feat: compound-PK foreign-key references — grammar + tests (ADR-0043)

Multi-column FK parsing on both surfaces: DSL from P.(a, b) to
C.(x, y) (parenthesized endpoint; single bare form unchanged) and
SQL FOREIGN KEY (a, b) REFERENCES P(x, y) incl. bare-reference
auto-expand. consume_fk_reference + the table-level/ALTER FK
parsers collect column lists; the from P. completion now offers
( (snapshots updated). 12 integration tests in
tests/it/compound_fk.rs cover parse (both surfaces), engine-enforced
FK, arity + partial-PK + per-pair-type-mismatch refusal,
--create-fk per-column, save->rebuild round-trip, undo (one step),
and single-column preservation. Mark T3 [x]; ADR-0043 implemented.

docs/adr/0043-compound-pk-foreign-key-references.md

@@ -2,8 +2,17 @@
 
 ## Status
 
-**Accepted** — 2026-06-09. All four genuine forks confirmed by the
+**Accepted + implemented** — 2026-06-09. Implementation landed the
-user at the recommended option: **F-A** full PK in order, **F-B**
+same day: the relationship model went list-based through all six
+layers (refactor commit `b14f019`, single-column preserved), then
+the DSL + SQL grammars gained multi-column parsing and the
+executor the full-PK/auto-expand/per-pair-type-compat/auto-name/
+`--create-fk`-per-column logic. Verified by 12 integration tests in
+`tests/it/compound_fk.rs` (parse both surfaces, engine-enforced FK,
+arity + partial-PK refusal, `--create-fk`, single-column
+preserved) on top of the existing single-column relationship
+suite. `requirements.md` **T3** is `[x]`. All four genuine forks
+confirmed by the user at the recommended option: **F-A** full PK in order, **F-B**
 house-style uniform column lists (no migration; back-compat not
 required), **F-C** parenthesized DSL lists, **F-D** bare table-level
 SQL FK auto-expands to the parent's full PK. Closes the one open

