Transitive dependencies unexpectedly renamed

[KhanMechAI]

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• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pixi, using pixi --version.

Reproducible example

Hey team, got one more for you
We’re trying to make our ROS node packages a bit more self-describing.
Each node depends on a private conda package, , from our http://prefix.dev/ channel. That package isn’t a rosdep key, so the idea was to declare it in package.xml and use extra-package-mappings to map it to the conda package directly, instead of having the backend turn it into ros-humble-....
This works fine when the package that carries the mapping is a direct dependency. But once it comes in transitively. In our case, the deploy/prod env depends on a leaf launch package, and that exec_depends the node packages, the mapping seems to disappear. The backend falls back to ros-humble-, and the solve fails because there are no candidates.
So in prod, the node packages are only ever resolved transitively, which is exactly the path where the mapping drops out.
I’ve put together a minimal repro, attached here. It only uses public packages, so no creds needed. pixi lock reproduces it. If I swap the root dep to the mapped member directly, it passes, which seems to point pretty clearly at the transitive resolution path dropping the mapping. README has the details.
pixi-ros-mapping-repro.zip

Issue description

No response

Expected behavior

Transitively resolved dependencies with extra-package-mappings are correctly resolved.

[ruben-arts]

First of we would love to fix this. Let me explain why this is a little complex as of right now.

• The backends are packages specific, so is it's configuration, as of right now.
• If we introduce a new default e.g. without the ros-<distro>- prefix it will create issues when you fork existing ros packages e.g. ros-humble-navigation2

As of today the only two ways are specifically defining in a pixi.toml or a map.

• Add this in the pixi.toml of the transitive dependencies:

  [package]
  name = "demo_pkg"
  version = "0.1.0"

• Add a package map to the main package that depends on these packages:

  my_robot_msgs:
  conda: [my-robot-msgs]

  Then add this to the pixi.toml

  [package.build.config]
  extra-package-mappings = [{ path = "my_package_map.yaml" }]

---

If those options are not sufficient for your workflow we might want to try to build a custom version of the pixi-build-ros backend where we change this behavior to see if we can make it more comfortable for your workflow. Where the packages are only prefixed with ros-distro when they are not available on the ros-index. And see if that works better.