Fix !post in round-robin mode, ❓ reaction VS16, image label

- !post falls back to newest unposted story for the channel when the
  in-memory queue is empty (the steady state under round-robin).
- Accept ❓️/❔️ (U+FE0F variation selector) as question reactions —
  the bare codepoints alone missed clients that render the colored emoji.
- Rewrite Guardian i.guim.co.uk thumbnails to width=1200 so we stop
  rejecting real images as "tracking pixels"; relabel the size warning.
- Log decrypt failures and reactions on events not in post_log so future
  silent drops surface instead of vanishing.

internal/ingestion/image.go

@@ -3,11 +3,32 @@ package ingestion
 import (
 	"log/slog"
 	"net/http"
+	"net/url"
 	"strconv"
 	"strings"
 	"time"
 )
 
+// NormalizeImageURL rewrites known CDN thumbnail URLs to a higher-resolution
+// variant. Currently handles Guardian's i.guim.co.uk, whose RSS feeds hand out
+// 140-px-wide thumbnails by default. Unrecognized hosts pass through unchanged.
+func NormalizeImageURL(raw string) string {
+	if raw == "" {
+		return raw
+	}
+	u, err := url.Parse(raw)
+	if err != nil || u.Host != "i.guim.co.uk" {
+		return raw
+	}
+	q := u.Query()
+	if q.Get("width") == "" {
+		return raw
+	}
+	q.Set("width", "1200")
+	u.RawQuery = q.Encode()
+	return u.String()
+}
+
 var imageClient = &http.Client{
 	Timeout: 10 * time.Second,
 	CheckRedirect: func(req *http.Request, via []*http.Request) error {
@@ -54,7 +75,7 @@ func ValidateImageURL(url string) bool {
 	if cl := resp.Header.Get("Content-Length"); cl != "" {
 		size, err := strconv.ParseInt(cl, 10, 64)
 		if err == nil && size <= 5120 {
-			slog.Warn("image validation: too small (likely tracking pixel)", "url", url, "size", size)
+			slog.Warn("image validation: small image (≤5KB), skipping", "url", url, "size", size)
 			return false
 		}
 	}

internal/ingestion/parser.go

@@ -55,7 +55,7 @@ func FetchFeed(feedURL string) ([]FeedItem, error) {
 			GUID:       itemGUID(item),
 			Headline:   strings.TrimSpace(item.Title),
 			Lede:       extractLede(item.Description),
-			ImageURL:   extractImageURL(item),
+			ImageURL:   NormalizeImageURL(extractImageURL(item)),
 			ArticleURL: strings.TrimSpace(item.Link),
 		}
 		if fi.GUID == "" || fi.ArticleURL == "" {