diff --git a/tests/conftest.py b/tests/conftest.py
index c4f47e3..4c75631 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -177,6 +177,21 @@ def _isolate_mam_state_dirs(_ambient_control_plane, tmp_path, monkeypatch):
     monkeypatch.setenv("MAM_ENV_FILE", str(state / ".mam.env.absent"))
 
 
+@pytest.fixture
+def own_workspace_root(tmp_path, monkeypatch):
+    """Issue #17: every `source lib.sh` rewrites $WORKSPACE_ROOT/.mam/shim/herdr,
+    and lib.sh derives this checkout when the variable is unset (a value naming
+    this checkout survives pytest_configure). A module whose shells inherit the
+    process environment opts in with `pytestmark = pytest.mark.usefixtures(
+    "own_workspace_root")`: they then write under this test's tmp_path instead.
+    mam_sandbox and a test's own WORKSPACE_ROOT run later and still win. Not
+    autouse: in-process code reads WORKSPACE_ROOT too (runner.py, mqtt_common)."""
+    root = tmp_path / ".mam-test-state" / "workspace"
+    root.mkdir(parents=True, exist_ok=True)
+    monkeypatch.setenv("WORKSPACE_ROOT", str(root))
+    return root
+
+
 @pytest.fixture
 def mam_sandbox(tmp_path, monkeypatch, request):
     """
diff --git a/tests/test_b19_headless_reconcile_fixes.py b/tests/test_b19_headless_reconcile_fixes.py
index 36c56c1..d916209 100644
--- a/tests/test_b19_headless_reconcile_fixes.py
+++ b/tests/test_b19_headless_reconcile_fixes.py
@@ -8,6 +8,10 @@ import pytest
 
