diff --git a/docker-dev/README.md b/docker-dev/README.md
index fa55c9b8..c728f431 100644
--- a/docker-dev/README.md
+++ b/docker-dev/README.md
@@ -86,10 +86,33 @@ Central nodes authenticate against the shared GLAuth at `10.100.0.35:3893` (base
 ## Headless deploy
 
 ```bash
-POST http://localhost:9200/api/deployments
-X-Api-Key: docker-dev-deploy-key
+./docker-dev/deploy.sh                  # trigger a deploy (no request body)
+./docker-dev/deploy.sh artifact.json    # …sending that JSON file as the request body
 ```
 
+`deploy.sh` polls `http://localhost:9200/health/ready` (every 2 s, up to 120 s) and only then
+issues the single, un-retried `POST http://localhost:9200/api/deployments` with
+`X-Api-Key: docker-dev-deploy-key`. Override the URL / key / timeout via `OTOPCUA_ADMIN_URL`,
+`OTOPCUA_DEPLOY_API_KEY`, `OTOPCUA_READY_TIMEOUT_SECONDS`.
+
+### First-POST 404
+
+The first headless POST after `up -d` was seen answering **404** ~40 s into boot (2026-08-17 live
+gate), clearing on retry. Neither end can produce it: the AdminUI maps every route synchronously
+before `RunAsync` (`Program.cs:740` maps the deploy API, `:803` runs) and that endpoint's only
+failure modes are 503 / 401 / 422 / 409 / 500 — it has no 404 path; and Traefik answers a *matched*
+router whose servers are all down with **503 "no available server"** (the checked-in
+`traefik-dynamic.yml` router is `PathPrefix(/)` → `otopcua-admin` with a `/health/active`
+healthCheck). Traefik's `api@internal` router (`PathPrefix(/api)`) is bound to the `:8080`
+entrypoint (host 8089), not `web`/`:9200`, so it does not shadow `/api/deployments` either. So a
+404 from `:9200` is Go's default "404 page not found" — **no router matched at that instant**;
+the mechanism is unconfirmed. The `--accesslog=true --accesslog.fields.defaultmode=keep` flags on
+the `traefik` service exist to diagnose the next occurrence: `docker compose -f
+docker-dev/docker-compose.yml logs traefik` and look for the request with an empty `RouterName`.
+The readiness gate in `deploy.sh` avoids the race (a 200 through `:9200` proves both a matched
+router and a live backend), so a 404 *after* the gate is new evidence and the script fails loudly
+saying so.
+
 ## Tear down
 
 ```bash
diff --git a/docker-dev/deploy.sh b/docker-dev/deploy.sh
new file mode 100755
index 00000000..4309f35b
--- /dev/null
+++ b/docker-dev/deploy.sh
@@ -0,0 +1,90 @@
+#!/usr/bin/env bash
+#
+# Readiness-gated headless deploy trigger for the docker-dev rig.
+#
+# Why the gate exists: the 2026-08-17 live gate saw the first
+# `POST http://localhost:9200/api/deployments` after `up -d` answer a transient 404
+# (~40 s into boot), which then cleared on a retry. That 404 can come from neither
+# end of the request: the AdminUI maps every route synchronously before RunAsync and
+# the deploy endpoint has no 404 path (503/401/422/409/500 only), and Traefik answers
+# a matched-router-with-all-servers-down as 503 "no available server". So the 404 means
+# no Traefik router matched at that instant. Polling /health/ready through :9200 until
+# it answers 200 proves both halves are in place — the router table carries the
+# otopcua-admin router AND a backend is up — before the single, un-retried POST.
+#
+# A 404 AFTER the gate is therefore new evidence, not the known boot race: it should be
+# investigated against the Traefik access log (`--accesslog=true` on the traefik service;
+# `docker compose -f docker-dev/docker-compose.yml logs traefik`), which records the
+# RouterName (empty on an unmatched request) for the failing call.
