feat(nix): add experimental rootless FHS package and desktop launcher

scripts/install-runtime.sh

@@ -3,6 +3,13 @@
 set -eu
 repo=$(CDPATH= cd -- "$(dirname -- "$0")/.." && pwd)
 cd "$repo"
+if [ -n "${DARLING_WORKSPACE:-}" ]; then
+  python3 scripts/nix-idle.py
+  python3 scripts/nix-state.py check-base || { echo 'Base runtime readiness missing; run darling-lol --update.' >&2; exit 1; }
+  python3 scripts/nix-state.py invalidate
+  # Prefix initialization is a setup-only exception to the runner launch gate.
+  export DARLING_SETUP=1
+fi
 python3 scripts/configure.py
 . build/runtime/tools/runtime-paths.sh
 if [ -d build/venv/bin ]; then PATH="$repo/build/venv/bin:$PATH"; export PATH; fi
@@ -16,7 +23,7 @@ prefix=$prefix_dir
 mkdir -p "$prefix/private/tmp"
 chmod 1777 "$prefix/private/tmp"
 # Build the system root store now that the prefix exists; Darling is stopped next anyway.
-python3 build/runtime/tools/ensure-darling-root-certificates.py ||
+python3 build/runtime/tools/ensure-darling-root-certificates.py || \
   echo 'Darling system root store not installed; the launcher retries it' >&2
 python3 build/runtime/tools/stop-darling-runtime.py
 sh build/runtime/tools/install-riot-presentation-runtime.sh
@@ -29,3 +36,9 @@ fi
 python3 build/runtime/tools/install-darling-system-profiler.py
 # Every guest process loads these overlays; refuse a set the compiler broke (check-darwin-tlv-calls.py).
 python3 build/runtime/tools/validate-riot-runtime.py
+# Mark this canonical prefix and configured guest ready only after validation.
+if [ -n "${DARLING_WORKSPACE:-}" ]; then
+  # Overlay installation can also refresh darlingserver; record the final base.
+  python3 scripts/nix-state.py stamp-base
+  python3 scripts/nix-state.py stamp
+fi