nats: drop the access to a certificate directory it no longer mounts

The mesh's broker certificate is the operator's, kept outside any module and
mounted read-only by whatever serves the bus; the controller declares that
access and now so does nats, the same way. A mount nothing declares is refused
at registration (ADR 0030), which is how this was found.

modules/nats/Dockerfile

@@ -9,8 +9,11 @@
 #
 # Unlike every other module's Dockerfile, this builds no TypeScript and uses no mesh base image:
 # the module's code is the server, which upstream already built. There is no BUILD_BASE here on
-# purpose — nothing is compiled.
-FROM nats@sha256:b83efabe3e7def1e0a4a31ec6e078999bb17c80363f881df35edc70fcb6bb927
+# purpose — nothing is compiled. The upstream image is declared in the manifest under build.on and
+# arrives as NATS_BASE, like every other base the mesh copies into its own store before a build
+# (novox/hq ADR 0097); the digest above is the index one for the reason given.
+ARG NATS_BASE
+FROM ${NATS_BASE}
 
 COPY entrypoint.sh /usr/local/bin/mesh-nats-entrypoint
 RUN chmod 0755 /usr/local/bin/mesh-nats-entrypoint

modules/nats/module.json

@@ -47,7 +47,7 @@
       "id": "server-conf",
       "type": "file",
       "path": "/var/lib/nats-module/conf/nats.conf",
-      "content": "# The nats module's own server settings. Declared by the module, because a port, a TLS path\n# and a store directory are properties of the container this module raises: they live in its\n# image and its mounts and change when it does.\n#\n# The mesh writes accounts.conf beside this one and nothing else. A controller that wrote the\n# whole file would have to be kept in step with a Dockerfile it never sees.\n\nport: 4222\nhttp: 127.0.0.1:8222\n\ntls {\n  cert_file: \"/tls/tls.crt\"\n  key_file: \"/tls/tls.key\"\n  ca_file: \"/tls/ca.crt\"\n}\n\n# **No `verify`, deliberately, and it was `verify: true` until a probe ran this image.** That\n# setting makes the server demand a *client* certificate, and nothing in the mesh presents one: a\n# host pins this server's exact certificate and authenticates with the password the mesh minted\n# (novox/hq ADR 0004, design 25 \u00a74), and so does a module's runtime. With it on, every connection\n# in the mesh is refused at the TLS handshake, before any password is looked at \u2014 and the error is\n# \"client didn't provide a certificate\", which reads as a client fault.\n#\n# TLS is still required: a tls block is what makes it required, and verify only decides whether\n# client certificates are checked. What is given up is a second factor the mesh has no machinery\n# to issue or rotate \u2014 a certificate per module per node \u2014 and what is kept is stronger than a\n# name check in both directions: an exact pin outward, a per-user password inward.\n\njetstream {\n  store_dir: \"/data\"\n}\n\n# Every user of the mesh, composed by the controller and rewritten whenever a module is\n# assigned, a node enrols or a person's access changes.\n#\n# **Relative, and in this same directory, because it has to be.** An absolute include path is\n# resolved relative to the including file's directory, not from the root: nats-server given\n# `include /etc/nats/accounts.conf` from /etc/nats-server/nats.conf looks for\n# /etc/nats-server/etc/nats/accounts.conf and refuses to start. Verified against the server.\ninclude accounts.conf\n",
+      "content": "# The nats module's own server settings. Declared by the module, because a port, a TLS path\n# and a store directory are properties of the container this module raises: they live in its\n# image and its mounts and change when it does.\n#\n# The mesh writes accounts.conf beside this one and nothing else. A controller that wrote the\n# whole file would have to be kept in step with a Dockerfile it never sees.\n\nport: 4222\nhttp: 127.0.0.1:8222\n\n# The mesh's own broker certificate \u2014 the one every machine already pins by fingerprint and the\n# controller already trusts (MESH_BROKER_CERTIFICATE). Serving the new bus with it means no\n# machine's pin changes when it moves, and no second certificate exists to be wrong about.\ntls {\n  cert_file: \"/tls/tls.crt\"\n  key_file: \"/tls/tls.key\"\n}\n\n# **No `verify`, deliberately, and it was `verify: true` until a probe ran this image.** That\n# setting makes the server demand a *client* certificate, and nothing in the mesh presents one: a\n# host pins this server's exact certificate and authenticates with the password the mesh minted\n# (novox/hq ADR 0004, design 25 \u00a74), and so does a module's runtime. With it on, every connection\n# in the mesh is refused at the TLS handshake, before any password is looked at \u2014 and the error is\n# \"client didn't provide a certificate\", which reads as a client fault.\n#\n# TLS is still required: a tls block is what makes it required, and verify only decides whether\n# client certificates are checked. What is given up is a second factor the mesh has no machinery\n# to issue or rotate \u2014 a certificate per module per node \u2014 and what is kept is stronger than a\n# name check in both directions: an exact pin outward, a per-user password inward.\n\njetstream {\n  store_dir: \"/data\"\n}\n\n# Every user of the mesh, composed by the controller and rewritten whenever a module is\n# assigned, a node enrols or a person's access changes.\n#\n# **Relative, and in this same directory, because it has to be.** An absolute include path is\n# resolved relative to the including file's directory, not from the root: nats-server given\n# `include /etc/nats/accounts.conf` from /etc/nats-server/nats.conf looks for\n# /etc/nats-server/etc/nats/accounts.conf and refuses to start. Verified against the server.\ninclude accounts.conf\n",
       "mode": "0644"
     },
     {
@@ -61,18 +61,24 @@
       "volumes": [
         "/var/lib/mesh-broker-nats:/data",
         "/var/lib/nats-module/conf:/etc/nats:ro",
-        "/var/lib/mesh-broker-nats-tls:/tls:ro"
+        "/var/lib/mesh-broker-tls:/tls:ro"
       ],
       "artifact": "server"
     }
   ],
   "accesses": [
     {
-      "path": "/var/lib/mesh-broker-nats-tls",
+      "path": "/var/lib/mesh-broker-tls",
       "mode": "read"
     }
   ],
   "build": {
+    "on": [
+      {
+        "arg": "NATS_BASE",
+        "image": "nats@sha256:b83efabe3e7def1e0a4a31ec6e078999bb17c80363f881df35edc70fcb6bb927"
+      }
+    ],
     "artifacts": [
       {
         "name": "server",