remove a link

- remove the link

=> should we allow having a un-linked node ?
before deletion ? or a global linter saying the chain is invalid ? <= it might imply to implement a dedicated feature: validate a chain

No files or tests are named in the issue. Start by tracing where link/edge removal is handled in the editor and where chain integrity is checked in the graph/model layer. Confirm current behavior for unlinked nodes and compare it to expected app logic, then update or add tests around link deletion to lock in that behavior. Issue is done when chain validation policy after deletion is implemented and verified.

Vom Indexierungsmodell aus dem Issue-Text verfasst.