The agent host's vault and SilverBullet (M5.4)

deploy/agent-host sets up the vault on nisse-host (infra/tofu#77) and
SilverBullet over it: the operator writes the vault, the agents' memory/
is read-only to it, and only the operator's Caddy reaches it, which
serves vault.dongar.net to the LAN. scripts/agent-host.sh installs and
checks it from here.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01J5Utyfzw7gF7UhjRDEtjTk

deploy/agent-host/silverbullet/compose.yaml

@@ -0,0 +1,26 @@
+# SilverBullet on the agent host: the operator's view of the vault (L10, M5.4).
+# Installed to /opt/stacks/silverbullet by ../setup.sh. No secrets here: its
+# accounts are made in its setup wizard and kept in its data folder.
+services:
+  silverbullet:
+    # Pinned: the docker role updates stacks' images nightly, and a pinned
+    # version only changes in a PR here.
+    image: ghcr.io/silverbulletmd/silverbullet:2.11.1-slim
+    restart: unless-stopped
+    environment:
+      PUID: "1000"
+      PGID: "1000"
+      SB_NAME: Nisse vault
+    ports:
+      # IPv4 only; setup.sh's firewall lets only the operator's Caddy in.
+      - "0.0.0.0:3000:3000"
+    volumes:
+      # Its own accounts and settings.
+      - /srv/nisse/silverbullet:/data
+      # The vault, the space's folder: the operator writes everything in it...
+      - /srv/nisse/vault:/vault
+      # ...except the agents' memory, which only the agents write (one writer
+      # per folder, enforced by the kernel).
+      - /srv/nisse/vault/memory:/vault/memory:ro
+    logging:
+      driver: journald  # logs go to the host's journal (L12)