diff --git a/CHANGELOG.md b/CHANGELOG.md
index 92b531e..9dbae26 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- **Test-suite tenant guard** - `tests/conftest.py` hard-fails the whole pytest session (exit code 1, zero tests run) if the effective tenant resolves to the production tenant `jpmschweitzer`, mirroring the guard library-desk applies on its side. Suite-level assertions pin that the session runs under `llm_tester` namespaces (Qdrant `memories_llm_tester`, Redis `session:llm_tester:*`), and the e2e isolation constants now derive from the shared `TEST_TENANT`/`PRODUCTION_TENANT` config constants instead of string literals
 - **Explicit tenant on every library-desk request** - the librarian client now resolves and sends the `user` parameter explicitly on every request (library-desk is removing its server-side default; a missing user would 422). The content extraction endpoints now carry the tenant too, `search_web` no longer falls back to a phantom `tatlock-librarian` user, and a client-level assertion rejects an empty/whitespace tenant before any bytes hit the wire. A parametrized sweep pins the wire contract for all 15 tenant-scoped client methods
 - **Tenant isolation guard** - non-production environments (development/testing) now FORCE the effective tenant to the reserved test tenant `llm_tester` (only `llm_tester` itself or a `test_`-prefixed override is accepted), regardless of `DEFAULT_USER` misconfiguration, at both config resolution and request-context resolution (`get_user()`). Startup refuses (clear error) when a non-production environment is explicitly configured with the production tenant `jpmschweitzer`, and one loud startup log line states the effective/forced tenant
 
diff --git a/tests/conftest.py b/tests/conftest.py
index 5bfa42f..68ce14a 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -12,11 +12,51 @@ from src.main import app
 
 
 @pytest.fixture(scope="session", autouse=True)
-def _initialize_app():
+def _tenant_guard():
+    """
+    Hard-fail the whole suite if the effective tenant resolves to the
+    production tenant ("jpmschweitzer").
+
+    Isolation is tenant-based: tests that touch shared services
+    (Qdrant memories collections, Wiki.js via library-desk, Neo4j,
+    Redis) must run under the reserved test tenant "llm_tester" (or a
+    test_-prefixed namespace). This mirrors the guard library-desk
+    applies on its side.
+    """
+    from src.core.config import PRODUCTION_TENANT, config
+    from src.core.context import get_default_user
+    from src.core.multi_tenancy import get_memory_collection_name
+
+    effective = get_default_user()
+    if (
+        effective == PRODUCTION_TENANT
+        or config.effective_default_user == PRODUCTION_TENANT
+    ):
+        pytest.exit(
+            f"TENANT GUARD: refusing to run the test suite - the effective "
+            f"tenant resolves to the production tenant '{PRODUCTION_TENANT}' "
+            f"(ENVIRONMENT={config.ENVIRONMENT.value}, "
+            f"DEFAULT_USER={config.DEFAULT_USER}). Tests must run under "
+            f"'llm_tester' or a test_-prefixed tenant.",
+            returncode=1,
+        )
+
+    # The Qdrant memories namespace derived from the effective tenant
+    # must never be the production collection.
+    assert get_memory_collection_name(effective) != get_memory_collection_name(
+        PRODUCTION_TENANT
+    ), "test suite would target the production memories collection"
+
+
+@pytest.fixture(scope="session", autouse=True)
+def _initialize_app(_tenant_guard):
     """
     Run application lifespan (Claude health check, household registration, etc.)
     once per test session. ASGITransport doesn't trigger lifespan events,
     so we call it explicitly.
+
+    Depends on _tenant_guard so the suite refuses to start under the
+    production tenant before any initialization happens.
     """
     from src.core.startup import initialize_application
     asyncio.run(initialize_application())
diff --git a/tests/core/test_tenant_guard.py b/tests/core/test_tenant_guard.py
index 4e020fd..b709f5b 100644
--- a/tests/core/test_tenant_guard.py
+++ b/tests/core/test_tenant_guard.py
@@ -141,6 +141,44 @@ class TestRequestContextGuard:
             assert get_user() == "alice"
 
 
+@pytest.mark.unit
+class TestSuiteRunsUnderTestTenant:
+    """
+    The live test session itself must resolve to the test tenant.
+
+    The session guard in tests/conftest.py hard-fails the suite when the
+    effective tenant is the production tenant; these tests assert the
+    namespaces every shared-service touch would use (Qdrant memories
+    collection, Redis session keys) are the llm_tester ones.
+    """
+
+    def test_effective_tenant_is_not_production(self):
+        from src.core.context import get_default_user
+
+        assert get_default_user() != PRODUCTION_TENANT
+
+    def test_effective_tenant_is_the_reserved_test_tenant(self):
+        from src.core.context import get_default_user
+
+        assert get_default_user() == TEST_TENANT
+
+    def test_memories_collection_namespace_is_test_tenant(self):
+        from src.core.context import get_default_user
+        from src.core.multi_tenancy import get_memory_collection_name
+
+        assert (
+            get_memory_collection_name(get_default_user())
+            == f"memories_{TEST_TENANT}"
+        )
+
+    def test_redis_session_namespace_is_test_tenant(self):
+        from src.core.context import get_default_user
+        from src.core.multi_tenancy import get_session_key
+
+        key = get_session_key(get_default_user(), "conv_test")
+        assert key.startswith(f"session:{TEST_TENANT}:")
+
+
 @pytest.mark.unit
 class TestStartupTenantGuardLog:
     """One loud startup log line states the effective tenant."""
diff --git a/tests/e2e/test_orchestration_e2e.py b/tests/e2e/test_orchestration_e2e.py
index 92520ad..e93c91f 100644
--- a/tests/e2e/test_orchestration_e2e.py
+++ b/tests/e2e/test_orchestration_e2e.py
@@ -26,12 +26,18 @@ from typing import AsyncGenerator
 from dataclasses import dataclass
 
 
+from src.core.config import PRODUCTION_TENANT, TEST_TENANT
+
 # Test configuration
 BASE_URL = "http://localhost:8777"
 QDRANT_URL = "http://localhost:6333"
 API_TIMEOUT = 120.0  # LLM calls can be slow
-TEST_USER = "llm_tester"
+# All e2e writes to shared services go to the reserved test tenant's
+# namespaces (Qdrant memories_llm_tester, wiki llm_tester scope) - never
+# the production tenant's.
+TEST_USER = TEST_TENANT
 TEST_COLLECTION = f"memories_{TEST_USER}"
+assert TEST_USER != PRODUCTION_TENANT
 
 
 @dataclass
@@ -986,7 +992,7 @@ class TestUserContextIsolation:
         in_test_collection = any(unique_value in v for v in test_values)
 
         # Check production collection (should NOT be there)
-        prod_collection = "memories_jpmschweitzer"
+        prod_collection = f"memories_{PRODUCTION_TENANT}"
         if await qdrant.collection_exists(prod_collection):
             prod_points = await qdrant.scroll_points(prod_collection)
             prod_values = [str(p.get("payload", {})) for p in prod_points]