add non-functional validation

refactors

.agents/invariants/PERFORMANCE_OPTIMIZATION_INVARIANT.md

@@ -29,8 +29,13 @@ Compiler representations may share analysis, planning, or code-generation
 work only when the emitted execution retains the same independent work,
 schedule semantics, scheduling granularity, and available parallelism.
 
-An optimization is acceptable only when its static runtime proxies are equal or
-better.
+Static runtime proxies are useful for screening changes, but they are not the
+latency authority. When comparable validation results are available for the
+same model, inputs, hardware configuration, and non-functional simulation
+configuration, the `Latency` reported by `validation/validate.py` is
+authoritative. An optimization is acceptable only when its static runtime
+proxies are equal or better, unless such a matched validation comparison
+demonstrates equal or better latency.
 
 ## Asymptotic cost
 
@@ -64,6 +69,7 @@ Do not:
 
 Every performance change must report before and after:
 
+- matched validation `Latency` when the changed execution can be simulated;
 - compiler wall time;
 - compiler peak RSS;
 - IR operation and value counts at the changed stage;
@@ -82,4 +88,5 @@ Every performance change must report before and after:
 ## Stop rule
 
 If compile time or memory improves but a runtime proxy worsens, stop and reject
-the change.
+the change unless a matched validation comparison demonstrates equal or better
+`Latency`. Proxy improvements do not override a validation latency regression.