fix(rss): emit accurate image enclosure MIME types

apps/web/lib/rss.test.ts

@@ -1,5 +1,6 @@
 import { describe, it, expect } from "vitest";
-import { buildRss } from "./rss";
+import { buildRss, mediaCardsToFeed } from "./rss";
+import type { MediaCard } from "./queries";
 
 describe("buildRss", () => {
   const xml = buildRss({
@@ -37,3 +38,67 @@ describe("buildRss", () => {
     expect(xml).not.toContain("hello]]></p>]]>");
   });
 });
+
+describe("mediaCardsToFeed", () => {
+  const card = (mediaUrl: string): MediaCard => ({
+    id: "media-1",
+    slug: "photo",
+    title: "Photo",
+    description: null,
+    mediaType: "image",
+    mediaUrl,
+    thumbnailUrl: null,
+    posterUrl: null,
+    sourceUrl: null,
+    sourceProvider: null,
+    truthLabel: "unknown",
+    truthConfidence: "unverified",
+    revealStatus: "revealed",
+    isFeatured: false,
+    isScoreEligible: true,
+    createdAt: "2026-01-01T00:00:00.000Z",
+    approvedAt: "2026-01-01T00:00:00.000Z",
+    stats: {
+      aiGuesses: 0,
+      notAiGuesses: 0,
+      totalGuesses: 0,
+      crowdAccuracy: 0,
+      aiPct: 0,
+    },
+    tags: [],
+  });
+
+  const channel = {
+    title: "Latest",
+    link: "https://aiornot.vote",
+    feedUrl: "https://aiornot.vote/rss.xml",
+    description: "Latest media",
+  };
+
+  it("uses the image URL's actual MIME type for RSS enclosures", () => {
+    const xml = mediaCardsToFeed(
+      [
+        card("https://cdn.example/photo.jpg"),
+        { ...card("https://cdn.example/generated.webp?width=1200"), id: "media-2", slug: "generated" },
+      ],
+      channel,
+    );
+
+    expect(xml).toContain('url="https://cdn.example/photo.jpg" type="image/jpeg"');
+    expect(xml).toContain(
+      'url="https://cdn.example/generated.webp?width=1200" type="image/webp"',
+    );
+  });
+
+  it("omits an enclosure when the image MIME type cannot be inferred", () => {
+    const xml = mediaCardsToFeed(
+      [card("https://picsum.photos/seed/example/1000/1250")],
+      channel,
+    );
+
+    expect(xml).not.toContain("<enclosure");
+    expect(xml).toContain(
+      '<img src="https://picsum.photos/seed/example/1000/1250"',
+    );
+  });
+});

apps/web/lib/rss.ts

@@ -19,6 +19,34 @@ function abs(url: string): string {
   return url.startsWith("/") ? `${env.appUrl}${url}` : url;
 }
 
+function imageMimeType(url: string): string | null {
+  let path = url;
+  try {
+    path = new URL(url, env.appUrl).pathname;
+  } catch {
+    path = url.split(/[?#]/, 1)[0] ?? "";
+  }
+
+  const extension = path.toLowerCase().match(/\.([a-z0-9]+)$/)?.[1];
+  switch (extension) {
+    case "jpg":
+    case "jpeg":
+      return "image/jpeg";
+    case "png":
+      return "image/png";
+    case "gif":
+      return "image/gif";
+    case "webp":
+      return "image/webp";
+    case "avif":
+      return "image/avif";
+    case "svg":
+      return "image/svg+xml";
+    default:
+      return null;
+  }
+}
+
 export type FeedItem = {
   title: string;
   link: string;
@@ -101,15 +129,18 @@ export function mediaCardsToFeed(
 ): string {
   return buildRss({
     ...channel,
-    items: cards.map((m) => ({
-      title: m.title,
-      link: `${env.appUrl}/m/${m.slug}`,
-      guid: `media:${m.id}`,
-      pubDate: m.approvedAt || m.createdAt,
-      descriptionHtml: mediaItemDescription(m),
-      categories: m.tags.filter((t) => !t.isAnswerSpoiler).map((t) => t.slug),
-      enclosure: m.mediaType === "image" ? { url: abs(m.mediaUrl), type: "image/webp" } : undefined,
-    })),
+    items: cards.map((m) => {
+      const enclosureType = m.mediaType === "image" ? imageMimeType(m.mediaUrl) : null;
+      return {
+        title: m.title,
+        link: `${env.appUrl}/m/${m.slug}`,
+        guid: `media:${m.id}`,
+        pubDate: m.approvedAt || m.createdAt,
+        descriptionHtml: mediaItemDescription(m),
+        categories: m.tags.filter((t) => !t.isAnswerSpoiler).map((t) => t.slug),
+        enclosure: enclosureType ? { url: abs(m.mediaUrl), type: enclosureType } : undefined,
+      };
+    }),
   });
 }