refactor(model-fallback): fully encapsulate session state in factory closure

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

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

src/create-managers.ts

@@ -5,6 +5,7 @@ import type { PluginContext, TmuxConfig } from "./plugin/types"
 import type { SubagentSessionCreatedEvent } from "./features/background-agent"
 import { BackgroundManager } from "./features/background-agent"
 import { SkillMcpManager } from "./features/skill-mcp-manager"
+import { createModelFallbackControllerAccessor } from "./hooks/model-fallback"
 import { initTaskToastManager } from "./features/task-toast-manager"
 import { TmuxSessionManager } from "./features/tmux-subagent"
 import * as openclawRuntimeDispatch from "./openclaw/runtime-dispatch"
@@ -12,6 +13,7 @@ import { registerManagerForCleanup } from "./features/background-agent/process-c
 import { createConfigHandler } from "./plugin-handlers"
 import { log } from "./shared"
 import { markServerRunningInProcess } from "./shared/tmux/tmux-utils/server-health"
+import type { ModelFallbackControllerAccessor } from "./hooks/model-fallback"
 
 type CreateManagersDeps = {
   BackgroundManagerClass: typeof BackgroundManager
@@ -38,6 +40,7 @@ export type Managers = {
   backgroundManager: BackgroundManager
   skillMcpManager: SkillMcpManager
   configHandler: ReturnType<typeof createConfigHandler>
+  modelFallbackControllerAccessor: ModelFallbackControllerAccessor
 }
 
 export function createManagers(args: {
@@ -119,11 +122,13 @@ export function createManagers(args: {
     pluginConfig,
     modelCacheState,
   })
+  const modelFallbackControllerAccessor = createModelFallbackControllerAccessor()
 
   return {
     tmuxSessionManager,
     backgroundManager,
     skillMcpManager,
     configHandler,
+    modelFallbackControllerAccessor,
   }
 }