fix: make code <file> work in serve-web terminals

.devcontainer/Dockerfile

@@ -77,7 +77,7 @@ RUN curl -Lo /usr/local/bin/kubectl https://dl.k8s.io/release/v${VERSION_KUBECTL
 
 
 RUN apt update \
-    && apt install tmux dnsutils telnet iputils-ping jq certbot nethogs nload vim -y \
+    && apt install tmux dnsutils telnet iputils-ping jq certbot nethogs nload vim socat -y \
     && apt clean -y
 RUN curl -Lo /usr/local/bin/kind https://kind.sigs.k8s.io/dl/v${VERSION_KIND}/kind-linux-amd64 \
     && chmod +x /usr/local/bin/kind
@@ -201,6 +201,77 @@ RUN curl -sS https://downloads.1password.com/linux/keys/1password.asc | \
 
 RUN mkdir -p /home/vscode/.vscode-server/data/Machine/ && echo '{"workbench.colorTheme": "VS Code Dark"}' > /home/vscode/.vscode-server/data/Machine/settings.json
 
+# The apt `code` package installs the desktop (Electron) binary at /usr/bin/code.
+# In these headless serve-web/tunnel sessions there is no X display, so running
+# `code <file>` in the terminal crashes ("Missing X server or $DISPLAY").
+# Drop a wrapper on $HOME/.local/bin (first on the interactive PATH, see .zshrc/.bashrc
+# below) that forwards to the serve-web/remote-cli shim, which opens files in a running
+# VS Code window over its $VSCODE_IPC_HOOK_CLI socket. The wrapper picks the newest shim
+# so it survives VS Code updates, and routes to the newest live window socket so it keeps
+# working in long-lived shells (e.g. tmux) whose captured socket has gone stale (see the
+# inline comments). Only affects interactive shells; build-time `code --install-extension`
+# above still resolves to /usr/bin/code.
+RUN mkdir -p /home/vscode/.local/bin \
+    && printf '%s\n' \
+        '#!/usr/bin/env sh' \
+        '# Route `code` to the VS Code serve-web/remote CLI shim instead of the GUI desktop' \
+        '# binary (/usr/bin/code), which has no display in this container and crashes.' \
+        '' \
+        '# 0. tunnel/serve-web are full-CLI subcommands the remote-cli shim does not implement' \
+        '#    (it would treat "tunnel" as a filename to open) and they need no window socket.' \
+        '#    Hand them to the real /usr/bin/code, which dispatches them to its bundled CLI and' \
+        '#    runs fine headless. Use the absolute path -- calling `code` here would recurse' \
+        '#    into this wrapper.' \
+        'case "$1" in' \
+        '  tunnel|serve-web) exec /usr/bin/code "$@" ;;' \
+        'esac' \
+        '' \
+        '# 1. Locate the remote CLI shim. There is one per installed VS Code build and the' \
+        '#    path embeds a build hash, so pick the newest to survive VS Code updates. The' \
+        '#    -x check turns a found-but-not-executable match into the friendly error below' \
+        '#    instead of an opaque `exec: Permission denied`.' \
+        'shim=$(ls -t "$HOME"/.vscode/cli/serve-web/*/bin/remote-cli/code \' \
+        '              "$HOME"/.vscode-server/bin/*/bin/remote-cli/code \' \
+        '              "$HOME"/.vscode-server/cli/servers/*/server/bin/remote-cli/code \' \
+        '              2>/dev/null | head -n1)' \
+        'if [ -z "$shim" ] || [ ! -x "$shim" ]; then' \
+        '  echo "code: no usable VS Code remote CLI shim found; is a serve-web/remote session running?" >&2' \
+        '  exit 1' \
+        'fi' \
+        '' \
+        '# 2. Choose the IPC socket of the window to open files in. $VSCODE_IPC_HOOK_CLI is' \
+        '#    captured when the shell starts, so a long-lived shell (e.g. a tmux server that' \
+        '#    outlives a VS Code reconnect) keeps pointing at an OLD window. That old socket' \
+        '#    often still accepts connections, so files silently open in a window you can no' \
+        '#    longer see. VS Code creates one socket per window/connection under /tmp, so the' \
+        '#    newest is your current window: prefer the newest socket that still accepts a' \
+        '#    connection, falling back to older ones. If none is reachable, keep whatever the' \
+        '#    environment provided so socket-less subcommands (code --version, etc.) still work.' \
+        '#    LIMITATION: "newest socket" is the current window only with a single window/tab' \
+        '#    open. With multiple windows, or after an extension-host reload, files may open in' \
+        '#    another window -- serve-web exposes no API to target a specific window, so this is' \
+        '#    the best heuristic available.' \
+        'ipc_live() {' \
+        '  [ -S "$1" ] || return 1' \
+        '  # Best-effort connect probe to skip sockets whose window has gone away. socat is' \
+        '  # optional here: if it is not installed, treat an existing socket as usable. The' \
+        '  # timeout bounds the connect so a pathological socket can never wedge `code`.' \
+        '  command -v socat >/dev/null 2>&1 || return 0' \
+        '  timeout 2 socat -u OPEN:/dev/null UNIX-CONNECT:"$1" >/dev/null 2>&1' \
+        '}' \
+        'for sock in $(ls -t /tmp/vscode-ipc-*.sock 2>/dev/null); do' \
+        '  if ipc_live "$sock"; then' \
+        '    VSCODE_IPC_HOOK_CLI="$sock"' \
+        '    export VSCODE_IPC_HOOK_CLI' \
+        '    break' \
+        '  fi' \
+        'done' \
+        '' \
+        '# 3. Hand off to the shim, preserving every argument and its exit status.' \
+        'exec "$shim" "$@"' \
+        > /home/vscode/.local/bin/code \
+    && chmod +x /home/vscode/.local/bin/code
+
 # Add backup warning to .zshrc for vscode user
 RUN echo '\n# === Backup & Git Reminder ===' | tee -a /home/vscode/.zshrc && \
     echo 'echo -e "\e[1;31m⚠️  WARNING: No backups are configured. You are responsible for any data loss.\e[0m"' | tee -a /home/vscode/.zshrc && \