feat(spark_submit): extra_args kwarg for non-conf spark-submit flags

The function had hardcoded --master / --deploy-mode / --queue /
--executor-memory / --executor-cores / --num-executors plus a
`spark_conf` dict for --conf, with no way to pass other flags like
--jars, --py-files, --files, --driver-memory, --name, etc.

Add `extra_args: dict[str, str] | None = None` that emits `--{key}
{value}` pairs, placed after the --conf loop and before the script
path. Default None preserves the existing cmd shape exactly.

Structured (dict) instead of raw list[str] so LLM agents writing
tool-call payloads can't accidentally pack flag+value into a single
string. Key order in the dict is preserved.

Tests: 4 cases — None default, single pair, multiple pairs in order,
no collision with spark_conf. uv run pytest -> 175 passed.

tests/unit/test_spark_submit.py

@@ -50,6 +50,82 @@ def test_build_command_uses_provided_master_and_deploy_mode():
     assert cmd[-1] == "/tmp/jobs/job_001.py"
 
 
+def test_extra_args_none_default():
+    cmd = build_spark_submit_command(
+        master="yarn",
+        deploy_mode="cluster",
+        script_path="/tmp/jobs/job_001.py",
+        queue="default",
+        executor_memory="4G",
+        executor_cores=2,
+        num_executors=2,
+    )
+    # No extra flags between --conf block and script_path.
+    assert cmd[-1] == "/tmp/jobs/job_001.py"
+
+
+def test_extra_args_single_pair():
+    cmd = build_spark_submit_command(
+        master="yarn",
+        deploy_mode="cluster",
+        script_path="/tmp/jobs/job_001.py",
+        queue="default",
+        executor_memory="4G",
+        executor_cores=2,
+        num_executors=2,
+        extra_args={"jars": "hdfs:///libs/foo.jar"},
+    )
+    script_idx = cmd.index("/tmp/jobs/job_001.py")
+    assert cmd[script_idx - 2 : script_idx] == [
+        "--jars",
+        "hdfs:///libs/foo.jar",
+    ]
+
+
+def test_extra_args_multiple_pairs_preserve_order():
+    cmd = build_spark_submit_command(
+        master="yarn",
+        deploy_mode="cluster",
+        script_path="/tmp/jobs/job_001.py",
+        queue="default",
+        executor_memory="4G",
+        executor_cores=2,
+        num_executors=2,
+        extra_args={
+            "driver-memory": "2G",
+            "name": "my-job",
+            "py-files": "hdfs:///libs/udf.py",
+        },
+    )
+    script_idx = cmd.index("/tmp/jobs/job_001.py")
+    extras = cmd[script_idx - 6 : script_idx]
+    assert extras == [
+        "--driver-memory", "2G",
+        "--name", "my-job",
+        "--py-files", "hdfs:///libs/udf.py",
+    ]
+
+
+def test_extra_args_does_not_collide_with_spark_conf():
+    cmd = build_spark_submit_command(
+        master="yarn",
+        deploy_mode="cluster",
+        script_path="/tmp/jobs/job_001.py",
+        queue="default",
+        executor_memory="4G",
+        executor_cores=2,
+        num_executors=2,
+        spark_conf={"spark.executor.memory": "8G"},
+        extra_args={"driver-memory": "2G"},
+    )
+    script_idx = cmd.index("/tmp/jobs/job_001.py")
+    # --conf entries come before --extra_args entries.
+    assert cmd[script_idx - 4 : script_idx] == [
+        "--conf", "spark.executor.memory=8G",
+        "--driver-memory", "2G",
+    ]
+
+
 def test_build_command_supports_standalone_master():
     cmd = build_spark_submit_command(
         master="spark://master:7077",