feat: Add robust cross-platform port availability check

- Introduce `port_check_available` function
- Use platform-specific tools (`lsof`, `ss`, `netstat`)
- Fallback to socket binding for port checks
- Integrate port check before running `ttyd`
- Simplify `tmux kill-session` error handling

lib/osal/core/port_check.v

@@ -0,0 +1,123 @@
+module core
+
+import os
+import net
+
+// Check if a port is available (free) on the local machine
+// Returns an error if the port is already in use
+pub fn port_check_available(port int) ! {
+	$if macos {
+		// On macOS, try lsof first, then fallback to netstat, then socket binding
+		if check_port_with_lsof(port)! {
+			return
+		}
+		// If lsof failed, try netstat as fallback
+		if check_port_with_netstat(port)! {
+			return
+		}
+		// If both failed, use socket binding as final fallback
+		check_port_with_socket_binding(port)!
+	} $else $if linux {
+		// On Linux, try ss first, then netstat, then socket binding
+		if check_port_with_ss(port)! {
+			return
+		}
+		// If ss failed, try netstat as fallback
+		if check_port_with_netstat(port)! {
+			return
+		}
+		// If both failed, use socket binding as final fallback
+		check_port_with_socket_binding(port)!
+	} $else {
+		// For other platforms, use socket binding directly
+		check_port_with_socket_binding(port)!
+	}
+	// If we reach here, the port is available
+}
+
+// Check port availability using lsof (macOS/Linux)
+fn check_port_with_lsof(port int) !bool {
+	// First check if lsof is available
+	lsof_check := os.execute('which lsof')
+	if lsof_check.exit_code != 0 {
+		return false // lsof not available, caller should try another method
+	}
+
+	result := os.execute('lsof -i :${port}')
+	if result.exit_code == 0 {
+		// Port is in use, extract process info from lsof output
+		lines := result.output.split('\n')
+		if lines.len > 1 {
+			// Parse the first process line to get basic info
+			fields := lines[1].split_any(' \t').filter(it.len > 0)
+			if fields.len >= 2 {
+				process_name := fields[0]
+				pid := fields[1]
+				return error('Port ${port} is already in use by process "${process_name}" (PID: ${pid})')
+			}
+		}
+		return error('Port ${port} is already in use')
+	}
+	return true // Port is available
+}
+
+// Check port availability using ss (Linux)
+fn check_port_with_ss(port int) !bool {
+	// First check if ss is available
+	ss_check := os.execute('which ss')
+	if ss_check.exit_code != 0 {
+		return false // ss not available, caller should try another method
+	}
+
+	result := os.execute('ss -tulpn | grep ":${port} "')
+	if result.exit_code == 0 {
+		// Port is in use, extract process info from ss output
+		lines := result.output.split('\n')
+		if lines.len > 0 && lines[0].len > 0 {
+			// ss output format: proto recv-q send-q local_address:port peer_address:port process
+			fields := lines[0].split_any(' \t').filter(it.len > 0)
+			if fields.len >= 6 {
+				protocol := fields[0]
+				local_addr := fields[4]
+				process_info := fields[6] // Usually contains "users:(("process",pid,fd))"
+				return error('Port ${port} is already in use by ${protocol} service at ${local_addr} (${process_info})')
+			}
+		}
+		return error('Port ${port} is already in use')
+	}
+	return true // Port is available
+}
+
+// Check port availability using netstat (cross-platform fallback)
+fn check_port_with_netstat(port int) !bool {
+	// First check if netstat is available
+	netstat_check := os.execute('which netstat')
+	if netstat_check.exit_code != 0 {
+		return false // netstat not available, caller should try another method
+	}
+
+	// Use netstat to check for listening ports
+	mut result := os.Result{}
+	$if windows {
+		result = os.execute('netstat -an | findstr ":${port} "')
+	} $else {
+		result = os.execute('netstat -tuln | grep ":${port} "')
+	}
+
+	if result.exit_code == 0 {
+		// Port is in use
+		return error('Port ${port} is already in use (detected by netstat)')
+	}
+	return true // Port is available
+}
+
+// Check port availability by attempting to bind to it (most reliable fallback)
+fn check_port_with_socket_binding(port int) ! {
+	// Try to create a TCP listener on the port
+	mut listener := net.listen_tcp(.ip, ':${port}') or {
+		return error('Port ${port} is already in use')
+	}
+	// If we successfully bound to the port, close it immediately
+	listener.close() or {}
+	// Port is available
+}

lib/osal/tmux/tmux_session.v

@@ -305,9 +305,7 @@ pub fn (mut s Session) stop() ! {
 	s.kill_all_processes()!
 
 	// Then kill the tmux session itself
-	osal.execute_silent('tmux kill-session -t ${s.name}') or {
-		return error("Can't delete session ${s.name} - This may happen when session is not found: ${err}")
-	}
+	osal.execute_silent('tmux kill-session -t ${s.name}') or { return }
 }
 
 // Kill all processes in all windows and panes of this session
@@ -328,6 +326,11 @@ pub fn (mut s Session) kill_all_processes() ! {
 
 // Run ttyd for this session so it can be accessed in the browser
 pub fn (mut s Session) run_ttyd(args TtydArgs) ! {
+	// Check if the port is available before starting ttyd
+	osal.port_check_available(args.port) or {
+		return error('Cannot start ttyd for session ${s.name}: ${err}')
+	}
+
 	target := '${s.name}'
 
 	// Add -W flag for write access if editable mode is enabled

lib/osal/tmux/tmux_window.v

@@ -349,6 +349,11 @@ pub mut:
 
 // Run ttyd for this window so it can be accessed in the browser
 pub fn (mut w Window) run_ttyd(args TtydArgs) ! {
+	// Check if the port is available before starting ttyd
+	osal.port_check_available(args.port) or {
+		return error('Cannot start ttyd for window ${w.name}: ${err}')
+	}
+
 	target := '${w.session.name}:@${w.id}'
 
 	// Add -W flag for write access if editable mode is enabled