diff --git a/changelog.d/894-install-credential-file-channel.fixed.md b/changelog.d/894-install-credential-file-channel.fixed.md
new file mode 100644
index 000000000..ec1c9fdde
--- /dev/null
+++ b/changelog.d/894-install-credential-file-channel.fixed.md
@@ -0,0 +1,16 @@
+- **Install-time credentials now survive `apk add`.** The operator-chosen
+  admin password and private-WiFi key are delivered through root-only
+  staged secret files (`/tmp/tollgate-admin-password`,
+  `/tmp/tollgate-wifi-key`), consumed — unlinked on first read — by the
+  setup script: apk-tools on 25.12 does not hand the installer's
+  environment to package scripts, so the previously documented
+  `TOLLGATE_ADMIN_PASSWORD=… apk add …` flow silently degraded to a random
+  provisional credential the operator never chose (found end-to-end on the
+  vlab installer lane). Mode-600 is enforced with a `find -perm` gate —
+  the minimal busybox on real router images ships without `stat`, which
+  the first revision used and which refused every staging — and the
+  environment channel remains for manual re-runs. The installer-contract
+  lane (#892) asserts the whole contract: staged secret becomes root's
+  hash (sha256crypt-verified), nothing plaintext in the install output,
+  files consumed
+  ([#894](https://github.com/OpenTollGate/tollgate-module-basic-go/pull/894)).
diff --git a/packaging/files/etc/uci-defaults/99-tollgate-setup b/packaging/files/etc/uci-defaults/99-tollgate-setup
index bf945a215..e0d2f2cf5 100755
--- a/packaging/files/etc/uci-defaults/99-tollgate-setup
+++ b/packaging/files/etc/uci-defaults/99-tollgate-setup
@@ -1257,17 +1257,55 @@ generate_admin_password() {
 
 # The operator may CHOOSE the admin credential at install time instead of
 # receiving a generated one they have to write down in the seconds it is on
-# screen. This is the supported mechanism because uci-defaults run from the
-# package manager with no controlling terminal: there is nowhere to hold a
-# prompt, so the choice arrives in the environment.
-#
-#   TOLLGATE_ADMIN_PASSWORD='…' apk add --allow-untrusted /tmp/tollgate-wrt.apk
-#
-# The value is taken as-is (no trimming — a deliberate leading/trailing space
-# is the operator's business) and is NEVER echoed: it is already known to the
-# operator, so printing it would only leak it into the install log.
+# screen. uci-defaults run from the package manager with no controlling
+# terminal, so there is nowhere to hold a prompt: the choice has to arrive
+# through a side channel. There are two, because apk-tools on 25.12 does not
+# hand the installer's environment to the package scripts (verified
+# end-to-end on the vlab lane, #888):
+#
+#  - the ROOT-ONLY STAGED FILE, which works through `apk add`:
+#
+#      printf '%s' 'my-password' > /tmp/tollgate-admin-password
+#      printf '%s' 'my-wifi-key'   > /tmp/tollgate-wifi-key
+#      chmod 600 /tmp/tollgate-admin-password /tmp/tollgate-wifi-key
+#      apk add --allow-untrusted /tmp/tollgate-wrt.apk
+#
+#    Each file is CONSUMED — unlinked on first read — so a stale file can
+#    never re-apply an old password on a later boot, and the value never
+#    sits on a world-readable path (the operator's 600 is preserved; a file
+#    staged world-readable is refused).
+#
+#  - the ENVIRONMENT, which works for a manual re-run of this script (and
+#    for installers that do preserve their environment):
+#
+#      TOLLGATE_ADMIN_PASSWORD='…' /etc/uci-defaults/99-tollgate-setup
+#
+# The values are taken as-is (no trimming — a deliberate leading/trailing
+# space is the operator's business) and are NEVER echoed: they are already
+# known to the operator, so printing them would only leak them into the
+# install log.
+consume_install_secret() { # <path> — print a root-staged secret once, then unlink it
+    [ -r "$1" ] || return 0
+    # Mode gate via find -perm, not stat -c: the minimal busybox on real
+    # router images ships without the stat applet (verified on 25.12.5 x86),
+    # and an unreadable mode answer must never fall open.
+    if [ -z "$(find "$1" -maxdepth 0 -perm 0600 2>/dev/null)" ]; then
+        log "ERROR: staged install secret $1 must be mode 600 (root-only) — refusing to read it"
+        rm -f "$1"
+        return 0
+    fi
+    local value
+    value="$(head -n 1 "$1" 2>/dev/null)"
+    rm -f "$1"
+    [ -n "$value" ] && printf '%s' "$value"
+}
+
 operator_chosen_admin_password() {
-    printf '%s' "${TOLLGATE_ADMIN_PASSWORD:-}"
+    if [ -n "${TOLLGATE_ADMIN_PASSWORD:-}" ]; then
+        printf '%s' "$TOLLGATE_ADMIN_PASSWORD"
+        return 0
+    fi
+    consume_install_secret "${TOLLGATE_ADMIN_PASSWORD_FILE:-/tmp/tollgate-admin-password}"
 }
 
 # Marks a credential this package GENERATED rather than one the operator
@@ -2323,7 +2361,16 @@ setup_private_network() {
         # Operator chose it (install-time prompt, B) — never generated-and-printed.
         private_key="$TOLLGATE_PRIVATE_WIFI_PASSWORD"
         log "Private WiFi key set from TOLLGATE_PRIVATE_WIFI_PASSWORD (not printed)"
-    elif [ -z "$private_key" ]; then
+    fi
+    if [ -z "$private_key" ]; then
+        # The apk-reliable channel, same contract as the admin password's
+        # (#888): consumed on read, mode-600 enforced, never echoed.
+        private_key="$(consume_install_secret "${TOLLGATE_WIFI_PASSWORD_FILE:-/tmp/tollgate-wifi-key}")"
+        if [ -n "$private_key" ]; then
+            log "Private WiFi key set from the staged install file (not printed)"
+        fi
+    fi
+    if [ -z "$private_key" ]; then
         # Memorable password: 3 words + 2-digit number. Single
         # /dev/urandom read, awk picks words — avoids forking per word.
         # NOT printed: the owner sets their own in the board's first-run page