TTP EXTENSION · MODEL COMPATIBILITY

Compatibility is evidence, not metadata.

When an artifact's model differs from the current authoritative model, exact identity mismatch should not automatically mean either “reuse” or “discard.” Reuse requires a scoped, identity-bound compatibility proof.

Canonical rule

READ ARTIFACT MODEL M_then
↓
RESOLVE CURRENT MODEL M_now
↓
M_then == M_now ?
  ├─ yes → ordinary applicability checks
  └─ no
       ↓
   RESOLVE COMPATIBILITY PROOF C
       ↓
   VERIFY C BINDS
   from-model + to-model
   + artifact identity
   + rule identity
   + current state/scope
       ↓
   EVALUATE PREDICATE NOW
     ├─ false / unknown → HOLD / RECOMPUTE
     └─ true → eligible for current-owner adoption
↓
FENCED COMMIT
↓
PROVE MODEL HISTORY → COMPATIBILITY → EFFECT

I71–I74

• I71 — Model-version mismatch does not by itself prove incompatibility; compatibility must be proved.
• I72 — Compatibility proof must bind exact model identities, artifact identity, and current state/scope.
• I73 — A global compatibility flag is not equivalence evidence for every artifact.
• I74 — Failed or unknown compatibility proof requires hold, revalidation, or recomputation before consequence.

Verified scoped example

v1: min(limit, 2×price)
v2: min(limit, 2×price + tax_rate)

proof predicate:
tax_rate >= 0
AND
2×price >= limit

inside scope:
v1 == v2 == limit

outside scope:
proof fails closed

A successful compatibility proof is not a statement that two model versions are globally interchangeable. It proves equivalence only for the identities and state assumptions it binds.

VERSION DIFFERENCE IS A QUESTION. COMPATIBILITY PROOF IS THE ANSWER.