docs: add optional RAG failure taxonomy to troubleshooting

docs/TROUBLESHOOTING.md

@@ -210,6 +210,41 @@ When many concurrent requests hit a rate-limited provider, OmniRoute uses mutex
 
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+## Optional RAG / LLM failure taxonomy (16 problems)
+
+Some OmniRoute users place the gateway in front of RAG or agent stacks. In those setups it is common to see a strange pattern: OmniRoute looks healthy (providers up, routing profiles ok, no rate limit alerts) but the final answer is still wrong.
+
+In practice these incidents usually come from the downstream RAG pipeline, not from the gateway itself.
+
+If you want a shared vocabulary to describe those failures you can use the WFGY ProblemMap, an external MIT license text resource that defines sixteen recurring RAG / LLM failure patterns. At a high level it covers:
+
+- retrieval drift and broken context boundaries  
+- empty or stale indexes and vector stores  
+- embedding versus semantic mismatch  
+- prompt assembly and context window issues  
+- logic collapse and overconfident answers  
+- long chain and agent coordination failures  
+- multi agent memory and role drift  
+- deployment and bootstrap ordering problems
+
+The idea is simple:
+
+1. When you investigate a bad response, capture:
+   - user task and request
+   - route or provider combo in OmniRoute
+   - any RAG context used downstream (retrieved documents, tool calls, etc)
+2. Map the incident to one or two WFGY ProblemMap numbers (`No.1` … `No.16`).
+3. Store the number in your own dashboard, runbook, or incident tracker next to the OmniRoute logs.
+4. Use the corresponding WFGY page to decide whether you need to change your RAG stack, retriever, or routing strategy.
+
+Full text and concrete recipes live here (MIT license, text only):
+
+[WFGY ProblemMap README](https://github.com/onestardao/WFGY/blob/main/ProblemMap/README.md)
+
+You can ignore this section if you do not run RAG or agent pipelines behind OmniRoute.
+
+---
+
 ## Still Stuck?
 
 - **GitHub Issues**: [github.com/diegosouzapw/OmniRoute/issues](https://github.com/diegosouzapw/OmniRoute/issues)