fix(athena): guide callers to background_wait when athena-junior is force-backgrounded

When athena-junior is force-backgrounded (caller passed run_in_background=false),
the response now instructs the caller to use background_wait instead of
background_output, preventing repeated polling loops.

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

@@ -799,7 +799,11 @@ describe("sisyphus-task", () => {
       )
 
       //#then — should be forced to background despite run_in_background=false
-      expect(String(result)).toContain("Background task launched")
+      const resultStr = String(result)
+      expect(resultStr).toContain("Background task launched")
+      expect(resultStr).toContain("background_wait")
+      expect(resultStr).toContain("automatically backgrounded")
+      expect(resultStr).not.toContain("System notifies on completion")
     }, { timeout: 10000 })
 
     test("athena-junior with run_in_background=true still runs in background normally", async () => {
@@ -857,8 +861,11 @@ describe("sisyphus-task", () => {
         toolContext
       )
 
-      //#then — should still be background
-      expect(String(result)).toContain("Background task launched")
+      //#then — should still be background but with normal (non-forced) message
+      const resultStr = String(result)
+      expect(resultStr).toContain("Background task launched")
+      expect(resultStr).toContain("System notifies on completion")
+      expect(resultStr).not.toContain("automatically backgrounded")
     }, { timeout: 10000 })
   })
 

src/tools/delegate-task/tools.ts

@@ -263,7 +263,8 @@ export function createDelegateTask(options: DelegateTaskToolOptions): ToolDefini
       })
 
       if (effectiveRunInBackground) {
-        return executeBackgroundTask(args, ctx, options, parentContext, agentToUse, categoryModel, systemContent, fallbackChain)
+        const wasForced = isAthenaJunior && !runInBackground
+        return executeBackgroundTask(args, ctx, options, parentContext, agentToUse, categoryModel, systemContent, fallbackChain, wasForced)
       }
 
       return executeSyncTask(args, ctx, options, parentContext, agentToUse, categoryModel, systemContent, modelInfo, fallbackChain)