From c9fab347068284d8a88bce805f0ec79f3bdee3bf Mon Sep 17 00:00:00 2001
From: Charles Packer <packercharles@gmail.com>
Date: Thu, 15 Jan 2026 22:39:53 -0800
Subject: [PATCH] fix: Task tool subagent spawn and isolated block labels
 (#561)

Co-authored-by: Letta <noreply@letta.com>
---
 src/agent/subagents/builtin/recall.md       |  2 +-
 src/agent/subagents/manager.ts              |  2 +-
 src/cli/components/SubagentGroupDisplay.tsx |  2 +-
 src/headless.ts                             | 16 ++++++++--
 src/tests/headless-input-format.test.ts     | 34 +++++++++++++++++++++
 5 files changed, 50 insertions(+), 6 deletions(-)

diff --git a/src/agent/subagents/builtin/recall.md b/src/agent/subagents/builtin/recall.md
index 161359a..e0378e6 100644
--- a/src/agent/subagents/builtin/recall.md
+++ b/src/agent/subagents/builtin/recall.md
@@ -3,7 +3,7 @@ name: recall
 description: Search conversation history to recall past discussions, decisions, and context
 tools: Skill, Bash, Read, BashOutput
 model: haiku
-memoryBlocks: human, persona
+memoryBlocks: human, persona, skills, loaded_skills
 mode: stateless
 ---
 
diff --git a/src/agent/subagents/manager.ts b/src/agent/subagents/manager.ts
index 25d2bc4..34e1ca8 100644
--- a/src/agent/subagents/manager.ts
+++ b/src/agent/subagents/manager.ts
@@ -308,7 +308,7 @@ function buildSubagentArgs(
   userPrompt: string,
 ): string[] {
   const args: string[] = [
-    "--new",
+    "--new-agent",
     "--system",
     type,
     "--model",
diff --git a/src/cli/components/SubagentGroupDisplay.tsx b/src/cli/components/SubagentGroupDisplay.tsx
index 2072386..598eeea 100644
--- a/src/cli/components/SubagentGroupDisplay.tsx
+++ b/src/cli/components/SubagentGroupDisplay.tsx
@@ -290,7 +290,7 @@ export const SubagentGroupDisplay = memo(() => {
   const hasErrors = agents.some((a) => a.status === "error");
 
   return (
-    <Box flexDirection="column">
+    <Box flexDirection="column" marginTop={1}>
       <GroupHeader
         count={agents.length}
         allCompleted={allCompleted}
diff --git a/src/headless.ts b/src/headless.ts
index a2f06bd..6a839e4 100644
--- a/src/headless.ts
+++ b/src/headless.ts
@@ -471,6 +471,16 @@ export async function handleHeadlessCommand(
   // Determine which conversation to use
   let conversationId: string;
 
+  // Only isolate blocks that actually exist on this agent
+  // If initBlocks is undefined, agent has default blocks (all ISOLATED_BLOCK_LABELS exist)
+  // If initBlocks is defined, only isolate blocks that are in both lists
+  const isolatedBlockLabels: string[] =
+    initBlocks === undefined
+      ? [...ISOLATED_BLOCK_LABELS]
+      : ISOLATED_BLOCK_LABELS.filter((label) =>
+          initBlocks.includes(label as string),
+        );
+
   if (specifiedConversationId) {
     // User specified a conversation to resume
     try {
@@ -496,7 +506,7 @@ export async function handleHeadlessCommand(
         // Conversation no longer exists, create new
         const conversation = await client.conversations.create({
           agent_id: agent.id,
-          isolated_block_labels: [...ISOLATED_BLOCK_LABELS],
+          isolated_block_labels: isolatedBlockLabels,
         });
         conversationId = conversation.id;
       }
@@ -504,7 +514,7 @@ export async function handleHeadlessCommand(
       // No matching session, create new conversation
       const conversation = await client.conversations.create({
         agent_id: agent.id,
-        isolated_block_labels: [...ISOLATED_BLOCK_LABELS],
+        isolated_block_labels: isolatedBlockLabels,
       });
       conversationId = conversation.id;
     }
@@ -513,7 +523,7 @@ export async function handleHeadlessCommand(
     // This ensures isolated message history per CLI invocation
     const conversation = await client.conversations.create({
       agent_id: agent.id,
-      isolated_block_labels: [...ISOLATED_BLOCK_LABELS],
+      isolated_block_labels: isolatedBlockLabels,
     });
     conversationId = conversation.id;
   }
diff --git a/src/tests/headless-input-format.test.ts b/src/tests/headless-input-format.test.ts
index 8a6eae7..1148bb2 100644
--- a/src/tests/headless-input-format.test.ts
+++ b/src/tests/headless-input-format.test.ts
@@ -453,4 +453,38 @@ describe("input-format stream-json", () => {
     },
     { timeout: 200000 },
   );
+
+  test(
+    "Task tool with explore subagent works",
+    async () => {
+      // Prescriptive prompt to ensure Task tool is used
+      const objects = (await runBidirectional(
+        [
+          JSON.stringify({
+            type: "user",
+            message: {
+              role: "user",
+              content:
+                "You MUST use the Task tool with subagent_type='explore' to find TypeScript files (*.ts) in the src directory. " +
+                "Return only the subagent's report, nothing else.",
+            },
+          }),
+        ],
+        [],
+        300000, // 5 min timeout - subagent spawn + execution can be slow
+      )) as WireMessage[];
+
+      // Should have a successful result
+      const result = objects.find(
+        (o): o is ResultMessage => o.type === "result",
+      );
+      expect(result).toBeDefined();
+      expect(result?.subtype).toBe("success");
+
+      // Should have auto_approval events (Task tool was auto-approved via --yolo)
+      const autoApprovals = objects.filter((o) => o.type === "auto_approval");
+      expect(autoApprovals.length).toBeGreaterThan(0);
+    },
+    { timeout: 320000 },
+  );
 });