flake: add local-dev app, DID-based label defaults in devshell

Add nix run .#local-dev app that wraps contrib/local-dev.sh for the tmux
orchestrator. Update the devshell hook to read the owner DID from
nix/vm-data/atproto/owner-did (if present from a previous session) and
construct TANGLED_LABEL_DEFAULTS and TANGLED_LABEL_GFI env vars.

Also add tmux to devshell nativeBuildInputs and ensure the VM launcher
creates the atproto data directory when in local-dev mode.

Set TANGLED_DEV=true in local-dev mode so the appview uses DevDirectory
for .test TLD handle resolution via the local PDS.

Signed-off-by: Alessio Caiazza <[e-mail]>

flake.nix

···
           pkgs.tailwindcss
           pkgs.nixos-shell
           pkgs.redis
+          pkgs.tmux
           pkgs.coreutils # for those of us who are on systems that use busybox (alpine)
           packages'.lexgen
           packages'.treefmt-wrapper
···
 
           # When TANGLED_VM_LOCAL_DEV=1, point the appview at local AT Protocol services
           if [[ "''${TANGLED_VM_LOCAL_DEV:-0}" != "0" ]]; then
+            export TANGLED_DEV=true
             export TANGLED_PLC_URL="http://localhost:2582"
             export TANGLED_PDS_HOST="http://localhost:2583"
             export TANGLED_PDS_ADMIN_SECRET="tangled-local-dev"
             export TANGLED_JETSTREAM_ENDPOINT="ws://localhost:6008/subscribe"
+
+            # If a DID file exists from a previous session, set up label defaults
+            _did_file="$PWD/nix/vm-data/atproto/owner-did"
+            if [[ -s "$_did_file" ]]; then
+              _did=$(cat "$_did_file")
+              _base="at://$_did/sh.tangled.label.definition"
+              export TANGLED_LABEL_DEFAULTS="$_base/wontfix,$_base/good-first-issue,$_base/duplicate,$_base/documentation,$_base/assignee"
+              export TANGLED_LABEL_GFI="$_base/good-first-issue"
+              echo "local-dev: label defaults loaded from $_did"
+            fi
             echo "local-dev: appview configured for local AT Protocol stack"
           fi
         '';
···
               cd "$rootDir"
 
               mkdir -p nix/vm-data/{knot,repos,spindle,spindle-logs}
+              if [[ "''${TANGLED_VM_LOCAL_DEV:-0}" != "0" ]]; then
+                mkdir -p nix/vm-data/atproto
+              fi
 
               export TANGLED_VM_DATA_DIR="$rootDir/nix/vm-data"
               exec ${pkgs.lib.getExe
···
             '';
           })
           + /bin/launch-vm;
+      };
+      local-dev = {
+        type = "app";
+        program = toString (pkgs.writeShellScript "local-dev" ''
+          export PATH="${pkgs.tmux}/bin:$PATH"
+          rootDir=$(jj --ignore-working-copy root 2>/dev/null || git rev-parse --show-toplevel 2>/dev/null) || {
+            echo "error: can't find repo root"
+            exit 1
+          }
+          exec bash "$rootDir/contrib/local-dev.sh" "$@"
+        '');
       };
       gomod2nix = {
         type = "app";