fix(thinking): improve model lookup and validation

internal/registry/model_registry.go

@@ -132,6 +132,21 @@ func GetGlobalRegistry() *ModelRegistry {
 	return globalRegistry
 }
 
+// LookupModelInfo searches the dynamic registry first, then falls back to static model definitions.
+//
+// This helper exists because some code paths only have a model ID and still need Thinking and
+// max completion token metadata even when the dynamic registry hasn't been populated.
+func LookupModelInfo(modelID string) *ModelInfo {
+	modelID = strings.TrimSpace(modelID)
+	if modelID == "" {
+		return nil
+	}
+	if info := GetGlobalRegistry().GetModelInfo(modelID); info != nil {
+		return info
+	}
+	return LookupStaticModelInfo(modelID)
+}
+
 // SetHook sets an optional hook for observing model registration changes.
 func (r *ModelRegistry) SetHook(hook ModelRegistryHook) {
 	if r == nil {