+#
+# Usage:
+#   ./deploy.sh                  # no body (matches the bare README snippet)
+#   ./deploy.sh artifact.json    # send that file as the JSON request body
+#   cat artifact.json | ./deploy.sh
+#
+set -euo pipefail
+
+BASE_URL="${OTOPCUA_ADMIN_URL:-http://localhost:9200}"
+DEPLOY_URL="$BASE_URL/api/deployments"
+READY_URL="$BASE_URL/health/ready"
+API_KEY="${OTOPCUA_DEPLOY_API_KEY:-docker-dev-deploy-key}"
+READY_TIMEOUT_SECONDS="${OTOPCUA_READY_TIMEOUT_SECONDS:-120}"
+READY_POLL_SECONDS=2
+
+# --- 1. readiness gate -------------------------------------------------------
+echo "Waiting for $READY_URL (up to ${READY_TIMEOUT_SECONDS}s)..."
+deadline=$(( $(date +%s) + READY_TIMEOUT_SECONDS ))
+ready=0
+while [ "$(date +%s)" -lt "$deadline" ]; do
+    code="$(curl -s -o /dev/null -w "%{http_code}" "$READY_URL" || true)"
+    if [ "$code" = "200" ]; then
+        ready=1
+        break
+    fi
+    echo "  not ready yet (HTTP ${code:-000}); retrying in ${READY_POLL_SECONDS}s"
+    sleep "$READY_POLL_SECONDS"
+done
+
+if [ "$ready" -ne 1 ]; then
+    echo "ERROR: $READY_URL did not return 200 within ${READY_TIMEOUT_SECONDS}s — not posting." >&2
+    echo "       Check the stack is up: docker compose -f docker-dev/docker-compose.yml ps" >&2
+    exit 1
+fi
+echo "Ready. Posting deployment..."
+
+# --- 2. the single, un-retried POST ------------------------------------------
+curl_args=(-s -w '\n%{http_code}' -X POST "$DEPLOY_URL"
+           -H "X-Api-Key: $API_KEY"
+           -H "Content-Type: application/json")
+
+if [ "$#" -ge 1 ]; then
+    [ -f "$1" ] || { echo "ERROR: body file not found: $1" >&2; exit 2; }
+    curl_args+=(--data-binary "@$1")
+elif [ ! -t 0 ]; then
+    curl_args+=(--data-binary @-)
+fi
+
+response="$(curl "${curl_args[@]}")"
+status="$(printf '%s' "$response" | tail -n1)"
+body="$(printf '%s' "$response" | sed '$d')"
+
+echo "HTTP $status"
+if [ -n "$body" ]; then printf '%s\n' "$body"; fi
+
+case "$status" in
+    2*)
+        exit 0
+        ;;
+    404)
+        echo "ERROR: POST $DEPLOY_URL returned 404 AFTER the readiness gate passed." >&2
+        echo "       This is NEW evidence — the AdminUI deploy endpoint has no 404 path and a" >&2
+        echo "       down backend answers 503, so no Traefik router matched this request." >&2
+        echo "       Inspect the Traefik access log (RouterName is empty on an unmatched request):" >&2
+        echo "         docker compose -f docker-dev/docker-compose.yml logs traefik" >&2
+        exit 1
+        ;;
+    *)
+        echo "ERROR: POST $DEPLOY_URL failed with HTTP $status." >&2
+        exit 1
+        ;;
+esac
diff --git a/docker-dev/docker-compose.yml b/docker-dev/docker-compose.yml
index 3ab758c0..97abc07c 100644
--- a/docker-dev/docker-compose.yml
+++ b/docker-dev/docker-compose.yml
@@ -914,6 +914,14 @@ services:
       - --providers.file.filename=/etc/traefik/dynamic.yml
       - --providers.file.watch=true
       - --api.insecure=true
+      # Access log, on deliberately: the 2026-08-17 live gate saw a transient 404 on the
+      # first POST /api/deployments (~40 s after boot) that can only mean "no router
+      # matched" — the AdminUI has no 404 path on that endpoint and a matched router with
+      # every server down answers 503. `defaultmode=keep` keeps RouterName/ServiceName in
+      # each line, which is empty on an unmatched request — that is how the next
+      # occurrence gets diagnosed. See docker-dev/README.md §"First-POST 404".
+      - --accesslog=true
+      - --accesslog.fields.defaultmode=keep
     ports:
       - "9200:80"  # host port 9200 → traefik :80 entrypoint (80 conflicts with scadabridge-traefik)
       - "8089:8080"  # 8080 conflicts with the sister scadalink dev stack