[DEFERRED] Exhaustive cache-invalidity and hostile-input matrix

[krisoshea-eth]

Status

Tracking shell only. This is not current core work and must not be started without explicit maintainer promotion and bounded rescoping.

Why it remains useful

The essential fail-closed tests do not exhaust every malformed cache state or hostile API input.

Activation trigger

• Core cache and reveal semantics are stable.
• QA-01 and SEC-01 identify concrete residual risks.
• Maintainers prioritize deeper hardening.
• A scoped Conditional package with owner, reviewer, evidence, and stop rule is approved.

Boundary

Core covers the named essential invalidity, mismatch, expiry, duplicate, rejection, and resource cases; this shell tracks broader hardening only.

[linear-code]

LOD-44