M1: composition root and harness run -p debug command

Adds the harness-app composition root wiring config, providers, tools, and the engine loop together, plus the harness run -p "<prompt>" debug command in harness-tui::main for driving a one-shot prompt end-to-end from the CLI.

crates/harness-tui/src/main.rs

@@ -1,3 +1,86 @@
-fn main() {
-    println!("harness {}", env!("CARGO_PKG_VERSION"));
+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]");
+}
+
+fn parse_run_args(args: &[String]) -> Option<(String, Option<String>)> {
+    let mut prompt = None;
+    let mut model = None;
+    let mut i = 0;
+    while i < args.len() {
+        match args[i].as_str() {
+            "-p" | "--prompt" => {
+                prompt = args.get(i + 1).cloned();
+                i += 2;
+            }
+            "-m" | "--model" => {
+                model = args.get(i + 1).cloned();
+                i += 2;
+            }
+            _ => i += 1,
+        }
+    }
+    prompt.map(|p| (p, model))
+}
+
+async fn run(args: &[String]) -> i32 {
+    let Some((prompt, model_arg)) = parse_run_args(args) else {
+        print_usage();
+        return 2;
+    };
+
+    let cwd = match std::env::current_dir() {
+        Ok(cwd) => cwd,
+        Err(e) => {
+            eprintln!("error: could not read cwd: {e}");
+            return 1;
+        }
+    };
+
+    let app = match harness_app::App::init(cwd) {
+        Ok(app) => app,
+        Err(e) => {
+            eprintln!("error: {e}");
+            return 1;
+        }
+    };
+
+    let model_ref = model_arg
+        .or_else(|| app.config.model.clone())
+        .unwrap_or_else(|| DEFAULT_MODEL.to_string());
+
+    match app.run_prompt(prompt, &model_ref).await {
+        Ok((RunOutcome::Stopped, session_id)) => {
+            let text = app.final_text(&session_id).await.unwrap_or_default();
+            println!("{text}");
+            0
+        }
+        Ok((RunOutcome::Aborted, _)) => {
+            eprintln!("run aborted");
+            1
+        }
+        Ok((RunOutcome::Errored { message }, _)) => {
+            eprintln!("error: {message}");
+            1
+        }
+        Err(e) => {
+            eprintln!("error: {e}");
+            1
+        }
+    }
+}
+
+#[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
+    };
+    std::process::exit(exit_code);
 }