Resolve a giphy token with no metadata to look it up in

`![gif](giphy|zUW23b6FmzB5e)` is a token, not an address, and the only thing
that turned it into one was a lookup in the comment's own `media_metadata`.
Reddit ships plenty of comments carrying such a token and no `media_metadata`
at all, and with nothing to look it up in the token itself was what the
comment showed.

Giphy is the one of the three token kinds whose id means something off
Reddit, so that one can be resolved without the lookup. A variant name after
the id is dropped: Giphy does not serve every variant of every gif, but the
full one is always there.

The other two still resolve only through the metadata. An emote id and an
upload id name nothing outside Reddit, so with no entry for them there is
still nothing to point them at.

Closes #10

Co-Authored-By: Claude Opus 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01PLkmgp1fWbA4XbarxKdRKt

test/reddit.test.ts

@@ -224,13 +224,63 @@ test('a target that is already an address is left alone', () => {
 });
 
 test('a token with no entry, or a broken one, is not invented', () => {
-  assert.equal(resolveInlineImages('![gif](giphy|missing)', GIPHY), '![gif](giphy|missing)');
+  // An upload id and an emote id mean nothing off Reddit, so with no entry to
+  // look them up in there is nothing to point them at.
+  assert.equal(resolveInlineImages('![img](missing)', GIPHY), '![img](missing)');
   assert.equal(
     resolveInlineImages('![img](gone)', { gone: { status: 'failed', e: 'Image' } }),
     '![img](gone)',
   );
 });
 
+test('a giphy token resolves even when the comment carried no metadata', () => {
+  // Reddit ships plenty of these with no `media_metadata` at all. The id in
+  // the token is Giphy's own, so it does not need Reddit to be readable.
+  assert.equal(
+    resolveInlineImages('![gif](giphy|zUW23b6FmzB5e)', undefined),
+    '![gif](https://i.giphy.com/media/zUW23b6FmzB5e/giphy.gif)',
+  );
+  assert.equal(
+    resolveInlineImages('![gif](giphy|missing)', GIPHY),
+    '![gif](https://i.giphy.com/media/missing/giphy.gif)',
+  );
+});
+
+test('the metadata still wins where there is any, being what Reddit will serve', () => {
+  assert.match(resolveInlineImages('![gif](giphy|Ve7wX45gaOFmw8eeEM)', GIPHY), /redd\.it/);
+});
+
+test('a variant name after the id is dropped, not all of them being served', () => {
+  assert.equal(
+    resolveInlineImages('![gif](giphy|zUW23b6FmzB5e|downsized)', undefined),
+    '![gif](https://i.giphy.com/media/zUW23b6FmzB5e/giphy.gif)',
+  );
+});
+
+test('only a giphy token is guessed at, and only a well-formed one', () => {
+  for (const token of ['emote|t5_2th52|4358', 'giphy|', 'giphy|../evil', 'giphy|a|b|c']) {
+    assert.equal(resolveInlineImages(`![x](${token})`, undefined), `![x](${token})`);
+  }
+});
+
+test('a real comment carrying a giphy token gets the gif', () => {
+  // Captured from the post itself: the comment has the token and no
+  // `media_metadata`, which is the shape that used to show the token instead.
+  const post = toPost(fixture('reddit/video.json'), URL_);
+  const all: string[] = [];
+  const walk = (list: typeof post.comments) => {
+    for (const comment of list ?? []) {
+      if (comment.text) all.push(comment.text);
+      walk(comment.replies);
+    }
+  };
+  walk(post.comments);
+
+  const gif = all.find((text) => text.includes('giphy'));
+  assert.ok(gif, 'the fixture should still carry a giphy comment');
+  assert.match(gif, /!\[gif\]\(https:\/\/i\.giphy\.com\/media\/QfzMP70zmNQiDf5sGP\/giphy\.gif\)/);
+});
+
 test('inline images survive the walk into the comment tree', () => {
   const { comments } = commentsFrom({
     data: {