STOP, HELP, and consent

• Techs opt themselves in. The invite asks; only a YES and a completed signup turns texting on. Owners cannot opt a tech in on their behalf.
• STOP means stop. Reply STOP (or UNSUBSCRIBE, QUIT, CANCEL, END) and Holler confirms once, then goes silent instantly, everywhere. START re-opts in. HELP answers with what Holler is and how to reach support.
• First texts carry no links. Holler introduces itself and asks; the signup link only comes after a tech replies YES.
• Every message is logged. Inbound and outbound, with an idempotency ledger that makes duplicate sends structurally impossible.