The flag was an opt-in escape hatch for the cross-tenant leak the rest
of the patch closes — flipping it on (env var or constructor param)
re-enables exactly the VERIA-54 primitive on either backend. There is
no operational need that the secure path doesn't already meet:
- Qdrant: legacy points without ``litellm_cache_key`` payload are
excluded by the must-clause filter and treated as misses; new sets
populate the cache key, so cold-start lasts only as long as the
natural cache rebuild.
- Redis: existing unscoped index can't carry the new schema; the init
path falls back to ``{name}_isolated`` (and recreates it on stale
schema), leaving the legacy index untouched.
Drop the constructor param, env-var fallback, ``_using_legacy_unscoped_index``
flag, the legacy-reuse branch in ``_init_semantic_cache``, and the
matching guards in set/get paths. Update tests to drop the legacy-mode
cases and assert the secure-only behaviour.
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