Feature Request: New restore-side notification between mount tree restoration and `pivot_root`

[captainmo1]

Problem

There is currently no CRIU notification hook that satisfies both of the following constraints simultaneously:

1. The container mount tree is fully restored (mounts are at their final paths, not staged under /tmp/.criu.mntns.*/mnt-*)
2. pivot_root has not yet been called

This gap makes it impossible to implement correct prestart/createRuntime OCI hook integration under CRIU restore

existing notifications

None of the existing notifications satisfy both constraints:

Notification	Pre-pivot_root?	Mount tree at final paths?	Notes
setup-namespaces	✅	❌	Mount tree not yet restored at all
post-setup-namespaces	✅	❌	Under mount-v2 engine, mounts are still staged under /tmp/.criu.mntns.*/mnt-*
post-restore	❌	✅	pivot_root has already happened

Proposed Solution

Expose a new restore-side notification, e.g. post-mounts or pre-pivot fired after the mount tree is fully restored to its final paths but before the pivot_root call.

Context

This was surfaced while implementing CRIU checkpoint/restore support in a runc issue

[github-actions]

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