uuid not null,
+    unique (org_id, user_id)
+);
+create table public.pins (
+    id uuid primary key,
+    label text not null,
+    spot point,
+    unique (label, spot)
+);
+"#;
+        let db = PgDatabase::fold(&parse::split_and_parse(schema));
+        let out = build_entities(&db);
+
+        let membership = out
+            .entities
+            .iter()
+            .find(|(_, e)| e.name == "Membership")
+            .map(|(_, e)| e)
+            .unwrap();
+        assert_eq!(
+            membership.unique,
+            vec![vec!["org_id".to_string(), "user_id".to_string()]],
+            "UNIQUE(org_id, user_id) must survive as the entity's composite `unique`"
+        );
+        // Each column names a declared field (the shape JC0559 accepts), so the
+        // group round-trips to a buildable `CREATE UNIQUE INDEX`.
+        for col in &membership.unique[0] {
+            assert!(membership.fields.iter().any(|f| &f.name == col));
+        }
+
+        // `spot point` is an unmappable type → dropped field + its composite unique
+        // over it can't be built, so the constraint gaps rather than silently drops.
+        let pin = out
+            .entities
+            .iter()
+            .find(|(_, e)| e.name == "Pin")
+            .map(|(_, e)| e)
+            .unwrap();
+        assert!(
+            pin.unique.is_empty(),
+            "a group over a dropped column must not be emitted"
+        );
+        assert!(
+            out.gaps.iter().any(|g| g.kind
+                == crate::platform::migrate::gaps::GapKind::UnmappedType
+                && g.source.contains("unique(label, spot)")
+                && g.reason.contains("spot")),
+            "the unrepresentable composite unique must raise a gap: {:?}",
+            out.gaps
+        );
+    }
+
     #[test]
     fn naming_helpers_are_deterministic() {
         assert_eq!(entity_name("order_items"), "OrderItem");
diff --git a/crates/jerrycan/src/platform/migrate/pgmodel.rs b/crates/jerrycan/src/platform/migrate/pgmodel.rs
index 17a5489..f4872f6 100644
--- a/crates/jerrycan/src/platform/migrate/pgmodel.rs
+++ b/crates/jerrycan/src/platform/migrate/pgmodel.rs
@@ -34,6 +34,11 @@ pub struct PgTable {
     pub columns: Vec<PgColumn>,
     pub pk: Vec<String>,
     pub fks: Vec<PgFk>,
+    /// Table-level multi-column `UNIQUE(a, b, …)` constraints (≥2 columns).
+    /// Single-column uniqueness stays on the column (`PgColumn.unique`); these
+    /// carry the composite invariant a lone column cannot, emitted as the
+    /// entity's composite `unique` (issue #115).
+    pub composite_uniques: Vec<Vec<String>>,
     pub rls_enabled: bool,
     pub line: usize,
 }
@@ -504,11 +509,26 @@ fn apply_table_constraint(table: &mut PgTable, constraint: &TableConstraint) {
             }
         }
         TableConstraint::Unique(u) => {
-            if u.columns.len() == 1
-                && let Some(name) = ident_of_expr(&u.columns[0].column.expr)
-                && let Some(col) = table.columns.iter_mut().find(|col| col.name == name)
-            {
-                col.unique = true;
+            if u.columns.len() == 1 {
+                if let Some(name) = ident_of_expr(&u.columns[0].column.expr)
+                    && let Some(col) = table.columns.iter_mut().find(|col| col.name == name)
+                {
+                    col.unique = true;
+                }
+            } else {
+                // Multi-column `UNIQUE(a, b, …)`: a composite invariant no single
+                // column carries — captured for the entity's composite `unique`
+                // (#115), never silently dropped. A UNIQUE constraint's columns are
+                // always plain identifiers, so all resolve; capture only a fully
+                // resolved group.
+                let cols: Vec<String> = u
+                    .columns
+                    .iter()
+                    .filter_map(|c| ident_of_expr(&c.column.expr))
+                    .collect();
+                if cols.len() == u.columns.len() && cols.len() >= 2 {
+                    table.composite_uniques.push(cols);
+                }
             }
         }
         TableConstraint::ForeignKey(fk) => {