fix: vision(#623): disinto-chat sandbox hardening (#706)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker/chat/Dockerfile

@@ -15,8 +15,8 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     python3 \
     && rm -rf /var/lib/apt/lists/*
 
-# Non-root user
-RUN useradd -m -u 1000 -s /bin/bash chat
+# Non-root user — fixed UID 10001 for sandbox hardening (#706)
+RUN useradd -m -u 10001 -s /bin/bash chat
 
 # Copy application files
 COPY server.py /usr/local/bin/server.py
@@ -28,4 +28,8 @@ RUN chmod +x /entrypoint-chat.sh /usr/local/bin/server.py
 USER chat
 WORKDIR /var/chat
 
+EXPOSE 8080
+HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
+  CMD python3 -c "import urllib.request; urllib.request.urlopen('http://localhost:8080/')" || exit 1
+
 ENTRYPOINT ["/entrypoint-chat.sh"]

docker/chat/entrypoint-chat.sh

@@ -12,6 +12,16 @@ log() {
     printf '[%s] %s\n' "$(date -u '+%Y-%m-%d %H:%M:%S UTC')" "$*" | tee -a "$LOGFILE"
 }
 
+# Sandbox sanity checks (#706) — fail fast if isolation is broken
+if [ -e /var/run/docker.sock ]; then
+    log "FATAL: /var/run/docker.sock is accessible — sandbox violation"
+    exit 1
+fi
+if [ "$(id -u)" = "0" ]; then
+    log "FATAL: running as root (uid 0) — sandbox violation"
+    exit 1
+fi
+
 # Verify Claude CLI is available (expected via volume mount from host).
 if ! command -v claude &>/dev/null; then
     log "FATAL: claude CLI not found in PATH"