feat: include only dsh-context in agent VM setup

Install through the upstream CLI before Web startup, preserve existing profile state and skip completed installs. Keep pnpm's SQLite store on the guest cache disk and map the caller to namespace root for 9p atomic saves, without host-root privileges.

Cover context-only installation, retries, idempotence and preservation with offline checks. Validate real VM boot, ports, Firefox and a live DSH/context launch using a disposable profile.

agent-vm/module.nix

@@ -22,6 +22,8 @@ let
     ];
     text = ''
       export npm_config_cache=/var/cache/dsh/npm
+      # pnpm's SQLite index needs a local filesystem, not the shared 9p mount.
+      export pnpm_config_store_dir=/var/cache/dsh/pnpm
       # Explicitly rolling upstream, not a pretend-reproducible Nix derivation.
       exec npm exec --yes --package=@deepseek-ai/dsh@latest -- ${dshNode} "$@"
     '';
@@ -356,6 +358,8 @@ in
         cp --update=none --no-preserve=mode \
           ${./skills/playwright-firefox/SKILL.md} \
           /root/.agents/skills/playwright-firefox/SKILL.md
+        # Required plugin setup uses the mounted profile, never the host or store.
+        ${pkgs.bash}/bin/bash ${./context.sh} ${cfg.package}/bin/dsh
       '';
       serviceConfig = {
         User = "root";
@@ -387,6 +391,8 @@ in
                 ) (map (port: "${net.hostAddress}:${toString port}") (lib.range net.webPort net.webPortEnd))
               )
         );
+        # First-time DSH/plugin downloads run in ExecStartPre, not at Nix build time.
+        TimeoutStartSec = "10min";
         Restart = "on-failure";
         RestartSec = 3;
         UMask = "0077";