fix(events): ignore server heartbeat and avoid draining empty queue

Add an ignore list for server events (e.g. "server.heartbeat") so noisy heartbeats
don't trigger rendering. Also guard ThrottlingEmitter:_drain to skip calling the
process function when there are no items to process, avoiding unnecessary work.

Author: sudo-tee

lua/opencode/event_manager.lua

@@ -183,6 +183,7 @@ local log = require('opencode.log')
 --- @field state_cwd_listener function|nil Listener for state.current_cwd updates
 --- @field is_started boolean Whether the event manager is started
 --- @field captured_events table[] List of captured events for debugging
+--- @field events_to_ignore string[] List of event types to ignore from server
 --- @field throttling_emitter ThrottlingEmitter Throttle instance for batching events
 local EventManager = {}
 EventManager.__index = EventManager
@@ -198,6 +199,7 @@ function EventManager.new()
     is_started = false,
     captured_events = {},
     _parts_by_id = {},
+    events_to_ignore = { 'server.heartbeat' },
   }, EventManager)
 
   local throttle_ms = config.ui.output.rendering.event_throttle_ms
@@ -553,6 +555,10 @@ function EventManager:_subscribe_to_server_events(server)
   local api_client = state.api_client
 
   local emitter = function(event)
+    if not event or not event.type or vim.tbl_contains(self.events_to_ignore, event.type) then
+      log.debug('Ignoring event from server: %s', vim.inspect(event))
+      return
+    end
     self.throttling_emitter:enqueue(event)
   end
 

lua/opencode/throttling_emitter.lua

@@ -46,7 +46,9 @@ function ThrottlingEmitter:_drain()
   local items_to_process = self.queue
   self.queue = {}
 
-  self.process_fn(items_to_process)
+  if #items_to_process > 0 then
+    self.process_fn(items_to_process)
+  end
 
   -- double check that items weren't added while processing
   if #self.queue > 0 and not self.drain_scheduled then