lo l1b goodtimes and bgrates write out bad cdfs

[tmplummer]

Change Summary

Overview

Fix bug from latest Lo bugfix that caused coordinates to not be in the dataset. I introduced this bug by miscalling assign_coords.
Added check that coordinates are in output datasets.

Closes: #3217

[Copilot]

Pull request overview

Fixes a regression in IMAP-Lo L1B background-rates/goodtimes generation where epoch/esa_step were not being written as coordinates (leading to malformed CDFs and downstream xarray isel(epoch=...) failures in L1C processing).

Changes:

• Correctly add epoch and esa_step to the combined L1B dataset and explicitly mark them as coordinates.
• Adjust esa_step coordinate values to match the expected 1-based ESA step numbering (1..N).
• Add test assertions to ensure required coordinates exist in the L1B bgrates/goodtimes outputs.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
imap_processing/lo/l1b/lo_l1b.py	Fixes coordinate assignment for epoch/esa_step in the L1B bgrates+goodtimes dataset prior to splitting/writing.
imap_processing/tests/lo/test_lo_l1b.py	Adds regression checks ensuring produced datasets include expected coordinates.

Comments suppressed due to low confidence (1)

imap_processing/tests/lo/test_lo_l1b.py:2226

• For a more direct guard against the downstream isel(epoch=...) failure, consider asserting that epoch is a real dimension on the goodtimes dataset (e.g., "epoch" in l1b_goodtimes_ds.dims) in addition to checking for an epoch coordinate.

    # Check that goodtimes dataset is cdf-able by writing to file
    _ = write_cdf(l1b_goodtimes_ds)
    assert "epoch" in l1b_goodtimes_ds.coords

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[laspsandoval]

Looks good. Thanks Tim.