The issue was that handleEditLesson was setting lessonForm.chapters to a direct
reference of lesson.chapters instead of creating a copy. This caused mutations
to the form to also modify the lesson objects in the lessons array state.
When editing lesson 3 with chapters, then switching to edit lesson 2 (which had
no chapters), the form would still show lesson 3's chapters because it was
referencing the same array object.
Fix: Use spread operator [...lesson.chapters] to create a shallow copy of the
chapters array, preventing shared references between form state and lessons state.
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Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
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