M2: TUI — EngineHandle, ratatui app, markdown renderer, permission modal, session picker, snapshot tests

Builds the ratatui TUI: EngineHandle bridging the async engine to the render loop, chat viewport rendering with a markdown renderer, input handling, a permission modal wired to the real oneshot ask path, and a session picker. Adds TestBackend snapshot tests covering empty session, tool cards (running/completed/error), permission modal, session picker, and message rendering.

crates/harness-tui/src/main.rs

@@ -1,9 +1,19 @@
+mod app;
+mod input;
+mod markdown;
+mod modal;
+mod render;
+mod state;
+mod terminal;
+
+use std::path::PathBuf;
+
 use harness_core::event::RunOutcome;
 
 const DEFAULT_MODEL: &str = "anthropic/claude-sonnet-4-5";
 
 fn print_usage() {
-    eprintln!("usage: harness run -p \"<prompt>\" [-m provider/model]");
+    eprintln!("usage: harness [run -p \"<prompt>\" [-m provider/model]] | [tui]");
 }
 
 fn parse_run_args(args: &[String]) -> Option<(String, Option<String>)> {
@@ -26,7 +36,7 @@ fn parse_run_args(args: &[String]) -> Option<(String, Option<String>)> {
     prompt.map(|p| (p, model))
 }
 
-async fn run(args: &[String]) -> i32 {
+async fn run_headless(args: &[String]) -> i32 {
     let Some((prompt, model_arg)) = parse_run_args(args) else {
         print_usage();
         return 2;
@@ -49,7 +59,7 @@ async fn run(args: &[String]) -> i32 {
     };
 
     let model_ref = model_arg
-        .or_else(|| app.config.model.clone())
+        .or_else(|| app.config().model.clone())
         .unwrap_or_else(|| DEFAULT_MODEL.to_string());
 
     match app.run_prompt(prompt, &model_ref).await {
@@ -73,14 +83,74 @@ async fn run(args: &[String]) -> i32 {
     }
 }
 
+fn log_dir() -> PathBuf {
+    dirs::data_dir()
+        .unwrap_or_else(std::env::temp_dir)
+        .join("ai-harness")
+        .join("log")
+}
+
+fn setup_tracing() -> anyhow::Result<tracing_appender::non_blocking::WorkerGuard> {
+    let log_dir = log_dir();
+    std::fs::create_dir_all(&log_dir)?;
+    let file_appender = tracing_appender::rolling::daily(log_dir, "harness-tui.log");
+    let (non_blocking, guard) = tracing_appender::non_blocking(file_appender);
+    tracing_subscriber::fmt()
+        .with_writer(non_blocking)
+        .with_env_filter(tracing_subscriber::EnvFilter::from_default_env())
+        .init();
+    Ok(guard)
+}
+
+async fn run_tui() -> i32 {
+    let cwd = match std::env::current_dir() {
+        Ok(cwd) => cwd,
+        Err(e) => {
+            eprintln!("error: could not read cwd: {e}");
+            return 1;
+        }
+    };
+
+    let _guard = match setup_tracing() {
+        Ok(guard) => guard,
+        Err(e) => {
+            eprintln!("error: could not initialize logging: {e}");
+            return 1;
+        }
+    };
+
+    let mut app = match crate::app::App::new(cwd).await {
+        Ok(app) => app,
+        Err(e) => {
+            tracing::error!(error = %e, "failed to start TUI");
+            eprintln!("error: {e}");
+            return 1;
+        }
+    };
+
+    if let Err(e) = app.run().await {
+        tracing::error!(error = %e, "TUI error");
+        eprintln!("error: {e}");
+        return 1;
+    }
+    0
+}
+
 #[tokio::main(flavor = "current_thread")]
 async fn main() {
     let args: Vec<String> = std::env::args().skip(1).collect();
-    let exit_code = if args.first().map(String::as_str) == Some("run") {
-        run(&args[1..]).await
-    } else {
-        println!("harness {}", env!("CARGO_PKG_VERSION"));
-        0
+    let exit_code = match args.first().map(String::as_str) {
+        Some("run") => run_headless(&args[1..]).await,
+        Some("tui") | None => run_tui().await,
+        Some("help") | Some("--help") | Some("-h") => {
+            print_usage();
+            0
+        }
+        Some(cmd) => {
+            eprintln!("unknown command: {cmd}");
+            print_usage();
+            2
+        }
     };
     std::process::exit(exit_code);
 }