fix: incorrect function call handling with session in non-REPL

[LifetimeMistake]

Hello, this is quite a fascinating project you've got here!
I have this niche use-case where I'm trying to use it on commandline by manually setting the session ID with the -s and --save-session argument, but found that the model's response does not get saved if it used a function call.

I believe this is due to you calling exit_session before processing the tool results here:

aichat/src/main.rs

Lines 201 to 213 in 514a368

	config.write().exit_session()?;
	if need_send_tool_results(&tool_results) {
	start_directive(
	config,
	input.merge_tool_call(output, tool_results),
	code_mode,
	abort_signal,
	)
	.await
	} else {
	Ok(())
	}

Moving the start_directive recursion before the exit_session call seems to fix session handling and the save flag gets applied properly.

I am 99% sure this doesn't break any other functionality, but I'm not very familiar with the codebase -- Please double-check this before considering a merge. Cheers.