test(engine): regression for cross-type id-collision in indexed traversal

A node id is unique only within a type, so a Person and a Company can share an
id string. A variable-length traversal over a cross-type edge (WorksAt) must
structurally stop after one hop. This test builds a graph where 'shared' is both
a Person and a Company id and asserts worksAt{1,2} returns only the one-hop
company. It fails today: the indexed path's single string interner de-interns
the hop-1 Company id back to the colliding Person id and runs a hop-2 scan that
matches that Person's edges, emitting a spurious second-hop company (indexed
["other","shared"] vs csr ["shared"]).

crates/omnigraph/tests/traversal_indexed.rs

@@ -14,6 +14,7 @@ mod helpers;
 use arrow_array::{Array, StringArray};
 
 use omnigraph::db::Omnigraph;
+use omnigraph::loader::{LoadMode, load_jsonl};
 use omnigraph::table_store::{IndexCoverage, TableStore};
 use omnigraph_compiler::ir::ParamMap;
 use serial_test::serial;
@@ -183,3 +184,52 @@ async fn indexed_finds_unindexed_appended_edge() {
         "indexed traversal must see the freshly-appended, unindexed edge"
     );
 }
+
+// Regression: a node `id` is unique only WITHIN a type, so a `Person` and a
+// `Company` can share an id string. A variable-length traversal over a
+// cross-type edge (`worksAt`, Person -> Company) must structurally stop after
+// one hop — a Company is not a `worksAt` source — so `worksAt{1,2}` returns
+// exactly the one-hop companies. Before the structural hop-cap, the indexed
+// path's single string interner de-interned the hop-1 Company id back to the
+// colliding Person id and ran a hop-2 `worksAt src IN (...)` scan that matched
+// that same-string Person's edges, emitting a spurious second-hop company the
+// CSR path never produces. `both_modes` (csr == indexed == auto) plus the
+// golden assert catch both the divergence and an over-emitting shared bug.
+#[tokio::test]
+#[serial]
+async fn cross_type_id_collision_does_not_bleed_into_second_hop() {
+    const SCHEMA: &str = r#"
+node Person { name: String @key }
+node Company { name: String @key }
+edge WorksAt: Person -> Company
+"#;
+    // `shared` is BOTH a Person id and a Company id. alice worksAt the Company
+    // `shared`; the Person `shared` worksAt the Company `other`.
+    const DATA: &str = r#"{"type":"Person","data":{"name":"alice"}}
+{"type":"Person","data":{"name":"shared"}}
+{"type":"Company","data":{"name":"shared"}}
+{"type":"Company","data":{"name":"other"}}
+{"edge":"WorksAt","from":"alice","to":"shared"}
+{"edge":"WorksAt","from":"shared","to":"other"}"#;
+    const QUERY: &str = r#"
+query reach($name: String) {
+    match {
+        $p: Person { name: $name }
+        $p worksAt{1,2} $c
+    }
+    return { $c.name }
+}
+"#;
+    let dir = tempfile::tempdir().unwrap();
+    let uri = dir.path().to_str().unwrap();
+    let mut db = Omnigraph::init(uri, SCHEMA).await.unwrap();
+    load_jsonl(&mut db, DATA, LoadMode::Overwrite).await.unwrap();
+
+    let got = both_modes(&mut db, QUERY, "reach", &params(&[("$name", "alice")])).await;
+    assert_eq!(
+        got,
+        vec!["shared"],
+        "cross-type worksAt{{1,2}} must return only the one-hop company; a hop-2 \
+         result means the id-string collision bled across types"
+    );
+}