Motivation

Avoid allocating a fully backed 4 GiB temporary file for every tracked task on Windows.

Background

The parity backend deliberately retains the previous file-backed resource model. Marking that file sparse allows the logical mapping to remain 4 GiB while physical allocation follows the small prefix actually used by fspy records.

Changes

• Creates the owner backing file as temporary and delete-on-close.
• Calls FSCTL_SET_SPARSE before extending the file.
• Falls back to ordinary sizing for filesystems that explicitly report sparse files as unsupported.
• Continues to propagate access-denied, invalid-parameter, and other unexpected sparse setup errors.
• Opens sender views directly through the decoded named mapping without reopening or recomputing the backing path.
• Orders owner fields so the view, mapping handle, and backing file close safely.
• Adds logical-versus-allocated-size, endpoint allocation, sparse fallback, hard-error, direct-open, changed-environment, and cleanup coverage.
• Adds the Windows performance changelog entry.