 from lib_py.layout import compute_2xk_layout
 
+# 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")
+
 
 def test_bug2_headless_layout_does_not_overflow():
     """Verify Bug 2: w=0, h=0 in headless mode does not trigger overflow."""
diff --git a/tests/test_b8_send_keys_verification.py b/tests/test_b8_send_keys_verification.py
index 43af495..1c9afe2 100644
--- a/tests/test_b8_send_keys_verification.py
+++ b/tests/test_b8_send_keys_verification.py
@@ -2,6 +2,10 @@ 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")
+
 def test_send_keys_safe_b8_verification(tmp_path):
     """Verify that send_keys_safe for agy sessions goes through submission verification and does not return 0 blindly on failure."""
     # Test script that mocks herdr commands and tests send_keys_safe behavior for agy
diff --git a/tests/test_issue17_workspace_root_isolation.py b/tests/test_issue17_workspace_root_isolation.py
new file mode 100644
index 0000000..e5f1d93
--- /dev/null
+++ b/tests/test_issue17_workspace_root_isolation.py
@@ -0,0 +1,92 @@
+"""Issue #17 follow-up (v4.8.7 review): no test writes into the workspace it
+inherited. Every `source lib.sh` rewrites $WORKSPACE_ROOT/.mam/shim/herdr, and
+lib.sh derives the checkout when the variable is unset; conftest keeps a
+WORKSPACE_ROOT that names this checkout. So the danger is the checkout itself -
+the live workspace when the suite runs in the main checkout from an agent pane.
+
+- W1: a copy of this checkout runs one test of every module whose shells used
+  to inherit the root, with WORKSPACE_ROOT naming the copy: the copy gets no
+  .mam at all (the modules now use own_workspace_root or pin a root).
+- W2: test_orc_onboard's environment, taken at import, does not carry the
+  import-time WORKSPACE_ROOT into a later call.
+"""
+from __future__ import annotations
+
+import os
+import re
+import shutil
+import subprocess
+import sys
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parent.parent
+TESTS = REPO_ROOT / "tests"
+
+# one test per module that sourced lib.sh (or ran the wrapper / run_loop.sh)
+# with the inherited root; each wrote <checkout>/.mam/shim/herdr at 6b00b6e
+NODES = [
+    "tests/test_version_consistency.py::test_mam_version_is_not_env_overridable",
+    "tests/test_b19_headless_reconcile_fixes.py::test_fullscreen_tip_is_not_a_blocking_dialog",
+    "tests/test_b19_headless_reconcile_fixes.py::test_bug4_slow_settling_pane_success",
+    "tests/test_b8_send_keys_verification.py::test_send_keys_safe_b8_verification",
+    "tests/test_issue6_fail_closed.py::test_t1_25_stop_session_cancels_redispatched_job_with_pinned_token",
+    "tests/test_loop_cli.py::test_help_lists_creator_not_target_agent",
+    "tests/test_issue5_phase3_loop.py::test_p3_02_run_loop_wrapper_help_lists_same_as_bash",
+    "tests/test_issue5_phase4_runtime.py::test_p4_03_freeze_bypass_by_default",
+    "tests/test_o3_scoped_guard.py::test_b13_no_freeze_switch_disables_reexec",
+    "tests/test_issue25_plan_reuse.py::test_p7b_the_legacy_shell_loop_refuses_the_option",
+    "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",
+]
+
+
+def _copy_checkout(dst: Path) -> None:
+    files = subprocess.run(["git", "-C", str(REPO_ROOT), "ls-files", "-co", "--exclude-standard"],
+                           capture_output=True, text=True, check=True).stdout.splitlines()
+    for rel in files:
+        src = REPO_ROOT / rel
+        if src.is_file() and not rel.startswith(("nats-docker/", ".mam/")):
+            (dst / rel).parent.mkdir(parents=True, exist_ok=True)
+            shutil.copy2(src, dst / rel)
+
+
+def test_w1_no_test_writes_into_the_checkout_it_runs_in(tmp_path):
+    copy = tmp_path / "checkout"
+    _copy_checkout(copy)
+    assert not (copy / ".mam").exists()
+    env = {k: v for k, v in os.environ.items() if not k.startswith(("HERDR_", "MAM_", "MQTT_", "SKS_"))}
+    env.update(WORKSPACE_ROOT=str(copy), AGENT_PYTHON_BIN=sys.executable, PYTHONDONTWRITEBYTECODE="1")
+    env.pop("PYTHONPATH", None)
+    res = subprocess.run([sys.executable, "-m", "pytest", "-p", "no:cacheprovider", "-q", "-x",
+                          f"--basetemp={tmp_path / 'bt'}", *NODES],
+                         capture_output=True, text=True, cwd=str(copy), env=env, timeout=900)
+    assert res.returncode == 0, res.stdout[-3000:] + res.stderr[-2000:]
+    summary = res.stdout.strip().splitlines()[-1]  # some nodes are parametrized: at least one test each
+    assert int(re.search(r"(\d+) passed", summary).group(1)) >= len(NODES) and "skipped" not in summary, summary
+    written = sorted(str(p.relative_to(copy)) for p in (copy / ".mam").rglob("*")) if (copy / ".mam").exists() else []
+    assert written == [], f"tests wrote into the checkout they ran in: {written}"
+
+
+_ONBOARD_PROBE = r"""
+import os, sys
+from pathlib import Path
+sys.path.insert(0, sys.argv[1])
+import test_orc_onboard as m          # imported while WORKSPACE_ROOT is the sentinel
+ws = Path(sys.argv[2])
+os.environ["WORKSPACE_ROOT"] = str(ws)  # what mam_sandbox sets later
+m.run_find_uuid(str(ws), "claude")
+"""
+
+
+def test_w2_onboard_does_not_carry_its_import_time_root(tmp_path):
+    sentinel, ws = tmp_path / "sentinel", tmp_path / "fixture-ws"
+    sentinel.mkdir()
+    ws.mkdir()
+    env = {k: v for k, v in os.environ.items() if not k.startswith(("HERDR_", "MAM_", "MQTT_", "SKS_"))}
+    env.update(WORKSPACE_ROOT=str(sentinel), HOME=str(tmp_path), PYTHONDONTWRITEBYTECODE="1")
+    res = subprocess.run([sys.executable, "-c", _ONBOARD_PROBE, str(TESTS), str(ws)], capture_output=True,
+                         text=True, env=env, cwd=str(tmp_path), timeout=120)
+    assert res.returncode == 0, res.stderr[-2000:]
+    assert sorted(str(p.relative_to(sentinel)) for p in sentinel.rglob("*")) == [], "written into the import-time root"
+    assert (ws / ".mam" / "shim" / "herdr").is_file(), "the call's own root got lib.sh's shim"
diff --git a/tests/test_issue21_worktree_prereqs.py b/tests/test_issue21_worktree_prereqs.py
index b091832..c81e975 100644
--- a/tests/test_issue21_worktree_prereqs.py
+++ b/tests/test_issue21_worktree_prereqs.py
@@ -543,7 +543,8 @@ def _create(tmp: Path, ws: Path, env=None) -> subprocess.CompletedProcess:
 
