feat: better version management

packages/release/release.nix

@@ -1,8 +1,11 @@
 # release.nix
 {
   pkgs,
-  readVersion,
-  writeVersion,
+  # Source of truth is always $ROOT_DIR/VERSION.
+  # Format:
+  #   line 1: X.Y.Z
+  #   line 2: CHANNEL (stable|alpha|beta|rc|internal|...)
+  #   line 3: N (prerelease number, 0 for stable)
   postVersion ? "",
   versionFiles ? [ ],
   channels ? [
@@ -34,8 +37,34 @@ let
       [
         channelList
         versionFilesScript
-        readVersion
-        writeVersion
+        ''
+          if [[ ! -f "$ROOT_DIR/VERSION" ]]; then
+            echo "Error: missing $ROOT_DIR/VERSION" >&2
+            exit 1
+          fi
+
+          base_line="$(sed -n '1p' "$ROOT_DIR/VERSION" | tr -d '\r')"
+          channel_line="$(sed -n '2p' "$ROOT_DIR/VERSION" | tr -d '\r')"
+          n_line="$(sed -n '3p' "$ROOT_DIR/VERSION" | tr -d '\r')"
+
+          # Backward compatibility: old single-line format.
+          if [[ -z "$channel_line" ]]; then
+            printf '%s\n' "$base_line"
+          elif [[ "$channel_line" == "stable" ]]; then
+            printf '%s\n' "$base_line"
+          else
+            printf '%s-%s.%s\n' "$base_line" "$channel_line" "$n_line"
+          fi
+        ''
+        ''
+          channel_to_write="$CHANNEL"
+          n_to_write="''${PRERELEASE_NUM:-1}"
+          if [[ "$channel_to_write" == "stable" || -z "$channel_to_write" ]]; then
+            channel_to_write="stable"
+            n_to_write="0"
+          fi
+          printf '%s\n%s\n%s\n' "$BASE_VERSION" "$channel_to_write" "$n_to_write" > "$ROOT_DIR/VERSION"
+        ''
         postVersion
       ]
       (builtins.readFile ./release.sh);