Ship a firewall backend, and correct three claims review disproved

Review of #28 found the iptables exclusion was justified by a false premise,
and I confirmed it: `wireguard-tools` declares `Recommends: nftables | iptables`,
`--no-install-recommends` strips it, and `wg-quick`'s add_default() shells out
to a firewall backend with no `type -p` guard. Measured on the image as this PR
shipped it:

    [#] iptables-restore -n
    /usr/bin/wg-quick: line 32: iptables-restore: command not found
    wg-quick EXIT=127

That fires for `AllowedIPs = 0.0.0.0/0` — every stock full-tunnel config from
every provider — not for a desktop client's killswitch as the comment claimed.
Split tunnels are unaffected.

Ship `nftables` rather than `iptables`: wg-quick prefers it (`type -p nft`, so
with both installed iptables is dead weight), it is first in the package's own
Recommends, and it is half the size.

The review's proposed fix stopped there; it does not hold. Adding nftables does
not make wg-quick work on this host, and neither does iptables:

    Warning: Extension CONNMARK revision 0 not supported, missing kernel module?

`Table=auto` routes by fwmark and needs xt_CONNMARK from the *host* kernel.
WSL2 has none and containers have no /lib/modules to load one from. So this
fixes native Linux and Docker Desktop for Mac — which other WHP users are on —
and cannot fix Docker Desktop for Windows, where the answer is to add routes
with `ip route` directly. Documented rather than left to be rediscovered.

Also from review:

- "`ip` and `wg` are always present" was false. A project keeps the base image
  it was first built from, so this reaches new projects only. Reworded to match
  the wording already used for the Playwright libraries, and `/usr/bin/wg` added
  to FEATURE_PROBES so an existing project is *told* it is missing VPN tooling
  and prompted to migrate, rather than finding out via `wg: command not found`.
- "no client is installed" contradicted shipping `wg` four lines earlier. The
  true claim is that no tunnel is configured or started.
- The size figure measured against bare ubuntu:24.04, which over-counts by the
  ~209 kB of libelf1t64 the real base already has, and covered one arch. Now
  measured against the current base on amd64 and stated for arm64 too, per the
  standard CLAUDE.md sets for the Playwright layer.
- `/run` persistence conflated two mechanisms: same-container files on a
  stop/start, `docker commit` on a recreation. Both stated, plus the corollary
  that key material written to /run ends up inside a snapshot image — observed,
  a `wg.priv` was already sitting in one.
- The DNS bullet presented a Docker Desktop address as the general case. Now
  leads with the mechanism, notes 127.0.0.11 on a user-defined network is
  unaffected, and adds the two things the advice omitted: a resolver the tunnel
  can reach (or it leaks every query), and pinning the endpoint via the old
  gateway (or the tunnel routes through itself).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -203,7 +203,8 @@ docker exec stdout → tokio task → emit("terminal-output-{sessionId}") → li
 ### Container (`container/`)
 
