fix(backend): preserve nullable loop item foreign keys

[FicoHu]

Summary by CodeRabbit

• Bug Fixes

  • Improved handling of optional delivery fields when saving and updating items on MySQL.
  • Preserved empty parent and due-date values while converting only required completion dates.
  • Applied consistent behavior during both item updates and task status changes.

• Tests

  • Added regression coverage for MySQL date and parent-field handling.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: 14862198-a952-4ceb-bb78-adda12095608

📥 Commits

Reviewing files that changed from the base of the PR and between 6a232fc and e108cb6.

📒 Files selected for processing (3)

• backend/app/models/delivery.py
• backend/app/services/loop_items/service.py
• backend/tests/schemas/test_delivery.py

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📝 Walkthrough

Walkthrough

The change adds cached SQLAlchemy schema inspection for loop_items. MySQL sentinel conversion now targets only non-nullable attributes. Insert, TODO update, and task-start flows use the detected attributes. Tests cover nullable parent_id and due_at.

Changes

MySQL null adaptation

Layer / File(s)	Summary
Schema-aware value adaptation backend/app/models/delivery.py	The delivery model detects and caches non-nullable loop_items attributes. MySQL adaptation and insert handling use this set.
Loop-item service integration backend/app/services/loop_items/service.py, backend/tests/schemas/test_delivery.py	TODO updates and task-start transitions use schema-derived attributes. Tests verify selective sentinel conversion for MySQL values.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Possibly related PRs

• wecode-ai/Wegent#2200: Introduced the MySQL dialect adaptation logic extended by this change.
• wecode-ai/Wegent#2405: Modified related MySQL sentinel conversion in the delivery and loop-item service code.

Suggested reviewers: micro66

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: preserving nullable loop item foreign keys during backend database adaptation.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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