Test the scope defaults, the backlog gate and the database reader

The gate tests use a canned shell runner, and two of them build a real
slopo-shaped SQLite file to prove the warm-database hole is closed: the summary
line says zero new units while the database says 8,607 unembedded, and the gate
must believe the database.

Those fixtures insert in one transaction. Row-by-row they were 8,607 individual
fsyncs, which took two minutes and timed the suite out - worth knowing before
writing another one.

test/client.test.js

@@ -191,7 +191,7 @@ test('the card renders a control for every setting the Host accepts', () => {
     'Extra embedding parameters',
     'slopo executable',
     'Source directory',
-    'Exclude patterns',
+    'Extra exclude patterns',
     'State directory',
     'Ignore file',
     'Foreground timeout',
@@ -253,7 +253,7 @@ test('clearing a field is an unset, so it re-inherits rather than becoming empty
 test('an exclude list round-trips through comma-separated text', async () => {
   const { draw, react } = registered()
   const scope = fakeScope({ ...READY, value: { embeddingModel: 'm', embeddingDimensions: 1 } })
-  inputFor(draw(scope), 'Exclude patterns').props.onChange({ target: { value: '**/test/**, *.min.js' } })
+  inputFor(draw(scope), 'Extra exclude patterns').props.onChange({ target: { value: '**/test/**, *.min.js' } })
   react.reset()
   await buttonStartingWith(draw(scope), 'Save').props.onClick()
   assert.deepEqual(scope.calls.set, [['sourceDirExclude', ['**/test/**', '*.min.js']]])