Spots: a corrupt NZB is a result, not a reason to read the listing again

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/services/SpotService.ts

@@ -31,6 +31,9 @@ const MAX_IMAGE_SEGMENTS = 10
 /** A claimed spot whose worker died is taken again after this long. */
 const RECLAIM_AFTER = '1 hour'
 
+/** The NZB's articles were read, but they don't decode to an NZB (e.g. "invalid code lengths set"). */
+export class NzbUnreadable extends Error {}
+
 /**
  * A spot's title: from its XML, which is decoded properly (the Subject of a
  * raw header is read as ISO-8859-1), else from the header.
@@ -333,10 +336,17 @@ class SpotService {
       try {
         nzbXml = await this.readNzb(head)
       } catch (error: any) {
-        if (!/^4\d\d/.test(String(error.message))) throw error
-        // The NZB's articles are gone: the listing can't be downloaded any more.
-        update.error = 'NZB articles gone'
-        outcome = 'nzb-gone'
+        if (error instanceof NzbUnreadable) {
+          // Corrupt: reading it again won't help (LOG.md 2026-10-08 (12)).
+          update.error = `NZB unreadable: ${error.message}`.slice(0, 500)
+          outcome = 'nzb-unreadable'
+        } else if (/^4\d\d/.test(String(error.message))) {
+          // The NZB's articles are gone: the listing can't be downloaded any more.
+          update.error = 'NZB articles gone'
+          outcome = 'nzb-gone'
+        } else {
+          throw error
+        }
       }
       const nzb = nzbXml ? parseNzb(nzbXml) : null
       if (nzb && nzb.files.length > 0 && isDummyNzb(nzb, head.header.size)) {
@@ -405,7 +415,11 @@ class SpotService {
     if (segments.length === 0 || segments.length > MAX_NZB_SEGMENTS) return null
     const bodies = []
     for (const id of segments) bodies.push(await this.fetch(`BODY <${id.replace(/^<|>$/g, '')}>`))
-    return decodeSpotBinary(bodies).toString('utf8')
+    try {
+      return decodeSpotBinary(bodies).toString('utf8')
+    } catch (error: any) {
+      throw new NzbUnreadable(String(error.message))
+    }
   }
 
   /** Downloads the spot's compressed NZB and imports it as a release (D26). */