fix: address Cubic findings for runtime fallback child sessions

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/hooks/runtime-fallback/hook.ts

@@ -43,6 +43,7 @@ export function createRuntimeFallbackHook(
     sessionRetryInFlight: new Set(),
     sessionAwaitingFallbackResult: new Set(),
     sessionFallbackTimeouts: new Map(),
+    sessionStatusRetryKeys: new Map(),
   }
 
   const helpers = createAutoRetryHelpers(deps)