docs/adr/README.md

@@ -48,4 +48,4 @@ This directory contains the project's ADRs, recorded per
 - [ADR-0040 — A per-command completion marker (✓/✗) replaces the `[ok]` summary line](0040-completion-marker-replaces-ok-summary.md) — **Accepted 2026-05-30 (issue #9)**, amends ADR-0014 / ADR-0028 / ADR-0019 output conventions, builds on ADR-0037's mode-tagged echo. An audit of the whole command surface found the `[ok] <verb> <subject>` summary line duplicates the echo line above it (verb+subject) everywhere; its only unique contribution is the success-vs-error signal (and `explain select` even rendered `[ok] explain` with an empty subject post-ADR-0039). Decision: drop the `[ok]` line and the symmetric `"…" failed:` prefix; the echo line gains a trailing inline **✓** (green, success) / **✗** (red, failure) — `running:` becomes a pending state that resolves to `<input> ✓/✗` on completion (status set via the existing `rfind(Echo)` lookup). Content (row counts, structure, data, plan tree, teaching echo) unchanged. Scoped to the DSL/data/SQL family that has the redundant echo+`[ok]` pair; app-command `[ok]` lines (`rebuild`/`export`/`now editing`) are payload-bearing, have no echo to mark, and stay as-is. `ok.summary` retired; `dsl.failed` reduced to the rendered reason. Broad but mechanical snapshot churn. OOS: app-command `[ok]` lines, the `[WRN]` validity indicator, and the tag colours (issue #10)
 - [ADR-0041 — Copy the output panel to the system clipboard](0041-copy-output-to-clipboard.md) — **Accepted 2026-06-02 (issue #11)**, amends ADR-0003's app-command registry (adds **`copy`** / `copy all` / `copy last`). The friction it removes: filing a bug report meant terminal-selecting the output panel and fighting wrapping/borders. New **app-level command** (sigil-free, both modes): `copy` / `copy all` copy the whole panel; `copy last` copies from the most recent echo line to the end. **Mechanism — OSC 52 *and* native (`arboard`), always both**, because OSC 52 acceptance is undetectable (no terminal ack), so a true "fall back when unsupported" can't be built: emit the OSC 52 escape (no new dep — `base64`+`crossterm`; works over SSH; tmux-passthrough-wrapped via `$TMUX`), then a best-effort native write whose failure is ignored (headless host — OSC 52 carried it); the two carry identical content. **Format — plain text verbatim as rendered** (tags, `✓`/`✗`, box-drawing) joined by `\n`, without viewport padding/wrapping; a drift-lock test pins `OutputLine::plain_text` to `render_output_line`. `arboard` added **`--no-default-features`** (drops the `image` crate; X11-only on Linux — `wayland-data-control` deliberately omitted as it ~doubles the dep tree and OSC 52 covers native-Wayland). Security: write-only, scans clean for arboard's tree (cargo audit / osv-scanner / grype), 1Password-maintained, minimal surface. OOS: Markdown export, selection/range, a keybinding, OSC 52 read, `screen` passthrough
 - [ADR-0042 — H1a parse-error pedagogy in the grammar-tree era](0042-h1a-parse-error-pedagogy-grammar-tree.md) — **Accepted 2026-06-03.** Continues **H1a** from ADR-0021 against the ADR-0024 grammar tree (ADR-0021's chumsky mechanism is dead). Records the **baseline already shipped** — per-command `usage:` block (38 `parse.usage.*` templates), available-commands fallback, structural "after `…`, expected …" wording, source-derived ident slot labels ("table name"/"column name"), curated `parse.custom.*` near-miss messages, and the ADR-0027/0033/0036 schema-aware `[ERR]` diagnostics — so H1a is *substantially* delivered at the intent level. Defines the remaining work as **(1)** a verified per-command **near-miss matrix** (`tests/typing_surface/` + `tests/it/parse_error_pedagogy.rs`) as the definition of done, test-first; **(2)** **friendlier literal expectation labels** — optional prose glosses on `Word`/`Punct`/`Flag` positions that *add* role context while always keeping the exact literal visible (e.g. "a filter clause: `where …` or `--all-rows`"); **(3)** **advanced-mode SQL** near-miss parity (RETURNING scope, CTE-arity positioning, `CROSS JOIN … ON`, INSERT…SELECT count) — **in scope**, kept distinct from ADR-0019 §OOS-2 which covers advanced-SQL *engine*-error sanitisation, a different layer. Catalog/anchor-phrase discipline (ADR-0019) preserved; no public API change. OOS: I3/I4, spell-correction, multi-error reporting, verbosity-gating the usage block
-- [ADR-0043 — Compound-primary-key foreign-key references (T3)](0043-compound-pk-foreign-key-references.md) — **Accepted 2026-06-09** (all four forks confirmed at the recommended option: full-PK matching, house-style uniform lists, parenthesized DSL syntax, bare-SQL-FK auto-expansion). Closes the open leg of `requirements.md` **T3**: a foreign key that *references* a parent's compound primary key. A 2026-06-09 audit found single-column FK woven through ~15–20 sites (metadata table, `RelationshipSchema`, `project.yaml` `RawEndpoint`, both grammar surfaces, executor FK-DDL emission, per-column type-compat, display) — earns an ADR, not an inline build. **Decision:** reference the parent's **full** compound PK, matched **positionally** to an equal-length child column list, per-pair `fk_target_type` compat (ADR-0011, element-wise); DSL `from <P>.(a, b) to <C>.(x, y)` (single form unchanged), SQL `FOREIGN KEY (x, y) REFERENCES P(a, b)` (extend the existing one-cap lists; bare table-level FK auto-expands to the parent PK when arities match). **Storage — no migration (back-compat not required, user-confirmed 2026-06-09; no installed base):** the relationship endpoint joins the list convention `project.yaml` *already* uses — `columns: [a, b]` like `primary_key: [id]` and index `columns: [...]` (the endpoint was the lone scalar `column:` holdout); the metadata `TEXT` columns are unchanged and store the list as a uniform JSON array (`["id"]` even for single — SQLite has no array type). No F3 migrator, no version bump; accepted trade-off is that a pre-change `project.yaml` with relationships won't load (clean cutover). In-memory model goes list-based (`Vec<String>`) through all six layers; the enforced FK is the rebuilt child-table DDL (`FOREIGN KEY (a,b) REFERENCES P(x,y)`), one relationship = one undo step (ADR-0013). Genuine forks escalated: matching policy (full-PK vs subset), storage (house-style uniform lists vs normalized table), DSL syntax (parenthesized vs repeated-dotted), bare-SQL-FK auto-expansion. OOS: subset/non-PK (UNIQUE-targeted) FK references; any single-column behaviour change
+- [ADR-0043 — Compound-primary-key foreign-key references (T3)](0043-compound-pk-foreign-key-references.md) — **Accepted + implemented 2026-06-09** (all four forks confirmed at the recommended option: full-PK matching, house-style uniform lists, parenthesized DSL syntax, bare-SQL-FK auto-expansion). Closes `requirements.md` **T3** `[x]` — the relationship model went list-based across six layers (single-column preserved, no migration), DSL `from P.(a,b) to C.(x,y)` + SQL `FOREIGN KEY (a,b) REFERENCES P(x,y)` parse/execute/enforce, 12 tests in `tests/it/compound_fk.rs`. Closes the open leg of `requirements.md` **T3**: a foreign key that *references* a parent's compound primary key. A 2026-06-09 audit found single-column FK woven through ~15–20 sites (metadata table, `RelationshipSchema`, `project.yaml` `RawEndpoint`, both grammar surfaces, executor FK-DDL emission, per-column type-compat, display) — earns an ADR, not an inline build. **Decision:** reference the parent's **full** compound PK, matched **positionally** to an equal-length child column list, per-pair `fk_target_type` compat (ADR-0011, element-wise); DSL `from <P>.(a, b) to <C>.(x, y)` (single form unchanged), SQL `FOREIGN KEY (x, y) REFERENCES P(a, b)` (extend the existing one-cap lists; bare table-level FK auto-expands to the parent PK when arities match). **Storage — no migration (back-compat not required, user-confirmed 2026-06-09; no installed base):** the relationship endpoint joins the list convention `project.yaml` *already* uses — `columns: [a, b]` like `primary_key: [id]` and index `columns: [...]` (the endpoint was the lone scalar `column:` holdout); the metadata `TEXT` columns are unchanged and store the list **comma-joined** (`a,b`; the bare name for single — safe because identifiers are `[A-Za-z0-9_]+`). No F3 migrator, no version bump; accepted trade-off is that a pre-change `project.yaml` with relationships won't load (clean cutover). In-memory model goes list-based (`Vec<String>`) through all six layers; the enforced FK is the rebuilt child-table DDL (`FOREIGN KEY (a,b) REFERENCES P(x,y)`), one relationship = one undo step (ADR-0013). Genuine forks escalated: matching policy (full-PK vs subset), storage (house-style uniform lists vs normalized table), DSL syntax (parenthesized vs repeated-dotted), bare-SQL-FK auto-expansion. OOS: subset/non-PK (UNIQUE-targeted) FK references; any single-column behaviour change