 def _mutate(tmp: Path, code: str) -> None:
     res = subprocess.run(["bash", "-c", f"source {_skill(tmp, 'lib.sh')} && atomic_dump_yaml {tmp / '.mam' / 'agent-sessions.yaml'}"],
-                         input=code, capture_output=True, text=True)
+                         input=code, capture_output=True, text=True,
+                         env=dict(os.environ, WORKSPACE_ROOT=str(tmp)))  # Issue #17: not an inherited root
     assert res.returncode == 0, res.stderr
 
 
diff --git a/tests/test_issue25_plan_reuse.py b/tests/test_issue25_plan_reuse.py
index 5296967..c950185 100644
--- a/tests/test_issue25_plan_reuse.py
+++ b/tests/test_issue25_plan_reuse.py
@@ -24,6 +24,10 @@ from pathlib import Path
 
 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 = Path(__file__).resolve().parent.parent
 RUNNER_PY = REPO_ROOT / ".agents" / "skills" / "lib_py" / "loop" / "runner.py"
 RUN_LOOP_SH = REPO_ROOT / ".agents" / "skills" / "multi-agent-mux-loop" / "scripts" / "run_loop.sh"
diff --git a/tests/test_issue5_phase3_loop.py b/tests/test_issue5_phase3_loop.py
index a12549d..12ade47 100644
--- a/tests/test_issue5_phase3_loop.py
+++ b/tests/test_issue5_phase3_loop.py
@@ -29,6 +29,10 @@ if str(SKILLS) not in sys.path:
 
 from lib_py.loop import parser, checkpoint, runner
 
+# 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")
+
 
 def test_p3_01_strict_verdict_ignores_fenced_code():
     """P3-01: A verdict token inside markdown code fences must NOT be matched."""
diff --git a/tests/test_issue5_phase4_runtime.py b/tests/test_issue5_phase4_runtime.py
index 6b114d7..5d61b88 100644
--- a/tests/test_issue5_phase4_runtime.py
+++ b/tests/test_issue5_phase4_runtime.py
@@ -24,6 +24,10 @@ if str(SKILLS) not in sys.path:
 
 from lib_py.loop import eager, parser, checkpoint, runner
 
+# 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")
+
 
 def test_p4_01_eager_import_completeness_and_bytecode_inhibition(monkeypatch):
     """P4-01: Verify all core framework modules are eagerly loaded and bytecode writes disabled."""
diff --git a/tests/test_issue6_fail_closed.py b/tests/test_issue6_fail_closed.py
index 308b51d..dab0456 100644
--- a/tests/test_issue6_fail_closed.py
+++ b/tests/test_issue6_fail_closed.py
@@ -18,6 +18,10 @@ import pytest
 
 from _local_mqtt import local_broker_env
 
+# 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 = Path(__file__).resolve().parent.parent
 SKILLS = REPO_ROOT / ".agents" / "skills"
 WRAPPER = SKILLS / "multi-agent-mux-delegate-job" / "multi-agent-mux-delegate-job"
diff --git a/tests/test_loop_cli.py b/tests/test_loop_cli.py
index 41225b6..a45bec5 100644
--- a/tests/test_loop_cli.py
+++ b/tests/test_loop_cli.py
@@ -4,6 +4,11 @@
 import os
 import subprocess
 from pathlib import Path
+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 = Path(__file__).resolve().parent.parent
 RUN_LOOP_SH = REPO_ROOT / ".agents" / "skills" / "multi-agent-mux-loop" / "scripts" / "run_loop.sh"
diff --git a/tests/test_o3_scoped_guard.py b/tests/test_o3_scoped_guard.py
index 1a0b4d0..8618351 100644
--- a/tests/test_o3_scoped_guard.py
+++ b/tests/test_o3_scoped_guard.py
@@ -24,6 +24,10 @@ import time
 from pathlib import Path
 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 = Path(__file__).resolve().parent.parent
 GUARD_SCRIPT = REPO_ROOT / ".agents" / "hooks" / "loop_delegation_guard.sh"
 
diff --git a/tests/test_orc_onboard.py b/tests/test_orc_onboard.py
index ada9d33..3d5cbd9 100644
--- a/tests/test_orc_onboard.py
+++ b/tests/test_orc_onboard.py
@@ -7,19 +7,31 @@ import shutil
 import pytest
 from pathlib import Path
 
