snapshot: fix delete race producing stuck open_ref / empty clone entries

[schmidt-scaled]

Summary

Three independent fixes that together close the "Cannot remove snapshot because it is open" / EBUSY (-16) state where the snapshot ends up with non-zero open_ref but no clone entries and can only be cleared by restarting the host node (incident: aws_dual_soak 2026-04-30, 14 stuck snapshots).

Fixes

1. Random VUID dedupe & range bump (simplyblock_core/utils/__init__.py)

   • get_random_vuid range goes from 10k → 1M.
   • Both get_random_vuid and get_random_snapshot_vuid dedupe against numeric suffixes parsed out of existing CLN_/LVOL_/SNAP_ bdev names cluster-wide.
   • With ~10k lvols+snaps the legacy 10k range hit ~50% birthday-collision probability, which is what triggered the SPDK lvol with name ... already exists rejection, the mgmt async-delete, and the reuse-during-deletion sequence.

2. Reject snapshot/clone ops on pending-deletion targets (snapshot_controller.add / snapshot_controller.clone)

   • add rejects when source lvol is STATUS_IN_DELETION.
   • clone rejects when source snapshot has deleted=True or STATUS_IN_DELETION.
   • Closes the window between an async delete being issued and a fresh create slipping through against the same blob.

3. Snapshot delete waits for clone SPDK delete (snapshot_controller.delete)

   • A clone counts as "gone" only once its deletion_status field has been set (i.e. leader's delete_lvol_from_node returned). An IN_DELETION clone with no deletion_status is still SPDK-blocking and the snapshot is soft-deleted instead.
   • The clone's own delete-completion path re-triggers the hard delete once SPDK has actually released the bdev.

Test plan

• tests/test_snapshot_delete_race.py — 10 unit tests covering all three fixes (random vuid dedupe, add/clone rejection, delete waits for in-flight clone)
• full tests/ suite green (running)
• soak verification against AWS cluster after merge

🤖 Generated with Claude Code

[Hamdy-khader]

This function can be written like this:

def _used_bdev_name_numbers(db_controller):
    used = set()
    for lvol in db_controller.get_lvols():
        used.add(lvol.vuid)

    for snap in db_controller.get_snapshots():
        used.add(snap.vuid)
    return used