V3 deterministic XML validation and formatting capability pack. By-value connector composition (service_kind=cli, no separate ingredient): one local xmllint CLI ingredient exposes readiness, well-formedness validation, captured XML formatting, and ordered two-file XSD/RelaxNG validation operations. Fixed-function and reproducible: file inputs are materialized by the executor, formatted output is written only to an engine-managed output directory, schema validation returns only exit status, and recipes cannot pass arbitrary parser flags, DTD URLs, network fetches, shell wrappers, or caller-controlled output paths. Requires xmllint on PATH (Debian/Ubuntu: apt install libxml2-utils; macOS: xmllint ships with libxml2/system tools). Local and no-egress.