During a multi-commit git rebase, the same file (e.g. a Svelte root layout) can appear in conflicts at multiple commit stops. Each resolution carries forward, so if commit A's conflict resolution adds import { beforeNavigate } from '$app/navigation' (from master), and commit B's conflict resolution also adds import { beforeNavigate, goto } from '$app/navigation' (from the feature branch), the final file has a duplicate identifier declaration. Svelte's compiler rejects this with 'Identifier beforeNavigate has already been declared' — but the error only surfaces after the rebase completes, not at any individual conflict resolution step. The same class of bug applies to any language where duplicate imports/declarations are compile errors (TypeScript, Python, Rust).
After completing a multi-commit rebase that touched the same file at multiple stops, run the project's type checker / compiler immediately (before committing fixups or regenerating anything). Grep the conflicted file for duplicate import lines — especially when two conflict blocks in different commits both introduced the same symbol from the same module. The fix is to merge the imports into a single statement combining all needed symbols. In Svelte specifically: svelte-check catches this, but only when run against the full project; individual conflict resolution steps won't flag it because each step only sees its own merge result, not the cumulative effect.