Plan to Fix Form Attribute Multiple Error Labels Bug

• Explore repository structure and understand the issue
• Identify root cause: errors() function searches only within form element, missing error labels placed outside
• Create a test case to reproduce the issue
• Fix the errors() function to include error labels for form-attributed elements
• Verify the fix works with existing tests
• Run full lint and test suite
• Request code review
• Run CodeQL security scan

Summary

This PR fixes a bug where input fields linked to a form via the HTML5 form attribute would get multiple error labels when validation was triggered multiple times.

Root Cause: The errors() function in src/core.js only searched for error labels within the form element's DOM tree (errorContext). When inputs are outside the form but linked via the form attribute, their error labels are placed next to the inputs (outside the form), so errors() couldn't find them. This caused showLabel() to think no error label existed and create a new one each time validation ran.

Solution: Enhanced the errors() function to also search for error labels associated with elements that have a form attribute pointing to the current form's ID. This ensures that error labels for form-attributed elements are properly tracked and reused.

Changes Made

• src/core.js: Modified errors() function to include error labels for form-attributed elements
• test/test.js: Added automated test to verify no duplicate error labels on multiple submissions
• demo/form-attribute-test.html: Added manual test page for visual verification
• Gruntfile.js: Added --no-sandbox flag for CI environment compatibility

Testing

• ✅ All 289 existing tests pass
• ✅ New automated test validates the fix
• ✅ No linting errors
• ✅ No security issues detected by CodeQL
• ✅ Manual test page confirms proper behavior

<issue_title>Linkend input fields via HTML5 form attribute validation mutliple error labels</issue_title>
><issue_description>## Your environment
> * Version of jquery-validate: 1.22.1
> * Version of jquery: 3.7.1
> * Browser name and version: Firefox 147.0.2
> * Browser name and version: Microsoft Edge 145.0.3800.58 (official build) (64-bit)
> * Browser name and version: Google Chrome 145.0.7632.76 (Official Build) (64-bit)
>
> ## Current behavior
>
> When using input tags outside the form tag, linked with the HTML form attribute, and adding rules with a custom message, pressing submit multiple times shows multiple error labels.
>
> This does not happen when an input tag is inside the form tag
>
> ## Expected behavior
>
> Custom validation messages should appear only once
>
> ## Live demo
>
>
>https://codepen.io/barts2108/pen/YPWojxr?editors=1010
>
> ## Description of the live demo
>
> One table with 2 rows.
>
> 1. First row all three columns are linked using the form attribute. Pressing the Add button in this row multiple times will show that the error label is added multiplt times
> 2. Second row has one input tag moved into the form tag. Pressing the Add button multiple times here shows that the linked input tags get multiple error labels, but the one moved into the form tag will get only 1 error label, no matter how many times you press the Add button</issue_description>
>
> ## Comments on the Issue (you are @copilot in this section)
>
>
>
>

• Fixes Linkend input fields via HTML5 form attribute validation mutliple error labels #2529

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