diff --git a/Dockerfile b/Dockerfile
index dd3851c..3c47926 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -82,11 +82,22 @@ FROM debian:trixie-slim AS runtime
 # tzdata so the TZ env (set in compose) resolves — otherwise Go can't load the
 # zone and time.Now() stays UTC, and mavend answers clock/date queries and
 # evaluates quiet-hours in UTC.
+#
+# TZ is a build arg as well as an env because the image was self-inconsistent
+# without it (V-545): compose set TZ=Europe/Samara and Go read it, but
+# /etc/localtime still pointed at Etc/UTC, so anything asking the system zone
+# instead of the environment answered UTC. The reminder path shells out to
+# python dateparser, which is exactly such a caller. Compose passes the same
+# zone it already declares, so the zone is written in one place.
+ARG TZ=Etc/UTC
+ENV TZ=$TZ
 RUN apt-get update && apt-get install -y --no-install-recommends \
       ca-certificates libvulkan1 mesa-vulkan-drivers libgomp1 tzdata \
       python3 python3-pip && \
     pip3 install --no-cache-dir --break-system-packages 'dateparser==1.4.1' && \
     apt-get purge -y --auto-remove python3-pip && \
+    ln -snf "/usr/share/zoneinfo/$TZ" /etc/localtime && \
+    echo "$TZ" > /etc/timezone && \
     rm -rf /var/lib/apt/lists/*
 
 # runtime native libs: whisper/ggml (incl. vulkan) are real files in deps/lib.
diff --git a/docker-compose.yml b/docker-compose.yml
index ab84b8f..eb8a7aa 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -12,7 +12,12 @@ x-image: &image
   # build on EVERY service (same image name ⇒ built once) so `docker compose
   # build <anyservice>` actually rebuilds. With build on only one service, the
   # others silently no-op and you deploy a stale binary.
-  build: .
+  build:
+    context: .
+    # the zone is declared once, here. The image points /etc/localtime at it so
+    # a caller reading the system zone agrees with one reading TZ (V-545).
+    args:
+      TZ: Europe/Samara
   pull_policy: never   # only ever the locally-built image
   restart: unless-stopped
   # local time for clock/date replies AND quiet-hours evaluation. Change to