diff --git a/backend/tests/conftest.py b/backend/tests/conftest.py
index 64612e2..dcceedc 100644
--- a/backend/tests/conftest.py
+++ b/backend/tests/conftest.py
@@ -16,6 +16,7 @@ out dozens of times.
 """
 
 import asyncio
+import hashlib
 import os
 import socket
 import subprocess
@@ -54,9 +55,23 @@ TEST_TABLES = (
 )
 
 BACKEND_DIR = Path(__file__).resolve().parents[1]
-_COMPOSE_PROJECT = "agp-pytest"
-_EPHEMERAL_PG_PORT = 25432
-_EPHEMERAL_REDIS_PORT = 26379
+
+# A hardcoded project name/port here would mean every concurrent checkout
+# running `pytest` (e.g. several Claude Agent-tool subagents, each in their
+# own ~/agp/workspace/task_<id> clone) fights over the exact same Docker
+# Compose project and host ports -- one run's pytest_unconfigure teardown
+# can yank the ephemeral Postgres out from under a completely unrelated
+# concurrent run, surfacing as "connection was closed in the middle of
+# operation" with no obvious cause. Confirmed live 2026-09-15 running 3
+# parallel subagents. Same root cause and fix pattern as the agent_core
+# workspace/Docker-Compose collision documented in project_agp memory --
+# derive both the project name and the port from a hash of the checkout
+# directory, so different concurrent checkouts land on different projects/
+# ports while the same checkout is stable across repeated runs.
+_WORKSPACE_HASH = hashlib.sha256(str(BACKEND_DIR.parent).encode()).hexdigest()[:10]
+_COMPOSE_PROJECT = f"agp-pytest-{_WORKSPACE_HASH}"
+_EPHEMERAL_PG_PORT = 25400 + (int(_WORKSPACE_HASH, 16) % 100)
+_EPHEMERAL_REDIS_PORT = 26300 + (int(_WORKSPACE_HASH, 16) % 100)
 
 # Set by pytest_configure() when it starts container(s) it owns; torn down in
 # pytest_unconfigure.