fix(react-form): use fresh FieldApi in current render on name change

[xianjianlf2]

Closes #2238

Regression from #1893 (v1.27.0). On a name/form change, useField calls setFieldApi(new FieldApi(...)) during render but the current render keeps using the stale fieldApi state. React discards that render, yet the render prop still runs once against the stale FieldApi's store — which derives undefined for an array index that no longer exists after a removal, crashing strict render code.

Fix applies the canonical "adjust-state-during-render + local variable" pattern: build the new instance, use it for the rest of the current render, and still setFieldApi it (keeping the setState identity #1893 introduced for React Compiler safety) — restoring pre-1.27.0 correctness.

• Added a test that keys array items by stable id, removes a non-last item, and asserts the subfield never observes undefined; fails before, passes after.
• pnpm vitest run (react-form) → 126 passed, no type errors.

Summary by CodeRabbit

• Bug Fixes

  • Fixed field state updates when form or field names change during rendering.
  • Prevented array-field values from becoming undefined when removing non-last items.
  • Preserved the correct values and displayed content for remaining array items.

• Tests

  • Added regression coverage for stable, keyed array fields when items are removed.

[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: 9b3f1045-15cb-444c-a4c7-36366e3181dd

📥 Commits

Reviewing files that changed from the base of the PR and between 397ab97 and 09b74ac.

📒 Files selected for processing (2)

• packages/react-form/src/useField.tsx
• packages/react-form/tests/useField.test.tsx

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📝 Walkthrough

Walkthrough

useField now uses a newly created FieldApi immediately when its form or name changes. A regression test verifies that removing the first item from a stably keyed array preserves the shifted field value without transient undefined state.

Changes

FieldApi synchronization

Layer / File(s)	Summary
Synchronous FieldApi replacement and regression coverage packages/react-form/src/useField.tsx, packages/react-form/tests/useField.test.tsx	useField uses the replacement FieldApi during the current render and stores that same instance in state. The test verifies correct values and no undefined observations after removing a non-last keyed array item.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 33.33% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly summarizes the main fix: using a fresh FieldApi during render when the field name changes.
Description check	✅ Passed	The description explains the bug, fix, regression test, and verification results, though it omits the template's checklist and release-impact sections.
Linked Issues check	✅ Passed	The changes address #2238 by using the fresh FieldApi in-render and adding a regression test for uuid-keyed array removal.
Out of Scope Changes check	✅ Passed	The modified files stay focused on the reported useField regression and its test coverage, with no unrelated changes evident.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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