Excedrin

// To deploy: paste into a new project at script.google.com, adjust the RULES, run
// installTrigger() once, and approve the Gmail OAuth prompt.

// ==== Debug ====
// Logs go to the Executions view (left sidebar in the Apps Script editor).
var DEBUG_LOG = false; // note: JS lowercase false, not False

// ==== Rules ====
// header -> value regex -> list of actions.
// Regexes are unanchored (use ^...$ to match the whole value) and