.gitea/workflows/build-kernel.yml

@@ -56,8 +56,10 @@ jobs:
           # is then a shared mutable name and the builds race — whichever `docker
           # build` finishes last wins the tag, so both `docker create` calls
           # resolve to the same image and every job emits the same vermagic.
-          # A unique tag per kernel version isolates them.
-          img="iec-kbuild:${KERNEL_VERSION//[:\/]/-}"
+          # A unique tag per kernel version isolates them. Docker tags allow only
+          # [a-zA-Z0-9._-], so map ':' '/' '+' (all present in 1:6.12.93-1+rpt1)
+          # to '-'; the tag just needs to be unique and valid, not reversible.
+          img="iec-kbuild:${KERNEL_VERSION//[:\/+]/-}"
           # Builder image: toolchain + matching raspberrypi kernel headers.
           docker build --platform linux/arm64 \
             --build-arg DEBIAN_SUITE="$DEBIAN_SUITE" \