 - **`Dockerfile`** — Ubuntu 24.04 base with Claude Code, Node.js 22, Python 3.12, Rust, Docker CLI, git, gh, AWS CLI v2, ripgrep, pnpm, uv, ruff pre-installed, plus the shared
-  libraries a browser links against (see below)
+  libraries a browser links against (see below) and the VPN tooling the `vpn_support_enabled`
+  toggle grants capability for (`iproute2`, `wireguard-tools`, `nftables`)
 - **Browser runtime libraries are baked in; browser *binaries* are not.** A layer runs
   `npx --yes playwright@latest install-deps chromium` as root, so Playwright names its own
   dependencies and the list cannot rot against Ubuntu 24.04's `t64` renames or a new Chromium
@@ -316,9 +317,22 @@ container is created once by a very long function where a dropped capability is
   base-image migration — leaving a project holding the capability with nothing able to exercise it,
   and no error that points at why. `iptables` is deliberately absent; see the Dockerfile comment.
 - **Anything built on this fails open.** The network namespace is rebuilt on every start and no
-  service manager runs inside, so a tunnel never survives stop/start or recreation while `/run`
-  state persists through the snapshot and makes it look as though it did. Traffic silently reverts
-  to the real address. Any future autostart or killswitch work starts here.
+  service manager runs inside, so a tunnel never survives stop/start or recreation — while leftover
+  `/run` state makes it look as though it did. Note the two different mechanisms: `/run` is in the
+  writable layer, so on a stop/start it is simply the same container's files, and on a recreation
+  `docker commit` has carried it into the snapshot. Traffic silently reverts to the real address.
+  Any future autostart or killswitch work starts here.
+- **`/run` riding the snapshot means a VPN client's key material can end up in an image.** Verified:
+  a fresh container off the whp snapshot already contained the `wg.priv` a previous tunnel left in
+  `/run`. Anything writing key material there inherits the problem — the same `docker commit`
+  hazard as `triple-c.git-token-hash` and the custom-env fingerprint, in a directory that looks
+  ephemeral and is not. A VPN client that does this should delete its key on teardown.
+- **`wg-quick` full tunnels need `xt_CONNMARK` from the host kernel**, which WSL2 does not have and
+  a container cannot load; `Recommends: nftables | iptables` is also stripped by
+  `--no-install-recommends`, so `nftables` is baked explicitly. See the Dockerfile comment — the
+  short version is that shipping the backend fixes native Linux and Docker Desktop for Mac, nothing
+  fixes Docker Desktop for Windows, and adding the routes directly with `ip route` sidesteps it on
+  all three.
 
 ### Container Lifecycle
 

HOW-TO-USE.md

@@ -475,13 +475,18 @@ When enabled, the host Docker socket is mounted into the container so Claude Cod
 
 When enabled, the container is given the three things a VPN client needs to build a tunnel:
 the `NET_ADMIN` capability, the `/dev/net/tun` device, and the `net.ipv4.conf.all.src_valid_mark`
-sysctl that WireGuard requires. The `ip` and `wg` commands are always present to use them. This is
-**off by default**.
+sysctl that WireGuard requires. This is **off by default**.
+
+The `ip`, `wg` and `nft` commands ship in the container image so there is something able to use
+them. If your project's container was created from an older base image it will not have them, and
+`wg` will simply not be found — **migrating the project onto the current base image** is what picks
+them up. Installing them by hand with `sudo apt install wireguard-tools` works in the meantime, but
+lives in the writable layer, so it is undone by a **Reset** and by a migration.
 
 **This setting makes a tunnel possible; it does not make one.** Nothing is connected, no traffic is
-redirected, and no client is installed or started on your behalf. Enabling it and expecting the
+redirected, and no tunnel is configured or started on your behalf. Enabling it and expecting the
 container's traffic to start leaving through a VPN is the most common misreading of what it does —
-installing a client and routing traffic into it remains yours to do.
+configuring a tunnel and routing traffic into it remains yours to do.
 
