#3621

Summary

Auto-merge of duplicate siblings previously fired unconditionally in the moveThought reducer (drag & drop, indent/outdent, collapse/uncategorize, importText). When a thought was moved into a context that already contained a sibling with the same value, the two were merged and the source thought deleted — causing normal duplicate thoughts to silently disappear (e.g. #3621).

This narrows the merge gate so it only fires within metaprogramming-attribute contexts, where hierarchical merging of attribute subtrees (=children, =style, =pin, …) is required so a context never ends up with two of the same attribute. Normal duplicate siblings now coexist.

Change

Single surgical gate change in src/actions/moveThought.ts:

const isMetaMerge = isAttribute(sourceThought.value) || !!destinationContext?.some(isAttribute)
const duplicateThought =
  !sameContext && !skipMerge && sourceThought.value !== '' && isMetaMerge ? duplicateSubthought() : null

• isAttribute(sourceThought.value) — merges the attribute node itself when moved onto a context that already has it.
• destinationContext.some(isAttribute) — destination is inside a meta subtree; drives the hierarchical recursion (mergeThoughts moves each descendant back through moveThought, staying inside the meta subtree so duplicates merge all the way down).
• Existing guards preserved: sameContext (rerank), skipMerge (swapParent), empty-thought guard (Empty thought in a series of copied thoughts is not pasted on the destination #4448).

The merge machinery (mergeThoughts.ts, action export, swapParent skipMerge, importText collapse trick) is otherwise unchanged.

Tests

• moveThought.ts — converted merge-mechanics tests to meta-attribute versions (preserving merge coverage); added a duplicate normal siblings are not merged block including the Duplicate thought disappears when move onto the same indentation on root or the same parent #3621 regression.
• importText.ts — normal top-level import now produces coexisting duplicates; added a meta-attribute import-merge test.
• swapNote.ts, uncategorize.ts — updated expectations to reflect coexistence.

Notes

• Archive nuance (accepted): =archive is an attribute, so archiving duplicate thoughts still merges (no regression). A stricter "normal thoughts never merge on archive" is a possible follow-up.

Verification

• yarn lint clean, yarn test green (1423 passed).