refactor(test_helper): use public Hub#clients instead of @stack ivar (#2951)

Address code review feedback on the #2951 fix:

- Add a documented public Sentry::Hub#clients accessor returning all
  clients across the scope stack, and use it from
  TestHelper#sentry_test_transports instead of reaching into Hub's
  private @stack ivar. This keeps the test helper resilient to future
  Hub internals refactors. Covered by new hub_spec.rb examples.

- Replace the final inline teardown_sentry_test in the #2951 regression
  and Rack consecutive-requests describe blocks with an unconditional
  'after { teardown_sentry_test }' hook, matching the sibling describe
  style so cleanup runs even if an expectation fails mid-example. The
  intentional mid-scenario teardowns remain inline.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: solnic

sentry-ruby/lib/sentry/hub.rb

@@ -54,6 +54,12 @@ def current_client
       current_layer&.client
     end
 
+    # All clients bound across the hub's scope stack, base layer first.
+    # @return [Array<Client>]
+    def clients
+      @stack.map(&:client).compact
+    end
+
     def configuration
       current_client.configuration
     end

sentry-ruby/lib/sentry/test_helper.rb

@@ -112,7 +112,7 @@ def sentry_transport
     # @return [Array<Transport>]
     def sentry_test_transports
       [Sentry.get_current_hub, Sentry.get_main_hub].compact.uniq.flat_map do |hub|
-        hub.instance_variable_get(:@stack).map { |layer| layer.client&.transport }
+        hub.clients.map(&:transport)
       end.compact.uniq
     end
 

sentry-ruby/spec/sentry/hub_spec.rb

@@ -537,6 +537,20 @@
     end
   end
 
+  describe "#clients" do
+    it "returns the only client for a single-layer hub" do
+      expect(subject.clients).to eq([client])
+    end
+
+    it "returns every client across the scope stack, base layer first" do
+      new_client = Sentry::Client.new(configuration)
+      subject.push_scope
+      subject.bind_client(new_client)
+
+      expect(subject.clients).to eq([client, new_client])
+    end
+  end
+
   describe "#pop_scope" do
     it "pops the current scope" do
       prev_scope = subject.current_scope

sentry-ruby/spec/sentry/test_helper_spec.rb

@@ -93,6 +93,8 @@
   end
 
   describe "event leakage across clone_hub_to_current_thread (regression for #2951)" do
+    after { teardown_sentry_test }
+
     it "keeps sentry_events empty after setup_sentry_test even when an earlier request captured events through a cloned hub" do
       # Cycle 1: a normal test that uses the test helper.
       setup_sentry_test
@@ -114,8 +116,6 @@
       Sentry.clone_hub_to_current_thread
 
       expect(sentry_events).to be_empty
-
-      teardown_sentry_test
     end
   end
 
@@ -135,6 +135,8 @@
   end
 
   describe "Sentry::Rack::CaptureExceptions across consecutive requests (regression for #2951)", when: :rack_available? do
+    after { teardown_sentry_test }
+
     # Drives a single request through the real Rack middleware. The middleware
     # calls Sentry.clone_hub_to_current_thread before handing off to the app,
     # exactly like a Rails request spec would.
@@ -171,8 +173,6 @@ def captured_exception_messages
       expect(messages.size).to eq(1)
       expect(messages.first).to include("second-request")
       expect(messages).not_to include(a_string_including("first-request"))
-
-      teardown_sentry_test
     end
   end