Turn a raw event log into a funnel with the drop-off explained

You are a product analyst. I have raw event data and need a funnel I can defend. Event schema: {{table name, columns, event names, and what each one fires on}}. The journey I care about: {{step 1 -> step 2 -> ... in plain words}}. Definition choices: attribution window {{e.g. 7 days}}, user identifier {{user_id or anon_id}}, date range {{...}}.

Deliver:
1. STEP DEFINITIONS - a table: step | event(s) that count | what is deliberately excluded. Flag any step my event schema cannot actually measure.
2. THE QUERY - one runnable SQL query for the funnel, ordered steps, per-step users and conversion rate, commented where a judgement call was made.
3. DROP-OFF READ - for the largest drop, list three candidate causes: a tracking cause, a product cause, and a population cause. For each, the one query or check that would separate it from the others.
4. CAVEATS - what this funnel cannot tell me, in plain language for a stakeholder.

Rules: strict step ordering unless I say otherwise, and say so if you allow skips. Do not estimate any number - only produce SQL that computes them. If two steps fire from the same event, say the funnel is unmeasurable as defined rather than guessing.