added tool for checking deployment requirement

.forgejo/workflows/needs-deploy.sh

@@ -0,0 +1,44 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# Check for hostname argument
+if [[ $# -ne 1 ]]; then
+  echo "Usage: $0 <nixos-hostname>"
+  exit 1
+fi
+
+HOST="$1"
+REPO_PATH="git+file://$PWD"
+
+CURRENT_COMMIT=$(git rev-parse HEAD)
+PREV_COMMIT=$(git rev-parse HEAD^)
+
+# Check if the host exists at the current commit
+if ! nix eval --quiet --expr "
+  let
+    flake = builtins.getFlake \"${REPO_PATH}?rev=${CURRENT_COMMIT}\";
+  in
+    builtins.hasAttr \"${HOST}\" flake.nixosConfigurations
+"; then
+  echo "Error: Host '${HOST}' not found in nixosConfigurations at HEAD."
+  exit 1
+fi
+
+# Now check for derivation change
+RESULT=$(nix eval --raw --expr "
+  let
+    flake = builtins.getFlake;
+    prev = flake \"${REPO_PATH}?rev=${PREV_COMMIT}\";
+    curr = flake \"${REPO_PATH}?rev=${CURRENT_COMMIT}\";
+  in
+    if prev.nixosConfigurations.\"${HOST}\".config.system.build.toplevel !=
+       curr.nixosConfigurations.\"${HOST}\".config.system.build.toplevel
+    then \"changed\" else \"unchanged\"
+")
+
+# Output result
+if [[ $RESULT == "changed" ]]; then
+  echo "System derivation changed for host '${HOST}' — deploy!"
+else
+  echo "No change for host '${HOST}' — skip deployment."
+fi