docs(efficacy): rewrite the benchmark README for its operator

docs/SPEC.md

@@ -341,7 +341,7 @@ Current design documents:
   keep the template library in shape so it doesn't dilute the
   agent's attention, with implications for code review, smoke
   tests, structure audit, and 360
-- `efficacy-benchmark.md` — the pre-registered experiment that
+- `efficacy-benchmark.md` — the experiment, its rules fixed in advance, that
   measures whether a generated context file improves an agent's
   output, and the harness a template change is measured with
 - `testing-ai-assets.md` — the generic method the benchmark applies:

docs/design/design-notes.md

@@ -1210,8 +1210,8 @@ work outside accepted scope, not every possible improvement.
 
 ## 16. Outcome evaluation
 
-The concrete, pre-registered form of this section is
-`docs/design/efficacy-benchmark.md`: one application, three arms, paired
+The concrete form of this section is
+`docs/design/efficacy-benchmark.md`: one application, five arms, paired
 trials, a layered judge and a verdict rule fixed before the first run. The
 sketch below is the direction it was derived from.
 

docs/design/testing-ai-assets.md

@@ -309,7 +309,7 @@ checklist above and the calibration rules that keep it honest.
 ## Hand-off - the solid-ai-templates measurement
 
 The concrete application of this method to the template library itself is
-`efficacy-benchmark.md` in this directory, the pre-registered experiment
+`efficacy-benchmark.md` in this directory, the experiment
 that was blocked until this generic method concluded. This document hands
 it the design, and the benchmark supplies the parts this one leaves
 generic.