docs/requirements.md

@@ -399,30 +399,28 @@ since ADR-0027.)
   *(Implemented per ADR-0014; auto-fills omitted shortid
   columns and validates user-supplied values against the same
   alphabet and length range.)*
-- [/] **T3** Compound primary keys handled end-to-end (DSL,
+- [x] **T3** Compound primary keys handled end-to-end (DSL,
   storage, display, FK reference).
-  *(Partial, verified 2026-06-07: compound-PK **declaration**
+  *(Done 2026-06-09 via **ADR-0043**: the FK-reference leg now
-  (`with pk a(int),b(int)`), **storage** (`primary_key:
+  works on both surfaces — DSL `add 1:n relationship from
-  Vec<String>`), and **display** are present and tested.
+  P.(a, b) to C.(x, y)` and SQL `FOREIGN KEY (a, b) REFERENCES
-  **Missing: a FK that *references* a compound PK** —
+  P(x, y)` (bare `REFERENCES P` auto-expands to the full PK).
-  `db.rs` resolve/alter FK paths enforce a single
+  References the parent's full compound PK matched positionally,
-  `parent_column: String`; a bare `REFERENCES parent` on a
+  per-pair type-compat (ADR-0011); the FK is engine-enforced,
-  compound-PK table is refused as ambiguous, and multi-column FK
+  persisted (`columns: [a, b]` in `project.yaml`, comma-joined in
-  target syntax is not in the grammar. This is the one open
+  metadata), shown symmetrically by `describe`, and `--create-fk`
-  end-to-end leg of T3 — but a **codebase audit (2026-06-09)
+  creates one child column per parent PK column. The relationship
-  found it is not a small finish**: single-column FK is woven
+  model went list-based through all six layers, single-column
-  through ~15–20 sites across 6+ files — the
+  behaviour preserved (commit `b14f019`); 12 integration tests in
-  `__rdbms_playground_relationships` table schema, the
+  `tests/it/compound_fk.rs` plus the existing single-column suite
-  `RelationshipSchema` struct, the **`project.yaml` relationship
+  as the regression net. The earlier-noted (2026-06-07) breakdown:*
-  format** (`RawEndpoint { column }`), both grammar surfaces
+  *compound-PK **declaration** (`with pk a(int),b(int)`),
-  (`add 1:n relationship` + SQL `FOREIGN KEY`), the executor's FK
+  **storage** (`primary_key: Vec<String>`), and **display** were
-  DDL emission, and the per-column type-compat check. It needs a
+  already present and tested. The FK-reference leg — once an
-  **migration** (the metadata-table + yaml-format change, F3) and
+  ADR-first ~15–20-site change across the relationship model — is
-  an **ADR** to settle the design forks: compound-PK matching
+  what ADR-0043 delivered (back-compat dropped by user decision, so
-  policy (must an FK reference *all* PK columns, or a subset?),
+  no migration was needed). Subset / non-PK (UNIQUE-target) FK
-  per-pair type-compat semantics, the yaml multi-column shape, and
+  references stay out of scope.)*
-  back-compat for existing single-column projects. So this leg is
-  ADR-first, not a sweep item.)*
 
 ## Visualizations
 

src/dsl/grammar/ddl.rs

@@ -385,6 +385,36 @@ const ADD_COLUMN: Node = Node::Seq(ADD_COLUMN_NODES);
 // `writes_table: true` on each endpoint's table ident so the
 // `.<col>` slot narrows to that table's columns (handoff-13
 // §2.2 follow-up — mirrors DR_PARENT / DR_CHILD).
+// A single FK-endpoint column ident (narrows to the endpoint
+// table's columns via the table ident's `writes_table: true`).
+const AR_PARENT_COL: Node = Node::Ident {
+    source: IdentSource::Columns,
+    role: "parent_column",
+    validator: None,
+    highlight_override: None,
+    writes_table: false,
+    writes_column: false,
+    writes_user_listed_column: false,
+    writes_table_alias: false,
+    writes_cte_name: false,
+    writes_projection_alias: false,
+};
+// Compound endpoint: `( a, b, … )` — a comma-separated column list
+// in parens (ADR-0043). Same role as the single form, so the
+// builder collects either shape uniformly.
+const AR_PARENT_COL_LIST: Node = Node::Repeated {
+    inner: &AR_PARENT_COL,
+    separator: Some(&Node::Punct(',')),
+    min: 1,
+};
+const AR_PARENT_COLS_PAREN_NODES: &[Node] =
+    &[Node::Punct('('), AR_PARENT_COL_LIST, Node::Punct(')')];
+const AR_PARENT_COLS_PAREN: Node = Node::Seq(AR_PARENT_COLS_PAREN_NODES);
+// `from P.(a, b)` (compound) or `from P.col` (single) — Choice on
+// the first post-`.` token (`(` vs an ident), so order is safe.
+const AR_PARENT_COLS_CHOICES: &[Node] = &[AR_PARENT_COLS_PAREN, AR_PARENT_COL];
+const AR_PARENT_COLS: Node = Node::Choice(AR_PARENT_COLS_CHOICES);
+
 const AR_PARENT_NODES: &[Node] = &[
     Node::Ident {
         source: IdentSource::Tables,
@@ -394,25 +424,37 @@ const AR_PARENT_NODES: &[Node] = &[
         writes_table: true,
         writes_column: false,
         writes_user_listed_column: false,
-    writes_table_alias: false,
+        writes_table_alias: false,
-    writes_cte_name: false,
+        writes_cte_name: false,
-    writes_projection_alias: false,
+        writes_projection_alias: false,
     },
     Node::Punct('.'),
-    Node::Ident {
+    AR_PARENT_COLS,
-        source: IdentSource::Columns,
+];
-        role: "parent_column",
+const AR_PARENT: Node = Node::Seq(AR_PARENT_NODES);
-        validator: None,
+
-        highlight_override: None,
+const AR_CHILD_COL: Node = Node::Ident {
-        writes_table: false,
+    source: IdentSource::Columns,
-        writes_column: false,
+    role: "child_column",
-        writes_user_listed_column: false,
+    validator: None,
+    highlight_override: None,
+    writes_table: false,
+    writes_column: false,
+    writes_user_listed_column: false,
     writes_table_alias: false,
     writes_cte_name: false,
     writes_projection_alias: false,
-    },
+};
-];
+const AR_CHILD_COL_LIST: Node = Node::Repeated {
-const AR_PARENT: Node = Node::Seq(AR_PARENT_NODES);
+    inner: &AR_CHILD_COL,
+    separator: Some(&Node::Punct(',')),
+    min: 1,
+};
+const AR_CHILD_COLS_PAREN_NODES: &[Node] =
+    &[Node::Punct('('), AR_CHILD_COL_LIST, Node::Punct(')')];
+const AR_CHILD_COLS_PAREN: Node = Node::Seq(AR_CHILD_COLS_PAREN_NODES);
+const AR_CHILD_COLS_CHOICES: &[Node] = &[AR_CHILD_COLS_PAREN, AR_CHILD_COL];
+const AR_CHILD_COLS: Node = Node::Choice(AR_CHILD_COLS_CHOICES);
 
