fix(builder[here]): Use respawn-pane and set_environment instead of send_keys

Replace send_keys("export ...") and send_keys(window_shell) with tmux
primitives in --here mode:

- Environment: session.set_environment() + respawn-pane -e (inherited
  by new panes, no POSIX shell assumption)
- Shell replacement: respawn-pane -k (kills current process, starts
  fresh shell — no typing into foreground programs)
- Directory: respawn-pane -c (tmux primitive, no send_keys cd)

This eliminates all send_keys usage for infrastructure setup in --here
mode, matching teamocil's approach of using tmux primitives over
send_keys.  Fixes the fish/nu shell incompatibility and the "types
into vim" failure mode.

Closes #1031

Author: tony

src/tmuxp/workspace/builder.py

@@ -692,39 +692,44 @@ def iter_create_windows(
                 if panes and "start_directory" in panes[0]:
                     start_directory = panes[0]["start_directory"]
 
-                if start_directory:
-                    active_pane = window.active_pane
-                    if active_pane is not None:
-                        active_pane.send_keys(
-                            f"cd {shlex.quote(start_directory)}",
-                            enter=True,
-                        )
-
-                # Provision environment — no window.set_environment in tmux,
-                # so export into the active pane's shell
+                # Provision environment via tmux session env (inherited
+                # by new panes).  Matches teamocil, which does not inject
+                # env vars via send_keys at all.
                 environment = window_config.get("environment")
                 if panes and "environment" in panes[0]:
                     environment = panes[0]["environment"]
                 if environment:
-                    _here_pane = window.active_pane
-                    if _here_pane is not None:
-                        for _ekey, _eval in environment.items():
-                            _here_pane.send_keys(
-                                f"export {_ekey}={shlex.quote(str(_eval))}",
-                                enter=True,
-                            )
+                    for _ekey, _eval in environment.items():
+                        session.set_environment(_ekey, str(_eval))
 
-                # Provision window_shell — send to active pane
+                # Resolve window_shell
                 window_shell = window_config.get("window_shell")
                 try:
                     if panes[0]["shell"] != "":
                         window_shell = panes[0]["shell"]
                 except (KeyError, IndexError):
                     pass
-                if window_shell:
+
+                # Use respawn-pane to provision the reused pane with the
+                # correct directory, environment, and shell.  This avoids
+                # send_keys entirely — no POSIX shell assumption, no
+                # typing into foreground programs, no history pollution.
+                # Matches teamocil's approach of using tmux primitives
+                # over send_keys for infrastructure setup.
+                if start_directory or environment or window_shell:
                     _here_pane = window.active_pane
                     if _here_pane is not None:
-                        _here_pane.send_keys(window_shell, enter=True)
+                        _respawn_args: list[str] = ["respawn-pane", "-k"]
+                        if start_directory:
+                            _respawn_args.extend(["-c", start_directory])
+                        if environment:
+                            for _ekey, _eval in environment.items():
+                                _respawn_args.extend(
+                                    ["-e", f"{_ekey}={_eval}"],
+                                )
+                        if window_shell:
+                            _respawn_args.append(window_shell)
+                        _here_pane.cmd(*_respawn_args)
             else:
                 is_first_window_pass = self.first_window_pass(
                     window_iterator,

tests/workspace/test_builder.py

@@ -605,7 +605,7 @@ def test_here_mode_duplicate_session_name(
 def test_here_mode_provisions_environment(
     session: Session,
 ) -> None:
-    """--here mode exports environment variables into the active pane."""
+    """--here mode sets environment via session and respawn-pane, not send_keys."""
     from libtmux.test.retry import retry_until
 
     workspace: dict[str, t.Any] = {
@@ -625,6 +625,11 @@ def test_here_mode_provisions_environment(
     builder = WorkspaceBuilder(session_config=workspace, server=session.server)
     builder.build(session=session, here=True)
 
+    # Verify env var is set at session level (tmux primitive)
+    env = session.show_environment()
+    assert env.get("TMUXP_HERE_TEST") == "hello_here"
+
+    # Verify the respawned pane also sees the var
     pane = session.active_window.active_pane
     assert pane is not None