diff --git a/src/ucode/agents/pi.py b/src/ucode/agents/pi.py
index e7c1760..b27e427 100644
--- a/src/ucode/agents/pi.py
+++ b/src/ucode/agents/pi.py
@@ -1,4 +1,4 @@
-"""Pi coding agent: writes ~/.pi/agent/models.json with Databricks-backed providers.
+"""Pi coding agent: writes a ucode-private models.json with Databricks-backed providers.
 
 Pi (https://pi.dev) is a multi-provider coding agent. We register three
 providers in its `models.json`, each speaking the API dialect best suited to
@@ -108,7 +108,7 @@ def render_overlay(
     codex_models: list[str],
     gemini_models: list[str],
 ) -> tuple[dict, list[list[str]]]:
-    """Return (overlay, managed_key_paths) for ~/.pi/agent/models.json."""
+    """Return (overlay, managed_key_paths) for Pi's private agent config."""
     providers: dict = {}
     keys: list[list[str]] = [["model"]]
     # Pi expands header values that match an env var name. Our UA contains
@@ -237,7 +237,7 @@ def _refresh_forever(state: dict, stop_event: threading.Event) -> None:
 def build_runtime_env(token: str) -> dict[str, str]:
     env = os.environ.copy()
     env["OAUTH_TOKEN"] = token
-    env["HOME"] = str(PI_UCODE_HOME)
+    env["PI_CODING_AGENT_DIR"] = str(PI_CONFIG_DIR)
     return env
 
 
diff --git a/tests/test_agent_pi.py b/tests/test_agent_pi.py
index 0afc5fb..0d3be80 100644
--- a/tests/test_agent_pi.py
+++ b/tests/test_agent_pi.py
@@ -240,9 +240,13 @@ def test_sets_oauth_token(self):
         env = pi.build_runtime_env("tok")
         assert env["OAUTH_TOKEN"] == "tok"
 
-    def test_sets_ucode_home(self):
+    def test_sets_private_agent_dir_without_replacing_home(self, monkeypatch):
+        monkeypatch.setenv("HOME", "/real-user-home")
+
         env = pi.build_runtime_env("tok")
-        assert env["HOME"] == str(pi.PI_UCODE_HOME)
+
+        assert env["PI_CODING_AGENT_DIR"] == str(pi.PI_CONFIG_DIR)
+        assert env["HOME"] == "/real-user-home"
 
 
 class TestPiValidateCmd:
diff --git a/tests/test_e2e.py b/tests/test_e2e.py
index 025ced4..2cd9b89 100644
--- a/tests/test_e2e.py
+++ b/tests/test_e2e.py
@@ -911,14 +911,17 @@ def test_launch_pi_per_model(self, tmp_path, monkeypatch, e2e_state, e2e_workspa
             pytest.skip("No Pi-compatible models available on this workspace")
 
         monkeypatch.setattr(config_io_mod, "APP_DIR", tmp_path)
-        # Pi reads models.json below HOME/.pi/agent. Point both pi's runtime
-        # HOME and our writer at the same isolated tmp home.
+        # Point PI_CODING_AGENT_DIR and ucode's config writer at the same
+        # isolated directory without changing the process HOME.
         pi_home = tmp_path / "pi-home"
         pi_dir = pi_home / ".pi" / "agent"
         config_path = pi_dir / "models.json"
         backup_path = tmp_path / "pi-models.backup.json"
         monkeypatch.setattr(pi, "PI_UCODE_HOME", pi_home)
+        monkeypatch.setattr(pi, "PI_CONFIG_DIR", pi_dir)
         monkeypatch.setattr(pi, "PI_CONFIG_PATH", config_path)
+        monkeypatch.setattr(pi, "PI_SETTINGS_PATH", pi_dir / "settings.json")
+        monkeypatch.setattr(pi, "PI_SETTINGS_BACKUP_PATH", tmp_path / "pi-settings.backup.json")
         monkeypatch.setattr(pi, "PI_BACKUP_PATH", backup_path)
 
         failures = []
diff --git a/tests/test_e2e_user_agent.py b/tests/test_e2e_user_agent.py
index 884e663..e6cec21 100644
--- a/tests/test_e2e_user_agent.py
+++ b/tests/test_e2e_user_agent.py
@@ -325,7 +325,10 @@ def test_user_agent_arrives_at_gateway(self, tmp_path, monkeypatch, capture_serv
 
         monkeypatch.setattr(config_io_mod, "APP_DIR", tmp_path)
         monkeypatch.setattr(pi, "PI_UCODE_HOME", pi_home)
+        monkeypatch.setattr(pi, "PI_CONFIG_DIR", pi_dir)
         monkeypatch.setattr(pi, "PI_CONFIG_PATH", config_path)
+        monkeypatch.setattr(pi, "PI_SETTINGS_PATH", pi_dir / "settings.json")
+        monkeypatch.setattr(pi, "PI_SETTINGS_BACKUP_PATH", tmp_path / "pi-settings.backup.json")
         monkeypatch.setattr(pi, "PI_BACKUP_PATH", tmp_path / "pi.backup.json")
 
         state = {