feat: read gallery-dl sidecars for reel type and post dates

The .json sidecars published with the ARTMS fetch were inert: the scanner
fed them through the Instaloader path, where `node.edge_media_to_caption`
and `checkIsStory`'s `product_type` are both absent, so nothing happened.

They are now recognised structurally -- flat, with post_shortcode and
type, and none of the markers the other two JSON shapes carry -- and used
for three things:

- `type` sets post.isReel, which post-tabs prefers over every fallback.
  This is Instagram's own classification and it disagrees with ours a
  lot: of 781 items in "official_artms - reels", the sidecars say only
  360 are reels. The other 421 are feed videos the clips endpoint returns
  via include_feed_video, and the directory-based rule counted them all.
- `description` fills the caption where no .txt exists.
- `date` dates a post whose filename could not.

Also fixes date precedence. Only JDownloader highlights lack a date in
the filename, so parseArchiveFilename now marks those as mtime-derived
and the scanner lets any real date replace them -- previously the date
depended on which file the scan reached first.

Verified against real published files: a directory of three type=post and
three type=reel renders 6 in the grid and exactly the 3 reels in the
Reels tab.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/lib/archive-patterns.test.ts

@@ -10,6 +10,7 @@ describe('parseArchiveFilename — Instagram export format', () => {
       index: 1,
       ext: 'mp4',
       isStory: false,
+      dateFromMtime: false,
     });
   });
 
@@ -156,3 +157,35 @@ describe('gallery-dl / JDownloader naming interop', () => {
     expect(dated.date).toBe('2024-08-04');
   });
 });
+
+/**
+ * Highlights are the only files with no date in the name, so they fall back to
+ * mtime — which is when the file was written, not when it was posted. Callers
+ * need to know the difference to let a real date win.
+ */
+describe('dateFromMtime', () => {
+  const mtime = Date.parse('2026-08-17T00:00:00Z');
+
+  it('flags an undated highlight name as mtime-dated', () => {
+    const p = parseArchiveFilename('4utumn07 - C-IImhvpFuk.jpg', 'highlight', mtime)!;
+    expect(p.date).toBe('2026-08-17');
+    expect(p.dateFromMtime).toBe(true);
+  });
+
+  it('does not flag a highlight that carries its own date', () => {
+    const p = parseArchiveFilename('2024-08-04_4utumn07 - C-IImhvpFuk.jpg', 'highlight', mtime)!;
+    expect(p.date).toBe('2024-08-04');
+    expect(p.dateFromMtime).toBe(false);
+  });
+
+  it('never flags ordinary post or Instaloader names', () => {
+    expect(parseArchiveFilename('2023-04-19_u - ABC.mp4', 'posts', mtime)!.dateFromMtime).toBe(false);
+    expect(parseArchiveFilename('2024-01-01_12-00-00_UTC.jpg', 'posts', mtime)!.dateFromMtime).toBe(false);
+  });
+
+  it('leaves the date empty rather than guessing when no mtime is given', () => {
+    const p = parseArchiveFilename('4utumn07 - C-IImhvpFuk.jpg', 'highlight')!;
+    expect(p.date).toBe('');
+    expect(p.dateFromMtime).toBe(false);
+  });
+});

src/lib/archive-patterns.ts

@@ -30,6 +30,15 @@ export interface ParsedFilename {
   index: number;
   ext: string;
   isStory: boolean;
+  /**
+   * True when `date` is the file's mtime rather than anything Instagram said.
+   *
+   * Only highlights fetched by JDownloader lack a date in the filename, and
+   * their mtime is just when the file was written. Callers should let any real
+   * date win over this one — the same item is often also present under a
+   * gallery-dl name that does carry the date.
+   */
+  dateFromMtime: boolean;
 }
 
