The human grade vetoes every mechanical check

The pair probe initially reported BLOCKED and CONTEXT pairs as chartable: resolution, unit and overlap checks all passed, so it waved through pairs a human had judged incomparable. Now the grade overrides, and a trend requires five overlapping years rather than a shared endpoint.

Kept as a decision because the pull to let the automated check "win" will recur every time someone adds a pair. Units agreeing is necessary and nowhere near sufficient.