Document seed-controlled Krea2 evals

docs/krea2-prompt-guide.md

@@ -26,6 +26,23 @@ Avoid letting two sections describe incompatible camera or framing intents.
 - Analysis, scoring, and generator notes belong in chat or `sxcp_eval_log`.
 - Keep one experiment variable per cycle when possible.
 - Lock seed, character, location, and camera when testing wording changes.
+- Treat the MCP seed as transport metadata. Preserve it for prompt-only A/B tests
+  and do not write it into the visible prompt text.
+
+## Seed-Controlled A/B Tests
+
+Use one fixed seed when deciding whether prompt wording helped Krea2. A single
+image can justify a prompt-only retry when the mismatch is obvious, but a
+generator rule needs either repeated evidence or a generated prompt that is
+structurally wrong before rendering.
+
+When reviewing an eval payload, log:
+
+- emitted seed,
+- original generated prompt,
+- edited prompt,
+- image failure or improvement,
+- whether the change should stay prompt-only or become a generator patch.
 
 ## Camera And Composition