Validate token items and their parameters before projecting exact declared policy tokens. Keep malformed and non-token values unknown; retain separate grammar for other policy headers.
Validation: real pinned Chrome public CLI baseline/candidate, 101 focused checks and 90 overlapping final checks, 834 upstream item-vector adaptations with two permitted refusals, check:fast and docs:check. Other browser/platform and policy-specific MCP delivery unverified; no performance measurement. Refs #4677.