test: the commit check starts every request clean, and the fence docs claim what it holds

The test's own writes are committed before a request, so a handler's Core DML can no longer hide
in a transaction the test had already opened. The entry-point probe answers on a marked line the
API's logging cannot mix into. A listed commit whose function no longer commits fails the fence.
CLAUDE.md and the backend README now name what an AST cannot see; the route-commit tests no longer
claim their read-back holds the commit.

backend/tests/test_entry_points.py

@@ -9,6 +9,7 @@ schema on its own.
 """
 
 import ast
+import json
 import subprocess
 import sys
 from pathlib import Path
@@ -22,13 +23,16 @@ APP = BACKEND / "app"
 # Each `python -m` module the deployment starts, and the API's app module.
 ENTRY_POINTS = ("app.main", "app.worker", "app.downloads.runner")
 
+# The table list goes out on one marked line: the API's logging writes to the same stdout, and a
+# line it logs while importing is not the probe's answer.
+_MARK = "entry-point-tables:"
 _PROBE = (
-    "import importlib, sys\n"
+    "import importlib, json, sys\n"
     "importlib.import_module(sys.argv[1])\n"
     "from sqlalchemy.orm import configure_mappers\n"
     "from app.db import Base\n"
     "configure_mappers()\n"
-    "print('\\n'.join(sorted(Base.metadata.tables)))\n"
+    f"print({_MARK!r} + json.dumps(sorted(Base.metadata.tables)))\n"
 )
 
 
@@ -44,7 +48,9 @@ def test_each_entry_point_registers_the_whole_schema_on_its_own():
             check=False,
         )
         assert r.returncode == 0, (module, r.stderr[-2000:])
-        assert r.stdout.split() == whole, module
+        answer = [ln for ln in r.stdout.splitlines() if ln.startswith(_MARK)]
+        assert len(answer) == 1, (module, r.stdout[-2000:])
+        assert json.loads(answer[0].removeprefix(_MARK)) == whole, module
 
 
 def test_every_module_that_runs_as_a_process_is_listed():