Streaming markdown (#1920)

We wait until we have an entire newline, then format it with markdown and stream in to the UI. This reduces time to first token but is the right thing to do with our current rendering model IMO. Also lets us add word wrapping!

codex-rs/tui/src/lib.rs

@@ -39,6 +39,7 @@ pub mod insert_history;
 pub mod live_wrap;
 mod log_layer;
 mod markdown;
+mod markdown_stream;
 pub mod onboarding;
 mod shimmer;
 mod slash_command;
@@ -55,6 +56,8 @@ use color_eyre::owo_colors::OwoColorize;
 
 pub use cli::Cli;
 
+// (tests access modules directly within the crate)
+
 pub async fn run_main(
     cli: Cli,
     codex_linux_sandbox_exe: Option<PathBuf>,