diff --git a/docs/reference/trajectory-assessment.md b/docs/reference/trajectory-assessment.md
index 64e41d4b0c..4547a86106 100644
--- a/docs/reference/trajectory-assessment.md
+++ b/docs/reference/trajectory-assessment.md
@@ -24,7 +24,11 @@ not independent verification of a model's translation or judgments.
 The Codex observer reuses native Chat's shared authenticated HTTP transport.
 Credentials and refresh remain with Codex's existing signed-in account; the
 observer neither copies tokens nor imports user tool/rule configuration. Its
-explicit read-only sandbox, disabled shell/exec/web tools and fixed supplied
+child follows the desktop service's explicit `LOOPX_CHAT_CODEX_HOME` account
+selection rather than an unrelated inherited `CODEX_HOME`. Without that Chat
+selection, ordinary CLI account discovery remains unchanged. This selects an
+existing native account directory; it does not copy credentials or change login.
+The explicit read-only sandbox, disabled shell/exec/web tools and fixed supplied
 evidence remain in force. A failed provider attempt stays in job history and
 requires an explicit retry after the host problem is repaired.
 
diff --git a/loopx/capabilities/benchmark_toolkit/trajectory_assessment.py b/loopx/capabilities/benchmark_toolkit/trajectory_assessment.py
index e2d68e2468..f0c8e7c9a6 100644
--- a/loopx/capabilities/benchmark_toolkit/trajectory_assessment.py
+++ b/loopx/capabilities/benchmark_toolkit/trajectory_assessment.py
@@ -156,6 +156,12 @@ def execute(
         # rules. The shared host transport delegates credentials/refresh to
         # Codex; it supplies no endpoint, bearer token or account configuration.
         transport = shared_chatgpt_transport({}, {})
+        # The desktop service pins its Chat account independently of an
+        # unrelated terminal's CODEX_HOME. Use that existing host selection;
+        # leave ordinary CLI environments and Codex-owned credentials intact.
+        environment = dict(os.environ)
+        if chat_home := environment.get("LOOPX_CHAT_CODEX_HOME"):
+            environment["CODEX_HOME"] = chat_home
         provider = transport["model_provider"]
         transport_args = ["-c", f"model_provider={json.dumps(provider)}"]
         for key, value in transport["model_providers"][provider].items():
@@ -237,6 +243,7 @@ def execute(
                 stdin=prompt,
                 stdout=events,
                 stderr=errors,
+                env=environment,
                 text=True,
                 encoding="utf-8",
             )
diff --git a/tests/capabilities/test_trajectory_assessment.py b/tests/capabilities/test_trajectory_assessment.py
index d19728c4f0..3588fc2c98 100644
--- a/tests/capabilities/test_trajectory_assessment.py
+++ b/tests/capabilities/test_trajectory_assessment.py
@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import json
+import os
 from pathlib import Path
 import sys
 import threading
@@ -64,7 +65,8 @@ def prepared(tmp_path):
 
 
 def provider(
-    tmp_path: Path, *, delay=0, code=0, invalid=False, invalid_utf8=False
+    tmp_path: Path, *, delay=0, code=0, invalid=False, invalid_utf8=False,
+    expected_home=None,
 ) -> str:
     script = tmp_path / "codex-fixture"
     output = {
@@ -88,7 +90,7 @@ def provider(
     )
     script.write_text(
         f"""#!{sys.executable}
-import json,sys,time
+import json,os,sys,time
 from pathlib import Path
 assert "\\u539f\\u59cb\\u76ee\\u6807" in sys.stdin.buffer.read().decode("utf-8")
 options = dict(arg.split('=', 1) for index, arg in enumerate(sys.argv) if index > 0 and sys.argv[index-1] == '-c')
@@ -100,6 +102,8 @@ def provider(
 assert sys.argv[sys.argv.index('--sandbox')+1] == 'read-only'
 assert json.loads(options['web_search']) == 'disabled'
 assert 'shell_tool' in sys.argv and 'unified_exec' in sys.argv
+if {expected_home!r} is not None:
+    assert os.environ.get('CODEX_HOME') == {expected_home!r}
 time.sleep({delay})
 if {code}: sys.exit({code})
 Path(sys.argv[sys.argv.index('-o')+1]).write_bytes({payload!r})
@@ -112,6 +116,26 @@ def provider(
     return str(script)
 
 
+@pytest.mark.parametrize("chat_home", [None, "", "selected-chat-home"])
+def test_actual_child_uses_explicit_chat_account_not_unrelated_terminal(
+    prepared, tmp_path, monkeypatch, chat_home
+):
+    monkeypatch.setenv("CODEX_HOME", "unrelated-terminal-home")
+    if chat_home is None:
+        monkeypatch.delenv("LOOPX_CHAT_CODEX_HOME", raising=False)
+    else:
+        monkeypatch.setenv("LOOPX_CHAT_CODEX_HOME", chat_home)
+    expected = "selected-chat-home" if chat_home else "unrelated-terminal-home"
+    result = execute(
+        prepared, tmp_path / "jobs",
+        codex=provider(tmp_path, expected_home=expected),
+    )
+    assert result["status"] == "succeeded"
+    # Selection belongs to this child, not the server's process or saved input.
+    assert os.environ["CODEX_HOME"] == "unrelated-terminal-home"
+    assert "CODEX_HOME" not in result["config"]
+
+
 def test_actual_child_reuse_and_repair_of_derived_output(prepared, tmp_path):
     first = execute(prepared, tmp_path / "jobs", codex=provider(tmp_path))
     assert first["status"] == "succeeded" and first["usage"] == {