diff --git a/tests/test_issue17_workspace_root_isolation.py b/tests/test_issue17_workspace_root_isolation.py
index e5f1d93..50c7a9b 100644
--- a/tests/test_issue17_workspace_root_isolation.py
+++ b/tests/test_issue17_workspace_root_isolation.py
@@ -38,6 +38,8 @@ NODES = [
     "tests/test_orc_onboard.py::test_o12_onboard_add_uuid",
     "tests/test_workspace_scope.py::TestWorkspaceScope::test_derived_herdr_session_name",
     "tests/test_issue17_item4_decisions.py::test_c_cmd_wait",
+    "tests/test_o2_race_free_lock.py::test_o2_12_run_loop_exits_on_lock_failure",
+    "tests/test_o1_rebuttal.py::test_v3_rebut_option_parsing_and_budget",
 ]
 
 
diff --git a/tests/test_o1_rebuttal.py b/tests/test_o1_rebuttal.py
index a320fe9..be77a6f 100644
--- a/tests/test_o1_rebuttal.py
+++ b/tests/test_o1_rebuttal.py
@@ -7,6 +7,10 @@ import os
 import subprocess
 import pytest
 
+# Issue #17: shells started here inherit a WORKSPACE_ROOT of this test's own
+# (lib.sh would otherwise rewrite the checkout's .mam/shim/herdr).
+pytestmark = pytest.mark.usefixtures("own_workspace_root")
+
 REPO_ROOT = os.path.abspath(os.path.join(os.path.dirname(__file__), ".."))
 RUN_LOOP_SH = os.path.join(REPO_ROOT, ".agents", "skills", "multi-agent-mux-loop", "scripts", "run_loop.sh")
 RULES_MD = os.path.join(REPO_ROOT, ".agents", "MULTI_AGENT_RULES.md")
diff --git a/tests/test_o2_race_free_lock.py b/tests/test_o2_race_free_lock.py
index a3a392f..834cc1b 100644
--- a/tests/test_o2_race_free_lock.py
+++ b/tests/test_o2_race_free_lock.py
@@ -193,6 +193,9 @@ def test_o2_11_legacy_marker_respected(tmp_path):
         proc_dummy.wait()
 
 
+# Issue #17: run_loop.sh sources lib.sh, which rewrites $WORKSPACE_ROOT/.mam/shim/herdr;
+# only this test runs it (a module-wide mark would add an entry to o2_7's tmp_path).
+@pytest.mark.usefixtures("own_workspace_root")
 def test_o2_12_run_loop_exits_on_lock_failure(tmp_path):
     marker = tmp_path / "loop-guard-active"
     proc = acquire_bg(marker)