Make Ruby Saga compensations cancellation-proof

Run saga compensations with a detached Temporalio::Cancellation so they
still execute when the workflow is canceled mid-saga. Previously they
used the workflow cancellation, which is already canceled at that point,
so the compensation activities would be canceled before starting. This
is the Ruby equivalent of Python's asyncio.shield.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

references/ruby/patterns.md

@@ -214,21 +214,23 @@ class MyWorkflow < Temporalio::Workflow::Definition
       # 3. but then fails for some other reason (timeout, reporting metrics, etc.)
       # 4. the activity failed, but the effect (reserved inventory) already happened
       # So the compensation must handle both reserved and unreserved states.
-      compensations << lambda {
+      compensations << lambda { |cancellation|
         Temporalio::Workflow.execute_activity(
           ReleaseInventoryIfReserved, order,
-          start_to_close_timeout: 300
+          start_to_close_timeout: 300,
+          cancellation: cancellation
         )
       }
       Temporalio::Workflow.execute_activity(
         ReserveInventory, order,
         start_to_close_timeout: 300
       )
 
-      compensations << lambda {
+      compensations << lambda { |cancellation|
         Temporalio::Workflow.execute_activity(
           RefundPaymentIfCharged, order,
-          start_to_close_timeout: 300
+          start_to_close_timeout: 300,
+          cancellation: cancellation
         )
       }
       Temporalio::Workflow.execute_activity(
@@ -245,9 +247,12 @@ class MyWorkflow < Temporalio::Workflow::Definition
 
     rescue => e
       Temporalio::Workflow.logger.error("Order failed: #{e}, running compensations")
+      # Use a detached cancellation so compensations still run even if the workflow
+      # was canceled (the workflow's own cancellation is already canceled by then).
+      detached_cancel, = Temporalio::Cancellation.new
       compensations.reverse.each do |compensate|
         begin
-          compensate.call
+          compensate.call(detached_cancel)
         rescue => comp_err
           Temporalio::Workflow.logger.error("Compensation failed: #{comp_err}")
         end