swarm-nats, matrix: the queue's and matrix-ctl's store identity paths are their own, not the hive's

glue-nats-bao-identity.nix and glue-matrix-ctl-bao-identity.nix defaulted
deploy.nats.baoClient{Cert,Key}File and deploy.matrix.ctlBaoClient{Cert,Key}File
to siblings of deploy.bao.clientCertFile, the hive's own store reader. That
pointed a store host whose reader was moved at files nobody mints, and on a
queue or homeserver host without the store that held a placed hive reader
invented a nats.pem / matrix-ctl.pem path beside it.

Both glues are now gated on the store running on this host
(deploy.bao.enable, the condition glue-bao-tls.nix mints under) and name the
directory the minting unit writes to, through nix/host-modules/lib/bao-pki-dir.nix.

Host shapes:
- Store host, default reader: unchanged. The evaluated paths stay
  /var/lib/swarm-bao-pki/nats{,-key}.pem and
  /var/lib/swarm-bao-pki/matrix-ctl{,-key}.pem, and the rendered units are
  the same.
- Store host whose hive reader was moved: now gets the leaf minted there.
- Queue or homeserver host without the store, holding a hive reader and not
  naming these options: no default any more. It still evaluates (neither
  option has an eval assertion). swarm-bao-nats-tls exits 1 naming
  deploy.nats.baoClient{Cert,Key}File when the queue's certificate is missing
  or due for renewal; swarm-bao-matrix-oidc exits 1 naming
  ctlBaoClient{Cert,Key}File, and the swarm appservice render/publish units
  and the PKI bind mount no longer render. If that host had placed nats.pem
  or matrix-ctl.pem beside its hive reader, it worked before and now needs
  both options named.
- Hosts without the store and without a hive reader, and hosts naming the
  options: unchanged.

Both refusals and option descriptions now say the default comes from
deploy.bao.enable.

Refs #4921

nix/host-modules/glue-nats-bao-identity.nix

@@ -9,9 +9,10 @@
 # leaf, because the thing that owns a private key owns issuing from it. What
 # belongs here is the pairing: which paths `swarm-bao-nats-tls` presents.
 #
-# ⚠️ Gated on the leaf existing, not on the store being enabled — the same rule
-# ./glue-matrix-ctl-bao-identity.nix states: a swarm runs ONE queue, and the
-# hive hosting it need not be the hive hosting the store.
+# ⚠️ Gated on the store running on this host, the only place the leaf is
+# minted. Not on `deploy.bao.clientCertFile`, the hive's own reader: a queue
+# host need not run a hive. A queue host without the store gets no default
+# here; the operator places the queue's leaf and names it.
 #
 # Everything is `mkDefault`. An operator naming their own paths wins.
 {
@@ -20,18 +21,11 @@
   ...
 }:
 let
-  hyperhiveCfg = config.services.hyperhive;
-  deployCfg = hyperhiveCfg.deploy;
-  baoDeploy = deployCfg.bao;
-
-  # Where ./glue-bao-tls.nix puts the leaves, derived from the reader's own path
-  # rather than repeating that file's directory literal: an operator who moves
-  # the PKI moves both, and the two cannot drift apart.
-  haveMintedPki = baoDeploy.clientCertFile != null;
-  pkiDir = if haveMintedPki then builtins.dirOf baoDeploy.clientCertFile else null;
+  deployCfg = config.services.hyperhive.deploy;
+  pkiDir = import ./lib/bao-pki-dir.nix;
 in
 {
-  config = lib.mkIf (deployCfg.nats.enable && haveMintedPki) {
+  config = lib.mkIf (deployCfg.nats.enable && deployCfg.bao.enable) {
     services.hyperhive.deploy.nats = {
       baoClientCertFile = lib.mkDefault "${pkiDir}/nats.pem";
       baoClientKeyFile = lib.mkDefault "${pkiDir}/nats-key.pem";