Preserve the section delimiter in namespace enumeration - #115

The added test validates that the context-query API (query_namespace_context_data and the public query_namespace wrapper) finds rows stored under a sectioned namespace like conversation:thread-9f11, closing a double-sanitization regression. It is deterministic (TempDir, fixed content), correctly named, and accurately reflected in the PR description's invariant list; it introduces no new issues.

No findings.