Background execution with &

[cdprice02]

Detect a trailing & token (unquoted) at the end of a command line.

Behavior:

• Spawn the command without blocking the REPL
• Print the job number and PID: [1] 12345
• The parser should strip & from command arguments before execution

Example:

$ sleep 10 &
[1] 12345
$ echo 'I can run this immediately'
I can run this immediately

Acceptance criteria:

• Parser detects trailing &
• Command spawns in background without blocking
• Job number and PID are displayed
• Quoted & is not treated as background operator