Interop: an element id crosses C#, TypeScript, Python and Rust

The C# cultcache interop peer gains an object-list document (a deck of marks).
C# writes it with cache-minted ids; TypeScript, Python and Rust read the ids as
ordinary members, and TypeScript-written ids survive a C# read.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packages/cultcache-rs/examples/cultcache_interop.rs

@@ -26,6 +26,38 @@ struct CultCacheInteropNote {
     tags: Vec<String>,
 }
 
+// An object list: each mark is a positional array [label, id], the id an ordinary member at slot 1.
+#[derive(Clone, Debug, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
+struct CultCacheInteropMark(String, String);
+
+#[derive(Clone, Debug, PartialEq, Eq, DatabaseEntry)]
+#[cultcache(type = "cultcache.interop-deck", schema = "CultCacheInteropDeck")]
+struct CultCacheInteropDeck {
+    #[cultcache(key = 0)]
+    document_id: String,
+    #[cultcache(key = 1, default)]
+    marks: Vec<CultCacheInteropMark>,
+}
+
+fn read_deck(file: &str) -> Result<()> {
+    let mut cache = CultCache::new();
+    cache.register_entry_type::<CultCacheInteropDeck>()?;
+    cache.add_generic_backing_store(SingleFileMessagePackBackingStore::new(file))?;
+    cache.pull_all_backing_stores()?;
+    let decks = cache.get_all::<CultCacheInteropDeck>()?;
+    let deck = decks
+        .first()
+        .ok_or_else(|| anyhow!("no cultcache.interop-deck records found"))?;
+    println!(
+        "{}",
+        serde_json::to_string(&json!({
+            "documentId": deck.document_id,
+            "ids": deck.marks.iter().map(|mark| mark.1.clone()).collect::<Vec<_>>(),
+        }))?
+    );
+    Ok(())
+}
+
 fn main() -> Result<()> {
     let mut args = std::env::args().skip(1);
     let mode = args
@@ -37,6 +69,7 @@ fn main() -> Result<()> {
     match mode.as_str() {
         "write" => write_note(file, require_arg(&options, "runtime-id")?)?,
         "read" => read_note(file)?,
+        "read-deck" => read_deck(file)?,
         _ => return Err(anyhow!("unknown mode {mode}")),
     }
     Ok(())

packages/cultcache-ts/test/cult-cache.test.ts

@@ -1173,6 +1173,43 @@ test("CultCache v1 MessagePack stores are readable across TS, Rust, C#, and Pyth
   }
 });
 
+test("CultCache element ids cross C#, TypeScript, Python and Rust as ordinary members", async () => {
+  await buildInteropPeers();
+  const tempDir = await mkdtemp(join(tmpdir(), "cultcache-deck-"));
+  const file = join(tempDir, "deck.cc");
+  const written = await runJsonCommand("csharp-write-deck", dotnetCommand, [
+    csharpInteropDll, "write-deck", "--file", file,
+  ], cultLibRoot);
+  assert.equal(written.ids.length, 3);
+  assert.equal(new Set(written.ids).size, 3, "two look-alike marks got distinct ids");
+  for (const id of written.ids) assert.match(id, /^[0-9a-f]{12}$/u);
+
+  // TypeScript: the id is slot 1 of each mark, read from the raw payload.
+  const store = decode(await readFile(file)) as any[];
+  const payload = decode(store[2][0][3]) as any[];
+  assert.deepEqual(payload[1].map((mark: any[]) => mark[1]), written.ids);
+
+  // Python and Rust read the same store.
+  const python = await runJsonCommand("python-deck", pythonCommand, [
+    "-c",
+    "import msgpack,json,sys;s=msgpack.unpackb(open(sys.argv[1],'rb').read(),raw=False);p=msgpack.unpackb(s[2][0][3],raw=False);print(json.dumps({'ids':[m[1] for m in p[1]]}))",
+    file,
+  ], cultcachePyRoot);
+  assert.deepEqual(python.ids, written.ids);
+  const rust = await runJsonCommand("rust-read-deck", rustInteropBinary, ["read-deck", "--file", file], cultcacheRsRoot);
+  assert.deepEqual(rust.ids, written.ids);
+
+  // TypeScript writes the ids; C# keeps them.
+  const tsIds = ["t00000000001", "t00000000002", "t00000000003"];
+  store[2][0][3] = encode(["deck:csharp", [["twin", tsIds[0]], ["twin", tsIds[1]], ["other", tsIds[2]]]]);
+  const tsFile = join(tempDir, "ts-deck.cc");
+  await writeFile(tsFile, encode(store));
+  const back = await runJsonCommand("csharp-read-deck", dotnetCommand, [
+    csharpInteropDll, "read-deck", "--file", tsFile,
+  ], cultLibRoot);
+  assert.deepEqual(back.ids, tsIds);
+});
+
 test("CultCache interop reader accepts missing compatible trailing slots and rejects mismatched slots", async () => {
   const tempDir = await mkdtemp(join(tmpdir(), "cultcache-interop-"));
   const compatible = join(tempDir, "compatible.msgpack");

