TINY-4531: Long dropdown menu items will no longer misplace the entry.

[HAFRMO]

Related Ticket: TINY-4531

Description of Changes:
If we change the size of a dropdown component, re-place it on the screen to prevent an issue where very wide content would match it to window size and place it on the far left before the resizing could take affect

Pre-checks:

• Changelog entry added
• Tests have been added (if applicable)
• Branch prefixed with feature/, hotfix/ or spike/

Review:

• Milestone set
• Docs ticket created (if applicable)

GitHub issues (if applicable):

Summary by CodeRabbit

• Bug Fixes
  • Fixed dropdown menus with matchWidth enabled appearing misaligned when containing long content.

[coderabbitai]

Walkthrough

This pull request fixes a positioning bug in dropdown menus with matchWidth: true that could appear offset to the left. It adds a menu repositioning call to the dropdown opening handler and includes a browser test validating the corrected behavior.

Changes

Cohort / File(s)	Summary
Changelog Entry .changes/unreleased/alloy-TINY-4531-2026-02-20.yaml	Documents fix for dropdown menus with matchWidth appearing left of parent element when content is long.
Dropdown Positioning Fix modules/alloy/src/main/ts/ephox/alloy/dropdown/DropdownUtils.ts	Adds call to TieredMenu.repositionMenus(menu) in the onOpen handler to reposition menus when dropdown opens.
Browser Test modules/alloy/src/test/ts/browser/ui/dropdown/DropdownListMatchWidthTest.ts	New end-to-end test validating dropdown menu width behavior with matchWidth enabled, verifying menu positioning with fixed layout and correct left offset.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely summarizes the main fix: preventing long dropdown menu items from misplacing the entry, which aligns with the primary change of repositioning menus on dropdown open.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@modules/alloy/src/test/ts/browser/ui/dropdown/DropdownListMatchWidthTest.ts`:
- Line 95: The test description string in the it(...) call inside
DropdownListMatchWidthTest (the test named starting "TINY-4531: The dropdown
menu should be placed properly on the left side of the") is truncated; update
the description to a complete sentence such as "TINY-4531: The dropdown menu
should be placed properly on the left side of the dropdown trigger" (or another
accurate target like "input") so the test name clearly states its expectation;
edit the it(...) description in DropdownListMatchWidthTest.ts accordingly.