 /**
@@ -54,6 +63,7 @@ export const parseArchiveFilename = (
       index: indexStr ? parseInt(indexStr, 10) : 1,
       ext,
       isStory: Boolean(story),
+      dateFromMtime: false,
     };
   }
 
@@ -67,6 +77,7 @@ export const parseArchiveFilename = (
       index: indexStr ? parseInt(indexStr, 10) : 1,
       ext,
       isStory: Boolean(story),
+      dateFromMtime: false,
     };
   }
 
@@ -81,6 +92,7 @@ export const parseArchiveFilename = (
         index: 1,
         ext,
         isStory: false,
+        dateFromMtime: Boolean(mtime),
       };
     }
   }

src/lib/gallery-dl-sidecar.test.ts

@@ -0,0 +1,82 @@
+import { describe, expect, it } from 'vitest';
+import {
+  GalleryDlSidecar, isGalleryDlSidecar, sidecarDate, sidecarIsReel, sidecarSource,
+} from './gallery-dl-sidecar';
+
+// Trimmed from real files published to the archive on 2026-08-16.
+const REEL: GalleryDlSidecar = {
+  post_shortcode: 'Db-lNCoib9m', post_id: '3962768346034323302', type: 'reel',
+  date: '2026-08-13 11:00:44', post_date: '2026-08-13 11:00:44',
+  username: 'official_band', fullname: 'Official ARTMS',
+  description: 'Dancing in the spotlight', count: 1, likes: 22914,
+};
+const FEED_VIDEO: GalleryDlSidecar = { ...REEL, post_shortcode: 'DbdG9L9jU4m', type: 'post', count: 2 };
+const HIGHLIGHT: GalleryDlSidecar = {
+  post_shortcode: 'BATVdRZi_3', post_id: '18099435932626935', type: 'highlight',
+  date: '2026-08-08 16:22:09', username: 'official_band', count: 154,
+};
+
+describe('isGalleryDlSidecar', () => {
+  it('accepts a real sidecar', () => {
+    expect(isGalleryDlSidecar(REEL)).toBe(true);
+    expect(isGalleryDlSidecar(HIGHLIGHT)).toBe(true);
+  });
+
+  it('rejects an Instaloader GraphQL payload', () => {
+    expect(isGalleryDlSidecar({ node: { __typename: 'GraphVideo', shortcode: 'x' } })).toBe(false);
+    expect(isGalleryDlSidecar({ __typename: 'GraphImage', post_shortcode: 'x', type: 'post' })).toBe(false);
+  });
+
+  it('rejects an Instagram export manifest', () => {
+    expect(isGalleryDlSidecar({ media: [{ uri: 'a.jpg' }] })).toBe(false);
+    expect(isGalleryDlSidecar([{ media: [] }])).toBe(false);
+  });
+
+  it('rejects junk', () => {
+    for (const v of [null, undefined, 0, '', 'string', {}, { post_shortcode: 'x' }]) {
+      expect(isGalleryDlSidecar(v)).toBe(false);
+    }
+  });
+});
+
+describe('sidecarDate', () => {
+  it('takes the day from the timestamp', () => {
+    expect(sidecarDate(REEL)).toBe('2026-08-13');
+  });
+
+  it('falls back to post_date', () => {
+    expect(sidecarDate({ post_shortcode: 'x', post_date: '2024-01-02 03:04:05' })).toBe('2024-01-02');
+  });
+
+  it('returns empty when there is no usable date', () => {
+    expect(sidecarDate({ post_shortcode: 'x' })).toBe('');
+    expect(sidecarDate({ post_shortcode: 'x', date: 'not a date' })).toBe('');
+  });
+});
+
+describe('sidecarIsReel', () => {
+  it('distinguishes a reel from an ordinary feed video', () => {
+    // Both are single mp4s -- the lone-video heuristic cannot tell them apart.
+    expect(sidecarIsReel(REEL)).toBe(true);
+    expect(sidecarIsReel(FEED_VIDEO)).toBe(false);
+  });
+
+  it('declines to answer for stories and highlights', () => {
+    expect(sidecarIsReel(HIGHLIGHT)).toBeUndefined();
+    expect(sidecarIsReel({ post_shortcode: 'x', type: 'story' as const })).toBeUndefined();
+    expect(sidecarIsReel({ post_shortcode: 'x' })).toBeUndefined();
+  });
+});
+
+describe('sidecarSource', () => {
+  it('maps type onto the archive source kinds', () => {
+    expect(sidecarSource(REEL)).toBe('reels');
+    expect(sidecarSource(FEED_VIDEO)).toBe('posts');
+    expect(sidecarSource(HIGHLIGHT)).toBe('highlight');
+    expect(sidecarSource({ post_shortcode: 'x', type: 'story' as const })).toBe('stories');
+  });
+
+  it('is undefined for an unknown type', () => {
+    expect(sidecarSource({ post_shortcode: 'x' })).toBeUndefined();
+  });
+});

