Fix two bugs in last round's fixes, and stop --full hiding the Docker host

Round 3 found defects in code written an hour earlier. Both reproduced.

**The handshake poll accepted empty output as a completed handshake.**
`[ "$(… | awk '{print $2}')" != 0 ]` is *true* when `wg show` prints nothing —
which it does when the interface has no peer, and when the interface is gone
(that message goes to stderr). `until` suspends `set -e` and `pipefail`, so
nothing else caught it. The poll added last round to make "success without a
tunnel" impossible produced exactly that. Now requires a number greater than
zero, and waits 20s rather than 10 so a slow link is not rolled back needlessly.

**`down` still sat above the key registration.** Last round moved it below the
token and server-list fetches but not below `addKey`, which is the most
failure-prone of the three — one gateway, by CN, pinned certificate. So a
refused registration still tore down a working tunnel. It now runs after the
last fetch; the key is generated before but written after, since `down` deletes
it. SKILL.md said "after every network fetch has succeeded", which was false;
corrected.

**`up --full` made `host.docker.internal` unresolvable — and `status` said DNS
was fine.** That name is answered only by the resolver being replaced; it is not
in `/etc/hosts`. `gateway.rs` hands it to every container for the LiteLLM
gateway, and Ollama and custom endpoints default to it, so an agent running
`up --full` silently removed the project's model backend. The route was already
excluded; only the name was lost. Now resolved with the old resolver and pinned
into `/etc/hosts` before the swap, restored on teardown, and `status` probes it
— PIA answers public names happily, which is precisely why probing only
`api.anthropic.com` reported "ok". Documented as Trap 4.

**The rollback could abort halfway.** The trap's `{ … }` is not exempt from
`set -e`, and `down`'s `cat`/`tac`/`rm` had no `|| true` — so one failure left
the interface up with all traffic captured, after printing "rolling back".
`down` now runs under `set +e`, the trap tolerates its failure, and the
interface is deleted *first*, since that removes every route pointing at it.

**The account password had a real argv window.** curl does blank `-u`, but only
once running: sampling /proc/<pid>/cmdline caught the plaintext in 2 of 400
tries, between exec and the overwrite. Small, but it is the permanent password
and the token already had the fix. Moved onto the same stdin config — 0 of 400.
Review reported this as a 25-second exposure; that was a wrapper's argv, not
curl's.

entrypoint: the skill install stages into `$_dest.new` and swaps, so a failed
copy leaves the previous copy intact instead of a truncated SKILL.md and no
script, root-owned, on a persisted volume. Verified against a size-limited
filesystem.

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

container/entrypoint.sh

@@ -381,10 +381,18 @@ install_feature_skill() {
         # Not just $_dest: when Mission Control is off nothing else creates the
         # parent, so root would own it and `claude` could not add a skill there.
         chown claude:claude /home/claude/.claude/skills
+        # Stage then swap. Copying over the live path meant a failure (full
+        # volume, read-only mount) left a truncated SKILL.md and no script
+        # behind, root-owned, on a persisted volume — which Claude Code then
+        # discovers and loads.
+        rm -rf "$_dest.new"
+        cp -r "$_src" "$_dest.new" || {
+            rm -rf "$_dest.new"
+            echo "entrypoint: $_name skill install FAILED (copy from $_src); previous copy left intact"
+            return 1; }
+        chown -R claude:claude "$_dest.new"
         rm -rf "$_dest"
-        cp -r "$_src" "$_dest" || {
-            echo "entrypoint: $_name skill install FAILED (copy from $_src)"; return 1; }
-        chown -R claude:claude "$_dest"
+        mv "$_dest.new" "$_dest"
         echo "entrypoint: $_name skill installed to ~/.claude/skills/"
     elif [ -e "$_dest" ] || [ -L "$_dest" ]; then
         # -e/-L rather than -d: a leftover *file* at that path must go too.