Build 6021 incident pack

PHP rejected a generated navigation property typed as ?mixed. PHP's mixed already includes null, so the nullable prefix is a parse error.

Receipts

Pipeline review snapshot — the reporting contract and language checks reviewed for the article, with their evidence limits.
Sanitized generation report — schema, language, seed, options and build identity.
Sanitized relationship schema — the foreign-key shapes behind the sampled case.
PHP lint probe — minimal failing and fixed fragments in one executable script.

Replay the compiler boundary

bash replay.sh

Expected result: the script observes PHP rejecting ?mixed, then requires the corrected mixed shape to pass php -l.

Scope: this is a sanitized reconstruction of the incident evidence, not the original build artifact. It makes the recorded identity, schema shape and compiler rule inspectable; it does not regenerate the model.