fix: `generate quadlet` units are not project-prefixed (collision across projects)

[Jaro-c]

generate quadlet writes service-named units, not project-prefixed ones.

For a project sweep with a web service:

$ podup generate quadlet -o ./quad
wrote ./quad/web.container        # not sweep-web.container

[Container]
ContainerName=web                 # not sweep-web
Label=podup.project=sweep

Why this is a problem

• Collision across projects. Any two compose projects that both have a web service export web.container / ContainerName=web — installing both into ~/.config/containers/systemd clobbers one another.
• Inconsistent with the running stack. podup up names the container sweep-web; the Quadlet export names it web. The same compose file produces two different container identities depending on how you run it.

Fix

Prefix the unit filename and ContainerName= with the project (e.g. sweep-web.container / ContainerName=sweep-web), matching up's naming. (Worth a look from the quadlet-analyst on the exact convention.)

Found by running podup 1.3.0 against real Podman 5.4.2.

[Jaro-c]

Splitting this:

• ContainerName (the runtime collision — two projects both creating a container called web, and divergence from up's project-web) is fixed in fix(quadlet): default ContainerName to project-service #605: the default is now {project}-{service}.
• Unit filenames (web.container/default.network/data.volume → project-prefixed) remain. That one needs a coordinated rename across container/network/volume units plus an audit of every cross-unit reference (After=/Requires=/Network=/Volume=), and Quadlet-resolution verification, so it gets its own PR. Keeping this issue open for that part.

[Jaro-c]

Decision: keeping the unit-filename prefix as a low-priority follow-up, not doing it now.

• The runtime collision (two projects both creating a container named web, and divergence from up) is already fixed by fix(quadlet): default ContainerName to project-service #605 (ContainerName=project-service).
• Podman/podup is primarily rootless per-user: each user's units live in their own ~/.config/containers/systemd/, so two projects under different users never collide on web.container/default.network. The filename collision only bites the non-default cases — one user exporting several projects into the same dir, or the rootful shared /etc/containers/systemd/.
• The change itself is small but forces rewriting ~40 quadlet tests (mixed project names, cross-unit After=/Network=/Volume= refs) with real risk of emitting a quadlet that doesn't resolve — hard to fully verify without installed systemd units.

So: high cost + risk, low marginal value under the normal per-user model. Revisit if a multi-project-single-user or rootful workflow becomes a real use case.

[Jaro-c]

Re-elevating to P1 after a 3-layer confirmation (multi-agent audit → source re-read → upstream docs). I earlier under-rated this on a per-user-isolation argument; that was wrong.

The collision is real for the normal single-user case: Quadlet's standard directory ~/.config/containers/systemd/ is shared across a user's projects, and generate.rs:60-61 does fs::write(dir.join(filename), …) with no overwrite guard. Two projects each with a web service both emit web.container → the second silently clobbers the first. Same for network.rs:70/volume.rs:48 (data.volume, default.network).

Reinforced by the Podman 5 docs: Quadlet derives the unit/service name from the file name (web.container → web.service, default container systemd-web). ContainerName= (fixed in #605) overrides only the container name — it does not fix the file/service-name collision. So two projects also collide at the systemd web.service level, not just on disk.

Scope of the fix (the reason it was deferred): prefix every unit filename and every cross-unit reference (After=/Requires=/Network=/Volume=) with the project via a shared project_unit_stem(project, name), and update ~40 quadlet tests. Worth it — verify the generated units with podman-system-generator --dryrun.