openbao: make verify-parity --all host-aware

--all expanded to (dev beta prod) and then tried to check all three from
wherever it was run. No host carries all three: dev is on vps1, beta and prod
are on vps2. So --all could not succeed anywhere, and the way it failed was
misleading rather than obvious -- on vps1, prod resolves TG_BAO_APPROLE to
/etc/thermograph/openbao-approle, which on THAT box holds dev's credential, so
prod's check authenticated as tg-dev and took a 403 from tg-host-prod.hcl.
That reads like a policy bug. It is "wrong box".

--all now means "every environment that lives on THIS host". Residency is
decided by the environment's own address being bound here (TG_SSH_HOST against
the local interfaces), and skips are announced rather than silent.

Residency is deliberately NOT decided by TG_APP_DIR existing. That was the
first attempt and it was wrong: vps1 still carries a stale /opt/thermograph
from before the estate split (d5357d0, #106), so prod looked resident there and
got checked anyway. Verified against both live hosts. A leftover directory is
exactly the kind of thing that outlives the arrangement it belonged to.

Zero environments checked is now a FAILURE. Previously a run that skipped
everything would exit 0, and a green run is precisely what the 7-day cutover
gate counts -- "nothing was wrong" and "nothing was examined" must not look
alike. The success line reports how many were checked and says plainly that a
green run on one host says nothing about the other.

Live-verified on both boxes:
  vps1 --all -> dev PASS, beta and prod skipped, exit 0
  vps2 --all -> dev skipped, beta and prod checked (both currently failing on
                the three known stale common.yaml keys)

infra/openbao/verify-parity.sh

@@ -36,8 +36,13 @@ usage: verify-parity.sh (--all | --env <dev|beta|prod> ...)
 Renders each environment through BOTH backends and compares the resulting
 KEY=value sets. Prints key names and counts only, never values.
 
-Exit status: 0 = every requested environment is at parity; 1 = a mismatch.
+--all means "every environment that lives on THIS host", not all three: dev is
-Suitable as a CI / cron gate.
+on vps1, beta and prod are on vps2, so no single box can check them all. An
+environment with no checkout here is skipped out loud. Skipping every one of
+them is an error, not a pass.
+
+Exit status: 0 = every environment checked here is at parity; 1 = a mismatch,
+or nothing was checkable. Suitable as a CI / cron gate.
 EOF
   exit 2
 }
@@ -69,17 +74,43 @@ done
 . "$INFRA_DIR/deploy/render-secrets-openbao.sh"
 
 overall=0
+checked=0
 for env_name in "${TARGETS[@]}"; do
-  echo "== parity check: $env_name"
-
   # Per-environment topology: TG_BAO_APPROLE (beta's differs, because beta shares a
-  # filesystem with prod) and TG_SKIP_COMMON. Called inside the loop because --all
+  # filesystem with prod), TG_SKIP_COMMON and TG_APP_DIR. Called before the header
-  # walks three environments and the values differ per environment.
+  # line because --all walks three environments and may skip some of them.
   if ! thermograph_topology "$env_name"; then
     echo "!! unknown environment: $env_name" >&2
     overall=1; continue
   fi
 
+  # NO ENVIRONMENT CAN BE CHECKED FROM A HOST IT DOES NOT LIVE ON, and --all used to
+  # pretend otherwise. dev is on vps1; beta and prod are on vps2. Running --all
+  # anywhere therefore guaranteed a failure on whichever environments are elsewhere,
+  # and the failure was actively misleading: on vps1, prod resolves TG_BAO_APPROLE to
+  # /etc/thermograph/openbao-approle, which on THAT box holds dev's credential, so
+  # prod's check authenticated as tg-dev and took a 403. Fails closed, but reads like
+  # a policy bug rather than "wrong box".
+  #
+  # Identity comes from the ENVIRONMENT'S OWN ADDRESS being bound here, not from its
+  # checkout existing. The first version of this check tested for TG_APP_DIR and was
+  # wrong: vps1 still carries a stale /opt/thermograph from before the estate split,
+  # so prod looked resident there and was checked anyway. A leftover directory is
+  # exactly the kind of thing that outlives the arrangement it belonged to.
+  #
+  # Skipping is announced, never silent. A gate that quietly narrows what it checked
+  # is worse than one that fails, because the run still goes green.
+  if [ -n "${TG_SSH_HOST:-}" ] && command -v ip >/dev/null 2>&1; then
+    if ! ip -4 -o addr show 2>/dev/null | awk '{print $4}' | cut -d/ -f1 \
+         | grep -qxF "$TG_SSH_HOST"; then
+      echo "== parity check: $env_name — SKIPPED, lives on ${TG_HOST:-another host} (${TG_SSH_HOST}), not here"
+      continue
+    fi
+  fi
+
+  echo "== parity check: $env_name"
+  checked=$((checked + 1))
+
   # dev renders WITHOUT common on both backends. On the SOPS side that is a caller
   # flag; on the OpenBao side the policy also forbids it. Taking the flag from the
   # topology rather than re-deriving it here keeps the comparison apples-to-apples
@@ -167,11 +198,23 @@ for k in sorted(order):
   cleanup
 done
 
+# Zero environments checked is a FAILURE, not a pass. Otherwise a --all run on a
+# host that carries none of them — a new box, a renamed checkout, a typo'd --env —
+# exits 0 having verified nothing, and a green run is exactly what the 7-day gate
+# counts. "Nothing was wrong" and "nothing was examined" must not look alike.
+if [ "$checked" -eq 0 ]; then
+  echo
+  echo "!! nothing was checked: none of [${TARGETS[*]}] has a checkout on this host." >&2
+  echo "!! dev lives on vps1; beta and prod live on vps2. Run this where they are." >&2
+  exit 1
+fi
+
 if [ "$overall" = 0 ]; then
   echo
-  echo "PARITY OK for: ${TARGETS[*]}"
+  echo "PARITY OK — ${checked} environment(s) checked on this host."
   echo "Safe to consider flipping TG_SECRETS_BACKEND for these environments."
-  echo "Recommended gate before prod: 7 consecutive green runs on all three."
+  echo "Gate before prod: 7 consecutive green runs covering ALL THREE environments."
+  echo "That means both hosts — a green run here says nothing about the other box."
 else
   echo
   echo "PARITY FAILED — do NOT flip TG_SECRETS_BACKEND." >&2