fix(athena): always show background_wait guidance for athena-junior, not just when forced

The background_wait instruction was only shown when the caller passed
run_in_background=false (forced case). But callers passing true also need
the guidance since they were polling background_output instead. Now
athena-junior always gets background_wait instructions regardless of how
it was launched.

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

@@ -861,11 +861,11 @@ describe("sisyphus-task", () => {
         toolContext
       )
 
-      //#then — should still be background but with normal (non-forced) message
+      //#then — should also get background_wait guidance (athena-junior always gets it)
       const resultStr = String(result)
       expect(resultStr).toContain("Background task launched")
-      expect(resultStr).toContain("System notifies on completion")
-      expect(resultStr).not.toContain("automatically backgrounded")
+      expect(resultStr).toContain("background_wait")
+      expect(resultStr).toContain("automatically backgrounded")
     }, { timeout: 10000 })
   })
 

src/tools/delegate-task/tools.ts

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