diff --git a/pyproject.toml b/pyproject.toml
index 4249045..cd7bbc9 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -73,6 +73,19 @@ markers = [
 data_file = "/tmp/wherewolf/.coverage"
 timid = true
 
+[tool.ty.rules]
+# pyspark is an optional extra, so ty sees two different worlds. Without the extra
+# installed, `from pyspark.sql import ...` is an unresolved-import; with it, that
+# import resolves but `SparkSession.builder` does not (pyspark declares it as a
+# classproperty ty cannot follow), producing unresolved-attribute instead. The two
+# configurations therefore need opposite `ty: ignore` comments, and whichever set is
+# not needed is reported as an unused directive. CI's lint leg installs
+# `--extra spark`; a plain `uv sync` does not. Silencing unused-directive reports is
+# what lets both suppressions coexist. Do not remove the `ty: ignore` comments in
+# src/wherewolf/execution/spark_engine.py or tests/conftest.py because they look
+# unused locally — they are load-bearing in the other configuration.
+unused-ignore-comment = "ignore"
+
 [dependency-groups]
 dev = [
     "hatch>=1.17.0",
diff --git a/src/wherewolf/execution/spark_engine.py b/src/wherewolf/execution/spark_engine.py
index 8d01a47..e4dcbad 100644
--- a/src/wherewolf/execution/spark_engine.py
+++ b/src/wherewolf/execution/spark_engine.py
@@ -32,7 +32,7 @@ def _get_session(self) -> Any:
             spark_session = import_module("pyspark.sql").SparkSession
             root_session = (
                 # pyspark exposes `builder` dynamically, which ty cannot resolve.
-                spark_session.builder.appName("Wherewolf")
+                spark_session.builder.appName("Wherewolf")  # ty: ignore[unresolved-attribute]
                 .master("local[1]")
                 .config("spark.driver.memory", "512m")
                 .config("spark.ui.enabled", "false")
diff --git a/tests/conftest.py b/tests/conftest.py
index fcb0107..c048dd9 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -29,7 +29,7 @@ def spark_session() -> Iterator[Any]:
         )
 
         session = (
-            SparkSession.builder.appName("wherewolf-tests")
+            SparkSession.builder.appName("wherewolf-tests")  # ty: ignore[unresolved-attribute]
             .master("local[1]")
             .config("spark.driver.memory", "512m")
             .config("spark.ui.enabled", "false")