Diagnose dry-run valid-MS discovery reporting zero despite staged FIELD directories

[jakobtfaber]

Parent

Discovered during #16, under parent PRD #15.

What to build

Diagnose why batch_pipeline.py --dry-run reports Found 0 valid MS files for the staged 2026-01-25 hour-22 audit window even though the filesystem contains 11 .ms entries for that hour and each checked path has a FIELD directory. The current warning text says Skipping corrupt MS (no FIELD table), which may be misleading if the failure is actually CASA table access, adapter/runtime configuration, symlink target health, or another validation issue.

Acceptance criteria

• Reproduce the dry-run valid-MS discovery result for 2026-01-25 --start-hour 22 --end-hour 23.
• Capture the actual exception behind the current broad Skipping corrupt MS (no FIELD table) warning.
• Determine whether the staged MSs are corrupt, inaccessible through the configured table adapter, affected by environment/runtime setup, or incorrectly filtered.
• Update diagnostics so operators can distinguish a missing FIELD path from a table-open/runtime failure.
• Add focused test coverage for the discovered failure mode without requiring real telescope data.

Blocked by

None - can start immediately.

[jakobtfaber-2]

Resolved by #23, merged as 2a1e66a.

What changed:

• mosaic_day.find_valid_ms() now distinguishes missing FIELD, FIELD present but not a directory, and FIELD present but unreadable by the CASA table adapter.
• The unreadable case now logs the exception type and message, so the staged dry-run reports the actual RuntimeError: casatools is not installed... adapter/runtime failure instead of the misleading no FIELD table wording.
• Added mocked regression coverage in tests/test_mosaic_day_ms_discovery.py.

Validation:

• PYTHONPATH=/workspace python3 -m pytest tests/test_mosaic_day_ms_discovery.py tests/test_batch_pipeline_dry_run_quarantine.py -q
• ruff check scripts/mosaic_day.py tests/test_mosaic_day_ms_discovery.py
• ruff format --check scripts/mosaic_day.py tests/test_mosaic_day_ms_discovery.py
• Diagnose dry-run valid-MS discovery reporting zero despite staged FIELD directories #22 dry-run command exits 0 and now shows unreadable FIELD table: RuntimeError: casatools is not installed...

Note: GitHub closed this automatically from the merged PR.