 const AR_CHILD_NODES: &[Node] = &[
     Node::Ident {
@@ -423,23 +465,12 @@ const AR_CHILD_NODES: &[Node] = &[
         writes_table: true,
         writes_column: false,
         writes_user_listed_column: false,
-    writes_table_alias: false,
+        writes_table_alias: false,
-    writes_cte_name: false,
+        writes_cte_name: false,
-    writes_projection_alias: false,
+        writes_projection_alias: false,
     },
     Node::Punct('.'),
-    Node::Ident {
+    AR_CHILD_COLS,
-        source: IdentSource::Columns,
-        role: "child_column",
-        validator: None,
-        highlight_override: None,
-        writes_table: false,
-        writes_column: false,
-        writes_user_listed_column: false,
-    writes_table_alias: false,
-    writes_cte_name: false,
-    writes_projection_alias: false,
-    },
 ];
 const AR_CHILD: Node = Node::Seq(AR_CHILD_NODES);
 
@@ -1523,8 +1554,10 @@ fn build_sql_create_table(path: &MatchedPath, source: &str) -> Result<Command, V
             // consumed in `consume_fk_reference`, so they don't perturb
             // the element-boundary `depth` tracker.
             MatchedKind::Word("references") => {
+                // Inline FK is single-column (the column it sits on);
+                // a compound FK uses the table-level form (ADR-0043 D4).
                 let child_column = columns.last().map_or_else(String::new, |c| c.name.clone());
-                foreign_keys.push(consume_fk_reference(&mut items, None, child_column));
+                foreign_keys.push(consume_fk_reference(&mut items, None, vec![child_column]));
             }
             // Table-level `[constraint <name>] foreign key (<col>)
             // references <parent> [(<col>)] [on …]` (ADR-0035 §5, 4b).
@@ -1532,11 +1565,21 @@ fn build_sql_create_table(path: &MatchedPath, source: &str) -> Result<Command, V
                 if matches!(items.peek().map(|i| &i.kind), Some(MatchedKind::Word("key"))) {
                     items.next(); // `key`
                 }
-                // `( <child column> )`
+                // `( <child column> [, <child column>]* )` — a compound
+                // FK lists multiple child columns (ADR-0043).
                 if matches!(items.peek().map(|i| &i.kind), Some(MatchedKind::Punct('('))) {
                     items.next();
                 }
-                let child_column = items.next().map_or_else(String::new, |it| it.text.clone());
+                let mut child_columns = Vec::new();
+                while let Some(it) = items.peek() {
+                    match &it.kind {
+                        MatchedKind::Punct(')') => break,
+                        MatchedKind::Punct(',') => {
+                            items.next();
+                        }
+                        _ => child_columns.push(items.next().expect("peeked").text.clone()),
+                    }
+                }
                 if matches!(items.peek().map(|i| &i.kind), Some(MatchedKind::Punct(')'))) {
                     items.next();
                 }
@@ -1544,7 +1587,7 @@ fn build_sql_create_table(path: &MatchedPath, source: &str) -> Result<Command, V
                 if matches!(items.peek().map(|i| &i.kind), Some(MatchedKind::Word("references"))) {
                     items.next();
                 }
-                let fk = consume_fk_reference(&mut items, pending_fk_name.take(), child_column);
+                let fk = consume_fk_reference(&mut items, pending_fk_name.take(), child_columns);
                 foreign_keys.push(fk);
             }
             // Track paren depth for element-boundary detection. The
@@ -1660,23 +1703,35 @@ where
 fn consume_fk_reference<'a, I>(
     items: &mut std::iter::Peekable<I>,
     name: Option<String>,
-    child_column: String,
+    child_columns: Vec<String>,
 ) -> SqlForeignKey
 where
     I: Iterator<Item = &'a crate::dsl::walker::outcome::MatchedItem>,
 {
     let parent_table = items.next().map_or_else(String::new, |it| it.text.clone());
-    // Optional `( <parent column> )`.
+    // Optional `( <parent column> [, <parent column>]* )` — a
-    let mut parent_column = None;
+    // compound FK references multiple parent columns (ADR-0043).
-    if matches!(items.peek().map(|i| &i.kind), Some(MatchedKind::Punct('('))) {
+    // `None` for the bare `REFERENCES <parent>` form.
-        items.next(); // `(`
+    let parent_columns: Option<Vec<String>> =
-        if let Some(it) = items.next() {
+        if matches!(items.peek().map(|i| &i.kind), Some(MatchedKind::Punct('('))) {
-            parent_column = Some(it.text.clone());
+            items.next(); // `(`
-        }
+            let mut cols = Vec::new();
-        if matches!(items.peek().map(|i| &i.kind), Some(MatchedKind::Punct(')'))) {
+            while let Some(it) = items.peek() {
-            items.next(); // `)`
+                match &it.kind {
-        }
+                    MatchedKind::Punct(')') => break,
-    }
+                    MatchedKind::Punct(',') => {
+                        items.next();
+                    }
+                    _ => cols.push(items.next().expect("peeked").text.clone()),
+                }
+            }
+            if matches!(items.peek().map(|i| &i.kind), Some(MatchedKind::Punct(')'))) {
+                items.next(); // `)`
+            }
+            Some(cols)
+        } else {
+            None
+        };
     // `on <delete|update> <action>` clauses, in either order, 0..2.
     let mut on_delete = ReferentialAction::default_action();
     let mut on_update = ReferentialAction::default_action();
@@ -1692,12 +1747,9 @@ where
     }
     SqlForeignKey {
         name,
-        // Single-column for now; the parenthesized multi-column parse
+        child_columns,
-        // (`FOREIGN KEY (a, b) REFERENCES P(x, y)`) lands with the
-        // grammar-node change (ADR-0043).
-        child_columns: vec![child_column],
         parent_table,
-        parent_columns: parent_column.map(|c| vec![c]),
+        parent_columns,
         on_delete,
         on_update,
     }
@@ -2385,14 +2437,24 @@ fn build_alter_fk(path: &MatchedPath) -> SqlForeignKey {
     if matches!(items.peek().map(|i| &i.kind), Some(MatchedKind::Punct('('))) {
         items.next();
     }
-    let child_column = items.next().map_or_else(String::new, |it| it.text.clone());
+    // `( <child column> [, <child column>]* )` — compound FK (ADR-0043).
+    let mut child_columns = Vec::new();
+    while let Some(it) = items.peek() {
+        match &it.kind {
+            MatchedKind::Punct(')') => break,
+            MatchedKind::Punct(',') => {
+                items.next();
+            }
+            _ => child_columns.push(items.next().expect("peeked").text.clone()),
+        }
+    }
     if matches!(items.peek().map(|i| &i.kind), Some(MatchedKind::Punct(')'))) {
         items.next();
     }
     if matches!(items.peek().map(|i| &i.kind), Some(MatchedKind::Word("references"))) {
         items.next();
     }
-    consume_fk_reference(&mut items, None, child_column)
+    consume_fk_reference(&mut items, None, child_columns)
 }
 
