Clarify and strengthen state invariant tests

test/web/harbor-state.test.js

@@ -26,7 +26,7 @@ function deferred() {
   return { promise, resolve };
 }
 
-test('an older polling promise cannot replace a newer mutation snapshot', async () => {
+test('data invariant: an older polling promise cannot replace a newer mutation snapshot', async () => {
   let state = receive(initialHarborState, snapshot(1, 'one'));
   const poll = deferred();
   const mutation = deferred();
@@ -68,7 +68,7 @@ test('pending selection is cleared when its server disappears', () => {
   assert.equal(receive(state, snapshot(2, 'one', ['one'])).pendingServerId, '');
 });
 
-test('initial 500 and connection refusal become retryable boot failures', () => {
+test('data invariant: initial control outage is retryable without a fabricated snapshot', () => {
   const serverError = Object.assign(new Error('Internal Server Error'), { status: 500 });
   const refused = new TypeError('fetch failed');