implemented '<>' redirects, and the 'seek' builtin

'seek' is a wrapper around the lseek() syscall

added noclobber to core shopts and implemented '>|' redirection syntax

properly implemented fd close syntax

fixed saved fds being leaked into exec'd programs

src/libsh/error.rs

@@ -201,6 +201,7 @@ impl ShErr {
   pub fn is_flow_control(&self) -> bool {
     self.kind.is_flow_control()
   }
+	/// Promotes a shell error from a simple error to an error that blames a span
   pub fn promote(mut self, span: Span) -> Self {
     if self.notes.is_empty() {
       return self;
@@ -208,7 +209,9 @@ impl ShErr {
     let first = self.notes[0].clone();
     if self.notes.len() > 1 {
       self.notes = self.notes[1..].to_vec();
-    }
+    } else {
+			self.notes = vec![];
+		}
 
     self.labeled(span, first)
   }

src/libsh/guards.rs

@@ -147,11 +147,9 @@ impl RawModeGuard {
     let orig = ORIG_TERMIOS
       .with(|cell| cell.borrow().clone())
       .expect("with_cooked_mode called before raw_mode()");
-    tcsetattr(borrow_fd(*TTY_FILENO), termios::SetArg::TCSANOW, &orig)
-      .expect("Failed to restore cooked mode");
+    tcsetattr(borrow_fd(*TTY_FILENO), termios::SetArg::TCSANOW, &orig).ok();
     let res = f();
-    tcsetattr(borrow_fd(*TTY_FILENO), termios::SetArg::TCSANOW, &current)
-      .expect("Failed to restore raw mode");
+    tcsetattr(borrow_fd(*TTY_FILENO), termios::SetArg::TCSANOW, &current).ok();
     res
   }
 }

src/libsh/sys.rs

@@ -2,6 +2,14 @@ use std::sync::LazyLock;
 
 use crate::prelude::*;
 
+/// Minimum fd number for shell-internal file descriptors.
+const MIN_INTERNAL_FD: RawFd = 10;
+
 pub static TTY_FILENO: LazyLock<RawFd> = LazyLock::new(|| {
-  open("/dev/tty", OFlag::O_RDWR, Mode::empty()).expect("Failed to open /dev/tty")
+  let fd = open("/dev/tty", OFlag::O_RDWR, Mode::empty()).expect("Failed to open /dev/tty");
+  // Move the tty fd above the user-accessible range so that
+  // `exec 3>&-` and friends don't collide with shell internals.
+  let high = fcntl(fd, FcntlArg::F_DUPFD_CLOEXEC(MIN_INTERNAL_FD)).expect("Failed to dup /dev/tty high");
+  close(fd).ok();
+  high
 });