diff --git a/workspace/executor_helpers.py b/workspace/executor_helpers.py
index 35c8e7ca..95e73857 100644
--- a/workspace/executor_helpers.py
+++ b/workspace/executor_helpers.py
@@ -48,7 +48,16 @@ logger = logging.getLogger(__name__)
 
 WORKSPACE_MOUNT = "/workspace"
 CONFIG_MOUNT = "/configs"
-DEFAULT_MCP_SERVER_PATH = "/app/a2a_mcp_server.py"
+# Resolved relative to this module so it tracks the wheel install
+# location. The hardcoded "/app/a2a_mcp_server.py" was correct under
+# the pre-#87 monolithic-template layout, but post-universal-runtime
+# the file ships inside the molecule-ai-workspace-runtime wheel at
+# site-packages/molecule_runtime/, while /app/ now holds only
+# template-specific modules (adapter.py + the runtime-native executor).
+# Stale path → Claude Code SDK silently fails to spawn the MCP
+# subprocess → list_peers / delegate_task / a2a_send_message all
+# disappear from the agent's toolset.
+DEFAULT_MCP_SERVER_PATH = str(Path(__file__).parent / "a2a_mcp_server.py")
 DEFAULT_DELEGATION_RESULTS_FILE = "/tmp/delegation_results.jsonl"
 PLATFORM_HTTP_TIMEOUT_S = 5.0
 MEMORY_RECALL_LIMIT = 10
diff --git a/workspace/tests/test_executor_helpers.py b/workspace/tests/test_executor_helpers.py
index d9dd35fa..688f6044 100644
--- a/workspace/tests/test_executor_helpers.py
+++ b/workspace/tests/test_executor_helpers.py
@@ -23,6 +23,7 @@ Covers 100% of the public surface:
 from __future__ import annotations
 
 import json
+import os
 from pathlib import Path
 from types import SimpleNamespace
 from unittest.mock import AsyncMock, MagicMock, patch
@@ -88,6 +89,18 @@ def test_get_mcp_server_path_default(monkeypatch):
     assert get_mcp_server_path() == DEFAULT_MCP_SERVER_PATH
 
 
+def test_get_mcp_server_path_default_resolves_to_existing_file():
+    # Locks in the wheel-relative resolution: if a future refactor moves
+    # a2a_mcp_server.py out of the package directory or breaks the
+    # __file__-based lookup, Claude Code SDK silently fails to spawn the
+    # MCP subprocess and inter-agent tools (list_peers, delegate_task)
+    # vanish at runtime. This assertion catches that at unit-test time.
+    assert os.path.exists(DEFAULT_MCP_SERVER_PATH), (
+        f"DEFAULT_MCP_SERVER_PATH points at a missing file: "
+        f"{DEFAULT_MCP_SERVER_PATH}"
+    )
+
+
 def test_get_mcp_server_path_env_override(monkeypatch):
     monkeypatch.setenv("A2A_MCP_SERVER_PATH", "/custom/mcp.py")
     assert get_mcp_server_path() == "/custom/mcp.py"