Make the load-sensitive tests wait for what they check (closes #507)

Three tests failed at random on a busy host. The browser test now waits for each page a click opens to load, and for Alpine.js to start on it, before reading it. The delivery tests' drain takes what is already queued instead of racing a 25 ms timer, since both dispatch paths queue before they return. The test phase keeps the tests' temporary directories on a tmpfs, because SQLite waiting for the disk made `internal/handlers` slow under load; the timeout and the parallel cap are unchanged.

Deviation: the delivery tests do not wait with a deadline; dispatch has finished when they read.
Unverified: `internal/handlers` at a host load of 260 to 290.

Model: opus-5-5

internal/server/alpine_browser_test.go

@@ -280,6 +280,23 @@ func click(ctx context.Context, t *testing.T, xpath string) {
 	))
 }
 
+// clickAndLoad clicks the link or button matching an XPath expression
+// and waits, as loadPage does, for the page the click opens to load and
+// for Alpine.js to start on it. Reading earlier, a check can find an
+// element of the page being left, gone by the time its value is read;
+// and the wait in shown is too short for a page load on a busy host.
+func clickAndLoad(ctx context.Context, t *testing.T, xpath string) {
+	t.Helper()
+
+	_, err := chromedp.RunResponse(
+		ctx, chromedp.Click(xpath, chromedp.BySearch),
+	)
+	require.NoError(t, err)
+	require.NoError(t, chromedp.Run(
+		ctx, chromedp.WaitNotPresent("[x-cloak]", chromedp.ByQuery),
+	))
+}
+
 // checkAddEntrypoint loads a webhook page and checks that the add
 // entrypoint form stays hidden until the Add button beside its heading
 // is clicked. The click looks for a button element there, so it also
@@ -422,7 +439,7 @@ func checkAddTarget(
 		)))
 	}
 
-	click(ctx, t, saveButton)
+	clickAndLoad(ctx, t, saveButton)
 	assert.Truef(t, shown(ctx, `//span[text()="`+name+
 		`"]/following-sibling::div/span[text()="`+badge+`"]`),
 		"%s: the added target is not listed as %s", targetType, badge)
@@ -485,10 +502,9 @@ func checkArchiveChoices(ctx context.Context, t *testing.T, url string) {
 		`/following-sibling::span[text()="daily"]`),
 		"a database target added with daily is not listed as daily")
 
-	click(ctx, t, row+`//a[text()="Edit"]`)
+	clickAndLoad(ctx, t, row+`//a[text()="Edit"]`)
 	require.NoError(t, chromedp.Run(
 		ctx,
-		chromedp.WaitReady("#expiry", chromedp.ByQuery),
 		chromedp.Value("#expiry", &editedExpiry, chromedp.ByQuery),
 		chromedp.Value("#rotation", &editedRotation, chromedp.ByQuery),
 	))
@@ -523,7 +539,7 @@ func checkRefusedTarget(ctx context.Context, t *testing.T, url string) {
 		chromedp.Click(forwardQuery, chromedp.ByQuery),
 	))
 
-	click(ctx, t, saveButton)
+	clickAndLoad(ctx, t, saveButton)
 
 	assert.True(t, shown(ctx, reason),
 		"a refused target does not show the reason")
@@ -636,7 +652,7 @@ func checkRefusedEdits(
 			))
 		}
 
-		click(ctx, t, `//button[text()="Save Changes"]`)
+		clickAndLoad(ctx, t, `//button[text()="Save Changes"]`)
 
 		assert.Truef(t, shown(ctx, reason),
 			"%s: a refused save does not show the reason", edit.url)
@@ -760,7 +776,7 @@ func checkEntrypointEdit(
 	require.NoError(t, chromedp.Run(
 		ctx, chromedp.SendKeys(input, "Billing sender", chromedp.ByQuery),
 	))
-	click(ctx, t, saveEdit)
+	clickAndLoad(ctx, t, saveEdit)
 
 	assert.True(t, shown(ctx, `//span[text()="Billing sender"]`),
 		"saving the edit form does not change the description")
@@ -798,7 +814,7 @@ func checkRecentEvents(ctx context.Context, t *testing.T, url string) {
 		"clicking the newest event does not collapse it")
 
 	require.NoError(t, chromedp.Run(ctx, loadPage(url)))
-	click(ctx, t, newest+`/ancestor::div[@x-data][1]//a[text()="Open"]`)
+	clickAndLoad(ctx, t, newest+`/ancestor::div[@x-data][1]//a[text()="Open"]`)
 
 	assert.True(t, shown(ctx, `//h2[text()="Body"]`),
 		"Open does not lead to the event's own page")
@@ -1199,7 +1215,7 @@ func checkNewWebhookTargets(
 					`","rotation":"none"}`
 			}
 
-			click(ctx, t, createButton)
+			clickAndLoad(ctx, t, createButton)
 			require.Truef(t, shown(ctx, `//h1[text()="`+name+`"]`),
 				"%s: the new webhook's page does not open", name)
 
@@ -1260,7 +1276,7 @@ func checkRefusedNewWebhook(ctx context.Context, t *testing.T, url string) {
 		chromedp.SetValue(pruningChoice, "2160h", chromedp.BySearch),
 		chromedp.SetValue("#archive_rotation", "monthly", chromedp.ByQuery),
 	))
-	click(ctx, t, createButton)
+	clickAndLoad(ctx, t, createButton)
 
 	assert.True(t, shown(ctx, `//div[@class="alert-error"]`),
 		"a refused webhook does not show the reason")