src/lib/gallery-dl-sidecar.ts

@@ -0,0 +1,87 @@
+import { SourceKind } from '../types';
+
+/**
+ * gallery-dl `.json` metadata sidecars.
+ *
+ * Written one per post next to the media (see docs/gallery-dl.md). This is the
+ * only source in any archive format that states outright what a post *is* —
+ * `type` is Instagram's own classification, the `product_type: "clips"` signal
+ * carried through the listing response. Everything else the viewer knows about
+ * reels is guesswork from filenames and directory names.
+ *
+ * Deliberately separate from the two older JSON shapes the scanner reads:
+ *
+ *   Instagram export   `posts_1.json`, an array of entries with `media`
+ *   Instaloader        `.json.xz`, a GraphQL node under `node`
+ *   gallery-dl         this — flat, no wrapper
+ */
+export interface GalleryDlSidecar {
+  post_shortcode: string;
+  post_id?: string;
+  /** Instagram's own classification of the post. */
+  type?: 'post' | 'reel' | 'story' | 'highlight';
+  /** Local-time "YYYY-MM-DD HH:MM:SS" — gallery-dl is configured to emit local. */
+  date?: string;
+  post_date?: string;
+  username?: string;
+  fullname?: string;
+  description?: string;
+  count?: number;
+  likes?: number;
+  post_url?: string;
+}
+
+/**
+ * Recognise a gallery-dl sidecar.
+ *
+ * Checked structurally rather than by filename, because the older formats are
+ * also plain `.json`. `node` and `__typename` are what an Instaloader or
+ * export payload carries, and their absence is what makes this shape
+ * unambiguous.
+ */
+export const isGalleryDlSidecar = (data: unknown): data is GalleryDlSidecar => {
+  if (!data || typeof data !== 'object' || Array.isArray(data)) return false;
+  const o = data as Record<string, unknown>;
+  return typeof o.post_shortcode === 'string'
+    && typeof o.type === 'string'
+    && o.node === undefined
+    && o.__typename === undefined
+    && o.media === undefined;
+};
+
+/** The ISO date (YYYY-MM-DD) a sidecar reports, or '' if it carries none. */
+export const sidecarDate = (s: GalleryDlSidecar): string => {
+  const raw = s.date || s.post_date || '';
+  const day = raw.slice(0, 10);
+  return /^\d{4}-\d{2}-\d{2}$/.test(day) ? day : '';
+};
+
+/**
+ * Whether the sidecar says this post is a reel.
+ *
+ * Returns undefined rather than false for stories and highlights: those are
+ * neither reels nor grid posts, and answering "no" would let them be counted
+ * as ordinary posts.
+ */
+export const sidecarIsReel = (s: GalleryDlSidecar): boolean | undefined => {
+  if (s.type === 'reel') return true;
+  if (s.type === 'post') return false;
+  return undefined;
+};
+
+/**
+ * Which source kind the sidecar implies, for cross-checking the directory.
+ *
+ * A reel shared to the profile grid legitimately appears under `posts`, so a
+ * disagreement is not an error — the directory says where the file was
+ * fetched from, `type` says what Instagram considers it.
+ */
+export const sidecarSource = (s: GalleryDlSidecar): SourceKind | undefined => {
+  switch (s.type) {
+    case 'reel': return 'reels';
+    case 'post': return 'posts';
+    case 'story': return 'stories';
+    case 'highlight': return 'highlight';
+    default: return undefined;
+  }
+};

