[Bug]: Ingested `simulation_start_date` shifts to previous day for `env_run` date-only values

[tomvothecoder]

What happened?

When a case archive contains a date-only RUN_STARTDATE in env_run.xml, the ingested simulation_start_date can appear one day earlier after persistence or rendering.

Example:

• env_run.xml contains <entry id="RUN_STARTDATE" value="2019-08-01" />
• the stored or rendered value shows 2019-07-31 17:00:00

The XML parser appears to read the correct date string. The shift likely happens later, when the backend converts the date-only value into a timezone-aware datetime and stores it in a timezone-aware database column. Database or browser-local timezone rendering can then show the previous calendar day.

Steps to reproduce

1. Ingest an archive containing env_run.xml with RUN_TYPE=startup and RUN_STARTDATE=2019-08-01.
2. Inspect the created simulation record in PostgreSQL or in the UI.
3. Observe that simulation_start_date is shown as 2019-07-31 17:00:00, or otherwise resolves to the previous day in a timezone west of UTC.

What did you expect to happen?

simulation_start_date should preserve the calendar date from env_run.xml and remain 2019-08-01 regardless of database session timezone or browser locale.

Environment

• Repository: E3SM-Project/simboard
• Area: backend ingestion, simulation persistence, and date rendering
• Observed from macOS on 2026-05-05
• Most likely reproducible in timezones west of UTC, such as America/Los_Angeles during DST

Relevant code or screenshots

• backend/app/features/ingestion/parsers/case_docs.py reads RUN_STARTDATE directly and returns the raw date string.
• backend/app/features/ingestion/ingest.py::_parse_datetime_field parses date-only strings and assigns UTC to naive datetimes.
• backend/app/features/simulation/models.py stores simulation_start_date as DateTime(timezone=True).
• Frontend date helpers construct new Date(...) and format in local time, which can also surface the previous calendar day.

Anything else?

Likely root cause: a date-only field is being modeled as an absolute timestamp.

Potential fixes:

• Store simulation_start_date and simulation_end_date as date-only values.
• Keep these fields timezone-neutral through API and UI formatting instead of converting them through local time.

A regression test should cover ingesting RUN_STARTDATE=2019-08-01 and asserting that the persisted and displayed calendar date remains 2019-08-01.

[tomvothecoder]

Hey @wlin7, I found a bug in SimBoard where the simulation start date from the env_run.xml file is being converted incorrectly. This should be an easy fix.