diff --git a/tests/conftest.py b/tests/conftest.py
index dbfc8ef0..4b6b8f46 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -125,6 +125,13 @@ def _port_in_use(port):
         return sock.connect_ex(("127.0.0.1", port)) == 0
 
 
+# Set once app_server has successfully started, so pytest_runtest_setup can
+# detect a mid-session crash (e.g. resource exhaustion on a constrained CI
+# runner) and fail every subsequent HTTP-dependent test with one clear
+# diagnostic instead of a wall of opaque connection-refused errors.
+_APP_SERVER_STATE = {"proc": None, "log_path": None}
+
+
 @pytest.fixture(scope="session")
 def app_server(test_db_path):
     if _port_in_use(PORT):
@@ -192,7 +199,11 @@ def app_server(test_db_path):
     _set_setting("rate_limit_per_minute", "1000000")
     _set_setting("rate_limit_window_seconds", "60")
 
+    _APP_SERVER_STATE["proc"] = proc
+    _APP_SERVER_STATE["log_path"] = log_file.name
+
     yield proc
+    _APP_SERVER_STATE["proc"] = None
     try:
         proc.terminate()
         proc.wait(timeout=10)
@@ -207,6 +218,27 @@ def app_server(test_db_path):
             pass
 
 
+def pytest_runtest_setup(item):
+    proc = _APP_SERVER_STATE["proc"]
+    if proc is None or "tests/unit/" in item.nodeid:
+        return
+    exit_code = proc.poll()
+    if exit_code is None:
+        return
+    log_path = _APP_SERVER_STATE["log_path"]
+    try:
+        with open(log_path, "r", errors="replace") as f:
+            log_tail = f.read()[-5000:]
+    except OSError:
+        log_tail = "(log unavailable)"
+    pytest.fail(
+        f"app_server died mid-session (exit code {exit_code}). It was healthy "
+        f"earlier in this run and has since crashed - this is a shared-server "
+        f"failure, not a bug in {item.nodeid}. Server log tail:\n{log_tail}",
+        pytrace=False,
+    )
+
+
 @pytest.fixture(scope="session")
 def playwright_instance():
     from playwright.sync_api import sync_playwright