src/lib/post-tabs.test.ts

@@ -98,3 +98,44 @@ describe('postsForTab', () => {
     expect(postsForTab([post('A')], 'saved')).toEqual([]);
   });
 });
+
+/**
+ * Once an archive carries gallery-dl sidecars, the guesswork above is replaced
+ * by Instagram's own classification. These are the cases the heuristic got
+ * wrong (see docs/gallery-dl.md).
+ */
+describe('explicit isReel from a sidecar', () => {
+  it('beats the lone-video heuristic for an ordinary feed video', () => {
+    // A single mp4 that Instagram calls a post, not a reel — indistinguishable
+    // by shape alone.
+    const posts = [video('DbdG9L9jU4m', { isReel: false })];
+    expect(postsForTab(posts, 'reels')).toEqual([]);
+    expect(postsForTab(posts, 'posts')).toHaveLength(1);
+  });
+
+  it('recognises a reel that lives in the profile grid', () => {
+    // Shared to feed, so it sits in the base directory with source 'posts'.
+    const posts = [post('A'), video('C8FHM6EJl15', { source: 'posts', isReel: true })];
+    expect(postsForTab(posts, 'reels').map(p => p.id)).toEqual(['C8FHM6EJl15']);
+    expect(postsForTab(posts, 'posts')).toHaveLength(2);
+  });
+
+  it('beats the directory when both are present', () => {
+    const posts = [
+      video('u - reels/A', { source: 'reels', isReel: false }),
+      video('u - reels/B', { source: 'reels' }),
+    ];
+    // A is a feed video that the reels tab happened to return; B is unlabelled
+    // and falls back to its directory.
+    expect(postsForTab(posts, 'reels').map(p => p.id)).toEqual(['u - reels/B']);
+  });
+
+  it('falls back per post, so a mixed archive still works', () => {
+    const posts = [
+      video('labelled', { isReel: true }),
+      video('unlabelled'),
+      carousel('C'),
+    ];
+    expect(postsForTab(posts, 'reels').map(p => p.id)).toEqual(['labelled', 'unlabelled']);
+  });
+});

src/lib/post-tabs.ts

@@ -41,11 +41,16 @@ export const hasReelSource = (posts: Post[]): boolean => posts.some(p => p.sourc
  * or an old IGTV upload, all three of which are plain `GraphVideo` nodes
  * distinguished only by `product_type`.
  */
-export const makeIsReel = (posts: Post[]): ((post: Post) => boolean) => (
-  hasReelSource(posts)
+export const makeIsReel = (posts: Post[]): ((post: Post) => boolean) => {
+  const guess = hasReelSource(posts)
     ? (post: Post) => post.source === 'reels'
-    : (post: Post) => post.media.length === 1 && post.media[0]?.type === 'video'
-);
+    : (post: Post) => post.media.length === 1 && post.media[0]?.type === 'video';
+
+  // `isReel` comes from a gallery-dl sidecar and is Instagram's own answer, so
+  // it beats both fallbacks — per post, since an archive is usually a mix of
+  // files fetched before and after sidecars existed.
+  return (post: Post) => post.isReel ?? guess(post);
+};
 
 /** Preference order when the same post was fetched into more than one directory. */
 const SOURCE_RANK: Record<SourceKind, number> = { reels: 0, posts: 1, stories: 2, highlight: 3 };