Operator report: a Discord source showed the wrong post time. Listing the real downloads found every Discord folder on the instance (7 artist folders, ~1,600 media) in a directory named `None`, as `<date>_None_<original name>`, next to sidecars named `<original name>.json`.
The real sidecar settles why:
- gallery-dl's discord extractor emits `channel` as a plain string, the message as `message_id`, and the attachment position as `num`. It has no `id` key.
- The patterns asked for `{channel[name]}` and `{id}`. gallery-dl renders a missing field as "None" and carries on.
- The sidecar was named `{filename}.json`, the attachment's ORIGINAL name. find_sidecar never pairs that with `<date>_None_<name>.png`, so no Discord file ever got a Post or a post date. The card fell back to downloaded_at.
- Every `image.png` in a channel also overwrote the same `image.json`.
Fix (gallery_dl.py):
- The directory is `{channel}`.
- The filename is `{date:%Y%m%d}_{message_id}_{num:>02}_{filename}.{extension}`, unique per attachment.
- A discord-scoped metadata postprocessor names the sidecar exactly like the media minus its extension, so find_sidecar's first candidate matches. A per-source filename override re-derives the sidecar name. save_metadata=False drops it.
Guard (tests/test_gallery_dl_naming.py) renders the patterns through Python's formatter against a sanitized copy of the real sidecar (same keys and types, invented values). A missing key or a subscript into a string raises, which is the loud failure gallery-dl doesn't give. A positive control shows both shipped patterns fail it.
Existing broken downloads are NOT repaired by this. gallery-dl's archive already records them, so a re-run skips them, and their collided sidecars no longer describe them. That repair is a separate, destructive step for the operator to decide on.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SHQB1YukL3VyvMK8rcbmV9
bvandeusenandClaude Opus 5
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