diff --git a/services/pressbooks.sh b/services/pressbooks.sh
index 54b3f5d..aa3c514 100644
--- a/services/pressbooks.sh
+++ b/services/pressbooks.sh
@@ -311,7 +311,14 @@ _pressbooks_normalize_slug() {
 # code, never wp-config.php, .env, or any book's own content/DB rows).
 _pressbooks_install_plugins_and_themes() {
     local _dir="$1" _net="$2" _port="$3"
-    _pb_wpcli() { docker run --rm --network "$_net" -v "${_dir}/html:/var/www/html" --env-file "${_dir}/.env" wordpress:cli "$@"; }
+    # "wp" is spelled out explicitly rather than relying on the wordpress:cli
+    # entrypoint's own "wp help $1 && set -- wp $@" auto-detection — that
+    # probe itself runs through wp-cli's bootstrap, so anything that breaks
+    # the bootstrap (a bad wp-config.php, a missing bind mount) makes the
+    # probe fail *silently* and falls through to exec-ing the raw
+    # subcommand as if it were a binary ("core: not found") instead of
+    # surfacing the real error.
+    _pb_wpcli() { docker run --rm --network "$_net" -v "${_dir}/html:/var/www/html" -v "${_dir}/extra-config.php:/usr/local/etc/pressbooks/extra-config.php:ro" --env-file "${_dir}/.env" wordpress:cli wp "$@"; }
 
     local _plugin_url _book_url _aldine_url _publisher_url
     _plugin_url="$(_pressbooks_latest_zip_url pressbooks)"
@@ -608,7 +615,17 @@ PBCOMPOSE
     # Loads the file written above — see the comment there for why the PHP
     # itself doesn't live directly in this env var. This line has no "$" in
     # it at all, so it can't run into Compose's .env interpolation.
-    local _CONFIG_EXTRA="require '/usr/local/etc/pressbooks/extra-config.php';"
+    #
+    # Guarded with file_exists rather than a bare require: this same
+    # wp-config.php (baked once, on the persistent html/ volume) is also
+    # loaded by every ephemeral "docker run wordpress:cli ..." wp-cli
+    # invocation below, which only mounts html/ itself — a bare require
+    # here would fatal in any such container unless it also mounts
+    # extra-config.php at this exact path. Confirmed live: that fatal was
+    # swallowing wp-cli's own internal "is this a valid subcommand" probe,
+    # so "core install" ran as a literal, nonexistent "core" binary instead
+    # of being handed to wp-cli at all ("core: not found").
+    local _CONFIG_EXTRA="if (file_exists('/usr/local/etc/pressbooks/extra-config.php')) { require '/usr/local/etc/pressbooks/extra-config.php'; }"
 
     backup_if_exists .env
     cat > .env << PBENV
@@ -656,7 +673,8 @@ PBENV
         sleep 1; _tries=$((_tries + 1))
     done
 
-    _wpcli() { docker run --rm --network "$WP_NET" -v "$DIR/html:/var/www/html" --env-file "$DIR/.env" wordpress:cli "$@"; }
+    # "wp" spelled out explicitly — see _pb_wpcli's comment above for why.
+    _wpcli() { docker run --rm --network "$WP_NET" -v "$DIR/html:/var/www/html" -v "$DIR/extra-config.php:/usr/local/etc/pressbooks/extra-config.php:ro" --env-file "$DIR/.env" wordpress:cli wp "$@"; }
 
     log_info "Running wp-cli core install..."
     if ! _wpcli core install \
@@ -667,7 +685,9 @@ PBENV
             --admin_email="$PB_ADMIN_EMAIL" \
             --skip-email; then
         log_error "wp-cli core install failed — WordPress may not have been ready yet. Retry manually:"
-        log_error "  docker run --rm --network $WP_NET -v $DIR/html:/var/www/html --env-file $DIR/.env wordpress:cli core install ..."
+        log_error "  docker run --rm --network $WP_NET -v $DIR/html:/var/www/html \\"
+        log_error "    -v $DIR/extra-config.php:/usr/local/etc/pressbooks/extra-config.php:ro \\"
+        log_error "    --env-file $DIR/.env wordpress:cli wp core install ..."
         return 1
     fi
 
@@ -771,6 +791,7 @@ refreshes the Pressbooks plugin/themes to their latest release.
 ## wp-cli
 \`\`\`bash
 docker run --rm --network $WP_NET -v $DIR/html:/var/www/html \\
+    -v $DIR/extra-config.php:/usr/local/etc/pressbooks/extra-config.php:ro \\
     --env-file $DIR/.env wordpress:cli wp <command>
 \`\`\`