fix(ci): run on a label only the Crafter.Build runner carries

Master's last two runs (#368 and #370) failed in the Build step with

    The state dir (/root/.cache/flatpak-builder) is not on the same
    filesystem as the target dir (/workspace/Catcrafts/Crafter.Build)

while #369, the 2.2.0 tag run on the same commit with the same
flatpak-builder, passed. The difference was the runner. Since 14 October
the Hetzner box has a second privileged runner, cx33-org-flatpak, which
serves every Catcrafts repository under the label `flatpak` so their
package jobs can run crafter-build as a Flatpak. It mounts no host
volumes, deliberately, since any repository in the organisation can send
it jobs. Whenever it was idle first it took this job too, logged our four
volumes as "not a valid volume, will be ignored", and left the
flatpak-builder state on the container's overlay while the workspace sat
on a Docker volume. Even past that check it would have had no build
cache, no web root and no signing key.

The org runner's label is right for the jobs it was made for, and giving
it our volumes would hand the signing key to every repository in the
organisation. So the job asks for a label only its own runner carries:
`crafter-flatpak`, after the volumes and key directory that runner alone
allows. The runner on the host is relabelled to match
(/etc/forgejo-runner/config-flatpak.yaml, previous copy kept as
config-flatpak.yaml.bak-2026-10-31-label), so until this reaches master
a push there with the old `runs-on: flatpak` goes only to the org runner
and fails the same way.

AGENTS.md now says the label must stay unique and quotes the error a job
on the wrong runner stops with, so the next collision is found from the
log.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.forgejo/workflows/ci.yaml

@@ -6,11 +6,14 @@ name: Flatpak
 #                    Catcrafts repo and refresh the rolling `latest` release
 #   tag X.Y.Z     -> publish as `stable` and create release X.Y.Z
 #
-# The `flatpak` runner label is the privileged runner on the Hetzner box
-# (bubblewrap needs it) with four volumes allowed: the Sdk install, the
+# The `crafter-flatpak` runner label is the privileged runner on the Hetzner
+# box (bubblewrap needs it) with four volumes allowed: the Sdk install, the
 # flatpak-builder state (ccache and the LLVM module, so only crafter-build
 # itself rebuilds on a normal run), the published repo's web root, and the
 # repo signing key, which lives on the runner host and never in the forge.
+# No other runner carries that label. Plain `flatpak` also matches the
+# organisation's runner, which mounts none of those volumes; a job it picks
+# up fails before building anything.
 on:
   pull_request:
     branches: [master]
@@ -32,7 +35,7 @@ env:
 
 jobs:
   flatpak:
-    runs-on: flatpak
+    runs-on: crafter-flatpak
     container:
       image: archlinux:latest
       options: >-

AGENTS.md

@@ -152,7 +152,9 @@ These were decided deliberately. Do not undo them without the maintainer's say-s
 
 ## CI and publishing
 
-`.forgejo/workflows/ci.yaml` runs on the `flatpak` runner label: a dedicated privileged forgejo-runner on the Hetzner box (`forgejo-runner-flatpak.service`, config `/etc/forgejo-runner/config-flatpak.yaml`), registered to this repository only. It is privileged because bubblewrap inside the job container needs it, and separate from the other runners so that privilege is not shared with any other repository. Its config allows four volumes, which the workflow mounts: `crafter-flatpak-system` (the Sdk install at `/var/lib/flatpak`), `crafter-flatpak-builder` (flatpak-builder state and ccache, so the LLVM and WASI modules are rebuilt only when their sources change; a cold run takes about 80 minutes on 8 cores, a warm one a fraction of that), `/var/www/flatpak`, the web root Caddy serves as `https://flatpak.catcrafts.net/`, and `/etc/crafter-flatpak`, which holds the repo signing key (`signing-key.asc`, no passphrase, and `key-id`), generated once on the host and mounted read-only into the job; nothing is stored in the forge. The live repo at `/var/www/flatpak/repo` is canonical; builds are promoted into it with `flatpak build-commit-from`, never built into it.
+`.forgejo/workflows/ci.yaml` runs on the `crafter-flatpak` runner label: a dedicated privileged forgejo-runner on the Hetzner box (`forgejo-runner-flatpak.service`, config `/etc/forgejo-runner/config-flatpak.yaml`), registered to this repository only and the only runner with that label. It is privileged because bubblewrap inside the job container needs it, and separate from the other runners so that privilege is not shared with any other repository. Its config allows four volumes, which the workflow mounts: `crafter-flatpak-system` (the Sdk install at `/var/lib/flatpak`), `crafter-flatpak-builder` (flatpak-builder state and ccache, so the LLVM and WASI modules are rebuilt only when their sources change; a cold run takes about 80 minutes on 8 cores, a warm one a fraction of that), `/var/www/flatpak`, the web root Caddy serves as `https://flatpak.catcrafts.net/`, and `/etc/crafter-flatpak`, which holds the repo signing key (`signing-key.asc`, no passphrase, and `key-id`), generated once on the host and mounted read-only into the job; nothing is stored in the forge. The live repo at `/var/www/flatpak/repo` is canonical; builds are promoted into it with `flatpak build-commit-from`, never built into it.
+
+Keep the label unique to that runner. Plain `flatpak` also belongs to the organisation-wide runner (`forgejo-runner-org-flatpak.service`), which serves every Catcrafts repository and on purpose allows no volumes. Whenever this job lands there, flatpak-builder stops with `The state dir (/root/.cache/flatpak-builder) is not on the same filesystem as the target dir`; the top of the job log shows which runner took it and lists every volume it ignored.
 
 The key is made once, as root on the runner host, and the step fails with a message pointing here when it is missing: