ops(svos): U13 phase B — nh3-svos on v0.0.9 (schema 12), kernel app origin, seat-host and high-seat origins, bridge env on nh3-dev

Prime approved svos-dev's U13 pre-edit ask (2026-10-10 1639).
- B1: release afab123 on nh3-svos (kernel 0.0.9, migration 11->12) after a
  vzdump and an offline svos.db copy; app-terminal and app-postoffice held on
  b588510 by drop-ins until the edit.
- B2: --app-listen 127.0.0.1:8410 (drop-in) fronted by Caddy as
  svos-kernel.phasefinal.com on the LAN, allowlisted to nh3-dev; the path list
  adds /auth/kernel-key, which every connector client needs. DNS rewrite on
  the three internal AdGuards.
- B3/B4: svos-seathost (-> :8404) and svos-highseat (-> :8773) on nh3-dev's
  fleet Caddy, allowlisted to nh3-svos; /opt/svos apps env on nh3-dev with
  svos-postoffice[push] (althing-core 3.7.0 from althing 7a2a1c1) and
  svos-terminal. The fleet Caddyfile is now tracked in configs/.

configs/svos-front/Caddyfile

@@ -212,3 +212,47 @@ https://svos-terminal.phasefinal.com:443 {
 		}
 	}
 }
+
+# The kernel's app origin (U13 B2, 2026-10-10, Prime-approved; svoperatingsystem U9a and docs/operations/u13-svos-edit.md
+# "Before the edit" 1). Apps that run OFF this box reach the kernel here: from the U13 edit, app-terminal,
+# app-postoffice (the bridge) and app-high-seat, all on nh3-dev. LAN only, because nh3-dev is not on the mesh; the
+# internal AdGuards answer svos-kernel.phasefinal.com -> 10.100.50.43 and no MagicDNS record exists.
+# - Upstream is the kernel's SECOND listener, `serve --app-listen 127.0.0.1:8410` (configs/svos-kernel/20-app-listen.conf):
+#   a request there is never a human and loopback trust never applies, so every call authenticates with its own bearer.
+#   NO Basic auth, and Authorization passes through untouched.
+# - Source allowlisted to nh3-dev (10.100.10.50); anything else gets 403 from Caddy.
+# - Paths: svos-dev's app surface (/auth/enroll, /auth/proofs, /registry/*, /verbs/*, /seats/enroll) plus
+#   /auth/kernel-key, which every svos_connector client fetches to trust the kernel's signatures (client.kernel_key; it
+#   is also the joint runbook's B2 check: refused by the KERNEL with 401 without a credential). Anything else 404.
+# - Client identity/forwarding headers are deleted as on the other sites; the same 1 MiB body cap; nothing streams.
+https://svos-kernel.phasefinal.com:443 {
+	bind 10.100.50.43
+	tls {
+		dns cloudflare {env.CF_API_TOKEN}
+		resolvers 1.1.1.1 8.8.8.8
+	}
+	route {
+		request_header -Tailscale-User-*
+		request_header -X-Forwarded-*
+		request_header -Tailscale-Headers-Info
+		request_header -X-Real-IP
+		request_header -Forwarded
+		request_header -X-SVOS-Peer
+
+		request_body {
+			max_size 1MiB
+		}
+
+		@not_nh3_dev not remote_ip 10.100.10.50
+		handle @not_nh3_dev {
+			respond 403
+		}
+		@app_surface path /auth/enroll /auth/proofs /auth/kernel-key /registry/* /verbs/* /seats/enroll
+		handle @app_surface {
+			reverse_proxy 127.0.0.1:8410
+		}
+		handle {
+			respond 404
+		}
+	}
+}