+# 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 = Path(__file__).parent.parent
 LIB_SH = REPO_ROOT / ".agents" / "skills" / "lib.sh"
 ONBOARD_SH = REPO_ROOT / ".agents" / "skills" / "multi-agent-mux-orc-onboard" / "scripts" / "orc_onboard.sh"
 RECONCILE_SH = REPO_ROOT / ".agents" / "skills" / "multi-agent-mux-monitor" / "scripts" / "reconcile.sh"
 
 SCRUBBED_ENV = dict(os.environ)
-for k in ["CLAUDE_CODE_SESSION_ID", "ANTIGRAVITY_CONVERSATION_ID", "HERMES_SESSION_ID", "MAM_ORCHESTRATOR_UUIDS"]:
+for k in ["CLAUDE_CODE_SESSION_ID", "ANTIGRAVITY_CONVERSATION_ID", "HERMES_SESSION_ID", "MAM_ORCHESTRATOR_UUIDS",
+          "WORKSPACE_ROOT"]:
     SCRUBBED_ENV.pop(k, None)
 SCRUBBED_ENV["PYTHONPATH"] = f"{LIB_SH.parent}:{SCRUBBED_ENV.get('PYTHONPATH', '')}"
 
 
+def _scrubbed_env(root=None) -> dict:
+    """SCRUBBED_ENV (taken at import) with the WORKSPACE_ROOT of now: `root`,
+    else this test's (own_workspace_root / mam_sandbox) - never the one the
+    module was imported under (Issue #17: lib.sh rewrites <it>/.mam/shim/herdr)."""
+    return dict(SCRUBBED_ENV, WORKSPACE_ROOT=str(root or os.environ["WORKSPACE_ROOT"]))
+
+
 def run_onboard(args, env=None, cwd=None):
-    run_env = dict(SCRUBBED_ENV)
+    run_env = _scrubbed_env(cwd)
     if cwd:
         run_env["AGENT_SESSIONS_YAML"] = f"{cwd}/.mam/agent-sessions.yaml"
         run_env["YAML_PATH"] = f"{cwd}/.mam/agent-sessions.yaml"
@@ -31,7 +43,7 @@ def run_onboard(args, env=None, cwd=None):
 
 
 def run_find_uuid(ws, agent, target="", env=None):
-    run_env = dict(SCRUBBED_ENV)
+    run_env = _scrubbed_env(ws)
     run_env["AGENT_SESSIONS_YAML"] = f"{ws}/.mam/agent-sessions.yaml"
     run_env["YAML_PATH"] = f"{ws}/.mam/agent-sessions.yaml"
     run_env["HOME_DIR"] = ws
@@ -44,7 +56,7 @@ def run_find_uuid(ws, agent, target="", env=None):
 
 
 def run_verify_uuid(ws, agent, uuid, row=None, mode="discover", env=None):
-    run_env = dict(SCRUBBED_ENV)
+    run_env = _scrubbed_env(ws)
     run_env["AGENT_SESSIONS_YAML"] = f"{ws}/.mam/agent-sessions.yaml"
     run_env["YAML_PATH"] = f"{ws}/.mam/agent-sessions.yaml"
     run_env["HOME_DIR"] = ws
@@ -62,7 +74,7 @@ def dump_state(mam_sandbox, state):
     env = {"AGENT_SESSIONS_YAML": yaml_path, "YAML_PATH": yaml_path, "HOME_DIR": str(mam_sandbox)}
     state_str = json.dumps(state)
     cmd = f"source '{LIB_SH}' && atomic_dump_yaml '{yaml_path}' <<'PYEOF'\nd.update({state_str})\nPYEOF"
-    subprocess.run(["bash", "-c", cmd], env={**SCRUBBED_ENV, **env}, check=True)
+    subprocess.run(["bash", "-c", cmd], env={**_scrubbed_env(mam_sandbox), **env}, check=True)
     return env
 
