diff --git a/tests/conftest.py b/tests/conftest.py
index 946ab206..546639bc 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -4,6 +4,9 @@ from __future__ import annotations
 
 import pytest
 
+from strix.config import loader
+from strix.interface import platform_identity
+
 
 @pytest.fixture(autouse=True)
 def _isolate_mcp_config(
@@ -26,6 +29,24 @@ def _isolate_mcp_config(
     monkeypatch.delenv("STRIX_MCP_EXCLUDE", raising=False)
 
 
+@pytest.fixture(autouse=True)
+def _isolate_user_state(
+    monkeypatch: pytest.MonkeyPatch, tmp_path_factory: pytest.TempPathFactory
+) -> None:
+    """Keep the suite from writing the developer's real ``~/.strix`` files.
+
+    Code the tests drive persists the CLI config and the device identity at paths
+    that are fixed when the modules are imported (``Path.home()`` at import time),
+    so setting ``HOME`` per test is too late for them. Without this, running the
+    suite replaces ``~/.strix/cli-config.json`` (the stored model, API key and API
+    base) and ``~/.strix/cli-identity.json`` with whatever the last test wrote.
+    Tests that exercise these paths set their own after this runs.
+    """
+    state = tmp_path_factory.mktemp("strix-user-state")
+    monkeypatch.setattr(loader, "_DEFAULT_PATH", state / "cli-config.json")
+    monkeypatch.setattr(platform_identity, "IDENTITY_PATH", state / "cli-identity.json")
+
+
 @pytest.fixture(autouse=True)
 def _plain_terminal(monkeypatch: pytest.MonkeyPatch) -> None:
     """Make Rich output identical on every developer's machine.
diff --git a/tests/test_cloud_cli.py b/tests/test_cloud_cli.py
index 41962b9d..8626c939 100644
--- a/tests/test_cloud_cli.py
+++ b/tests/test_cloud_cli.py
@@ -17,10 +17,19 @@ import requests
 from rich.console import Console
 
 from strix.interface import cloud, platform_cli
-from strix.interface.cloud import http, render, runner, workspaces
+from strix.interface.cloud import billing, http, render, runner, workspaces
 from strix.interface.cloud.spec import GROUP_HELP, SPEC
 
 
+@pytest.fixture(autouse=True)
+def _wallet_cache_in_tmp(
+    monkeypatch: pytest.MonkeyPatch, tmp_path_factory: pytest.TempPathFactory
+) -> None:
+    """Keep the top-up flow's npm cache (``~/.strix/wallet-npm-cache``) out of the real home."""
+    cache = tmp_path_factory.mktemp("wallet-npm-cache")
+    monkeypatch.setattr(billing, "_wallet_npm_cache", lambda: cache)
+
+
 class FakeResponse:
     def __init__(
         self,
diff --git a/tests/test_telemetry_resume.py b/tests/test_telemetry_resume.py
index 9a0f92fd..6347996d 100644
--- a/tests/test_telemetry_resume.py
+++ b/tests/test_telemetry_resume.py
@@ -68,8 +68,10 @@ def test_scan_ended_reports_resumed_usage_delta(
 @pytest.mark.parametrize("telemetry", [posthog, scarf])
 def test_scan_ended_reports_all_fresh_run_usage(
     telemetry: Any,
+    tmp_path: Any,
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
+    monkeypatch.chdir(tmp_path)  # a run directory is created under ./strix_runs
     state = ReportState()
     state.record_sdk_usage(
         agent_id="agent",