test(app): add test for OnStart failure cleanup behavior

Verifies that when an OnStart hook fails, Start() returns the error
and OnStop hooks do not run (only internal cleanup like telemetry
flush executes).

Author: ravisuhag

app/app_test.go

@@ -174,4 +174,26 @@ func TestAppStartAndShutdown(t *testing.T) {
 
 		cancel()
 	})
+
+	t.Run("onStart failure returns error and runs cleanup", func(t *testing.T) {
+		var cleanupRan bool
+		a, err := app.New(
+			app.WithAddr("127.0.0.1:18955"),
+			app.WithOnStart(func(_ context.Context) error {
+				return fmt.Errorf("migration failed")
+			}),
+			app.WithOnStop(func(_ context.Context) error {
+				cleanupRan = true
+				return nil
+			}),
+		)
+		require.NoError(t, err)
+
+		err = a.Start(context.Background())
+		assert.Error(t, err)
+		assert.Contains(t, err.Error(), "migration failed")
+		// OnStop should NOT run — it runs only on graceful shutdown.
+		// cleanup() (telemetry flush) runs, but not onStop hooks.
+		assert.False(t, cleanupRan, "onStop hooks should not run on startup failure")
+	})
 }