tests/GameCult.Caching.InteropPeer/Program.cs

@@ -38,6 +38,12 @@ static async Task<int> ProgramMainAsync(string[] args)
             case "read":
                 await ReadAsync(file);
                 return 0;
+            case "write-deck":
+                await WriteDeckAsync(file);
+                return 0;
+            case "read-deck":
+                await ReadDeckAsync(file);
+                return 0;
             default:
                 throw new InvalidOperationException($"Unknown mode {mode}.");
         }
@@ -77,6 +83,31 @@ static async Task ReadAsync(string file)
     WriteJsonLine(note);
 }
 
+// A record with an object list: the cache mints each mark's element id, and every runtime reads it as an ordinary member.
+static async Task WriteDeckAsync(string file)
+{
+    var cache = BuildCache(file);
+    await cache.PullAllBackingStoresAsync();
+    var deck = new CultCacheInteropDeck
+    {
+        DocumentId = "deck:csharp",
+        Marks = [new CultCacheInteropMark { Label = "twin" }, new CultCacheInteropMark { Label = "twin" }, new CultCacheInteropMark { Label = "other" }]
+    };
+    await cache.AddAsync(deck, new CultRecordHandle<CultCacheInteropDeck>(new CultRecordKey(deck.DocumentId)));
+    cache.FlushAllBackingStores();
+    WriteDeckJsonLine(deck);
+}
+
+static async Task ReadDeckAsync(string file)
+{
+    var cache = BuildCache(file);
+    await cache.PullAllBackingStoresAsync();
+    WriteDeckJsonLine(cache.AllEntries.OfType<CultCacheInteropDeck>().Single());
+}
+
+static void WriteDeckJsonLine(CultCacheInteropDeck deck) =>
+    Console.Out.WriteLine(JsonSerializer.Serialize(new { documentId = deck.DocumentId, ids = deck.Marks.Select(mark => mark.Id).ToArray() }));
+
 // Two routed single-file stores: each file is a complete single-store snapshot holding only its own type.
 static void WriteRouted(string catalogFile, string runFile)
 {
@@ -176,3 +207,18 @@ public sealed class CultCacheInteropRunNote
     [Key(2)] public string AuthorRuntimeId { get; set; } = string.Empty;
     [Key(3)] public string Body { get; set; } = string.Empty;
 }
+
+[CultDocument("cultcache.interop-deck", "cultcache.interop_deck.v1")]
+[MessagePackObject]
+public sealed class CultCacheInteropDeck
+{
+    [Key(0)] [CultName] public string DocumentId { get; set; } = string.Empty;
+    [Key(1)] public List<CultCacheInteropMark> Marks { get; set; } = new();
+}
+
+[MessagePackObject]
+public sealed class CultCacheInteropMark
+{
+    [Key(0)] public string Label { get; set; } = string.Empty;
+    [Key(1)] [CultElementId] public string Id { get; set; } = string.Empty;
+}