 Without it, a client such as PIA, WireGuard or OpenVPN installs and its daemon starts normally, but
 the connection attempt **hangs until it times out** — a default container has no tun device to open
@@ -504,20 +509,29 @@ Things worth knowing:
 - A VPN client's kill switch applies to everything in the container, Claude Code included. If the
   tunnel drops, expect API calls to fail until it reconnects or the kill switch is turned off.
 - **No tunnel survives a restart.** The network namespace is built fresh every time the container
-  starts, and there is no service manager inside to reconnect anything. Files under `/run` may
-  persist via the snapshot and make it *look* like the tunnel is still configured, but after any
-  stop/start, Reset or recreation the interface and its routes are gone and traffic goes out your
-  real address again — with no error and nothing visibly different. Re-establish it after every
-  start, and check rather than assume.
-- **A full tunnel breaks DNS unless the client is told to leave private ranges alone.** Containers
-  resolve through an address on the Docker network (`192.168.65.7` under Docker Desktop) that sits
-  outside the container's own subnet, so a default route of `0.0.0.0/0` — or a `0.0.0.0/1` plus
-  `128.0.0.0/1` pair — captures it and sends every lookup into a tunnel that cannot carry it. The
-  symptom is total: Claude Code reports it cannot connect, because it cannot resolve
-  `api.anthropic.com`. Route `10.0.0.0/8`, `172.16.0.0/12`, `192.168.0.0/16` and `169.254.0.0/16`
-  via the original gateway, and use the VPN provider's own resolver for everything else. Note that
-  a health check which fetches an IP literal such as `1.1.1.1` passes cleanly while this is broken —
-  resolve a name instead.
+  starts, and there is no service manager inside to reconnect anything. Leftover state under `/run`
+  makes it *look* like the tunnel is still configured — that directory is in the container's
+  writable layer, so it is simply still there after a stop/start, and `docker commit` carries it
+  into the snapshot that a recreation is built from. Either way the interface and its routes are
+  gone and traffic goes out your real address again, with no error and nothing visibly different.
+  Re-establish it after every start, and check rather than assume.
+- **A full tunnel breaks DNS unless the client is told to leave private ranges alone.** Your
+  resolver is whatever `/etc/resolv.conf` says, and if that address is outside the container's own
+  subnet then a default route of `0.0.0.0/0` — or a `0.0.0.0/1` plus `128.0.0.0/1` pair — captures
+  it and sends every lookup into a tunnel that cannot carry it. Under Docker Desktop it is
+  `192.168.65.7`, which is exactly that case; on a user-defined Docker network it is `127.0.0.11`,
+  which is loopback and unaffected. Check yours rather than assuming. The symptom when it bites is
+  total: Claude Code reports it cannot connect, because it cannot resolve `api.anthropic.com`.
+  Route `10.0.0.0/8`, `172.16.0.0/12`, `192.168.0.0/16` and `169.254.0.0/16` via the original
+  gateway — and give the tunnel a resolver it can actually reach, normally the VPN provider's own,
+  or you have a tunnel that leaks every DNS query outside itself. Also pin the VPN endpoint's own
+  address via the original gateway, or the tunnel's encrypted packets try to route through the
+  tunnel. Note that a health check which fetches an IP literal such as `1.1.1.1` passes cleanly
+  while DNS is broken — resolve a name instead.
+- **`wg-quick` cannot bring up a full tunnel on Docker Desktop for Windows.** Its `Table=auto` mode
+  routes by firewall mark and needs `xt_CONNMARK` from the host kernel, which WSL2's does not have
+  and a container cannot load. Split tunnels (a specific `AllowedIPs`) work fine, as does adding
+  the routes yourself with `ip route`. Native Linux and Docker Desktop for Mac are unaffected.
 
 > This setting can only be changed when the container is stopped. Capabilities and devices are
 > fixed when a container is created, so toggling it recreates the container on the next start.

app/src-tauri/src/docker/migration.rs

@@ -135,6 +135,7 @@ pub const FEATURE_PROBES: &[(&str, &str)] = &[
     ("/usr/local/bin/triple-c-task-runner", "Scheduled task runner"),
     ("/usr/local/bin/triple-c-sso-refresh", "AWS SSO auto-refresh"),
     ("/opt/mission-control", "Mission Control (Flight Control)"),
+    ("/usr/bin/wg", "VPN support (WireGuard tools)"),
 ];
 
 /// Headroom demanded on Docker's storage backend on top of the measured

container/Dockerfile

@@ -36,6 +36,7 @@ RUN for i in 1 2 3 4 5; do \
     socat \
     iproute2 \
     wireguard-tools \
+    nftables \
     && rm -rf /var/lib/apt/lists/*
 
 # `libnss3-tools` above provides `certutil`. Chrome/Chromium read neither
@@ -44,22 +45,55 @@ RUN for i in 1 2 3 4 5; do \
 # corporate CA, no matter what the system trust store says. entrypoint.sh
 # degrades to a warning if it is ever missing.
 
