Add message links, suspect retries, and Discord preview recovery

docs/media-scraper.md

@@ -210,6 +210,25 @@ a cached still show a labeled placeholder, and playback streams only when the us
 GIF hover plays the animated GIF cached in `thumbs/` (the original is kept alongside the static
 frame and referenced by `anim_hash`), never the provider, so scrolling cannot spam anyone.
 
+## Failure policy and recovery
+
+The archive never treats a transient HTTP answer as a dead link on the first try.
+
+- A preview or download that fails with an HTTP status on Discord's CDN is retried once with a
+  **refreshed URL** from the source message (the signed link expires in about a day). Only if the
+  refreshed fetch fails is the row parked.
+- Parked rows become **suspects**: they get one delayed retry (about 50 s). The retry runs after
+  the batch, not immediately. If a batch is two-thirds suspect failures, the cooldown doubles
+  (floor 60 s) and the retries run before the next batch.
+- A suspect whose delayed retry fails again is left **unverified**: it is skipped by later passes,
+  so a finished backfill never churns over genuinely unavailable media. The Bot tab shows suspects
+  and unverified counts per member, and the progress bar fills blue for cached, gray for pending,
+  and red for failed rows.
+- **Recover Discord previews** is a one-shot task in the Bot tab: it walks every scrape's
+  Discord-CDN rows closed with HTTP errors, refreshes each URL through the message (slopbot REST or
+  the puppet, whichever the scrape used), and fetches the preview again. It starts paused; when it
+  finishes it moves to the task history. The code stays for reuse.
+
 ## Bot tab settings
 
 The Bot tab owns the tunables; they persist in `preferences.json` and apply to live jobs at once.