From fb686bd8b57c7a10affbca7a781c99c32455df78 Mon Sep 17 00:00:00 2001
From: Xavier Ruiz <github@xav.ie>
Date: Wed, 7 Jan 2026 17:33:43 -0500
Subject: [PATCH 1/2] test: add case for invalid buffer in tracking causing
 E5108

When a buffer is deleted externally, a race condition can leave stale
entries in tabscope's internal tracking. If `remove_tab_buffer` picks
the invalid buffer to show, it causes E5108: Invalid buffer id.

The test simulates this by wiping a buffer and re-adding its ID to
tracking, reproducing the race condition reliably.
---
 tests/main.bats      |  4 ++++
 tests/test-cases.lua | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/tests/main.bats b/tests/main.bats
index 3ff159e..a947150 100644
--- a/tests/main.bats
+++ b/tests/main.bats
@@ -91,3 +91,7 @@ EOF
 @test "remove local tab buffer that was last for tab" {
   run_case
 }
+
+@test "remove tab buffer when tracked buffer was deleted externally" {
+  run_case
+}
diff --git a/tests/test-cases.lua b/tests/test-cases.lua
index 395b2eb..fa8b5db 100644
--- a/tests/test-cases.lua
+++ b/tests/test-cases.lua
@@ -214,4 +214,36 @@ M.remove_local_tab_buffer_that_was_last_for_tab = function()
   helpers.assert_listed_buffers({ "first", "second" })
 end
 
+M.remove_tab_buffer_when_tracked_buffer_was_deleted_externally = function()
+  local tabscope = require("tabscope")
+  tabscope.setup()
+
+  -- Create buffers and visit them
+  local buf1 = vim.api.nvim_create_buf(true, false)
+  local buf2 = vim.api.nvim_create_buf(true, false)
+  vim.api.nvim_buf_set_name(buf1, "first")
+  vim.api.nvim_buf_set_name(buf2, "second")
+  vim.api.nvim_set_current_buf(buf1)
+  vim.api.nvim_set_current_buf(buf2)
+
+  -- Wipe buf1
+  vim.cmd("bwipeout! " .. buf1)
+  assert(not vim.api.nvim_buf_is_valid(buf1), "buf1 should be invalid after wipeout")
+
+  -- Simulate race condition: tracking contains ONLY buf2 and the invalid buf1
+  -- Use table replacement to ensure exact state, with invalid buffer ID first
+  local current_tab = vim.api.nvim_get_current_tabpage()
+  tabscope.tab_buffers._buffers_by_tab[current_tab] = {}
+  tabscope.tab_buffers._buffers_by_tab[current_tab][buf1] = true -- invalid, added first
+  tabscope.tab_buffers._buffers_by_tab[current_tab][buf2] = true -- valid, current
+
+  -- Close buf2 - tabscope must try to show buf1 (the only other tracked buffer)
+  -- Without the fix: "Invalid buffer id: X"
+  tabscope.remove_tab_buffer()
+
+  -- Should succeed without error
+  local listed = helpers.get_listed_buffers()
+  assert(#listed >= 1, "should have at least one buffer")
+end
+
 return M

From 23250a3193bed98601d786d81d9a51abd8d529d0 Mon Sep 17 00:00:00 2001
From: Xavier Ruiz <github@xav.ie>
Date: Wed, 7 Jan 2026 18:16:42 -0500
Subject: [PATCH 2/2] fix: validate buffer before showing in window

Check `nvim_buf_is_valid` before using a tracked buffer in
`show_another_buffer_for_window`. This prevents E5108 errors when the
internal tracking contains stale buffer IDs due to race conditions with
external buffer deletion.
---
 lua/tabscope/buffer-managers/tab.lua | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lua/tabscope/buffer-managers/tab.lua b/lua/tabscope/buffer-managers/tab.lua
index 0afd556..cbc58be 100644
--- a/lua/tabscope/buffer-managers/tab.lua
+++ b/lua/tabscope/buffer-managers/tab.lua
@@ -141,7 +141,7 @@ local function new(tracked_buffers)
     local show_another_buffer_for_window = function(tab, win)
       local another_buffer_to_show = -1
       for buffer, _ in pairs(m._buffers_by_tab[tab]) do
-        if buffer ~= id then
+        if buffer ~= id and vim.api.nvim_buf_is_valid(buffer) then
           another_buffer_to_show = buffer
           break
         end