fix rootless buildkit memory volume path

[areebahmeddd]

summary

closes #3422

• in rootless mode, buildkit stores data in /home/user/.local/share/buildkit instead of /var/lib/buildkit. the buildkit-root-volume-memory option was using the wrong path, so builds still used the filesystem even when ram storage was enabled.

ai model disclosure

used vscode copilot (claude sonnet 4.6) to understand the issue context and help generate a fix. changes were self-reviewed and verified via:

make validate-all
go build ./...

[thompson-shaun]

DCO is missing @areebahmeddd

[Copilot]

Pull request overview

This PR fixes Kubernetes rootless BuildKit deployments so the buildkit-root-volume-memory option correctly applies to the rootless BuildKit data directory (/home/user/.local/share/buildkit) instead of the rootful path (/var/lib/buildkit), ensuring RAM-backed builds work as intended in rootless mode (closes #3422).

Changes:

• Pass BuildKitRootVolumeMemory into the rootless pod template setup and apply it to the rootless EmptyDir volume.
• Avoid creating/mounting the rootful /var/lib/buildkit memory volume when running in rootless mode.
• Add unit tests covering rootless + memory, rootless without memory, and non-rootless + memory behavior.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
driver/kubernetes/manifest/manifest.go	Applies memory-backed EmptyDir configuration to the rootless BuildKit data path and prevents rootful mounts in rootless mode.
driver/kubernetes/manifest/manifest_test.go	Adds tests validating the correct EmptyDir medium/sizeLimit and mount paths for rootless and non-rootless cases.

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[areebahmeddd]

weird. i do use gpg signing automatically while committing but i force pushed my changes with the -s flag @thompson-shaun