 pub static SQL_ALTER_TABLE: CommandNode = CommandNode {

src/dsl/grammar/sql_create_table.rs

@@ -182,7 +182,15 @@ const FK_PARENT_COLUMN: Node = Node::Ident {
     writes_cte_name: false,
     writes_projection_alias: false,
 };
-static FK_PARENT_COL_NODES: &[Node] = &[Node::Punct('('), FK_PARENT_COLUMN, Node::Punct(')')];
+// `( a [, b]* )` — a compound FK references multiple parent columns
+// (ADR-0043). The `Repeated` separator handles the commas; a
+// single-column FK is the one-element case.
+const FK_PARENT_COL_LIST: Node = Node::Repeated {
+    inner: &FK_PARENT_COLUMN,
+    separator: Some(&Node::Punct(',')),
+    min: 1,
+};
+static FK_PARENT_COL_NODES: &[Node] = &[Node::Punct('('), FK_PARENT_COL_LIST, Node::Punct(')')];
 const FK_PARENT_COL_OPT: Node = Node::Optional(&Node::Seq(FK_PARENT_COL_NODES));
 
 // `REFERENCES <parent> [ ( <col> ) ] [on delete/update …]` — the inline
@@ -333,6 +341,13 @@ const FK_CHILD_COLUMN: Node = Node::Ident {
     writes_cte_name: false,
     writes_projection_alias: false,
 };
+// `( a [, b]* )` — a compound FK lists multiple child columns
+// (ADR-0043); single-column is the one-element case.
+const FK_CHILD_COL_LIST: Node = Node::Repeated {
+    inner: &FK_CHILD_COLUMN,
+    separator: Some(&Node::Punct(',')),
+    min: 1,
+};
 const FK_NAME: Node = Node::Ident {
     source: IdentSource::NewName,
     role: "fk_name",
@@ -354,7 +369,7 @@ static FOREIGN_KEY_BODY_NODES: &[Node] = &[
     Node::Word(Word::keyword("foreign")),
     Node::Word(Word::keyword("key")),
     Node::Punct('('),
-    FK_CHILD_COLUMN,
+    FK_CHILD_COL_LIST,
     Node::Punct(')'),
     Node::Word(Word::keyword("references")),
     FK_PARENT_TABLE,
@@ -374,7 +389,7 @@ static TABLE_FK_NAMED_NODES: &[Node] = &[
     Node::Word(Word::keyword("foreign")),
     Node::Word(Word::keyword("key")),
     Node::Punct('('),
-    FK_CHILD_COLUMN,
+    FK_CHILD_COL_LIST,
     Node::Punct(')'),
     Node::Word(Word::keyword("references")),
     FK_PARENT_TABLE,

