docs: add case studies for 4 key principles with industry cross-references

Enriched principles #6 (Cheapest Model per Task), #9 (Checkpoint/Resume),
#10 (Diagnose Before Retrying), and #29 (Emergency Stop) with 14 concrete
case studies and 24 industry cross-references including GitHub Copilot,
Knight Capital, Apache Kafka, Tesla Autopilot, and workspace-internal examples.

docs/status.md

@@ -1,5 +1,21 @@
 # Status Log
 
+## 2026-04-11 — Case Studies for Key Principles
+
+### Completed
+- Created `docs/examples/` directory with 4 case study documents
+- **#6 Cheapest Model per Task**: GitHub Copilot tiering, Anthropic model family routing, Colette two-pass pipeline
+- **#9 Checkpoint / Resume**: GitLab 2017 DB loss, Apache Kafka offsets, psyresearch paper ingestion
+- **#10 Diagnose Before Retrying**: Knight Capital $440M loss, AWS S3 2017 outage, microservice retry storms, agent retry loops
+- **#29 Emergency Stop**: Tesla Autopilot disengagement, AWS auto-scaling runaway, OpenAI spending caps, dispatch Not-Aus
+- Each case study includes: real-world scenario, followed vs violated analysis, industry cross-reference table, key insight summary
+- Total: 14 case studies across 4 principles, with 24 industry cross-references
+
+### What's Next
+- Add case studies for remaining high-impact principles (e.g., #2 Vertical Spike, #14 Parallel by Default, #26 PDCA)
+- Cross-link case studies from README.md principle entries
+- Consider blog post or talk format
+
 ## 2026-03-31 — Project Created
 
 ### Completed