feat(log): add rolling message log

src/messagelog.lua

@@ -0,0 +1,45 @@
+-- Rolling message log. Keeps a bounded tail of lines so the panel and the save
+-- file stay small while still reflecting recent events in order.
+
+local MessageLog = {}
+MessageLog.__index = MessageLog
+
+function MessageLog.new(capacity)
+  return setmetatable({ lines = {}, capacity = capacity or 32 }, MessageLog)
+end
+
+function MessageLog:add(line)
+  self.lines[#self.lines + 1] = line
+  while #self.lines > self.capacity do
+    table.remove(self.lines, 1)
+  end
+end
+
+function MessageLog:addAll(lines)
+  for _, line in ipairs(lines) do
+    self:add(line)
+  end
+end
+
+function MessageLog:last()
+  return self.lines[#self.lines]
+end
+
+function MessageLog:recent(count)
+  local out = {}
+  local from = math.max(1, #self.lines - count + 1)
+  for i = from, #self.lines do
+    out[#out + 1] = self.lines[i]
+  end
+  return out
+end
+
+function MessageLog:toData()
+  return { lines = self.lines, capacity = self.capacity }
+end
+
+function MessageLog.fromData(snapshot)
+  return setmetatable({ lines = snapshot.lines, capacity = snapshot.capacity }, MessageLog)
+end
+
+return MessageLog