tests/it/compound_fk.rs

@@ -0,0 +1,549 @@
+//! Integration tests for compound-primary-key foreign-key
+//! references (T3 / ADR-0043) — the DSL `add 1:n relationship`
+//! surface end to end.
+//!
+//! Covers: parse of the parenthesized multi-column endpoint;
+//! worker round-trip (declare a 2-column FK, FK is enforced,
+//! per-pair type-mismatch refused, arity mismatch refused);
+//! persistence round-trip (`columns: [a, b]`); display; and undo.
+
+use rdbms_playground::db::Database;
+use rdbms_playground::dsl::{
+    parse_command, ColumnSpec, Command, ReferentialAction, SqlForeignKey, Type, Value,
+};
+use rdbms_playground::persistence::Persistence;
+use rdbms_playground::project;
+
+// ---- parse layer ------------------------------------------------
+
+#[test]
+fn parenthesized_compound_endpoint_parses_to_column_lists() {
+    let cmd = parse_command(
+        "add 1:n relationship from Parent.(a, b) to Child.(x, y)",
+    )
+    .expect("parses");
+    match cmd {
+        Command::AddRelationship {
+            parent_table,
+            parent_columns,
+            child_table,
+            child_columns,
+            ..
+        } => {
+            assert_eq!(parent_table, "Parent");
+            assert_eq!(parent_columns, vec!["a".to_string(), "b".to_string()]);
+            assert_eq!(child_table, "Child");
+            assert_eq!(child_columns, vec!["x".to_string(), "y".to_string()]);
+        }
+        other => panic!("expected AddRelationship, got {other:?}"),
+    }
+}
+
+#[test]
+fn single_column_endpoint_still_parses_unparenthesized() {
+    let cmd = parse_command("add 1:n relationship from Parent.id to Child.pid")
+        .expect("parses");
+    match cmd {
+        Command::AddRelationship {
+            parent_columns,
+            child_columns,
+            ..
+        } => {
+            assert_eq!(parent_columns, vec!["id".to_string()]);
+            assert_eq!(child_columns, vec!["pid".to_string()]);
+        }
+        other => panic!("expected AddRelationship, got {other:?}"),
+    }
+}
+
+// ---- SQL surface (advanced mode) --------------------------------
+
+#[test]
+fn sql_table_level_compound_fk_parses_to_lists() {
+    let cmd = parse_command(
+        "create table City (country int, region_code int, \
+         foreign key (country, region_code) references Region(country, code))",
+    )
+    .expect("parses");
+    match cmd {
+        Command::SqlCreateTable { foreign_keys, .. } => {
+            assert_eq!(foreign_keys.len(), 1);
+            assert_eq!(
+                foreign_keys[0].child_columns,
+                vec!["country".to_string(), "region_code".to_string()],
+            );
+            assert_eq!(
+                foreign_keys[0].parent_columns,
+                Some(vec!["country".to_string(), "code".to_string()]),
+            );
+        }
+        other => panic!("expected SqlCreateTable, got {other:?}"),
+    }
+}
+
+#[test]
+fn sql_bare_compound_reference_parses_with_no_parent_columns() {
+    // `FOREIGN KEY (a, b) REFERENCES P` (no parent cols) — auto-expanded
+    // to the parent's full PK at execution (F-D).
+    let cmd = parse_command(
+        "create table City (country int, region_code int, \
+         foreign key (country, region_code) references Region)",
+    )
+    .expect("parses");
+    match cmd {
+        Command::SqlCreateTable { foreign_keys, .. } => {
+            assert_eq!(
+                foreign_keys[0].child_columns,
+                vec!["country".to_string(), "region_code".to_string()],
+            );
+            assert_eq!(foreign_keys[0].parent_columns, None);
+        }
+        other => panic!("expected SqlCreateTable, got {other:?}"),
+    }
+}
+
+#[test]
+fn sql_create_table_compound_fk_executes_and_enforces() {
+    let (_p, db, _dir) = open_project_db();
+    let rt = rt();
+    rt.block_on(async {
+        // Parent with a compound PK.
+        db.create_table(
+            "Region".to_string(),
+            vec![
+                ColumnSpec::new("country", Type::Int),
+                ColumnSpec::new("code", Type::Int),
+            ],
+            vec!["country".to_string(), "code".to_string()],
+            None,
+        )
+        .await
+        .expect("create Region");
+        // Child via the SQL path with a multi-column FK referencing the
+        // full compound PK (resolve_create_table_fks).
+        db.sql_create_table(
+            "City".to_string(),
+            vec![
+                ColumnSpec::new("country", Type::Int),
+                ColumnSpec::new("region_code", Type::Int),
+            ],
+            vec![],
+            vec![],
+            vec![],
+            vec![SqlForeignKey {
+                name: None,
+                child_columns: vec!["country".to_string(), "region_code".to_string()],
+                parent_table: "Region".to_string(),
+                parent_columns: Some(vec!["country".to_string(), "code".to_string()]),
+                on_delete: ReferentialAction::NoAction,
+                on_update: ReferentialAction::NoAction,
+            }],
+            false,
+            None,
+        )
+        .await
+        .expect("create City with compound FK");
+
+        db.insert(
+            "Region".to_string(),
+            Some(vec!["country".to_string(), "code".to_string()]),
+            vec![Value::Number("1".to_string()), Value::Number("10".to_string())],
+            None,
+        )
+        .await
+        .expect("insert parent");
+        let bad = db
+            .insert(
+                "City".to_string(),
+                Some(vec!["country".to_string(), "region_code".to_string()]),
+                vec![Value::Number("9".to_string()), Value::Number("9".to_string())],
+                None,
+            )
+            .await;
+        assert!(bad.is_err(), "compound FK violation refused by the engine");
+    });
+}
+
+// ---- worker round-trip ------------------------------------------
+
+fn rt() -> tokio::runtime::Runtime {
+    tokio::runtime::Builder::new_current_thread()
+        .enable_all()
+        .build()
+        .expect("tokio rt")
+}
+
+fn open_project_db() -> (project::Project, Database, tempfile::TempDir) {
+    let dir = tempfile::tempdir().expect("create tempdir");
+    let project =
+        project::open_or_create(None, Some(dir.path())).expect("open or create project");
+    let persistence = Persistence::new(project.path().to_path_buf());
+    let db = Database::open_with_persistence(project.db_path(), persistence)
+        .expect("open db with persistence");
+    (project, db, dir)
+}
+
+/// `Region(country int, code int)` compound PK + `City(country int,
+/// region_code int, name text)` — the child FK columns matching the
+/// parent PK by type (int → int).
+async fn seed_compound(db: &Database) {
+    db.create_table(
+        "Region".to_string(),
+        vec![
+            ColumnSpec::new("country", Type::Int),
+            ColumnSpec::new("code", Type::Int),
+        ],
+        vec!["country".to_string(), "code".to_string()],
+        None,
+    )
+    .await
+    .expect("create Region");
+    db.create_table(
+        "City".to_string(),
+        vec![
+            ColumnSpec::new("country", Type::Int),
+            ColumnSpec::new("region_code", Type::Int),
+            ColumnSpec::new("name", Type::Text),
+        ],
+        vec!["country".to_string()],
+        None,
+    )
+    .await
+    .expect("create City");
+}
+
+#[test]
+fn compound_fk_declares_enforces_and_round_trips() {
+    let (_p, db, _dir) = open_project_db();
+    let rt = rt();
+    rt.block_on(async {
+        seed_compound(&db).await;
+        // Declare the compound FK: City.(country, region_code) →
+        // Region.(country, code).
+        db.add_relationship(
+            Some("city_region".to_string()),
+            "Region".to_string(),
+            vec!["country".to_string(), "code".to_string()],
+            "City".to_string(),
+            vec!["country".to_string(), "region_code".to_string()],
+            ReferentialAction::NoAction,
+            ReferentialAction::NoAction,
+            false,
+            None,
+        )
+        .await
+        .expect("add compound relationship");
+
+        // The FK is enforced: a parent row exists for (1, 10); a
+        // child referencing it inserts, one referencing (9, 9) is
+        // refused by the engine.
+        db.insert(
+            "Region".to_string(),
+            Some(vec!["country".to_string(), "code".to_string()]),
+            vec![Value::Number("1".to_string()), Value::Number("10".to_string())],
+            None,
+        )
+        .await
+        .expect("insert parent row");
+        db.insert(
+            "City".to_string(),
+            Some(vec![
+                "country".to_string(),
+                "region_code".to_string(),
+                "name".to_string(),
+            ]),
+            vec![Value::Number("1".to_string()), Value::Number("10".to_string()), Value::Text("Metropolis".to_string())],
+            None,
+        )
+        .await
+        .expect("child row referencing an existing parent key inserts");
+        let violation = db
+            .insert(
+                "City".to_string(),
+                Some(vec![
+                    "country".to_string(),
+                    "region_code".to_string(),
+                    "name".to_string(),
+                ]),
+                vec![Value::Number("9".to_string()), Value::Number("9".to_string()), Value::Text("Nowhere".to_string())],
+                None,
+            )
+            .await;
+        assert!(
+            violation.is_err(),
+            "a child row with no matching compound parent key must be refused",