 
@@ -307,7 +319,7 @@ def test_o18_autodetect_via_env(mam_sandbox):
     }
     # Run inside subshell where command line matches claude
     cmd = f"export CLAUDE_CODE_SESSION_ID='{orc_uuid}' && exec -a claude bash '{ONBOARD_SH}'"
-    res = subprocess.run(["bash", "-c", cmd], capture_output=True, text=True, env={**SCRUBBED_ENV, **env}, cwd=str(mam_sandbox))
+    res = subprocess.run(["bash", "-c", cmd], capture_output=True, text=True, env={**_scrubbed_env(), **env}, cwd=str(mam_sandbox))
     assert res.returncode == 0
 
     res_list = run_onboard(["--list"], env=env, cwd=str(mam_sandbox))
@@ -327,7 +339,7 @@ def test_o20_validate_fails_on_non_list_orchestrator_uuids(mam_sandbox):
     env = {"AGENT_SESSIONS_YAML": str(mam_sandbox / ".mam" / "agent-sessions.yaml"), "YAML_PATH": str(mam_sandbox / ".mam" / "agent-sessions.yaml"), "HOME_DIR": str(mam_sandbox)}
     state_str = json.dumps(state)
     cmd = f"source '{LIB_SH}' && atomic_dump_yaml '{env['YAML_PATH']}' <<'PYEOF'\nd.update({state_str})\nPYEOF"
-    res = subprocess.run(["bash", "-c", cmd], env={**SCRUBBED_ENV, **env}, capture_output=True, text=True)
+    res = subprocess.run(["bash", "-c", cmd], env={**_scrubbed_env(), **env}, capture_output=True, text=True)
     assert res.returncode != 0
     assert "VALIDATE" in res.stderr or "VALIDATE" in res.stdout
 
@@ -339,7 +351,7 @@ def test_o21_validate_fails_on_duplicate_orchestrator_uuids(mam_sandbox):
     env = {"AGENT_SESSIONS_YAML": str(mam_sandbox / ".mam" / "agent-sessions.yaml"), "YAML_PATH": str(mam_sandbox / ".mam" / "agent-sessions.yaml"), "HOME_DIR": str(mam_sandbox)}
     state_str = json.dumps(state)
     cmd = f"source '{LIB_SH}' && atomic_dump_yaml '{env['YAML_PATH']}' <<'PYEOF'\nd.update({state_str})\nPYEOF"
-    res = subprocess.run(["bash", "-c", cmd], env={**SCRUBBED_ENV, **env}, capture_output=True, text=True)
+    res = subprocess.run(["bash", "-c", cmd], env={**_scrubbed_env(), **env}, capture_output=True, text=True)
     assert res.returncode != 0
 
 
@@ -349,7 +361,7 @@ def test_o22_validate_fails_on_empty_string_orchestrator_uuid(mam_sandbox):
     env = {"AGENT_SESSIONS_YAML": str(mam_sandbox / ".mam" / "agent-sessions.yaml"), "YAML_PATH": str(mam_sandbox / ".mam" / "agent-sessions.yaml"), "HOME_DIR": str(mam_sandbox)}
     state_str = json.dumps(state)
     cmd = f"source '{LIB_SH}' && atomic_dump_yaml '{env['YAML_PATH']}' <<'PYEOF'\nd.update({state_str})\nPYEOF"
-    res = subprocess.run(["bash", "-c", cmd], env={**SCRUBBED_ENV, **env}, capture_output=True, text=True)
+    res = subprocess.run(["bash", "-c", cmd], env={**_scrubbed_env(), **env}, capture_output=True, text=True)
     assert res.returncode != 0
 
 
@@ -367,7 +379,7 @@ if h1 == h2:
     sys.exit(1)
 PYEOF
 """
-    res = subprocess.run(["bash", "-c", cmd], env={**SCRUBBED_ENV, "AGENT_SESSIONS_YAML": yaml_path, "YAML_PATH": yaml_path}, capture_output=True, text=True)
+    res = subprocess.run(["bash", "-c", cmd], env={**_scrubbed_env(), "AGENT_SESSIONS_YAML": yaml_path, "YAML_PATH": yaml_path}, capture_output=True, text=True)
     assert res.returncode == 0
 
 
@@ -438,7 +450,7 @@ def test_o27_ignore_different_family_env_variable(mam_sandbox):
         "ANTIGRAVITY_CONVERSATION_ID": "72d2d251-5a06-486b-92e5-7e46a7a80d2e"
     }
     cmd = f"export ANTIGRAVITY_CONVERSATION_ID='72d2d251-5a06-486b-92e5-7e46a7a80d2e' && exec -a claude bash '{ONBOARD_SH}'"
-    res = subprocess.run(["bash", "-c", cmd], capture_output=True, text=True, env={**SCRUBBED_ENV, **env}, cwd=str(mam_sandbox))
+    res = subprocess.run(["bash", "-c", cmd], capture_output=True, text=True, env={**_scrubbed_env(), **env}, cwd=str(mam_sandbox))
     assert res.returncode == 3
 
