diff --git a/tests/test_agenda_budget.py b/tests/test_agenda_budget.py
index 2346ef8..a28b8dd 100644
--- a/tests/test_agenda_budget.py
+++ b/tests/test_agenda_budget.py
@@ -12,7 +12,7 @@
 import unittest
 from pathlib import Path
 
-os.environ.setdefault("DEEPGRAPH_DATABASE_URL", "")
+os.environ["DEEPGRAPH_DATABASE_URL"] = ""  # force SQLite tmpdir; never touch a real DB from the environment
 
 
 SAMPLE_AGENDA = {
diff --git a/tests/test_agenda_contract.py b/tests/test_agenda_contract.py
index 6f64289..c4c0d16 100644
--- a/tests/test_agenda_contract.py
+++ b/tests/test_agenda_contract.py
@@ -16,7 +16,7 @@
 from pathlib import Path
 
 # Force SQLite for tests
-os.environ.setdefault("DEEPGRAPH_DATABASE_URL", "")
+os.environ["DEEPGRAPH_DATABASE_URL"] = ""  # force SQLite tmpdir; never touch a real DB from the environment
 
 from contracts.agenda import (  # noqa: E402
     AgendaReview,
diff --git a/tests/test_agenda_orchestrator.py b/tests/test_agenda_orchestrator.py
index 21c8cc4..b9ff736 100644
--- a/tests/test_agenda_orchestrator.py
+++ b/tests/test_agenda_orchestrator.py
@@ -7,7 +7,7 @@
 import unittest
 from pathlib import Path
 
-os.environ.setdefault("DEEPGRAPH_DATABASE_URL", "")
+os.environ["DEEPGRAPH_DATABASE_URL"] = ""  # force SQLite tmpdir; never touch a real DB from the environment
 
 
 SAMPLE_AGENDA_DICT = {
diff --git a/tests/test_agenda_review_loop.py b/tests/test_agenda_review_loop.py
index f295827..e8eaaf0 100644
--- a/tests/test_agenda_review_loop.py
+++ b/tests/test_agenda_review_loop.py
@@ -11,7 +11,7 @@
 
 import httpx
 
-os.environ.setdefault("DEEPGRAPH_DATABASE_URL", "")
+os.environ["DEEPGRAPH_DATABASE_URL"] = ""  # force SQLite tmpdir; never touch a real DB from the environment
 
 
 SAMPLE_AGENDA_DICT = {
diff --git a/tests/test_agenda_routes.py b/tests/test_agenda_routes.py
index c2116e5..a3cbde2 100644
--- a/tests/test_agenda_routes.py
+++ b/tests/test_agenda_routes.py
@@ -14,7 +14,7 @@
 import unittest
 from pathlib import Path
 
-os.environ.setdefault("DEEPGRAPH_DATABASE_URL", "")
+os.environ["DEEPGRAPH_DATABASE_URL"] = ""  # force SQLite tmpdir; never touch a real DB from the environment
 
 
 SAMPLE_AGENDA_DICT = {
diff --git a/tests/test_agenda_scope.py b/tests/test_agenda_scope.py
index d663ad6..a6b5805 100644
--- a/tests/test_agenda_scope.py
+++ b/tests/test_agenda_scope.py
@@ -12,7 +12,7 @@
 import unittest
 from pathlib import Path
 
-os.environ.setdefault("DEEPGRAPH_DATABASE_URL", "")
+os.environ["DEEPGRAPH_DATABASE_URL"] = ""  # force SQLite tmpdir; never touch a real DB from the environment
 
 
 MEDICAL_AGENDA = {
diff --git a/tests/test_agenda_selector.py b/tests/test_agenda_selector.py
index 4c59282..5d241e1 100644
--- a/tests/test_agenda_selector.py
+++ b/tests/test_agenda_selector.py
@@ -7,7 +7,7 @@
 import unittest
 from pathlib import Path
 
-os.environ.setdefault("DEEPGRAPH_DATABASE_URL", "")
+os.environ["DEEPGRAPH_DATABASE_URL"] = ""  # force SQLite tmpdir; never touch a real DB from the environment
 
 
 SAMPLE_AGENDA_DICT = {
diff --git a/tests/test_direction_intake.py b/tests/test_direction_intake.py
index 82d3398..82f0a9c 100644
--- a/tests/test_direction_intake.py
+++ b/tests/test_direction_intake.py
@@ -14,7 +14,7 @@
 import unittest
 from pathlib import Path
 
-os.environ.setdefault("DEEPGRAPH_DATABASE_URL", "")
+os.environ["DEEPGRAPH_DATABASE_URL"] = ""  # force SQLite tmpdir; never touch a real DB from the environment
 
 sys.path.insert(0, str(Path(__file__).resolve().parents[1] / "scripts"))
 
diff --git a/tests/test_evidence_gate.py b/tests/test_evidence_gate.py
index e7e6915..5ed5517 100644
--- a/tests/test_evidence_gate.py
+++ b/tests/test_evidence_gate.py
@@ -13,7 +13,7 @@
 import unittest
 from pathlib import Path
 
-os.environ.setdefault("DEEPGRAPH_DATABASE_URL", "")
+os.environ["DEEPGRAPH_DATABASE_URL"] = ""  # force SQLite tmpdir; never touch a real DB from the environment
 
 
 SAMPLE_AGENDA_DICT = {
diff --git a/tests/test_evidence_gate_routes.py b/tests/test_evidence_gate_routes.py
index f0bd55a..c4eea41 100644
--- a/tests/test_evidence_gate_routes.py
+++ b/tests/test_evidence_gate_routes.py
@@ -13,7 +13,7 @@
 import unittest
 from pathlib import Path
 
-os.environ.setdefault("DEEPGRAPH_DATABASE_URL", "")
+os.environ["DEEPGRAPH_DATABASE_URL"] = ""  # force SQLite tmpdir; never touch a real DB from the environment
 
 
 SAMPLE_AGENDA_DICT = {
diff --git a/tests/test_manuscript_routes.py b/tests/test_manuscript_routes.py
index 0bd3913..32e854a 100644
--- a/tests/test_manuscript_routes.py
+++ b/tests/test_manuscript_routes.py
@@ -18,7 +18,7 @@
 import unittest
 from pathlib import Path
 
-os.environ.setdefault("DEEPGRAPH_DATABASE_URL", "")
+os.environ["DEEPGRAPH_DATABASE_URL"] = ""  # force SQLite tmpdir; never touch a real DB from the environment
 
 
 class ManuscriptRoutesSmokeTests(unittest.TestCase):