fix double wf registration w/ custom name bug

Author: maxdml

dbos/workflow.go

@@ -246,8 +246,12 @@ func registerWorkflow(ctx DBOSContext, workflowFQN string, fn WrappedWorkflowFun
 	}
 
 	// We need to get a mapping from custom name to FQN for registry lookups that might not know the FQN (queue, recovery)
+	// We also panic if we found the name was already registered (this could happen if registering two different workflows under the same custom name)
 	if len(customName) > 0 {
-		c.workflowCustomNametoFQN.Store(customName, workflowFQN)
+		if _, exists := c.workflowCustomNametoFQN.LoadOrStore(customName, workflowFQN); exists {
+			c.logger.Error("workflow function already registered", "custom_name", customName)
+			panic(newConflictingRegistrationError(customName))
+		}
 	} else {
 		c.workflowCustomNametoFQN.Store(workflowFQN, workflowFQN) // Store the FQN as the custom name if none was provided
 	}

dbos/workflows_test.go

@@ -327,6 +327,24 @@ func TestWorkflowsRegistration(t *testing.T) {
 		RegisterWorkflow(freshCtx, simpleWorkflow, WithWorkflowName("custom-workflow"))
 	})
 
+	t.Run("DifferentWorkflowsSameCustomName", func(t *testing.T) {
+		// Create a fresh DBOS context for this test
+		freshCtx := setupDBOS(t, false, false) // Don't check for leaks and don't reset DB
+
+		// First registration with custom name should work
+		RegisterWorkflow(freshCtx, simpleWorkflow, WithWorkflowName("same-name"))
+
+		// Second registration of different workflow with same custom name should panic with ConflictingRegistrationError
+		defer func() {
+			r := recover()
+			require.NotNil(t, r, "expected panic from registering different workflows with same custom name but got none")
+			dbosErr, ok := r.(*DBOSError)
+			require.True(t, ok, "expected panic to be *DBOSError, got %T", r)
+			assert.Equal(t, ConflictingRegistrationError, dbosErr.Code)
+		}()
+		RegisterWorkflow(freshCtx, simpleWorkflowError, WithWorkflowName("same-name"))
+	})
+
 	t.Run("RegisterAfterLaunchPanics", func(t *testing.T) {
 		// Create a fresh DBOS context for this test
 		freshCtx := setupDBOS(t, false, false) // Don't check for leaks and don't reset DB