mkOllamaModel: add diagnostics to help in packaging new models

pkgs/by-name/ollamaPackages/mkOllamaModel.nix

@@ -85,6 +85,32 @@ stdenv.mkDerivation {
     runHook postInstall
   '';
 
+  checkPhase = ''
+    runHook preCheck
+
+    # diagnostics for when packaging models: use the manifestBlob, systemBlob output here in your nix expression
+    echo "manifest:"
+    cat manifest
+
+    printBlob() {
+      local blobType="$1"
+      local blobHash=$(cat manifest | jq ".layers.[] | select(.mediaType == \"application/vnd.ollama.image.$blobType\") | .digest[7:]")
+      if [ -n "$blobHash" ]; then
+        printf "  %sBlob = %s;\n" "$blobType" "$blobHash"
+      fi
+    }
+
+    echo "blobs:"
+    printBlob model
+    printBlob params
+    printBlob system
+    printBlob ensureDoesntFailForNonExistentBlob
+
+    runHook postCheck
+  '';
+
+  doCheck = true;
+
   env.blobDir = "share/ollama/models/blobs";
   env.manifestDir = "share/ollama/models/manifests/registry.ollama.ai/library/${modelName}";
   env.variant = variant;