Event log: show only the events with a failed or a pending delivery (closes #390)

The event log gains three links above the list: All, Failed (N) and
Pending (N), carried in a `show` query parameter; any other value shows
every event. Failed lists the events with a failed delivery, Pending
those with one pending or retrying, each once, under the full list's
50-row limit and order. A filtered list finds the matching deliveries
through `idx_deliveries_status`, looks up their events by ID and sorts
them, and reads the rows of only the events shown; its counts read the
deliveries alone. The line beside the heading says what a filter
counts, and Replay returns to the list it was pressed in. The README
and the comments naming the query parameters the service reads include
`show`.

Model: opus-5-5

internal/handlers/delivery_replay_test.go

@@ -1,6 +1,7 @@
 package handlers_test
 
 import (
+	"io"
 	"net/http"
 	"net/http/httptest"
 	"strings"
@@ -471,6 +472,66 @@ func TestHandleDeliveryReplay_RefusesWhileEarlierReplayInFlight(
 	)
 }
 
+// TestHandleDeliveryReplay_ReturnsToTheListItWasPressedIn proves a
+// Replay pressed in the Failed list carries that list in its form and
+// returns to it, and that a show value the event log does not know
+// returns to the full log.
+func TestHandleDeliveryReplay_ReturnsToTheListItWasPressedIn(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	var (
+		h     *handlers.Handlers
+		sess  *session.Session
+		db    *database.Database
+		dbMgr *database.WebhookDBManager
+	)
+
+	app := newTestApp(t, &h, &sess, &db, &dbMgr)
+	app.RequireStart()
+
+	t.Cleanup(app.RequireStop)
+
+	wh := seedWebhook(t, db)
+	tgt := seedConfiguredTarget(
+		t, db, wh.ID, database.TargetTypeHTTP,
+		`{"url":"`+replayTargetURL+`"}`,
+	)
+
+	_, original := seedFailedDelivery(t, dbMgr, wh.ID, tgt.ID)
+
+	assert.Contains(t, renderSourceLogsPageWithQuery(
+		t, h, sess, wh.ID, "?show=failed",
+	), `name="show" value="failed"`)
+
+	// The second replay is refused, as the first is still queued.
+	for _, tc := range []struct{ show, location string }{
+		{"failed", "/hook/" + wh.ID +
+			"/events?notice=replay-queued&show=failed"},
+		{"made-up", "/hook/" + wh.ID + "/events?notice=replay-in-flight"},
+	} {
+		req := postRequest(
+			"/hook/"+wh.ID+"/deliveries/"+original.ID+"/replay",
+			authenticatedCookies(
+				t, sess, deleteTestUserID, deleteTestUsername,
+			),
+			map[string]string{
+				paramSourceID:   wh.ID,
+				paramDeliveryID: original.ID,
+			},
+		)
+		req.Body = io.NopCloser(strings.NewReader("show=" + tc.show))
+		req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+		w := httptest.NewRecorder()
+		h.HandleDeliveryReplay().ServeHTTP(w, req)
+
+		require.Equal(t, http.StatusSeeOther, w.Code, tc.show)
+		assert.Equal(t, tc.location, w.Header().Get("Location"), tc.show)
+	}
+}
+
 // TestHandleSourceLogs_RendersReplayControlAndBanner proves the action
 // reaches the page it belongs on: a finished delivery renders a POST
 // form carrying a CSRF token, and the outcome code a refusal redirects