-# `iproute2` and `wireguard-tools` above are what the VPN support toggle
-# (`vpn_support_enabled`) grants capability *for*. That toggle hands a project
-# CAP_NET_ADMIN and /dev/net/tun; without `ip` there is then no way to add a
-# route, and without `wg` no way to build the tunnel those two exist to serve —
-# a capability with nothing able to use it.
+# `iproute2`, `wireguard-tools` and `nftables` above are what the VPN support
+# toggle (`vpn_support_enabled`) grants capability *for*. That toggle hands a
+# project CAP_NET_ADMIN and /dev/net/tun; without `ip` there is then no way to
+# add a route, and without `wg` no way to build the tunnel those two exist to
+# serve — a capability with nothing able to use it.
 #
 # They are baked rather than left to a runtime `apt-get install` for the same
 # reason as the Playwright libraries below: the writable layer is re-paid after
 # every Reset and lost on base-image migration. A hand-installed `wg` therefore
 # works right up until an upgrade, then disappears and takes the tunnel with it
 # — silently, since a VPN that fails to come up looks exactly like one that was
-# never started. Together they are ~4.3 MB including dependencies.
+# never started.
 #
-# `iptables` is deliberately NOT here. The only thing that wants it is a desktop
-# VPN client's killswitch, and those clients need a GUI that a container has no
-# way to give them; leaving it out keeps the reach of CAP_NET_ADMIN smaller.
+# Measured against the *current base image*, not a bare ubuntu:24.04 — the base
+# already ships libelf1t64, so measuring on bare ubuntu over-counts by ~209 kB:
+# +9 packages, 5,614 kB on amd64 (4,153 kB of that is iproute2+wireguard-tools,
+# 1,461 kB is nftables). The same set on arm64 is 7,422 kB, measured against
+# ubuntu:24.04 since the arm64 base is not cached here.
+#
+# ## Why `nftables` specifically
+#
+# `wireguard-tools` declares `Recommends: nftables | iptables`, which the
+# `--no-install-recommends` above strips. That is not cosmetic: `wg-quick`'s
+# `add_default()` runs whenever a config has `AllowedIPs = 0.0.0.0/0` — i.e.
+# every stock full-tunnel config every provider hands out — and it shells out to
+# a firewall backend with no `type -p` guard. Measured without one:
+#
+#     [#] iptables-restore -n
+#     /usr/bin/wg-quick: line 32: iptables-restore: command not found
+#     wg-quick EXIT=127        (interface rolled back, split tunnels unaffected)
+#
+# `nftables` rather than `iptables` because `wg-quick` prefers it (`if type -p
+# nft`, so with both installed iptables is dead weight), it is the first
+# alternative in the package's own Recommends, and it is roughly half the size.
+#
+# This does NOT make `wg-quick`'s full-tunnel mode work everywhere. `Table=auto`
+# routes by fwmark and needs connection-mark tracking from the *host* kernel:
+#
+#     Warning: Extension CONNMARK revision 0 not supported, missing kernel module?
+#
+# WSL2's kernel has no `xt_CONNMARK` and containers have no /lib/modules to load
+# one from, so on Docker Desktop for Windows `wg-quick up` on a full tunnel fails
+# regardless of what is installed here. Native Linux and Docker Desktop for Mac
+# have it. Shipping the backend is what makes the difference on those two;
+# nothing shipped here can make the difference on WSL2, where the way out is to
+# add the routes with `ip route` instead of going through `wg-quick` at all.
+#
+# `iptables` is deliberately still NOT here: with `nftables` present `wg-quick`
+# never reaches for it, so it would add size and firewall surface for nothing.
 
 # Remove default ubuntu user to free UID 1000 for host-user remapping
 RUN if id ubuntu >/dev/null 2>&1; then userdel -r ubuntu 2>/dev/null || userdel ubuntu; fi \