Dedupe MicroMasters certificates in tfact_certificate and fix email-case user resolution #2381

Expected Behavior

A MicroMasters certificate earned on edX.org produces exactly one row in tfact_certificate, and MicroMasters users resolve to a user_fk regardless of email case.

Current Behavior

tfact_certificate unions int__edxorg__mitx_courserun_certificates (lines 45-61) and int__micromasters__course_certificates (lines 63-79). MicroMasters certs are earned on edX.org and both rows resolve courserun_fk to the same edxorg run (lines 247-252). The surrogate keys differ (user_id-based vs email-based), so the defensive dedup cannot catch the double-count.

Additionally, lines 241-243 join raw MicroMasters user_email against dim_user.email, which is lower()-ed — so mixed-case MM emails silently fail user_fk resolution (and the warn-severity test hides it).

Possible Solution

• Dedupe on (user, courserun) across sources with a documented precedence (or drop one source).
• lower() the fact-side email before joining.

Additional Details

dim_program has the same micromasters-vs-edxorg duality — check it alongside this fix.

P1. Part of #2375 (2026-07 dbt warehouse audit). Witan task: tk-dedupe-micromasters-certificates-in-tfact-certif-21659d.