+        );
+
+        // describe shows the compound endpoints symmetrically.
+        let city = db.describe_table("City".to_string(), None).await.unwrap();
+        let outbound = &city.outbound_relationships[0];
+        assert_eq!(
+            outbound.local_columns,
+            vec!["country".to_string(), "region_code".to_string()],
+        );
+        assert_eq!(
+            outbound.other_columns,
+            vec!["country".to_string(), "code".to_string()],
+        );
+    });
+}
+
+#[test]
+fn compound_fk_create_fk_makes_both_child_columns() {
+    let (_p, db, _dir) = open_project_db();
+    let rt = rt();
+    rt.block_on(async {
+        // Region(country, code) compound PK; City has neither FK column.
+        db.create_table(
+            "Region".to_string(),
+            vec![
+                ColumnSpec::new("country", Type::Int),
+                ColumnSpec::new("code", Type::Int),
+            ],
+            vec!["country".to_string(), "code".to_string()],
+            None,
+        )
+        .await
+        .expect("create Region");
+        db.create_table(
+            "City".to_string(),
+            vec![ColumnSpec::new("name", Type::Text)],
+            vec![],
+            None,
+        )
+        .await
+        .expect("create City");
+        // --create-fk creates both missing child columns, typed to the
+        // matching parent PK columns' fk_target_type (int → int).
+        db.add_relationship(
+            None,
+            "Region".to_string(),
+            vec!["country".to_string(), "code".to_string()],
+            "City".to_string(),
+            vec!["c_country".to_string(), "c_code".to_string()],
+            ReferentialAction::NoAction,
+            ReferentialAction::NoAction,
+            true,
+            None,
+        )
+        .await
+        .expect("add compound relationship with --create-fk");
+        let city = db.describe_table("City".to_string(), None).await.unwrap();
+        for col in ["c_country", "c_code"] {
+            assert!(
+                city.columns.iter().any(|c| c.name == col),
+                "--create-fk created `{col}`: {:?}",
+                city.columns.iter().map(|c| &c.name).collect::<Vec<_>>(),
+            );
+        }
+    });
+}
+
+#[test]
+fn compound_fk_arity_mismatch_is_refused() {
+    let (_p, db, _dir) = open_project_db();
+    let rt = rt();
+    rt.block_on(async {
+        seed_compound(&db).await;
+        // Two parent columns, one child column → arity mismatch.
+        let err = db
+            .add_relationship(
+                None,
+                "Region".to_string(),
+                vec!["country".to_string(), "code".to_string()],
+                "City".to_string(),
+                vec!["country".to_string()],
+                ReferentialAction::NoAction,
+                ReferentialAction::NoAction,
+                false,
+                None,
+            )
+            .await;
+        assert!(err.is_err(), "mismatched child/parent arity must be refused");
+    });
+}
+
+#[test]
+fn compound_fk_type_mismatch_per_pair_is_refused() {
+    let (_p, db, _dir) = open_project_db();
+    let rt = rt();
+    rt.block_on(async {
+        db.create_table(
+            "Region".to_string(),
+            vec![
+                ColumnSpec::new("country", Type::Int),
+                ColumnSpec::new("code", Type::Int),
+            ],
+            vec!["country".to_string(), "code".to_string()],
+            None,
+        )
+        .await
+        .expect("create Region");
+        // `bad` is `text` — incompatible with the `int` PK column it
+        // would pair with (per-pair type-compat, ADR-0011).
+        db.create_table(
+            "City".to_string(),
+            vec![
+                ColumnSpec::new("country", Type::Int),
+                ColumnSpec::new("bad", Type::Text),
+            ],
+            vec![],
+            None,
+        )
+        .await
+        .expect("create City");
+        let err = db
+            .add_relationship(
+                None,
+                "Region".to_string(),
+                vec!["country".to_string(), "code".to_string()],
+                "City".to_string(),
+                vec!["country".to_string(), "bad".to_string()],
+                ReferentialAction::NoAction,
+                ReferentialAction::NoAction,
+                false,
+                None,
+            )
+            .await;
+        assert!(err.is_err(), "a type-incompatible column pair must be refused");
+    });
+}
+
+#[test]
+fn compound_fk_survives_rebuild_from_text() {
+    // The riskiest round-trip: comma-encoded metadata + yaml
+    // `columns: [a, b]` → rebuild reconstructs the compound FK DDL.
+    let dir = tempfile::tempdir().expect("tempdir");
+    let project = project::open_or_create(None, Some(dir.path())).expect("open project");
+    let path = project.path().to_path_buf();
+    let rt = rt();
+    {
+        let db = Database::open_with_persistence(
+            project.db_path(),
+            Persistence::new(path.clone()),
+        )
+        .expect("open db");
+        rt.block_on(async {
+            seed_compound(&db).await;
+            db.add_relationship(
+                Some("city_region".to_string()),
+                "Region".to_string(),
+                vec!["country".to_string(), "code".to_string()],
+                "City".to_string(),
+                vec!["country".to_string(), "region_code".to_string()],
+                ReferentialAction::NoAction,
+                ReferentialAction::NoAction,
+                false,
+                Some("add 1:n relationship".to_string()),
+            )
+            .await
+            .expect("add compound relationship");
+        });
+    }
+    // Reopen and rebuild the database purely from the persisted
+    // project.yaml + data/.
+    let db = Database::open_with_persistence(project.db_path(), Persistence::new(path.clone()))
+        .expect("reopen db");
+    rt.block_on(async {
+        db.rebuild_from_text(path.clone(), None)
+            .await
+            .expect("rebuild from text");
+        // The compound FK is reconstructed and still enforced.
+        db.insert(
+            "Region".to_string(),
+            Some(vec!["country".to_string(), "code".to_string()]),
+            vec![Value::Number("1".to_string()), Value::Number("10".to_string())],
+            None,
+        )
+        .await
+        .expect("insert parent after rebuild");
+        let bad = db
+            .insert(
+                "City".to_string(),
+                Some(vec!["country".to_string(), "region_code".to_string()]),
+                vec![Value::Number("9".to_string()), Value::Number("9".to_string())],
+                None,
+            )
+            .await;
+        assert!(bad.is_err(), "compound FK still enforced after rebuild from text");
+        // Endpoints survived the round-trip intact.
+        let city = db.describe_table("City".to_string(), None).await.unwrap();
+        assert_eq!(
+            city.outbound_relationships[0].other_columns,
+            vec!["country".to_string(), "code".to_string()],
+        );
+    });
+}
+
+#[test]
+fn compound_fk_undo_removes_the_relationship() {
+    let dir = tempfile::tempdir().expect("tempdir");
+    let project = project::open_or_create(None, Some(dir.path())).expect("open project");
+    let db = Database::open_with_persistence_and_undo(
+        project.db_path(),
+        Persistence::new(project.path().to_path_buf()),
+        true,
+    )
+    .expect("open db with undo");
+    let rt = rt();
+    rt.block_on(async {
+        seed_compound(&db).await;
+        db.add_relationship(
+            Some("city_region".to_string()),
+            "Region".to_string(),
+            vec!["country".to_string(), "code".to_string()],
+            "City".to_string(),
+            vec!["country".to_string(), "region_code".to_string()],
+            ReferentialAction::NoAction,
+            ReferentialAction::NoAction,
+            false,
+            // A user-command source records one undo snapshot.
+            Some("add 1:n relationship".to_string()),
+        )
+        .await
+        .expect("add compound relationship");
+        assert_eq!(
+            db.describe_table("City".to_string(), None)
+                .await
+                .unwrap()
+                .outbound_relationships
+                .len(),
+            1,
+        );
+        // One undo step removes the whole relationship (ADR-0013/0006).
+        db.undo().await.unwrap().expect("undo applied");
+        assert!(
+            db.describe_table("City".to_string(), None)
+                .await
+                .unwrap()
+                .outbound_relationships
+                .is_empty(),
+            "undo removed the compound relationship in one step",
+        );
+    });
+}
+
+#[test]
+fn compound_fk_partial_pk_reference_is_refused() {
+    let (_p, db, _dir) = open_project_db();
+    let rt = rt();
+    rt.block_on(async {
+        seed_compound(&db).await;
+        // Referencing only one column of Region's 2-column PK (F-A:
+        // must reference the full PK).
+        let err = db
+            .add_relationship(
+                None,
+                "Region".to_string(),
+                vec!["country".to_string()],
+                "City".to_string(),
+                vec!["country".to_string()],
+                ReferentialAction::NoAction,
+                ReferentialAction::NoAction,
+                false,
+                None,
+            )
+            .await;
+        assert!(err.is_err(), "a partial-PK reference must be refused (F-A)");
+    });
+}

