Qualify extension constructors of namespaced modules by source path

Codex review on #9085: the module name of another file comes from its
compiled name, which in a namespaced project is `Base-MyNamespace`, so
completion inserted `Base-MyNamespace.Flag`. The name is turned into its
source path `MyNamespace.Base` first.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Kbf3gLMawVgtmiKy3TMBc3
Signed-off-by: Christoph Knittel <ck@cca.io>

Author: cknitt

analysis/src/type_utils.ml

@@ -449,7 +449,7 @@ let extension_constructors ~state ~package ~(current_file : File.t)
       in
       let path =
         if file.uri = current_file.uri then relative path scope_path
-        else file.module_name :: path
+        else Utils.flatten_any_namespace_in_path (file.module_name :: path)
       in
       {
         declared.item with

tests/analysis_tests/tests-namespaced-references/src/ExtensibleBase.res

@@ -0,0 +1,4 @@
+type attr = ..
+type attr += Flag | Size(int)
+
+let value: attr = Flag

tests/analysis_tests/tests-namespaced-references/src/ExtensibleUse.res

@@ -0,0 +1,4 @@
+let imported = ExtensibleBase.value
+
+// switch importe
+//               ^com

tests/analysis_tests/tests-namespaced-references/src/expected/ExtensibleBase.res.txt

@@ -0,0 +1,24 @@
+Complete src/ExtensibleUse.res 2:17
+XXX Not found!
+Completable: CexhaustiveSwitch Value[importe]
+Package opens Stdlib.place holder Pervasives.JsxModules.place holder MyNamespace.place holder
+Resolved opens 2 MyNamespace Stdlib
+ContextPath Value[importe]
+Path importe
+[
+  {
+    "detail": "MyNamespace.ExtensibleBase.attr",
+    "kind": 12,
+    "label": "imported",
+    "tags": []
+  },
+  {
+    "detail": "insert exhaustive switch for value",
+    "filterText": "imported",
+    "insertText": "imported {\n   | MyNamespace.ExtensibleBase.Flag => ${1:%todo}\n   | MyNamespace.ExtensibleBase.Size(_) => ${2:%todo}\n   | _ => ${3:%todo}\n   }",
+    "insertTextFormat": 2,
+    "kind": 15,
+    "label": "imported (exhaustive switch)",
+    "tags": []
+  }
+]