Revert "fix: preserve original source lvolID through failback cutover" (#1276)

[wmousa]

Reverts #1276 (789db7899) on R26.3.

Why

#1276 made every namespaced clone fail. sbctl snapshot clone died with:

Failed to add bdev to subsystem at requested nsid=1: nsid occupied and eviction
did not clear it [node 5b3af03f wanted nsid=1 max_namespaces=32
holds=[(1, '18d8dba1-9a11-452f-92c5-7fa6e8376b82')]]

Two hunks in add_lvol_on_node (simplyblock_core/controllers/lvol_controller.py) are responsible:

-        requested_nsid = primary_nsid
+        requested_nsid = primary_nsid or (lvol.ns_id or None)
...
-                if primary_nsid is not None:
+                if requested_nsid is not None:
                     return _fail_after_bdev(... "nsid occupied and eviction did not clear it")

LVol.ns_id has a model default of 1 — a legitimate nsid. snapshot_controller.clone() builds its record by hand and never resets it (the ordinary create path does, add_lvol_ha). Before #1276 only an explicit primary_nsid from a migration/fail-over caller could pin an nsid, so that default was inert. After #1276 the record's default became a request: every clone demanded nsid=1, which in a shared subsystem belongs to the subsystem's first lvol. The widened guard then refused to re-claim another subsystem, turning a recoverable placement into a hard failure.

--namespaced '' was no workaround: both CLI clone handlers pass args.namespaced as the 4th positional of clone(), which is pvc_name, so namespaced kept its default True (fixed separately).

Verification

• ruff check — clean
• mypy simplyblock_web simplyblock_cli simplyblock_core — only the 2 pre-existing tasks_runner_node_add.py annotation errors (that file is not in fix: preserve original source lvolID through failback cutover by swap… #1276, so they predate this revert)
• tests/unit — 1874 passed, 7 skipped, 23 subtests passed
• Revert applied with no conflicts (78 files, 848 insertions, 10559 deletions)

What this re-opens

This is a full revert, so the other fixes #1276 carried go with it. Before merging, please confirm these are acceptable to lose for now, or plan a narrower re-land:

• _evict_stale_namespace returns to indexing subsystem_get(...) (a dict) with [0] — the eviction that silently never ran
• fail-over's existing-copy guard returns to nqn-only matching — namespaced siblings can be silently skipped on a DR fail-over
• namespaced siblings can again scatter across different target primaries
• jc_set_dual_node is removed — a graceful sn shutdown on a 2-node cluster can abort the surviving node
• soak cases 7-9 and their test infrastructure are removed

Follow-up

The clone failure also has a one-line fix that is independent of this revert (snapshot_controller.py is not touched by #1276): reset lvol.ns_id = 0 in clone(), matching add_lvol_ha. Worth landing regardless so the model default can never be requested again.

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