A changed jail filter restarts fail2ban

fail2ban restarts when the composed jail file changes, and each filter is
a file of its own, so a module that changed only its failregex left the
running jail on the old pattern. The jail file now names each filter's
digest.

internal/catalogue/jails_into.go

@@ -1,6 +1,8 @@
 package catalogue
 
 import (
+	"crypto/sha256"
+	"encoding/hex"
 	"fmt"
 	"sort"
 	"strings"
@@ -43,8 +45,16 @@ func jailsInto(modules []Manifest, j *Jailing) []map[string]any {
 
 	out := make([]map[string]any, 0, len(jails)+1)
 	for _, d := range jails {
-		fmt.Fprintf(&composed, "\n# from %s\n[%s]\nenabled = true\nfilter = %s\n%s\n",
-			d.module, d.jail.Name, d.jail.Name, strings.TrimRight(d.jail.Jail, "\n"))
+		// **The filter's digest rides in the jail file.** fail2ban is restarted when this file
+		// changes, and the filter is a file of its own: a module that changed only what a failure
+		// looks like rewrote the filter on disk and left the running jail on the old pattern, with
+		// nothing said (novox/hq issue 191's rollout found it on gitea's sshd). Naming the filter's
+		// digest here makes a changed pattern a changed jail file, so the restart the service
+		// already takes on it covers the filter too.
+		sum := sha256.Sum256([]byte(d.jail.Failregex))
+		fmt.Fprintf(&composed, "\n# from %s, filter %s\n[%s]\nenabled = true\nfilter = %s\n%s\n",
+			d.module, hex.EncodeToString(sum[:])[:12], d.jail.Name, d.jail.Name,
+			strings.TrimRight(d.jail.Jail, "\n"))
 		// The filter is a file of its own, named as the jail's filter= references it.
 		out = append(out, map[string]any{
 			"id":   "filter-" + d.jail.Name,