diff --git a/backend/apps/agents/manager/builtin_mcp_servers.py b/backend/apps/agents/manager/builtin_mcp_servers.py
index 62842d44..698d728c 100644
--- a/backend/apps/agents/manager/builtin_mcp_servers.py
+++ b/backend/apps/agents/manager/builtin_mcp_servers.py
@@ -1,6 +1,7 @@
 """Register the always-on + delegation MCP servers (browser-agent, invoke-agent, meta,
-settings-meta) into the per-turn mcp_servers map. Lifted out of the agent loop; the server
-scripts live beside agent_manager.py, so the loop passes their directory in. Returns the
+settings-meta) into the per-turn mcp_servers map. The server scripts live in the agents
+package, so we resolve their directory off that package here, NOT off a dir a caller passes
+in: a caller in a moved file would compute the wrong dir (this bit us once). Returns the
 browser/invoke delegation tool-name lists the allowlist gate needs."""
 
 import os
@@ -19,8 +20,9 @@ def register_builtin_mcp_servers(
     session: AgentSession,
     builtin_perms: Dict[str, str],
     selected_browser_ids: Optional[List[str]],
-    agents_dir: str,
 ) -> Tuple[List[str], List[str]]:
+    import backend.apps.agents as p_agents_pkg
+    agents_dir = os.path.dirname(p_agents_pkg.__file__)
     browser_delegation_tools = ["CreateBrowserAgent", "BrowserAgent", "BrowserAgents"]
     browser_all_denied = all(
         builtin_perms.get(t, "always_allow") == "deny"
diff --git a/backend/apps/agents/manager/run/RunOptionsMixin.py b/backend/apps/agents/manager/run/RunOptionsMixin.py
index 4900a765..d1467ca4 100644
--- a/backend/apps/agents/manager/run/RunOptionsMixin.py
+++ b/backend/apps/agents/manager/run/RunOptionsMixin.py
@@ -4,7 +4,6 @@ options_kwargs (provider env, preset, thinking, resume/history), runs the pre-se
 and returns the ClaudeAgentOptions plus the bits the streaming turn needs. Mixin method: self.* and
 the gate hooks resolve across the MRO unchanged."""
 
-import os
 import json
 import logging
 from typing import Dict, List, Optional, Union
@@ -110,7 +109,7 @@ class RunOptionsMixin:
         mcp_servers = await self.build_mcp_servers(session.allowed_tools, session.active_mcps)
 
         browser_delegation_tools, invoke_agent_tools = register_builtin_mcp_servers(
-            mcp_servers, session, builtin_perms, selected_browser_ids, os.path.dirname(__file__)
+            mcp_servers, session, builtin_perms, selected_browser_ids
         )
 
 
diff --git a/backend/tests/test_builtin_mcp_servers.py b/backend/tests/test_builtin_mcp_servers.py
index 4feb6198..66eea134 100644
--- a/backend/tests/test_builtin_mcp_servers.py
+++ b/backend/tests/test_builtin_mcp_servers.py
@@ -2,6 +2,8 @@
 are always registered, the browser/invoke delegation servers register unless their tools are
 fully denied, and the delegation tool-name lists come back for the allowlist gate."""
 
+import os
+
 from backend.apps.agents.core.models import AgentSession
 from backend.apps.agents.manager.builtin_mcp_servers import register_builtin_mcp_servers
 
@@ -13,7 +15,7 @@ def p_session():
 def test_registers_always_on_and_delegation_servers():
     mcp_servers = {}
     browser_tools, invoke_tools = register_builtin_mcp_servers(
-        mcp_servers, p_session(), {}, None, "/agents")
+        mcp_servers, p_session(), {}, None)
     # always-on
     assert "openswarm-mcp-meta" in mcp_servers
     assert "openswarm-settings-meta" in mcp_servers
@@ -22,14 +24,18 @@ def test_registers_always_on_and_delegation_servers():
     assert "openswarm-invoke-agent" in mcp_servers
     assert browser_tools == ["CreateBrowserAgent", "BrowserAgent", "BrowserAgents"]
     assert invoke_tools == ["InvokeAgent"]
-    # server scripts resolve under the passed agents dir
-    assert mcp_servers["openswarm-mcp-meta"]["args"][0].startswith("/agents")
+    # Every registered server's script path must resolve to a file that ACTUALLY EXISTS.
+    # This is the assertion that catches a moved-caller resolving the wrong agents dir.
+    for name in ("openswarm-mcp-meta", "openswarm-settings-meta",
+                 "openswarm-browser-agent", "openswarm-invoke-agent"):
+        script = mcp_servers[name]["args"][0]
+        assert os.path.isfile(script), f"{name} script does not exist on disk: {script}"
 
 
 def test_fully_denied_delegation_servers_are_not_registered():
     mcp_servers = {}
     perms = {t: "deny" for t in ("CreateBrowserAgent", "BrowserAgent", "BrowserAgents", "InvokeAgent")}
-    register_builtin_mcp_servers(mcp_servers, p_session(), perms, None, "/agents")
+    register_builtin_mcp_servers(mcp_servers, p_session(), perms, None)
     assert "openswarm-browser-agent" not in mcp_servers   # all browser tools denied -> skip
     assert "openswarm-invoke-agent" not in mcp_servers
     assert "openswarm-mcp-meta" in mcp_servers             # always-on regardless