docs: clarify compat flags for openai-compatible local servers closes #2177

packages/coding-agent/docs/models.md

@@ -35,6 +35,32 @@ For local models (Ollama, LM Studio, vLLM), only `id` is required per model:
 
 The `apiKey` is required but Ollama ignores it, so any value works.
 
+Some OpenAI-compatible servers do not understand the `developer` role used for reasoning-capable models. For those providers, set `compat.supportsDeveloperRole` to `false` so pi sends the system prompt as a `system` message instead. If the server also does not support `reasoning_effort`, set `compat.supportsReasoningEffort` to `false` too.
+
+You can set `compat` at the provider level to apply to all models, or at the model level to override a specific model. This commonly applies to Ollama, vLLM, SGLang, and similar OpenAI-compatible servers.
+
+```json
+{
+  "providers": {
+    "ollama": {
+      "baseUrl": "http://localhost:11434/v1",
+      "api": "openai-completions",
+      "apiKey": "ollama",
+      "compat": {
+        "supportsDeveloperRole": false,
+        "supportsReasoningEffort": false
+      },
+      "models": [
+        {
+          "id": "gpt-oss:20b",
+          "reasoning": true
+        }
+      ]
+    }
+  }
+}
+```
+
 ## Full Example
 
 Override defaults when you need specific values: