fix(ibis): table_exists honors its database= argument (DEBT-9)

src/mountainash_data/backends/ibis/backend.py

@@ -483,8 +483,9 @@ def table(self, name: str, *, database: str | None = None) -> t.Any:
     def table_exists(
         self, name: str, database: str | None = None
     ) -> bool:
-        tables = self.list_tables()
-        return name in tables
+        # ibis exposes no native table_exists; scope the membership check to the
+        # requested namespace by forwarding database= through list_tables (DEBT-9).
+        return name in self.list_tables(namespace=database)
 
     def run_sql(
         self,

tests/test_unit/backends/ibis/test_backend.py

@@ -320,6 +320,45 @@ def test_table_exists_returns_bool():
         assert backend.table_exists("t") is True
 
 
+def test_table_exists_honors_database_namespace():
+    """table_exists(database=...) must scope the check to that namespace (DEBT-9).
+
+    A table living only in a non-default schema must be found via ``database=``
+    and must NOT be found in the default namespace, and vice versa.
+    """
+    with IbisBackend(dialect="duckdb", database=":memory:") as backend:
+        raw = backend.ibis_connection()
+        raw.raw_sql("CREATE SCHEMA tenant_a")
+        raw.raw_sql("CREATE TABLE tenant_a.sleep (id INTEGER)")
+        raw.raw_sql("CREATE TABLE main_only (id INTEGER)")
+
+        # Table exists only in tenant_a.
+        assert backend.table_exists("sleep", database="tenant_a") is True
+        assert backend.table_exists("sleep") is False
+        # Table exists only in the default namespace.
+        assert backend.table_exists("main_only") is True
+        assert backend.table_exists("main_only", database="tenant_a") is False
+
+
+def test_table_exists_forwards_database_to_introspection(monkeypatch):
+    """The ``database`` arg must reach the introspection call, not be dropped.
+
+    Guards the swallowed-error path: ``IbisConnection.list_tables`` returns ``[]``
+    on failure, so a test asserting only a bool return can pass on a version that
+    never forwards ``database``. Assert the forwarding directly.
+    """
+    with IbisBackend(dialect="sqlite", database=":memory:") as backend:
+        seen: dict[str, str | None] = {}
+
+        def fake_list_tables(namespace=None):
+            seen["namespace"] = namespace
+            return ["sleep"]
+
+        monkeypatch.setattr(backend, "list_tables", fake_list_tables)
+        assert backend.table_exists("sleep", database="tenant_a") is True
+        assert seen == {"namespace": "tenant_a"}
+
+
 def test_fluent_chaining():
     """Multiple fluent calls can be chained."""
     with IbisBackend(dialect="sqlite", database=":memory:") as backend: