fix(liquidsoap): switch append_history to let json.parse with typed record

old json.parse(default=...) silently failed on every track change so
recent-played always showed only one entry. modern let-form parses
the existing history file correctly.

config/liquidsoap.liq

@@ -36,25 +36,32 @@ def append_history(station, m) =
   filename = m["filename"]
   if filename != "" then
     history_path = "/now-playing/#{station}.history.json"
-    existing =
+    entry = {
-      if file.exists(history_path) then
+      title       = m["title"],
-        file.contents(history_path)
+      artist      = m["artist"],
-      else
+      album       = m["album"],
-        "[]"
+      filename    = filename,
-      end
+      started_at  = string(int_of_float(time()))
+    }
     arr =
-      try
+      if file.exists(history_path) then
-        json.parse(default=([] : [json]), existing)
+        existing = file.contents(history_path)
-      catch _ do
+        try
-        ([] : [json])
+          let json.parse (parsed : [{
+            title: string,
+            artist: string,
+            album: string,
+            filename: string,
+            started_at: string
+          }]) = existing
+          parsed
+        catch _ do
+          []
+        end
+      else
+        []
       end
-    entry = json()
+    new_arr = list.add(entry, list.prefix(49, arr))
-    entry.add("title", m["title"])
-    entry.add("artist", m["artist"])
-    entry.add("album", m["album"])
-    entry.add("filename", filename)
-    entry.add("started_at", string(int_of_float(time())))
-    new_arr = list.add(entry, list.prefix(50, arr))
     out_str = json.stringify(new_arr)
     file.write(data=out_str, atomic=true, temp_dir="/now-playing", history_path)
   end