diff --git a/src/features/background-agent/spawner.test.ts b/src/features/background-agent/spawner.test.ts
index d3896e55f..0d996ec19 100644
--- a/src/features/background-agent/spawner.test.ts
+++ b/src/features/background-agent/spawner.test.ts
@@ -466,4 +466,58 @@ describe("background-agent spawner fallback model promotion", () => {
     })
     expect(promptCalls[0]?.body?.variant).toBe("medium")
   })
+
+  test("strips leading zwsp from prompt body agent before promptAsync", async () => {
+    //#given
+    const promptCalls: Array<{ body?: { agent?: string } }> = []
+
+    const client = {
+      session: {
+        get: async () => ({ data: { directory: "/parent/dir" } }),
+        create: async () => ({ data: { id: "ses_child_clean_agent" } }),
+        promptAsync: async (args?: { body?: { agent?: string } }) => {
+          promptCalls.push(args ?? {})
+          return {}
+        },
+      },
+    }
+
+    const task = createTask({
+      description: "Test task",
+      prompt: "Do work",
+      agent: "\u200Bsisyphus-junior",
+      parentSessionID: "ses_parent",
+      parentMessageID: "msg_parent",
+    })
+
+    const item = {
+      task,
+      input: {
+        description: task.description,
+        prompt: task.prompt,
+        agent: task.agent,
+        parentSessionID: task.parentSessionID,
+        parentMessageID: task.parentMessageID,
+        parentModel: task.parentModel,
+        parentAgent: task.parentAgent,
+        model: task.model,
+      },
+    }
+
+    const ctx = {
+      client,
+      directory: "/fallback",
+      concurrencyManager: { release: () => {} },
+      tmuxEnabled: false,
+      onTaskError: () => {},
+    }
+
+    //#when
+    await startTask(item as any, ctx as any)
+    await new Promise((resolve) => setTimeout(resolve, 0))
+
+    //#then
+    expect(promptCalls).toHaveLength(1)
+    expect(promptCalls[0]?.body?.agent).toBe("sisyphus-junior")
+  })
 })
diff --git a/src/features/background-agent/spawner.ts b/src/features/background-agent/spawner.ts
index 3c2fd7e73..b549c706b 100644
--- a/src/features/background-agent/spawner.ts
+++ b/src/features/background-agent/spawner.ts
@@ -6,6 +6,7 @@ import { applySessionPromptParams } from "../../shared/session-prompt-params-hel
 import { subagentSessions } from "../claude-code-session-state"
 import { getTaskToastManager } from "../task-toast-manager"
 import { isInsideTmux } from "../../shared/tmux"
+import { stripAgentListSortPrefix } from "../../shared/agent-display-names"
 import type { ConcurrencyManager } from "./concurrency"
 
 export const FALLBACK_AGENT = "general"
@@ -168,11 +169,12 @@ export async function startTask(
       }
     : undefined
   const launchVariant = input.model?.variant
+  const normalizedAgent = stripAgentListSortPrefix(input.agent)
 
   applySessionPromptParams(sessionID, input.model)
 
   const promptBody = {
-    agent: input.agent,
+    agent: normalizedAgent,
     ...(launchModel ? { model: launchModel } : {}),
     ...(launchVariant ? { variant: launchVariant } : {}),
     system: input.skillContent,
@@ -180,7 +182,7 @@ export async function startTask(
       task: false,
       call_omo_agent: true,
       question: false,
-      ...getAgentToolRestrictions(input.agent),
+      ...getAgentToolRestrictions(normalizedAgent),
     },
     parts: [createInternalAgentTextPart(input.prompt)],
   }
diff --git a/src/tools/delegate-task/background-task.test.ts b/src/tools/delegate-task/background-task.test.ts
index 0d95dd1dd..84a7bc644 100644
--- a/src/tools/delegate-task/background-task.test.ts
+++ b/src/tools/delegate-task/background-task.test.ts
@@ -204,6 +204,50 @@ describeFn("executeBackgroundTask output/session metadata compatibility", () =>
     ])
   })
 
+  testFn("strips leading zwsp from agent name before launching background task", async () => {
+    //#given - display-sorted agent names should be normalized before manager launch
+    const launchCalls: unknown[] = []
+    const manager = {
+      launch: async (input: unknown) => {
+        launchCalls.push(input)
+        return {
+          id: "bg_clean_agent",
+          sessionID: "ses_clean_agent",
+          description: "Clean agent",
+          agent: "sisyphus-junior",
+          status: "running",
+        }
+      },
+      getTask: () => ({ sessionID: "ses_clean_agent" }),
+    }
+
+    //#when
+    await executeBackgroundTask(
+      {
+        description: "Clean agent",
+        prompt: "check",
+        run_in_background: true,
+        load_skills: [],
+      },
+      {
+        sessionID: "ses_parent",
+        callID: "call_clean_agent",
+        metadata: async () => {},
+        abort: new AbortController().signal,
+      },
+      { manager },
+      { sessionID: "ses_parent", messageID: "msg_clean_agent" },
+      "\u200Bsisyphus-junior",
+      undefined,
+      undefined,
+      undefined,
+    )
+
+    //#then
+    expectFn(launchCalls).toHaveLength(1)
+    expectFn((launchCalls[0] as { agent: string }).agent).toBe("sisyphus-junior")
+  })
+
   testFn("keeps launched background task alive when parent aborts before session id resolves", async () => {
     //#given - parallel tool execution can abort the parent call after launch succeeds
     const metadataCalls: any[] = []
diff --git a/src/tools/delegate-task/background-task.ts b/src/tools/delegate-task/background-task.ts
index 0dbb042ab..184325ec9 100644
--- a/src/tools/delegate-task/background-task.ts
+++ b/src/tools/delegate-task/background-task.ts
@@ -10,6 +10,7 @@ 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 { setSessionFallbackChain } from "../../hooks/model-fallback/hook"
+import { stripAgentListSortPrefix } from "../../shared/agent-display-names"
 
 function continueSessionSetup(args: {
   taskID: string
@@ -62,11 +63,12 @@ export async function executeBackgroundTask(
 
   try {
     const tddEnabled = executorCtx.sisyphusAgentConfig?.tdd
-    const effectivePrompt = buildTaskPrompt(args.prompt, agentToUse, tddEnabled)
+    const normalizedAgent = stripAgentListSortPrefix(agentToUse)
+    const effectivePrompt = buildTaskPrompt(args.prompt, normalizedAgent, tddEnabled)
     const task = await manager.launch({
       description: args.description,
       prompt: effectivePrompt,
-      agent: agentToUse,
+      agent: normalizedAgent,
       parentSessionID: parentContext.sessionID,
       parentMessageID: parentContext.messageID,
       parentModel: parentContext.model,
@@ -156,7 +158,7 @@ Do NOT call background_output now. Wait for <system-reminder> notification first
     return formatDetailedError(error, {
       operation: "Launch background task",
       args,
-      agent: agentToUse,
+      agent: stripAgentListSortPrefix(agentToUse),
       category: args.category,
     })
   }