fix: use build_host_url for GCP Vertex AI location fallback (#8185)

Signed-off-by: rdondeti <ravitez.dondeti@gmail.com>

crates/goose/src/providers/gcpvertexai.rs

@@ -72,7 +72,7 @@ fn build_vertex_url(
     let host_url = if configured_location == target_location {
         host.to_string()
     } else {
-        host.replace(configured_location, target_location)
+        GcpVertexAIProvider::build_host_url(target_location)
     };
 
     let base_url =
@@ -735,6 +735,60 @@ mod tests {
         assert!(url.as_str().contains("locations/europe-west1"));
     }
 
+    #[test]
+    fn test_build_vertex_url_global_location_fallback() {
+        // When configured_location is "global", the host is
+        // "https://aiplatform.googleapis.com" which does not contain "global".
+        // Falling back to a regional target_location must rebuild the host
+        // via build_host_url rather than string replacement.
+        let url = build_vertex_url(
+            "https://aiplatform.googleapis.com",
+            "global",
+            "test-project",
+            "claude-haiku-4-5@20251001",
+            ModelProvider::Anthropic,
+            "us-east5",
+            true,
+        )
+        .unwrap();
+
+        assert!(
+            url.as_str()
+                .starts_with("https://us-east5-aiplatform.googleapis.com"),
+            "Expected regional host for us-east5, got: {}",
+            url
+        );
+        assert!(
+            url.as_str().contains("locations/us-east5"),
+            "Expected locations/us-east5 in path, got: {}",
+            url
+        );
+        assert!(url.as_str().contains(":streamRawPredict"));
+    }
+
+    #[test]
+    fn test_build_vertex_url_global_location_same() {
+        // When both configured and target are "global", the host should stay as-is.
+        let url = build_vertex_url(
+            "https://aiplatform.googleapis.com",
+            "global",
+            "test-project",
+            "claude-haiku-4-5@20251001",
+            ModelProvider::Anthropic,
+            "global",
+            true,
+        )
+        .unwrap();
+
+        assert!(
+            url.as_str()
+                .starts_with("https://aiplatform.googleapis.com"),
+            "Expected global host, got: {}",
+            url
+        );
+        assert!(url.as_str().contains("locations/global"));
+    }
+
     #[test]
     fn test_provider_metadata() {
         let metadata = GcpVertexAIProvider::metadata();