Pass start_directory to new_session when building a session (#829)

This fixes a bug introduced in 2a4714e76b3a85b3391b05413f36623bcb1493f9
(#809) whereby the `start_directory` session config was no longer passed
to the `new_session` method when building a session. This resulted in
the session working directory is not being set correctly, so new
windows/panes created in the session, would not start in the expected
directory.

src/tmuxp/workspacebuilder.py

@@ -214,7 +214,8 @@ def build(self, session=None, append=False):
                         "start_directory"
                     ]
                 session = self.server.new_session(
-                    session_name=self.sconf["session_name"]
+                    session_name=self.sconf["session_name"],
+                    **new_session_kwargs,
                 )
 
             assert self.sconf["session_name"] == session.name

tests/fixtures/workspacebuilder/start_directory_session_path.yaml

@@ -0,0 +1,6 @@
+---
+session_name: sample_start_dir_session_path
+start_directory: '/usr'
+windows:
+  - panes:
+      -

tests/test_workspacebuilder.py

@@ -514,6 +514,28 @@ def f():
             assert retry_until(f)
 
 
+@pytest.mark.skipif(
+    has_lt_version("3.2a"), reason="needs format introduced in tmux >= 3.2a"
+)
+def test_start_directory_sets_session_path(server):
+    yaml_config = test_utils.read_config_file(
+        "workspacebuilder/start_directory_session_path.yaml"
+    )
+    sconfig = kaptan.Kaptan(handler="yaml")
+    sconfig = sconfig.import_config(yaml_config).get()
+    sconfig = config.expand(sconfig)
+    sconfig = config.trickle(sconfig)
+
+    builder = WorkspaceBuilder(sconf=sconfig, server=server)
+    builder.build()
+
+    session = builder.session
+    expected = "{0}|/usr".format(session.id)
+
+    cmd = server.cmd("list-sessions", "-F", "#{session_id}|#{session_path}")
+    assert expected in cmd.stdout
+
+
 def test_pane_order(session):
     """Pane ordering based on position in config and ``pane_index``.