Refactor GoModUpdater to improve go.sum reconciliation logic and update GoModGraph type annotation

Author: kbukum1

go_modules/lib/dependabot/go_modules/file_updater/go_mod_graph.rb

@@ -1,4 +1,4 @@
-# typed: strict
+# typed: strong
 # frozen_string_literal: true
 
 require "sorbet-runtime"

go_modules/lib/dependabot/go_modules/file_updater/go_mod_updater.rb

@@ -230,17 +230,8 @@ def update_files
             updated_go_sum = original_go_sum ? File.read("go.sum") : nil
             updated_go_mod = File.read("go.mod")
 
-            # Restore go.sum lines that were removed for modules unrelated
-            # to the update — Go tooling can over-prune /go.mod checksums.
             if original_go_sum && updated_go_sum
-              graph_after = GoModGraph.capture
-              unless graph_before.empty? || graph_after.empty?
-                updated_go_sum = reconcile_go_sum(
-                  original_go_sum,
-                  updated_go_sum,
-                  graph_before.changed_modules(graph_after)
-                )
-              end
+              updated_go_sum = reconcile_updated_go_sum(original_go_sum, updated_go_sum, graph_before)
             end
 
             { go_mod: updated_go_mod, go_sum: updated_go_sum }
@@ -423,6 +414,22 @@ def in_repo_path(&block)
           end
         end
 
+        # Captures the post-update module graph, diffs it against the
+        # pre-update graph, and restores over-pruned go.sum lines.
+        sig do
+          params(
+            original_go_sum: String,
+            updated_go_sum: String,
+            graph_before: GoModGraph
+          ).returns(String)
+        end
+        def reconcile_updated_go_sum(original_go_sum, updated_go_sum, graph_before)
+          graph_after = GoModGraph.capture
+          return updated_go_sum if graph_before.empty? || graph_after.empty?
+
+          reconcile_go_sum(original_go_sum, updated_go_sum, graph_before.changed_modules(graph_after))
+        end
+
         # Restores /go.mod checksum lines in go.sum that were removed for
         # modules unrelated to the dependency update. Go tooling can
         # over-prune these entries, causing CI failures downstream.