Full Spectrum Engine v1.2.0 - Observer I/O Envelope

v1.2.0 seals the Observer Input/Output Envelope contract.

Highlights:

• Observer Input/Output Envelope
• required unknowns
• Relationships and Gate contracts
• bounded L4 Candidate compatibility with external_effect=false

Verification: v1.2 black box 9/9, third-party RC baseline 178 passed, and later cumulative regression 246 passed.

Boundary: complete replay remains a v1.4 capability; this release does not authorize external effects.

Evidence: tagged source | Engine Wiki