feat(deploy): blackbox copier, alloy engine-validation gate, planner wiring

copy_alloy_config now validates the rendered config with the very
alloy image that will run it, before installing: a misplaced attribute
crash-loops the unit behind a green deploy, and no textual seam can
see it. copy_blackbox_config ships the prober config; the planner maps
the new unit and shared/blackbox/** to the blackbox-exporter service,
ordered before prometheus.

scripts/deploy-remote.sh

@@ -311,8 +311,45 @@ copy_loki_config() {
 }
 
 copy_alloy_config() {
-    run_privileged mkdir -p /opt/alloy/config
-    run_privileged cp shared/alloy/config.alloy /opt/alloy/config/config.alloy
+    # The repo config carries the token GRAFANA_HOST_LABEL; the installed copy
+    # carries the host's name, so Loki streams say WHICH machine's journal a
+    # line came from without a second config file per host.
+    # *_CONF_ROOT are test seams: the bats cases execute these copiers for
+    # real against a sandbox with a stubbed run_privileged.
+    local root="${ALLOY_CONF_ROOT:-/opt/alloy}" tmp
+    tmp="$(mktemp)"
+    sed "s/GRAFANA_HOST_LABEL/$TARGET/g" shared/alloy/config.alloy > "$tmp"
+    if ! grep -q "host = \"$TARGET\"," "$tmp" || grep -q "GRAFANA_HOST_LABEL" "$tmp"; then
+        echo "alloy config: host-label substitution failed" >&2
+        rm -f "$tmp"
+        return 1
+    fi
+    # Syntax gate: alloy's config language has no schema — a misplaced
+    # attribute (e.g. `on_error` outside the json stage) parses only at RUN
+    # time, and the unit then crash-loops with a healthy-looking deploy.
+    # Validate against the very image that will run it, before installing.
+    # Skipped only in the bats sandbox (no image there).
+    if [ "$root" = "/opt/alloy" ] || podman image exists localhost/franksdank/alloy:latest 2>/dev/null; then
+        if ! podman run --rm -v "$tmp:/c.alloy:ro" \
+                --entrypoint /usr/bin/alloy localhost/franksdank/alloy:latest \
+                validate /c.alloy; then
+            echo "alloy config: validate FAILED against the pinned image" >&2
+            rm -f "$tmp"
+            return 1
+        fi
+    fi
+    run_privileged mkdir -p "$root/config"
+    run_privileged cp "$tmp" "$root/config/config.alloy"
+    rm -f "$tmp"
+}
+
+copy_blackbox_config() {
+    # Single-file mount target: the unit binds this exact path into
+    # /etc/blackbox_exporter/config.yml. cp (not cp -r) keeps it one file.
+    # BLACKBOX_CONF_ROOT is the same test seam.
+    local root="${BLACKBOX_CONF_ROOT:-/opt/blackbox}"
+    run_privileged mkdir -p "$root"
+    run_privileged cp shared/blackbox/blackbox.yml "$root/blackbox.yml"
 }
 
 copy_grafana_provisioning() {
@@ -563,6 +600,9 @@ deploy_observability() {
             ;;
         cadvisor)
             ;;
+        blackbox-exporter)
+            copy_blackbox_config
+            ;;
         *)
             echo "unknown observability service: $service" >&2
             return 2
@@ -577,6 +617,7 @@ deploy_observability() {
         loki) wait_for_health loki http://127.0.0.1:3100/ready 60 ;;
         node-exporter) wait_for_health node-exporter http://127.0.0.1:9100/metrics 60 ;;
         cadvisor) wait_for_health cadvisor http://127.0.0.1:8080/healthz 90 ;;
+        blackbox-exporter) wait_for_health blackbox-exporter http://127.0.0.1:9115/-/healthy 60 ;;
     esac
 }