diff --git a/api/models.py b/api/models.py
index 8d6363e6..0969958e 100644
--- a/api/models.py
+++ b/api/models.py
@@ -3392,21 +3392,30 @@ class _ExternalSessionView:
 
 
 def get_session_for_file_ops(sid: str):
-    """Return a session-like object for file-manager handlers.
+    """Return a profile-authorized session-like object for file-manager handlers.
 
     Tries ``get_session`` first (preserves all existing behavior for WebUI
-    sessions). If that raises ``KeyError``, checks state.db; when the session
-    exists there, returns an ``_ExternalSessionView`` whose ``workspace`` is
-    the active WebUI workspace. If neither has the session, re-raises
+    sessions) and only returns that session when its stored profile belongs to
+    the active request profile.  If that lookup fails, checks state.db; when the
+    session exists there, returns an ``_ExternalSessionView`` whose ``workspace``
+    is the active WebUI workspace. If neither has the session, re-raises
     ``KeyError`` so callers continue to return their existing 404.
     """
     try:
-        return get_session(sid, metadata_only=True)
+        session = get_session(sid, metadata_only=True)
     except KeyError:
         if state_db_has_session(sid):
             return _ExternalSessionView(str(sid), str(get_last_workspace()))
         raise
 
+    from api.profiles import _profiles_match, get_active_profile_name
+
+    if not _profiles_match(
+        getattr(session, 'profile', None), get_active_profile_name()
+    ):
+        raise KeyError(sid)
+    return session
+
 
 def _active_state_db_path() -> Path:
     """Return state.db for the active Hermes profile, degrading to HERMES_HOME."""
diff --git a/tests/test_file_manager_external_session.py b/tests/test_file_manager_external_session.py
index 0acac148..eb6e5c86 100644
--- a/tests/test_file_manager_external_session.py
+++ b/tests/test_file_manager_external_session.py
@@ -11,9 +11,12 @@ Covers:
 
 from __future__ import annotations
 
+import io
 import re
 import sqlite3
 from pathlib import Path
+from types import SimpleNamespace
+from urllib.parse import urlparse
 
 import pytest
 
@@ -107,7 +110,8 @@ def models_module():
 
 def test_get_session_for_file_ops_webui_passthrough(models_module, monkeypatch):
     """(a) WebUI session — delegates to get_session, no state.db consulted."""
-    sentinel = object()
+    profiles_module = pytest.importorskip("api.profiles")
+    sentinel = SimpleNamespace(profile=None)
     called = {"get_session": 0, "state_db": 0}
 
     def fake_get_session(sid, metadata_only=False):
@@ -120,11 +124,88 @@ def test_get_session_for_file_ops_webui_passthrough(models_module, monkeypatch):
 
     monkeypatch.setattr(models_module, "get_session", fake_get_session)
     monkeypatch.setattr(models_module, "state_db_has_session", fake_has)
+    monkeypatch.setattr(profiles_module, "get_active_profile_name", lambda: "default")
     result = models_module.get_session_for_file_ops("webui-sid")
     assert result is sentinel
     assert called == {"get_session": 1, "state_db": 0}
 
 
+def test_get_session_for_file_ops_rejects_foreign_profile(
+    models_module, monkeypatch, tmp_path
+):
+    """WebUI sessions must belong to the active profile before file access."""
+    profiles_module = pytest.importorskip("api.profiles")
+    foreign_session = SimpleNamespace(profile="research", workspace=str(tmp_path))
+    called = {"get_session": 0, "state_db": 0}
+
+    def fake_get_session(sid, metadata_only=False):
+        called["get_session"] += 1
+        return foreign_session
+
+    def fake_has(_sid):
+        called["state_db"] += 1
+        return True
+
+    monkeypatch.setattr(models_module, "get_session", fake_get_session)
+    monkeypatch.setattr(models_module, "state_db_has_session", fake_has)
+    monkeypatch.setattr(profiles_module, "get_active_profile_name", lambda: "default")
+
+    with pytest.raises(KeyError):
+        models_module.get_session_for_file_ops("foreign-webui-sid")
+    # A found-but-foreign WebUI sidecar is an authorization failure, not a
+    # missing-session condition that can fall through to the state.db fallback.
+    assert called == {"get_session": 1, "state_db": 0}
+
+
+def test_file_read_rejects_foreign_profile_session(
+    models_module, monkeypatch, tmp_path
+):
+    """A default-profile file route cannot read a named-profile workspace."""
+    profiles_module = pytest.importorskip("api.profiles")
+    routes_module = pytest.importorskip("api.routes")
+    workspace = tmp_path / "named-workspace"
+    workspace.mkdir()
+    (workspace / "marker.txt").write_text("foreign profile marker")
+    session = models_module.Session(
+        session_id="foreign-profile-file-read",
+        workspace=str(workspace),
+        profile="research",
+    )
+    models_module.SESSIONS[session.session_id] = session
+
+    class Handler:
+        command = "GET"
+        headers = {}
+
+        def __init__(self):
+            self.status = None
+            self.headers_sent = []
+            self.wfile = io.BytesIO()
+
+        def send_response(self, code):
+            self.status = code
+
+        def send_header(self, key, value):
+            self.headers_sent.append((key, value))
+
+        def end_headers(self):
+            pass
+
+    monkeypatch.setattr(profiles_module, "get_active_profile_name", lambda: "default")
+    try:
+        handler = Handler()
+        routes_module._handle_file_read(
+            handler,
+            urlparse(
+                "/api/file?session_id=foreign-profile-file-read&path=marker.txt"
+            ),
+        )
+        assert handler.status == 404
+        assert b"foreign profile marker" not in handler.wfile.getvalue()
+    finally:
+        models_module.SESSIONS.pop(session.session_id, None)
+
+
 def test_get_session_for_file_ops_state_db_fallback(
     models_module, monkeypatch, tmp_path
 ):