Expose report run timestamps

[MaxGhenis]

Summary

• Stamp report output runs with requested_at on creation.
• Stamp started_at and finished_at when a report run reaches a terminal status.
• Surface the selected display run timestamps on report output responses.

Root cause

The report_output_runs schema had timestamp columns, but report run creation and synchronization left them null and report responses did not expose selected run timestamps. The frontend therefore had no reliable backend run time to display.

Validation

• FLASK_DEBUG=1 PYTHONPATH=/Users/maxghenis/PolicyEngine/policyengine-api-report-run-timestamps uv run --extra dev pytest tests/unit/services/test_report_output_service.py tests/unit/services/test_report_run_service.py -q
• FLASK_DEBUG=1 uv run --extra dev ruff check policyengine_api/services/report_output_service.py policyengine_api/services/report_run_service.py tests/unit/services/test_report_output_service.py tests/unit/services/test_report_run_service.py
• FLASK_DEBUG=1 uv run --extra dev ruff format --check policyengine_api/services/report_output_service.py policyengine_api/services/report_run_service.py tests/unit/services/test_report_output_service.py tests/unit/services/test_report_run_service.py

Deployment note

• Depends on Stabilize live integration tests #3556 due to intermittent integration test flakiness that is currently preventing a successful API v1 deploy.

[codecov]

Codecov Report

❌ Patch coverage is 84.82759% with 22 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.81%. Comparing base (5f71127) to head (1fd9618).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
policyengine_api/services/report_output_service.py	86.40%	8 Missing and 6 partials ⚠️
policyengine_api/endpoints/household.py	42.85%	4 Missing ⚠️
policyengine_api/routes/report_output_routes.py	33.33%	1 Missing and 1 partial ⚠️
policyengine_api/services/run_sync_utils.py	90.47%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3546      +/-   ##
==========================================
- Coverage   78.94%   77.81%   -1.13%     
==========================================
  Files          65       65              
  Lines        3762     3877     +115     
  Branches      662      697      +35     
==========================================
+ Hits         2970     3017      +47     
- Misses        614      683      +69     
+ Partials      178      177       -1     

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