inbound-antispam-panel: the filter reads its signing key for every message

The routine kept the key after its first read. SelfPost makes a new key
when the file is lost or damaged, or a backup brings back another, and
rspamd would then have gone on signing with the old one - every verdict
unrecorded - until someone restarted the sidecar. The file is one short
line; reading it per message costs nothing worth keeping a copy for.

The guide says what never needs doing: nothing of rspamd's is cleared
after a change of the lists or the key; a restart is for a change of
its own configuration only.

Prompted by the owner's question whether rspamd's cache needs clearing
(2026-10-12).

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

docs/guide.md

@@ -868,8 +868,11 @@ recompute. The key is `data/antispam/filter.key`: SelfPost creates it on its
 first start with the inbound relay on, and the sidecar reads it from the
 directory it already mounts - there is nothing to configure. If Inbound › Log
 shows *selfpost* for mail the filter did judge, the sidecar is running without
-this file or started before the key existed: copy `antispam/rspamd/` again and
-restart the sidecar.
+this file: copy `antispam/rspamd/` again and restart the sidecar. Nothing of
+rspamd's needs clearing, then or after a change of the lists or of the key: it
+rereads the list files by itself and reads the key anew for every message. A
+restart is needed only for a change of its own configuration - the files of
+`antispam/rspamd/`.
 
 The same directory holds
 [multimap.conf](../deploy/antispam/rspamd/multimap.conf), the rules for the