feat(daemon): entrypoint with single-instance lock and lazy socket bind

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/spaceshd/src/launchd.rs

@@ -0,0 +1,4 @@
+use anyhow::Result;
+pub fn install_agent() -> Result<()> {
+    anyhow::bail!("install-agent implemented in Task 16")
+}

crates/spaceshd/src/main.rs

@@ -1,8 +1,35 @@
+mod launchd;
 mod lifecycle;
 mod registry;
 mod server;
 mod surface;
 
-fn main() {
+use anyhow::Result;
-    println!("spaceshd skeleton");
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    let arg = std::env::args().nth(1);
+    match arg.as_deref() {
+        Some("install-agent") => {
+            launchd::install_agent()?;
+            println!("launchd agent installed");
+            Ok(())
+        }
+        Some("--help") | Some("-h") => {
+            println!("spaceshd [install-agent]");
+            Ok(())
+        }
+        _ => run_daemon().await,
+    }
+}
+
+async fn run_daemon() -> Result<()> {
+    let Some(_lock) = lifecycle::acquire_instance_lock()? else {
+        eprintln!("another spaceshd is already running");
+        return Ok(());
+    };
+    lifecycle::clear_stale_socket()?;
+    let sock = lifecycle::socket_path()?;
+    eprintln!("spaceshd listening on {}", sock.display());
+    server::serve(&sock).await
 }