fix: principle #27 — add grain of salt, clarify scope (prototyping vs production)

README.md

@@ -283,16 +283,16 @@ Plan-Do-Check-Act after every sprint, not just at the end. Check catches bugs be
 
 **Origin:** Sprint 1-3 each had a PDCA cycle that caught rate limiting issues, SSE race conditions, and Caddy routing gaps.
 
-### 27. Test in Production, Not in Mocks
+### 27. Test in Production (for fast prototyping)
 
-For single-user tools: test against the real deployment. Mocks hide integration bugs.
+For single-user tools in rapid prototyping: test against the real deployment. Mocks hide integration bugs. **Grain of salt:** This applies to MVPs and personal tools. For multi-user, shared, or safety-critical systems, use proper staging environments and test suites.
 
-- `curl` against the live API after each deploy
-- Try the PWA on your actual phone
-- Submit real jobs through the real worker
-- Read the real debug logs
+- Fast prototyping: `curl` against live API, try PWA on real phone, submit real jobs
+- Production-grade: staging environment, automated test suite, canary deploys
+- The principle is about speed of feedback, not skipping quality gates
+- Know when you've graduated from prototype to product — then add proper testing
 
-**Origin:** "Committe regelmäßig und test in production — keine mocks!"
+**Origin:** "Committe regelmäßig und test in production — keine mocks!" (during rapid MVP sprint)
 
 ### 28. Changelog as First-Class Artifact