Revert "Merge pull request #3825 from tw-yshuang/fix/delegated-child-session-early-failure-fallback"

This reverts commit cd33f3a397, reversing
changes made to 521c99cf0b.

src/tools/delegate-task/background-task.ts

@@ -6,31 +6,26 @@ import { buildTaskPrompt } from "./prompt-builder"
 import { publishToolMetadata } from "../../features/tool-metadata-store"
 import { formatDetailedError } from "./error-formatting"
 import { getSessionTools } from "../../shared/session-tools-store"
+import { SessionCategoryRegistry } from "../../shared/session-category-registry"
 import { QUESTION_DENIED_SESSION_PERMISSION } from "../../shared/question-denied-session-permission"
 import { stripAgentListSortPrefix } from "../../shared/agent-display-names"
 import { buildTaskMetadataBlock } from "../../features/tool-metadata-store/task-metadata-contract"
 import { resolveMetadataModel } from "./resolve-metadata-model"
-import { registerDelegatedChildSessionBootstrap } from "../../shared/delegated-child-session-bootstrap"
 
 function registerBackgroundSessionContext(args: {
   sessionId: string
-  promptText: string
   fallbackChain?: FallbackEntry[]
   category?: string
   modelFallbackControllerAccessor?: ExecutorContext["modelFallbackControllerAccessor"]
 }): void {
-  registerDelegatedChildSessionBootstrap({
-    sessionID: args.sessionId,
-    promptText: args.promptText,
-    fallbackChain: args.fallbackChain,
-    category: args.category,
-    modelFallbackControllerAccessor: args.modelFallbackControllerAccessor,
-  })
+  args.modelFallbackControllerAccessor?.setSessionFallbackChain(args.sessionId, args.fallbackChain)
+  if (args.category) {
+    SessionCategoryRegistry.register(args.sessionId, args.category)
+  }
 }
 
 function continueSessionSetup(args: {
   taskID: string
-  promptText: string
   manager: ExecutorContext["manager"]
   timing: ReturnType<typeof getTimingConfig>
   fallbackChain?: FallbackEntry[]
@@ -60,7 +55,6 @@ function continueSessionSetup(args: {
 
       registerBackgroundSessionContext({
         sessionId,
-        promptText: args.promptText,
         fallbackChain: args.fallbackChain,
         category: args.category,
         modelFallbackControllerAccessor: args.modelFallbackControllerAccessor,
@@ -150,7 +144,6 @@ export async function executeBackgroundTask(
       onAbort: () => {
         continueSessionSetup({
           taskID: task.id,
-          promptText: effectivePrompt,
           manager,
           timing,
           fallbackChain,
@@ -167,6 +160,15 @@ export async function executeBackgroundTask(
       return `Task failed to start (status: ${updatedTask.status}).\n\nTask ID: ${task.id}`
     }
 
+    if (sessionId) {
+      registerBackgroundSessionContext({
+        sessionId,
+        fallbackChain,
+        category: args.category,
+        modelFallbackControllerAccessor: executorCtx.modelFallbackControllerAccessor,
+      })
+    }
+
     const resolvedModel = resolveMetadataModel(categoryModel, parentContext.model)
     const metadata = {
       prompt: args.prompt,