fix(spltis): resizer breaking split ordering integrity on history navigation

[synoet]

Fix split panels rendering in wrong order on browser back navigation

When two splits are open (e.g. /component/channels + /channel/), closing the left split and then using browser back navigation restores the correct URL but renders the panels on the wrong sides.

Root cause: Resize.Panel passes its index prop to solver.addPanel(panel, index), which uses a falsy guard to check the index:

let index = ndx && ndx < order().length ? ndx : order().length;

When index === 0, 0 is falsy in JS, so the panel is appended at the end instead of inserted at position 0.

Fix: Replace the truthiness check with a null check: ndx != null && ndx < order().length.

[coderabbitai]

Walkthrough

A new test file was introduced for the createResizeSolver function with comprehensive test coverage for the addPanel method. Concurrently, a bug fix was applied to the solver logic that corrects the insertion index validation. The previous condition treated 0 as falsy and skipped it, causing panels to be appended instead of inserted at index zero. The updated condition explicitly checks for null or undefined values, allowing zero to be recognized as a valid insertion position. Tests verify insertion at different indices, appending behavior, and duplicate prevention.

Poem

🐰 A panel at zero—once lost to the void,
Now finds its true place, bugs well destroyed!
Tests dance and verify, index by index,
Insertion flows smoothly—no more need to fix!

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 50.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly addresses the main bug fix: resizer breaking split ordering on history navigation, matching the core change in solver.ts.
Description check	✅ Passed	The pull request description clearly explains the bug (panels rendering in wrong order on browser back navigation), identifies the root cause (falsy check treating 0 as invalid), and describes the fix (null check instead).

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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 synoet/fix-resizer-breaking-split-order

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[github-actions]

Preview: https://synoet-fix-resizer-breaking-sp-ylo018.preview.macro.com/app (1d69c93)

[Nikolay-Pomytkin]

nice