document deno scrolls situation

shelf/README.org

@@ -0,0 +1,26 @@
+* Scroll conventions
+** Deno
+Each Deno scroll:
+
+- is an immediate subdirectory of ~./deno~
+- contains a Deno lockfile
+
+  Unless you're trying to shoot yourself or downstream dep maintainers in the foot.
+- contains a ~scroll.nix~ file
+- defines ~cache-command~ field in ~scroll.nix~
+
+  ~cache-command~ triggers Deno cache build, putting cache in $DENO_DIR.
+- does not use JSR dependencies
+
+  They have heavily timestamped metadata and therefore do not support
+  reproducible builds.
+- can use NPM dependencies
+
+~.lock~, ~.json~ and ~.jsonc~ files are recursively hashed
+to determine if the cache is updated.
+
+In that case a new entry needs to be added in knownHashes.
+
+All scrolls currently are to use the same Deno version defined by the flake.
+
+See ~./deno-workflow.nix~ for details.

shelf/deno/hjq/scroll.nix

@@ -1,3 +1,16 @@
 {
+  name = "hjq";
+
+  description = "Drop-in jq replacement for HJSON that tries to preserve comments";
+  
+  inputs = {
+    stdin = "HJSON";
+    jq_filter = "string";
+  };
+  
+  outputs = {
+    stdout = "HJSON";
+  };
+  
   cache-command = "deno cache --reload main.ts";
 }