fix(datebox): keep optional field valid after backspace clear

[desmondinho]

Description

Closes #301

When a LumexDatebox is bound to a nullable type with Required="false" and Clearable="true", pressing Backspace to clear the field puts it into an error state instead of the expected valid empty state.

The browser's native <input type="date"> is segmented (year/month/day). Backspacing one segment makes the value serialize to "" per the HTML spec, but the input also gains validity.badInput = true with a non-empty validationMessage ("Please enter a valid value."). The component was unconditionally surfacing that native message via LumexInputFieldBase.SetValidationMessageAsync, so the field flipped to invalid even though the bound value parsed cleanly to null.

What's been done?

• In LumexInputFieldBase.SetValidationMessageAsync, skip the native validationMessage probe when the field is non-required and empty — an empty value on an optional field is valid by definition. This also benefits LumexNumbox and LumexTextbox, which share the same base.
• Added a regression test (ShouldStayValidWhenClearedAndNotRequired) that simulates the browser returning a badInput message and asserts the cleared, non-required field stays valid (data-invalid="false") with Value == null.

Checklist

• My code follows the project's coding style and guidelines.
• I have included inline docs for my changes, where applicable.
• I have added, updated or removed tests according to my changes.
• All tests are passing.
• There's an open issue for the PR that I am making.

Summary by CodeRabbit

Bug Fixes

• Non-required input fields now correctly display as valid when cleared, instead of potentially showing validation errors
• Improved validation handling for optional fields to properly recognize empty values as valid state

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 2d2a306b-7121-4b17-9b88-6727c0778134

📥 Commits

Reviewing files that changed from the base of the PR and between a859e5a and 59aad2b.

📒 Files selected for processing (2)

• src/LumexUI/Components/Bases/LumexInputFieldBase.razor.cs
• tests/LumexUI.Tests/Components/Datebox/DateboxTests.razor

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📝 Walkthrough

Walkthrough

This PR addresses the invalid state issue when clearing a non-required LumexDatebox with backspace. The fix adds an early-exit condition in SetValidationMessageAsync that treats empty non-required fields as valid without consulting the browser validation API, and includes a test verifying the corrected behavior.

Changes

Non-Required Empty Field Validation Fix

Layer / File(s)	Summary
Validation Logic src/LumexUI/Components/Bases/LumexInputFieldBase.razor.cs	SetValidationMessageAsync now skips the JS validation call and sets ValidationMessage to null when the field is non-required and empty, avoiding false invalid states.
Test Infrastructure & Verification tests/LumexUI.Tests/Components/Datebox/DateboxTests.razor	JS interop handler for validation messages is stored in a reusable field, and a new test ShouldStayValidWhenClearedAndNotRequired verifies that clearing a non-required LumexDatebox leaves it in a valid state.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐰 A datebox once sad when cleared with care,
Now stays quite content in the empty air.
Not required, so when backspace was pressed,
Validation sleeps—no fuss, just rest!
hop hop 🌱

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main fix: keeping optional datebox fields valid when cleared via backspace, which is the primary change in the PR.
Description check	✅ Passed	The description comprehensively covers the issue, root cause, and all changes made, matching the required template structure with all sections properly filled out.
Linked Issues check	✅ Passed	The code changes directly address issue #301 by modifying SetValidationMessageAsync to skip native validation messages for non-required empty fields and adding the regression test as specified.
Out of Scope Changes check	✅ Passed	All changes are scoped to fixing the reported issue: the base class logic for empty optional fields and the test case validating the fix behavior.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/datebox-invalid-state-on-clear

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.11%. Comparing base (19b89dc) to head (59aad2b).
⚠️ Report is 178 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #307      +/-   ##
==========================================
- Coverage   96.95%   93.11%   -3.85%     
==========================================
  Files          70      166      +96     
  Lines        1542     2756    +1214     
  Branches      150      405     +255     
==========================================
+ Hits         1495     2566    +1071     
- Misses         28       98      +70     
- Partials       19       92      +73     

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