Display peer cursors in vim with yellow highlight

adapters/vim/collab.vim

@@ -3,12 +3,15 @@ vim9script
 # collab.vim - collaborative editing adapter for collabd
 # requires: bun, collabd daemon running
 
+highlight PeerCursor ctermbg=yellow guibg=yellow ctermfg=black guifg=black
+
 var bridge_job: job = null_job
 var bridge_channel: channel = null_channel
 var connected = false
 var ready = false
 var room = ""
 var suppressing = false
+var peer_match_ids: dict<number> = {}
 
 # path to bridge script (adjust as needed)
 const bridge_script = expand('<sfile>:p:h') .. '/bridge.ts'
@@ -42,6 +45,8 @@ def OnOutput(ch: channel, msg: string)
         ApplyRemoteContent(data.text)
     elseif data.type == 'peers'
         echom '[collab] peers: ' .. data.count
+    elseif data.type == 'cursor'
+        ShowPeerCursor(data.data)
     elseif data.type == 'error'
         echoerr '[collab] ' .. data.message
     endif
@@ -69,6 +74,30 @@ def SendBuffer()
     Send({type: 'content', text: content})
 enddef
 
+def ShowPeerCursor(data: dict<any>)
+    const client_id = string(data.clientId)
+
+    # Clear previous highlight for this peer
+    if has_key(peer_match_ids, client_id)
+        silent! matchdelete(peer_match_ids[client_id])
+    endif
+
+    # Highlight the cursor position (line, col are 0-indexed from bridge)
+    const line_nr = data.line + 1
+    const col_nr = data.col + 1
+
+    # Create a 1-char highlight at cursor position
+    const pattern = '\%' .. line_nr .. 'l\%' .. col_nr .. 'c.'
+    peer_match_ids[client_id] = matchadd('PeerCursor', pattern, 10)
+enddef
+
+def ClearPeerCursors()
+    for id in values(peer_match_ids)
+        silent! matchdelete(id)
+    endfor
+    peer_match_ids = {}
+enddef
+
 export def Connect(room_name: string)
     if bridge_job != null_job
         Disconnect()
@@ -112,6 +141,7 @@ export def Disconnect()
         bridge_job = null_job
         bridge_channel = null_channel
     endif
+    ClearPeerCursors()
     connected = false
     ready = false
     room = ""