fix(tui): attribute `TermResponse` to source channel #40330

Problem: Attach-time terminal probes cannot distinguish responses from
different attached UIs.

Solution: Identify the UI by RPC channel id in `TermResponse` and make
`vim.tty.request()` filter responses by channel.

3 files changed, 39 insertions, 29 deletions

diff --git a/runtime/lua/vim/_core/defaults.lua b/runtime/lua/vim/_core/defaults.lua
index 73d85a7283..b508827c3b 100644
--- a/runtime/lua/vim/_core/defaults.lua
+++ b/runtime/lua/vim/_core/defaults.lua
@@ -922,7 +922,7 @@ do
   --- @param sync boolean When true (a TTY is present at startup), also send a
   --- DSR probe and synchronously wait so 'background' is set before user config,
   --- warning (E1568) if the terminal never answers the DSR.
-  local function detect_background(sync)
+  local function detect_background(sync, chan)
     -- Re-create (clear) the handler's augroup on each call so only the
     -- most-recently-attached TUI's handler remains.
     local bg_group = vim.api.nvim_create_augroup('nvim.tty.background', {})
@@ -938,36 +938,40 @@ do
     -- also reacts to runtime theme changes; the per-response bg_user_set() guard
     -- stops it once the user pins 'background'.
     local did_dsr_response = false
-    vim.tty.request(osc11 .. (sync and dsr or ''), { group = bg_group, timeout = 0 }, function(resp)
-      -- DSR response that should come after the OSC 11 response if the terminal
-      -- supports it.
-      if sync and string.match(resp, '^\027%[0n$') then
-        did_dsr_response = true
-        -- Don't stop listening: the bg response may come after the DSR response
-        -- if the terminal handles requests out of sequence. In that case, the bg
-        -- will simply be set later in the startup sequence.
-        return
-      end
+    vim.tty.request(
+      osc11 .. (sync and dsr or ''),
+      { group = bg_group, timeout = 0, chan = chan },
+      function(resp)
+        -- DSR response that should come after the OSC 11 response if the terminal
+        -- supports it.
+        if sync and string.match(resp, '^\027%[0n$') then
+          did_dsr_response = true
+          -- Don't stop listening: the bg response may come after the DSR response
+          -- if the terminal handles requests out of sequence. In that case, the bg
+          -- will simply be set later in the startup sequence.
+          return
+        end
 
-      -- Never override an explicit user value: stop once the user pins it.
-      if bg_user_set() then
-        return true
-      end
+        -- Never override an explicit user value: stop once the user pins it.
+        if bg_user_set() then
+          return true
+        end
 
-      local r, g, b = parseosc11(resp)
-      if r and g and b then
-        local rr = parsecolor(r)
-        local gg = parsecolor(g)
-        local bb = parsecolor(b)
-
-        if rr and gg and bb then
-          local luminance = (0.299 * rr) + (0.587 * gg) + (0.114 * bb)
-          local bg = luminance < 0.5 and 'dark' or 'light'
-          -- Use :noautocmd to suppress OptionSet event; OSC11 response may arrive after VimEnter.
-          vim.cmd('noautocmd set background=' .. bg)
+        local r, g, b = parseosc11(resp)
+        if r and g and b then
+          local rr = parsecolor(r)
+          local gg = parsecolor(g)
+          local bb = parsecolor(b)
+
+          if rr and gg and bb then
+            local luminance = (0.299 * rr) + (0.587 * gg) + (0.114 * bb)
+            local bg = luminance < 0.5 and 'dark' or 'light'
+            -- Use :noautocmd to suppress OptionSet event; OSC11 response may arrive after VimEnter.
+            vim.cmd('noautocmd set background=' .. bg)
+          end
         end
       end
-    end)
+    )
 
     if not sync then
       return
@@ -1133,7 +1137,7 @@ do
       -- runtime theme changes (mode 2031 -> TUI re-queries -> |TermResponse|);
       -- the per-response bg_user_set() guard preserves an explicit user value.
       if vim.o.ttyfast then
-        detect_background(false)
+        detect_background(false, ui.chan)
       end
     end)
   end
diff --git a/runtime/lua/vim/_meta/events.lua b/runtime/lua/vim/_meta/events.lua
index 364d706bf6..a88464ac5c 100644
--- a/runtime/lua/vim/_meta/events.lua
+++ b/runtime/lua/vim/_meta/events.lua
@@ -60,4 +60,5 @@ error('Cannot require a meta file')
 --- @field cursor integer[]
 
 --- @class vim.event.termresponse.data
+--- @field chan integer
 --- @field sequence string
diff --git a/runtime/lua/vim/tty.lua b/runtime/lua/vim/tty.lua
index 6771efe849..06b8eddcec 100644
--- a/runtime/lua/vim/tty.lua
+++ b/runtime/lua/vim/tty.lua
@@ -10,10 +10,11 @@ local M = {}
 ---
 ---@param payload string Sequence to send via nvim_ui_send(). Use empty string ('') to just register
 ---                      a listener (no sending).
----@param opts? { timeout?: integer, on_timeout?: fun(), group?: integer|string }
+---@param opts? { timeout?: integer, on_timeout?: fun(), group?: integer|string, chan?: integer }
 ---       - `timeout` (default: 1000) ms to wait before giving up, or 0 for never (caller must remove the autocmd).
 ---       - `on_timeout` optional fn called when the timeout fires.
 ---       - `group`: augroup for the TermResponse autocmd.
+---       - `chan`: only handle responses from this channel.
 ---@param on_response fun(resp:string):boolean? Called for each TermResponse. Return `true` to stop listening.
 ---@return integer # autocmd id of the TermResponse handler.
 function M.request(payload, opts, on_response)
@@ -32,7 +33,11 @@ function M.request(payload, opts, on_response)
     'TermResponse',
     opts.group,
     { nested = true },
+    ---@param ev {data: vim.event.termresponse.data}
     function(ev)
+      if opts.chan and ev.data.chan ~= opts.chan then
+        return
+      end
       local stop = on_response(ev.data.sequence)
       -- If on_response is done, cancel the timeout so on_timeout doesn't fire spuriously.
       if stop and timer and not timer:is_closing() then