Fix/orders custom fields mapping

[btravisebsco]

Purpose

Orders customFields mappings defined in the JSON mapping file were not being applied to transformed order output. This caused configured custom fields to be silently dropped for both top-level purchase orders and embedded purchase order lines.

Changes Made in this PR

• Added schema injection logic in the orders mapper to dynamically register mapped customFields keys before transformation.
• Supported both mapping paths:
  • top-level order custom fields
  • embedded PO line custom fields
• Kept compatibility with both schema variants for line arrays by using the detected line key.
• Added a regression test that verifies custom field mapping is preserved in output for:
  • order-level custom fields
  • PO line-level custom fields

Code Review Specifics

• Please focus review on:
  • Dynamic schema mutation safety and maintainability
  • Behavior across schema variants for purchase order lines
  • Regression test realism and coverage of expected mapping behavior

Task Checklist

• Ran nox -rs safety
• Ran pre-commit run --all-files
• Tests cover new or modified code
• Ran test suite: nox -rs tests
• Code runs and outputs default usage info: cd src; poetry run python3 -m folio_migration_tools -h
• Documentation updated

Warning Checklist

• New dependencies added
• Includes breaking changes

How to Verify

1. Check out branch fix/orders-custom-fields-mapping.

2. Run targeted regression tests:

   pytest test_orders_mapper.py

3. Confirm the custom fields test passes and validates that mapped custom fields are present in transformed order output for both:

   • customFields.
   • line-array customFields.

Open Questions

• Should customFields support additional non-string types from mapping configuration, or remain string-only as currently implemented?

Learn Anything Cool?

Schema-defined open objects with empty properties can still block mapper traversal if mapping logic depends on explicit schema properties. Dynamically injecting mapped keys into schema is an effective way to preserve strict mapper behavior while enabling custom field extensibility.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

❌ Patch coverage is 80.70175% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.80%. Comparing base (3374380) to head (a6bf445).

Files with missing lines	Patch %	Lines
..._tools/mapping_file_transformation/order_mapper.py	76.59%	6 Missing and 5 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1027      +/-   ##
==========================================
- Coverage   81.80%   81.80%   -0.01%     
==========================================
  Files         117      117              
  Lines       18444    18501      +57     
  Branches     2137     2148      +11     
==========================================
+ Hits        15089    15135      +46     
- Misses       2919     2925       +6     
- Partials      436      441       +5     

Flag	Coverage Δ
unittests	81.80% <80.70%> (-0.01%)	⬇️

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