fix(model-fallback): expose session fallback chains to background tasks

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

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

src/hooks/model-fallback/fallback-state-controller.ts

@@ -15,6 +15,7 @@ type ModelFallbackStateLike = {
 export type ModelFallbackStateController = {
   lastToastKey: Map<string, string>
   setSessionFallbackChain: (sessionID: string, fallbackChain: FallbackEntry[] | undefined) => void
+  getSessionFallbackChain: (sessionID: string) => FallbackEntry[] | undefined
   clearSessionFallbackChain: (sessionID: string) => void
   setPendingModelFallback: (
     sessionID: string,
@@ -45,6 +46,10 @@ export function createModelFallbackStateController(input: {
     sessionFallbackChains.delete(sessionID)
   }
 
+  function getSessionFallbackChain(sessionID: string): FallbackEntry[] | undefined {
+    return sessionFallbackChains.get(sessionID)
+  }
+
   function setPendingModelFallback(
     sessionID: string,
     agentName: string,
@@ -123,6 +128,7 @@ export function createModelFallbackStateController(input: {
   return {
     lastToastKey,
     setSessionFallbackChain,
+    getSessionFallbackChain,
     clearSessionFallbackChain,
     setPendingModelFallback,
     getNextFallback,