Anchor service metadata patterns so foreach paths do not prefix-match

metaflow/plugins/metadata_providers/service.py

@@ -363,7 +363,9 @@ def filter_tasks_by_metadata(
             if field_name:
                 query_params["metadata_field_name"] = field_name
             if pattern:
-                query_params["pattern"] = pattern
+                # The service performs an unanchored regex search, so anchor the
+                # pattern to match the local provider's fullmatch behavior.
+                query_params["pattern"] = "^(?:%s)$" % pattern
 
         url = ServiceMetadataProvider._obj_path(flow_name, run_id, step_name)
         url = f"{url}/filtered_tasks?{urlencode(query_params)}"

test/unit/test_service_metadata_provider.py

@@ -0,0 +1,24 @@
+from urllib.parse import parse_qs, urlparse
+
+from metaflow.plugins.metadata_providers.service import ServiceMetadataProvider
+
+
+def test_filter_tasks_by_metadata_anchors_patterns(monkeypatch):
+    captured = {}
+
+    def fake_request(cls, callback, url, method, *args, **kwargs):
+        captured["url"] = url
+        return [], None
+
+    monkeypatch.setattr(ServiceMetadataProvider, "_request", classmethod(fake_request))
+
+    def forwarded_pattern(pattern):
+        ServiceMetadataProvider.filter_tasks_by_metadata(
+            "Flow", "run", "middle", "foreach-execution-path", pattern
+        )
+        query = parse_qs(urlparse(captured["url"]).query)
+        return query.get("pattern", [None])[0]
+
+    assert forwarded_pattern("middle:1") == "^(?:middle:1)$"
+    assert forwarded_pattern("middle:1,.*") == "^(?:middle:1,.*)$"
+    assert forwarded_pattern(".*") is None