### Check existing issues - [x] I've verified that this bug isn't described by any existing issues. ### Bug description In `base: core26` builds, it's very easy to end up in a [UsrMerge](https://wiki.debian.org/UsrMerge) conflict between parts, e.g. if you want to install scripts into `/bin` in the snap. If any part ends up staging `base-files` (which most of them will), that will conflict as seen below, because in one part `/bin` is a symlink, and a folder in another. I can't make the [`{enable,disable}-usrmerge` `build-attribute`s](https://documentation.ubuntu.com/snapcraft/stable/reference/project-file/snapcraft-yaml/#parts.%3Cpart-name%3E.build-attributes) to help, either. The only way around this seems to be sprinkling `organize: { bin: usr/local/bin }` or so, anywhere you want to install an executable into a snap… but that's not pleasant to snapcrafters… Plugins are also affected and need `*-parameters` to redirect the install prefix. ### Steps to reproduce ```sh mkdir -p foo/bin snapcraft --verbose # with the yaml below ``` ### Environment Snapped, Ubuntu 25.10 ``` snapcraft 8.14.4.post81 ``` ### snapcraft.yaml ```yaml name: usrmerge-bug base: core26 build-base: devel version: '0.1' summary: usrmerge bug description: | usrmerge bug grade: devel confinement: devmode parts: whatever: plugin: nil stage-packages: - base-files my-part: plugin: dump source: foo ``` ### Log output ```shell Parts 'whatever' and 'my-part' list the following files, but with different contents or permissions: bin # or, with enable-usrmerge on "my-part": :: + cp --archive --link --no-dereference . /root/parts/my-part/install :: cp: cannot overwrite non-directory '/root/parts/my-part/install/./bin' with directory './bin' ```