fix: Parse maas models for gcp vertex provider (#5816)

crates/goose/src/providers/formats/gcpvertexai.rs

@@ -68,6 +68,9 @@ pub enum GcpVertexAIModel {
     Claude(ClaudeVersion),
     /// Gemini model family with specific versions
     Gemini(GeminiVersion),
+    /// MaaS (Model as a Service) models from Model Garden
+    /// Contains (publisher, full_model_name)
+    MaaS(String, String),
 }
 
 /// Represents available versions of the Claude model for goose.
@@ -126,6 +129,7 @@ impl fmt::Display for GcpVertexAIModel {
                 GeminiVersion::Pro25 => "gemini-2.5-pro",
                 GeminiVersion::Generic(name) => name,
             },
+            Self::MaaS(_, model_name) => model_name,
         };
         write!(f, "{model_id}")
     }
@@ -137,10 +141,12 @@ impl GcpVertexAIModel {
     /// Each model family has a well-known location based on availability:
     /// - Claude models default to Ohio (us-east5)
     /// - Gemini models default to Iowa (us-central1)
+    /// - MaaS models default to Iowa (us-central1)
     pub fn known_location(&self) -> GcpLocation {
         match self {
             Self::Claude(_) => GcpLocation::Ohio,
             Self::Gemini(_) => GcpLocation::Iowa,
+            Self::MaaS(_, _) => GcpLocation::Iowa,
         }
     }
 }
@@ -162,6 +168,15 @@ impl TryFrom<&str> for GcpVertexAIModel {
             "gemini-2.5-pro-preview-05-06" => Ok(Self::Gemini(GeminiVersion::Pro25Preview)),
             "gemini-2.5-flash" => Ok(Self::Gemini(GeminiVersion::Flash25)),
             "gemini-2.5-pro" => Ok(Self::Gemini(GeminiVersion::Pro25)),
+            // MaaS models (Model as a Service from Model Garden)
+            _ if s.ends_with("-maas") => {
+                let publisher = s
+                    .split('-')
+                    .next()
+                    .ok_or_else(|| ModelError::UnsupportedModel(s.to_string()))?
+                    .to_string();
+                Ok(Self::MaaS(publisher, s.to_string()))
+            }
             // Generic models based on prefix matching
             _ if s.starts_with("claude-") => {
                 Ok(Self::Claude(ClaudeVersion::Generic(s.to_string())))
@@ -202,28 +217,32 @@ impl RequestContext {
 
     /// Returns the provider associated with the model.
     pub fn provider(&self) -> ModelProvider {
-        match self.model {
+        match &self.model {
             GcpVertexAIModel::Claude(_) => ModelProvider::Anthropic,
             GcpVertexAIModel::Gemini(_) => ModelProvider::Google,
+            GcpVertexAIModel::MaaS(publisher, _) => ModelProvider::MaaS(publisher.clone()),
         }
     }
 }
 
 /// Represents available model providers.
-#[derive(Debug, Clone, PartialEq, Eq, Copy)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub enum ModelProvider {
     /// Anthropic provider (Claude models)
     Anthropic,
     /// Google provider (Gemini models)
     Google,
+    /// MaaS provider (Model as a Service from Model Garden)
+    MaaS(String),
 }
 
 impl ModelProvider {
     /// Returns the string representation of the provider.
-    pub fn as_str(&self) -> &'static str {
+    pub fn as_str(&self) -> String {
         match self {
-            Self::Anthropic => "anthropic",
-            Self::Google => "google",
+            Self::Anthropic => "anthropic".to_string(),
+            Self::Google => "google".to_string(),
+            Self::MaaS(publisher) => publisher.clone(),
         }
     }
 }
@@ -305,6 +324,12 @@ pub fn create_request(
         GcpVertexAIModel::Gemini(_) => {
             create_google_request(model_config, system, messages, tools)?
         }
+        GcpVertexAIModel::MaaS(_, _) => {
+            // TODO: Branch on publisher for format selection once we know which
+            // MaaS providers use which formats (e.g., OpenAI vs Google format)
+            // For now, default to Google format since most use generateContent endpoint
+            create_google_request(model_config, system, messages, tools)?
+        }
     };
 
     Ok((request, context))
@@ -322,6 +347,7 @@ pub fn response_to_message(response: Value, request_context: RequestContext) ->
     match request_context.provider() {
         ModelProvider::Anthropic => anthropic::response_to_message(&response),
         ModelProvider::Google => google::response_to_message(response),
+        ModelProvider::MaaS(_) => google::response_to_message(response),
     }
 }
 
@@ -337,6 +363,7 @@ pub fn get_usage(data: &Value, request_context: &RequestContext) -> Result<Usage
     match request_context.provider() {
         ModelProvider::Anthropic => anthropic::get_usage(data),
         ModelProvider::Google => google::get_usage(data),
+        ModelProvider::MaaS(_) => google::get_usage(data),
     }
 }
 

crates/goose/src/providers/gcpvertexai.rs

@@ -197,6 +197,7 @@ impl GcpVertexAIProvider {
         let endpoint = match provider {
             ModelProvider::Anthropic => "streamRawPredict",
             ModelProvider::Google => "generateContent",
+            ModelProvider::MaaS(_) => "generateContent",
         };
 
         // Construct path for URL
@@ -586,8 +587,12 @@ mod tests {
 
     #[test]
     fn test_model_provider_conversion() {
-        assert_eq!(ModelProvider::Anthropic.as_str(), "anthropic");
-        assert_eq!(ModelProvider::Google.as_str(), "google");
+        assert_eq!(ModelProvider::Anthropic.as_str(), "anthropic".to_string());
+        assert_eq!(ModelProvider::Google.as_str(), "google".to_string());
+        assert_eq!(
+            ModelProvider::MaaS("qwen".to_string()).as_str(),
+            "qwen".to_string()
+        );
     }
 
     #[test]