id: no-param-reassign
language: TypeScript
message: "Do not reassign function parameters — create a new variable instead"
severity: warning
note: |
  Reassigning parameters makes code harder to debug and reason about.
  It can cause unexpected side effects when the caller's reference changes.
  Create a new variable with a descriptive name instead.
  
  BAD: function update(user) { user = { ...user, active: true }; }
  GOOD: function update(user) { const updated = { ...user, active: true }; }
rule:
  pattern: |
    function $FUNC($PARAM, $$$) {
      $PARAM = $VALUE
    }