From 39d94a4af67b7f00e8a82afcdf642b57b746abcc Mon Sep 17 00:00:00 2001
From: YeonGyu-Kim <code.yeon.gyu@gmail.com>
Date: Thu, 5 Mar 2026 10:50:44 +0900
Subject: [PATCH] fix(task): disambiguate background task_id metadata

---
 src/tools/delegate-task/background-task.test.ts | 2 ++
 src/tools/delegate-task/background-task.ts      | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/tools/delegate-task/background-task.test.ts b/src/tools/delegate-task/background-task.test.ts
index 25f8f2c2..e244f7cc 100644
--- a/src/tools/delegate-task/background-task.test.ts
+++ b/src/tools/delegate-task/background-task.test.ts
@@ -103,6 +103,7 @@ describeFn("executeBackgroundTask output/session metadata compatibility", () =>
     expectFn(result).toContain("<task_metadata>")
     expectFn(result).toContain("session_id: ses_sub_123")
     expectFn(result).toContain("task_id: ses_sub_123")
+    expectFn(result).toContain("background_task_id: bg_resolved")
     expectFn(result).toContain("Background Task ID: bg_resolved")
     expectFn(metadataCalls).toHaveLength(1)
     expectFn(metadataCalls[0].metadata.sessionId).toBe("ses_sub_123")
@@ -150,6 +151,7 @@ describeFn("executeBackgroundTask output/session metadata compatibility", () =>
     //#then - late session id still propagates to task metadata contract
     expectFn(result).toContain("session_id: ses_late_123")
     expectFn(result).toContain("task_id: ses_late_123")
+    expectFn(result).toContain("background_task_id: bg_late")
     expectFn(metadataCalls).toHaveLength(1)
     expectFn(metadataCalls[0].metadata.sessionId).toBe("ses_late_123")
   })
diff --git a/src/tools/delegate-task/background-task.ts b/src/tools/delegate-task/background-task.ts
index 2b385b26..aedd0b3e 100644
--- a/src/tools/delegate-task/background-task.ts
+++ b/src/tools/delegate-task/background-task.ts
@@ -78,7 +78,7 @@ export async function executeBackgroundTask(
     }
 
     const taskMetadataBlock = sessionId
-      ? `\n\n<task_metadata>\nsession_id: ${sessionId}\ntask_id: ${sessionId}\n</task_metadata>`
+      ? `\n\n<task_metadata>\nsession_id: ${sessionId}\ntask_id: ${sessionId}\nbackground_task_id: ${task.id}\n</task_metadata>`
       : ""
 
     return `Background task launched.