 
@@ -451,7 +463,7 @@ def test_o28_use_family_matched_env_variable(mam_sandbox):
         "ANTIGRAVITY_CONVERSATION_ID": orc_uuid
     }
     cmd = f"export ANTIGRAVITY_CONVERSATION_ID='{orc_uuid}' && exec -a agy bash '{ONBOARD_SH}'"
-    res = subprocess.run(["bash", "-c", cmd], capture_output=True, text=True, env={**SCRUBBED_ENV, **env}, cwd=str(mam_sandbox))
+    res = subprocess.run(["bash", "-c", cmd], capture_output=True, text=True, env={**_scrubbed_env(), **env}, cwd=str(mam_sandbox))
     assert res.returncode == 0
 
     res_list = run_onboard(["--list"], env=env, cwd=str(mam_sandbox))
@@ -467,7 +479,7 @@ def test_o29_fresh_claude_session_detection(mam_sandbox):
         "CLAUDE_CODE_SESSION_ID": orc_uuid
     }
     cmd = f"export CLAUDE_CODE_SESSION_ID='{orc_uuid}' && exec -a claude bash '{ONBOARD_SH}'"
-    res = subprocess.run(["bash", "-c", cmd], capture_output=True, text=True, env={**SCRUBBED_ENV, **env}, cwd=str(mam_sandbox))
+    res = subprocess.run(["bash", "-c", cmd], capture_output=True, text=True, env={**_scrubbed_env(), **env}, cwd=str(mam_sandbox))
     assert res.returncode == 0
 
     res_list = run_onboard(["--list"], env=env, cwd=str(mam_sandbox))
@@ -484,7 +496,7 @@ def test_o30_argv_precedes_env(mam_sandbox):
         "CLAUDE_CODE_SESSION_ID": env_uuid
     }
     cmd = f"export CLAUDE_CODE_SESSION_ID='{env_uuid}' && exec -a claude bash '{ONBOARD_SH}' --uuid {argv_uuid}"
-    res = subprocess.run(["bash", "-c", cmd], capture_output=True, text=True, env={**SCRUBBED_ENV, **env}, cwd=str(mam_sandbox))
+    res = subprocess.run(["bash", "-c", cmd], capture_output=True, text=True, env={**_scrubbed_env(), **env}, cwd=str(mam_sandbox))
     assert res.returncode == 0
 
     res_list = run_onboard(["--list"], env=env, cwd=str(mam_sandbox))
diff --git a/tests/test_version_consistency.py b/tests/test_version_consistency.py
index f155224..00332a8 100644
--- a/tests/test_version_consistency.py
+++ b/tests/test_version_consistency.py
@@ -6,6 +6,11 @@ import re
 import subprocess
 from pathlib import Path
 import yaml
+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 = Path(__file__).resolve().parent.parent
 LIB_SH = REPO_ROOT / ".agents" / "skills" / "lib.sh"
diff --git a/tests/test_workspace_scope.py b/tests/test_workspace_scope.py
index 6688ccf..2084861 100644
--- a/tests/test_workspace_scope.py
+++ b/tests/test_workspace_scope.py
@@ -27,7 +27,9 @@ class TestWorkspaceScope(unittest.TestCase):
         cmd = f"source {lib_sh} && env -u HERDR_SESSION_NAME -u HERDR_SERVER_NAME bash -c 'source {lib_sh} && resolve_herdr_session \"test-session\" \"{self.ws_dir}\"'"
         # `source` is a bash builtin; on hosts where /bin/sh is dash `shell=True`
         # fails with "source: not found" (Issue #28), so run the string under bash.
-        res = subprocess.run(["bash", "-c", cmd], capture_output=True, text=True)
+        # Issue #17: lib.sh rewrites $WORKSPACE_ROOT/.mam/shim/herdr - this test's own, not an inherited one
+        res = subprocess.run(["bash", "-c", cmd], capture_output=True, text=True,
+                             env=dict(os.environ, WORKSPACE_ROOT=self.ws_dir))
         self.assertEqual(res.returncode, 0, f"Command failed: {res.stderr}")
         parent = os.path.basename(os.path.dirname(os.path.abspath(self.ws_dir))).lower().replace('_', '-')
         work = os.path.basename(os.path.abspath(self.ws_dir)).lower().replace('_', '-')