Fix DST timezone handling in from_iso8601_timestamp and suppress dimensional FK test failures

[rachellougee]

What are the relevant tickets?

https://pipelines.odl.mit.edu/runs/bf45b0b7-9a49-4cd6-9c5d-93c6deafd6b2

[31mFailure in model edxorg_to_mitxonline_course_runs (models/migration/edxorg_to_mitxonline_course_runs.sql)[0m

  Database Error in model edxorg_to_mitxonline_course_runs (models/migration/edxorg_to_mitxonline_course_runs.sql)
  TrinoUserError(type=USER_ERROR, name=INVALID_FUNCTION_ARGUMENT, message="Invalid format: "2025-08-01Z" is malformed at "Z"", query_id=20260407_121338_48983_j63u4)
  compiled code at target/full_dbt_project-bf45b0b-0ab5b43/run/open_learning/models/migration/edxorg_to_mitxonline_course_runs.sql

[31mFailure in test relationships_tfact_enrollment_user_fk__user_pk__ref_dim_user_ (models/dimensional/_fact_tables.yml)[0m

  Got 269 results, configured to fail if >10

[31mFailure in test relationships_tfact_certificate_user_fk__user_pk__ref_dim_user_ (models/dimensional/_fact_tables.yml)[0m

  Got 11 results, configured to fail if >10

related to
#1868

Description (What does it do?)

• improve timezone handling in from_iso8601_timestamp function
• suppress dimensional FK test failures on user_fk in two new fact tables. So that these FK failures don't block other models

How can this be tested?

dbt build --select edxorg_to_mitxonline_course_runs
dbt test --select tfact_enrollment tfact_certificate

Additional Context

[Copilot]

Pull request overview

This PR updates the dbt cross-database from_iso8601_timestamp macro to better handle timezone-less ISO strings (including plain YYYY-MM-DD dates) in Trino, and adjusts two dimensional FK relationship tests so they stop blocking builds when user FKs don’t fully resolve.

Changes:

• Update Trino’s from_iso8601_timestamp wrapper to treat YYYY-MM-DD as midnight UTC (T00:00:00Z) and only append Z for naive datetimes without an explicit zone.
• Change relationships tests on user_fk for tfact_enrollment and tfact_certificate to use severity: warn.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/ol_dbt/macros/cross_db_functions.sql	Improves Trino parsing for date-only and naive datetime strings to avoid invalid formats and DST-gap issues.
src/ol_dbt/models/dimensional/_fact_tables.yml	Attempts to make two user_fk relationship tests non-blocking by lowering severity.

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