feat: Add ExtraBody/ExtraFields support for custom OpenAI-compatible API parameters

- Modified getProviderOptions() to accept extraBody parameter
- Map provider config extra_body to Fantasy's extra_fields
- Updated all call sites in coordinator.go and agent_tool.go
- Enables Z.AI GLM thinking mode and other custom parameters

This works with the Fantasy fork that has ExtraFields support.

Author: Jesssullivan

internal/agent/coordinator.go

@@ -142,6 +142,7 @@ func getProviderOptions(model Model, providerCfg config.ProviderConfig) fantasy.
 	cfgOpts := []byte("{}")
 	providerCfgOpts := []byte("{}")
 	catwalkOpts := []byte("{}")
+	extraBodyOpts := []byte("{}")
 
 	if model.ModelCfg.ProviderOptions != nil {
 		data, err := json.Marshal(model.ModelCfg.ProviderOptions)
@@ -164,9 +165,24 @@ func getProviderOptions(model Model, providerCfg config.ProviderConfig) fantasy.
 		}
 	}
 
+	// Merge extra_body from provider config (for Z.AI GLM thinking mode, etc.)
+	// Map it to extra_fields which Fantasy's ExtraFields expects
+	if providerCfg.ExtraBody != nil && len(providerCfg.ExtraBody) > 0 {
+		extraBodyData := map[string]any{
+			"extra_fields": providerCfg.ExtraBody,
+		}
+		data, err := json.Marshal(extraBodyData)
+		if err == nil {
+			extraBodyOpts = data
+		} else {
+			slog.Warn("Failed to marshal extra_body from provider config", "error", err)
+		}
+	}
+
 	readers := []io.Reader{
 		bytes.NewReader(catwalkOpts),
 		bytes.NewReader(providerCfgOpts),
+		bytes.NewReader(extraBodyOpts),
 		bytes.NewReader(cfgOpts),
 	}