Add getpid, exec_bg, spawn_thread, sleep_secs builtins; fix fs_write arity

bin/el/src/main.rs

@@ -2411,6 +2411,61 @@ fn dispatch_builtin(
             BuiltinResult::Handled
         }
 
+        // ── Process / thread builtins ─────────────────────────────────────────
+
+        "getpid" => {
+            stack.push(Value::Int(std::process::id() as i64));
+            BuiltinResult::Handled
+        }
+
+        "exec_bg" => {
+            let cmd_str = match stack.pop().unwrap_or(Value::Nil) {
+                Value::Str(s) => s,
+                _ => { stack.push(Value::Int(-1)); return BuiltinResult::Handled; }
+            };
+            let mut parts = cmd_str.split_whitespace();
+            let prog = match parts.next() {
+                Some(p) => p.to_string(),
+                None => { stack.push(Value::Int(-1)); return BuiltinResult::Handled; }
+            };
+            let args_vec: Vec<String> = parts.map(|s| s.to_string()).collect();
+            let pid = std::process::Command::new(&prog)
+                .args(&args_vec)
+                .spawn()
+                .map(|child| child.id() as i64)
+                .unwrap_or(-1);
+            stack.push(Value::Int(pid));
+            BuiltinResult::Handled
+        }
+
+        "spawn_thread" => {
+            let fn_name = match stack.pop().unwrap_or(Value::Nil) {
+                Value::Str(s) => s,
+                _ => { stack.push(Value::Nil); return BuiltinResult::Handled; }
+            };
+            let instr_arc = SERVE_INSTRUCTIONS.with(|si| si.borrow().clone());
+            let fn_arc = SERVE_FN_TABLE.with(|sf| sf.borrow().clone());
+            if let (Some(instr_arc), Some(fn_arc)) = (instr_arc, fn_arc) {
+                std::thread::spawn(move || {
+                    if let Some(&entry) = fn_arc.get(&fn_name) {
+                        run_sub_interpreter(&instr_arc, &fn_arc, entry);
+                    }
+                });
+            }
+            stack.push(Value::Nil);
+            BuiltinResult::Handled
+        }
+
+        "sleep_secs" => {
+            let n = match stack.pop().unwrap_or(Value::Nil) {
+                Value::Int(n) => n as u64,
+                _ => 1,
+            };
+            std::thread::sleep(std::time::Duration::from_secs(n));
+            stack.push(Value::Nil);
+            BuiltinResult::Handled
+        }
+
         // ── String utility builtins ───────────────────────────────────────────
 
         "str_replace" => {

crates/el-types/src/types.rs

@@ -192,9 +192,13 @@ impl TypeEnv {
         for name in &["fs_read"] {
             env.functions.insert(name.to_string(), str_fn(vec![s.clone()], s.clone()));
         }
-        for name in &["fs_write","fs_append","fs_exists","fs_mkdir","fs_remove","fs_is_dir"] {
+        for name in &["fs_exists","fs_mkdir","fs_remove","fs_is_dir"] {
             env.functions.insert(name.to_string(), str_fn(vec![u.clone()], b.clone()));
         }
+        // fs_write and fs_append take (path, content) — two arguments
+        for name in &["fs_write","fs_append"] {
+            env.functions.insert(name.to_string(), str_fn(vec![s.clone(), s.clone()], b.clone()));
+        }
         env.functions.insert("fs_list".into(), str_fn(vec![s.clone()], Type::Unknown));
         env.functions.insert("fs_list_recursive".into(), str_fn(vec![s.clone()], Type::Unknown));
         env.functions.insert("path_join".into(), str_fn(vec![s.clone(), s.clone()], s.clone()));
@@ -234,8 +238,12 @@ impl TypeEnv {
         env.functions.insert("args".into(), str_fn(vec![], Type::Unknown));
         env.functions.insert("exit".into(), str_fn(vec![i.clone()], Type::Void));
         env.functions.insert("sleep_ms".into(), str_fn(vec![i.clone()], Type::Void));
+        env.functions.insert("sleep_secs".into(), str_fn(vec![i.clone()], Type::Void));
         env.functions.insert("timestamp".into(), str_fn(vec![], s.clone()));
         env.functions.insert("readline".into(), str_fn(vec![s.clone()], s.clone()));
+        env.functions.insert("getpid".into(), str_fn(vec![], i.clone()));
+        env.functions.insert("exec_bg".into(), str_fn(vec![s.clone()], i.clone()));
+        env.functions.insert("spawn_thread".into(), str_fn(vec![s.clone()], Type::Void));
 
         // ANSI color builtins
         for name in &["color_cyan","color_green","color_red","color_yellow","color_bold","color_dim"] {