[SaladDay]

Windows session scans can fail to publish snapshots or retire cache directories because cc-switch still holds lock-file handles inside the directory being renamed.

Release those child handles while retaining the existing parent scope/root lock through the rename. This keeps active builders and readers protected and preserves atomic pointer publication. The change covers publishing, generation collection, and CLI/query namespace retirement; it does not change session scanning, parsing, or cache formats.

Extend the existing reader-lifetime test to check eventual generation retirement, add query-startup coverage for live versus abandoned namespaces, and run the full paged-manifest suite in the existing Windows CI job.

Validation:

• 38 paged-manifest tests and 8 session-command tests passed locally in isolated directories.
• cargo fmt --check and git diff --check passed.
• cargo clippy --lib --no-default-features completed with existing warnings outside the changed lines.
• Windows CI: all 38 paged-manifest tests passed, along with the default Windows CLI build check.
• Rust CI: Linux library checks, 4,567 library unit tests (2 ignored), 10 binary tests, selected integration tests, and formatting passed.
• A fresh independent blind review found no blocking issues; its isolated library-only manifest run also passed all 38 tests.

Closes #542