diff --git a/ci/Dockerfile b/ci/Dockerfile
index ea534d6e..2a02b586 100644
--- a/ci/Dockerfile
+++ b/ci/Dockerfile
@@ -1,12 +1,11 @@
 FROM alpine:3.20
 
-# Rebuild 2026-04-19 — previous :latest index referenced missing blobs (404 on 98f718c8 / 27d5ab83)
-
 # Pin versions to match CI requirements
 ARG TERRAFORM_VERSION=1.5.7
 ARG TERRAGRUNT_VERSION=0.99.4
 ARG SOPS_VERSION=3.9.4
 ARG KUBECTL_VERSION=1.34.0
+ARG VAULT_VERSION=1.18.1
 
 # Install system packages (single layer)
 RUN apk add --no-cache \
@@ -36,6 +35,16 @@ RUN curl -fsSL "https://dl.k8s.io/release/v${KUBECTL_VERSION}/bin/linux/amd64/ku
     -o /usr/local/bin/kubectl \
     && chmod +x /usr/local/bin/kubectl
 
+# Vault CLI — required by scripts/tg for Tier 1 stack PG credential reads
+# and Tier 0 advisory locks. Pinned to server version (1.18.1). Without this
+# the CI pipeline surfaces the misleading "Cannot read PG credentials" error
+# because scripts/tg swallows stderr ("vault: not found").
+RUN curl -fsSL "https://releases.hashicorp.com/vault/${VAULT_VERSION}/vault_${VAULT_VERSION}_linux_amd64.zip" \
+    -o /tmp/vault.zip \
+    && unzip /tmp/vault.zip -d /usr/local/bin/ \
+    && rm /tmp/vault.zip \
+    && vault version
+
 # Provider cache directory (shared across stacks)
 ENV TF_PLUGIN_CACHE_DIR=/tmp/terraform-plugin-cache
 ENV TF_PLUGIN_CACHE_MAY_BREAK_DEPENDENCY_LOCK_FILE=1
diff --git a/scripts/tg b/scripts/tg
index 8cb38e20..15cea845 100755
--- a/scripts/tg
+++ b/scripts/tg
@@ -72,12 +72,23 @@ if [ -n "$STACK_NAME" ]; then
   else
     # Tier 1: PG backend — fetch credentials from Vault
     if [ -z "${PG_CONN_STR:-}" ]; then
-      PG_CREDS=$(vault read -format=json database/static-creds/pg-terraform-state 2>/dev/null) || {
-        echo "ERROR: Cannot read PG credentials from Vault. Run: vault login -method=oidc" >&2
+      # Pre-flight: vault CLI must be available. Previously CI failed with a
+      # misleading "Cannot read PG credentials" message because the Alpine CI
+      # image lacked the vault binary — the 2>/dev/null below swallowed the
+      # real "vault: not found" error. Fail fast with a clear message instead.
+      if ! command -v vault >/dev/null 2>&1; then
+        echo "ERROR: vault CLI not found on PATH. Install it or use an image that includes it (ci/Dockerfile)." >&2
+        exit 1
+      fi
+      VAULT_OUT=$(vault read -format=json database/static-creds/pg-terraform-state 2>&1) || {
+        echo "ERROR: Cannot read PG credentials from Vault. Vault output follows:" >&2
+        echo "$VAULT_OUT" >&2
+        echo "" >&2
+        echo "Hint: humans run 'vault login -method=oidc'; CI auths via K8s SA (role=ci)." >&2
         exit 1
       }
-      PG_USER=$(echo "$PG_CREDS" | jq -r .data.username)
-      PG_PASS=$(echo "$PG_CREDS" | jq -r .data.password)
+      PG_USER=$(echo "$VAULT_OUT" | jq -r .data.username)
+      PG_PASS=$(echo "$VAULT_OUT" | jq -r .data.password)
       export PG_CONN_STR="postgres://${PG_USER}:${PG_PASS}@10.0.20.200:5432/terraform_state?sslmode=disable"
     fi
   fi