podman farm can't handle multiple arches in --platform

[Firstyear]

Issue Description

I am using podman on a mac to coordinate a farm build. In this configuration, arm64 platforms can not be used.

podman farm build --local=false --platforms="linux/arm64" -f  Dockerfile -t some:tag

Builder "sle15sp7-builder.firstyear.id.au" ready  <<-- this is a linux/arm64 builder.
...
Farm "testfarm" ready
Error: scheduling builds: no builder capable of building for platform "linux/arm64" available
make: *** [proxy_farm] Error 125

This also affects freebsd/arm64 as well. both freebsd/amd64 and linux/amd64 work correctly and can have builds dispatched.

Steps to reproduce the issue

Steps to reproduce the issue

1. Add a remote arm64/aarch64 builder via podman system connection add ...
2. Create a build farm podman farm create ...
3. Add the builder to said farm podman farm update ....
4. Attempt a build with the farm podman farm build ....

Describe the results you received

Unable to schedule on any arm64 hosts.

Describe the results you expected

Able to schedule on arm64 hosts.

podman info output

# podman -c sle15sp7-builder.firstyear.id.au  version
Client:        Podman Engine
Version:       5.6.2
API Version:   5.6.2
Go Version:    go1.25.1
Built:         Wed Oct  1 00:50:46 2025
Build Origin:  brew
OS/Arch:       darwin/arm64  << remote coordinator

Server:       Podman Engine
Version:      4.9.5
API Version:  4.9.5
Go Version:   go1.25.3
Built:        Wed Nov  5 22:00:00 2025
OS/Arch:      linux/arm64  << remote builder that can't be used.

...

Server:       Podman Engine
Version:      4.9.5
API Version:  4.9.5
Go Version:   go1.25.3
Built:        Wed Nov  5 22:00:00 2025
OS/Arch:      linux/amd64   << remote builder that CAN be used (note the architecture difference).

Podman in a container

No

Privileged Or Rootless

Privileged

Upstream Latest Release

No

Additional environment details

MacOS 15.7.2 with podman 5.6.2 from brew.
Build hosts are SLE-15-SP7 with podman 4.9.5

Additional information

Only affects scheduling to arm64 hosts - amd64 hosts can be built on.

[Firstyear]

Okay, this looks to be related to #27585 - there is not adequate information provided about platform support in error messages here. If there was more info about what platforms each builder supported, I would have seen it was actually linux/amd64/v8 .

So this should be a UX improvement that when a --platform request in a farm build can't be satisfied, the error message should output the supported platforms of each farm node so that the user can determine what mistake that they may have made. Similar the aforementioned bug should still be actioned so people can determine ahead of time what platforms their builders support.