fix: enable runtime fallback for delegated child sessions (#2357)

src/hooks/runtime-fallback/fallback-retry-dispatcher.ts

@@ -0,0 +1,55 @@
+import type { AutoRetryHelpers } from "./auto-retry"
+import type { HookDeps, FallbackState } from "./types"
+import { HOOK_NAME } from "./constants"
+import { log } from "../../shared/logger"
+import { prepareFallback } from "./fallback-state"
+
+type DispatchFallbackRetryOptions = {
+  sessionID: string
+  state: FallbackState
+  fallbackModels: string[]
+  resolvedAgent?: string
+  source: string
+}
+
+export async function dispatchFallbackRetry(
+  deps: HookDeps,
+  helpers: AutoRetryHelpers,
+  options: DispatchFallbackRetryOptions,
+): Promise<void> {
+  const result = prepareFallback(
+    options.sessionID,
+    options.state,
+    options.fallbackModels,
+    deps.config,
+  )
+
+  if (result.success && deps.config.notify_on_fallback) {
+    await deps.ctx.client.tui
+      .showToast({
+        body: {
+          title: "Model Fallback",
+          message: `Switching to ${result.newModel?.split("/").pop() || result.newModel} for next request`,
+          variant: "warning",
+          duration: 5000,
+        },
+      })
+      .catch(() => {})
+  }
+
+  if (result.success && result.newModel) {
+    await helpers.autoRetryWithFallback(
+      options.sessionID,
+      result.newModel,
+      options.resolvedAgent,
+      options.source,
+    )
+    return
+  }
+
+  log(`[${HOOK_NAME}] Fallback preparation failed`, {
+    sessionID: options.sessionID,
+    source: options.source,
+    error: result.error,
+  })
+}