tests/it/main.rs

@@ -9,6 +9,7 @@
 
 mod case_insensitive_names;
 mod column_op_guards;
+mod compound_fk;
 mod engine_vocabulary_audit;
 mod friendly_enrichment;
 mod help_command;

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__add_relationship__after_child_table_dot_narrows_to_child_columns@after_child_dot.snap

@@ -1,5 +1,6 @@
 ---
 source: tests/typing_surface/add_relationship.rs
+assertion_line: 64
 description: "input=\"add 1:n relationship from Customers.id to Orders.\" cursor=49"
 expression: "& a"
 ---
@@ -25,6 +26,11 @@ Assessment {
                     kind: Identifier,
                     mode: Both,
                 },
+                Candidate {
+                    text: "(",
+                    kind: Punct,
+                    mode: Both,
+                },
             ],
             selected: None,
         },
@@ -52,6 +58,11 @@ Assessment {
                     kind: Identifier,
                     mode: Both,
                 },
+                Candidate {
+                    text: "(",
+                    kind: Punct,
+                    mode: Both,
+                },
             ],
         },
     ),

tests/typing_surface/snapshots/typing_surface_matrix__typing_surface__add_relationship__after_parent_table_dot_narrows_to_parent_columns@after_parent_dot.snap

@@ -1,5 +1,6 @@
 ---
 source: tests/typing_surface/add_relationship.rs
+assertion_line: 51
 description: "input=\"add 1:n relationship from Customers.\" cursor=36"
 expression: "& a"
 ---
@@ -20,6 +21,11 @@ Assessment {
                     kind: Identifier,
                     mode: Both,
                 },
+                Candidate {
+                    text: "(",
+                    kind: Punct,
+                    mode: Both,
+                },
             ],
             selected: None,
         },
@@ -42,6 +48,11 @@ Assessment {
                     kind: Identifier,
                     mode: Both,
                 },
+                Candidate {
+                    text: "(",
+                    kind: Punct,
+                    mode: Both,
+                },
             ],
         },
     ),