diff --git a/src/lh_harness/adapters/claude_code.py b/src/lh_harness/adapters/claude_code.py
index 8586b09..c6410e3 100644
--- a/src/lh_harness/adapters/claude_code.py
+++ b/src/lh_harness/adapters/claude_code.py
@@ -62,8 +62,9 @@ def __init__(
             ]
         )
 
-        # MCP support remains opt-in. --strict-mcp-config keeps unrelated
-        # user/project MCP servers out of every role.
+        # MCP support remains opt-in. The --strict-mcp-config flag appended to
+        # command_parts below keeps unrelated user/project MCP servers out of
+        # every role.
         mcp_config = mcp_config or os.getenv("LH_HARNESS_CLAUDECODE_MCP_CONFIG")
         if mcp_config:
             candidate = Path(mcp_config).expanduser()
@@ -98,6 +99,10 @@ def __init__(
             "stream-json",
             "--verbose",
             "--dangerously-skip-permissions",
+            # Role isolation: without this the CLI also loads every MCP server
+            # the operator has configured at user or project scope. With it,
+            # a role sees only the servers in an explicit --mcp-config.
+            "--strict-mcp-config",
         ]
         deny_tools = [*policy.disallowed_tools, *path_deny_rules(hidden_paths)]
         if deny_tools:
diff --git a/tests/test_claude_code_adapter.py b/tests/test_claude_code_adapter.py
new file mode 100644
index 0000000..4573feb
--- /dev/null
+++ b/tests/test_claude_code_adapter.py
@@ -0,0 +1,71 @@
+from __future__ import annotations
+
+import json
+import shlex
+from pathlib import Path
+
+import pytest
+
+from lh_harness.adapters.claude_code import ClaudeCodeAdapter
+from lh_harness.adapters.claude_permissions import ClaudeRole
+
+
+ROLES: tuple[ClaudeRole, ...] = (
+    "manager",
+    "cli_executor",
+    "gui_executor",
+    "cli_auditor",
+    "gui_auditor",
+    "auditor_format_repair",
+    "final_response",
+)
+
+
+def _tokens(adapter: ClaudeCodeAdapter) -> list[str]:
+    return shlex.split(adapter.command_template.replace("< {prompt_path}", ""))
+
+
+def _adapter(role: ClaudeRole, **overrides: object) -> ClaudeCodeAdapter:
+    kwargs: dict[str, object] = {
+        "model": "claude-sonnet-5",
+        "role": role,
+        "workspace_path": "/tmp/ws",
+        "prompt_dir": "/tmp/prompts",
+    }
+    kwargs.update(overrides)
+    return ClaudeCodeAdapter(**kwargs)  # type: ignore[arg-type]
+
+
+@pytest.mark.parametrize("role", ROLES)
+def test_every_role_ignores_the_operator_mcp_registries(role: ClaudeRole) -> None:
+    """No role may inherit user- or project-scope MCP servers.
+
+    The CLI loads `~/.claude.json` and a workspace `.mcp.json` unless it is told
+    not to, so an operator's unrelated servers otherwise reach every episode.
+    """
+    assert "--strict-mcp-config" in _tokens(_adapter(role))
+
+
+def test_a_configured_mcp_config_is_still_the_only_source(tmp_path: Path) -> None:
+    """An explicit plugin config is loaded, and remains the sole source."""
+    config = tmp_path / "computer-use.mcp.json"
+    config.write_text(json.dumps({"mcpServers": {}}), encoding="utf-8")
+
+    tokens = _tokens(_adapter("cli_executor", mcp_config=str(config)))
+
+    assert tokens[tokens.index("--mcp-config") + 1] == str(config.resolve())
+    assert "--strict-mcp-config" in tokens
+
+
+def test_the_environment_mcp_config_is_scoped_the_same_way(
+    monkeypatch, tmp_path: Path
+) -> None:
+    """`LH_HARNESS_CLAUDECODE_MCP_CONFIG` widens the allow-list, not the scope."""
+    config = tmp_path / "env.mcp.json"
+    config.write_text(json.dumps({"mcpServers": {}}), encoding="utf-8")
+    monkeypatch.setenv("LH_HARNESS_CLAUDECODE_MCP_CONFIG", str(config))
+
+    tokens = _tokens(_adapter("cli_auditor"))
+
+    assert tokens[tokens.index("--mcp-config") + 1] == str(config.resolve())
+    assert "--strict-mcp-config" in tokens