Feat v0.5.2 chat surface (#32)

Co-authored-by: Jeffrey Smith <jasafpro@gmail.com>
Co-committed-by: Jeffrey Smith <jasafpro@gmail.com>

packages/chat/script.star

@@ -0,0 +1,39 @@
+# Chat Surface — Starlark Backend (v0.1.0)
+#
+# Thin surface layer on top of chat-core library.
+# Only handles typing indicator broadcast — all CRUD is
+# delegated to chat-core's own API routes.
+#
+# Modules: json, realtime
+
+def _resp(status, data):
+    return {"status": status, "body": json.encode(data), "headers": {"Content-Type": "application/json"}}
+
+
+def on_request(req):
+    path   = req["path"]
+    method = req["method"]
+    user_id = req.get("user_id", "")
+
+    # POST /typing/:conversation_id — broadcast typing indicator
+    if method == "POST" and path.startswith("/typing/"):
+        cid = path[len("/typing/"):]
+        if not cid:
+            return _resp(400, {"error": "conversation_id required"})
+
+        body = json.decode(req.get("body", "{}"))
+        display_name = str(body.get("display_name", ""))
+
+        realtime.publish(
+            "conversation:" + cid,
+            "typing",
+            {
+                "participant_id": user_id,
+                "display_name": display_name,
+                "conversation_id": cid,
+            },
+        )
+
+        return _resp(200, {"ok": True})
+
+    return _resp(404, {"error": "not found"})