fix(diff): keep Neovim alive when a handler raises during a failed openDiff setup

.agents/skills/verify-diff-lifecycle/covered.lock

@@ -3,11 +3,11 @@ file lua/claudecode/config.lua 787fa0432d1d77d7
 == lua/claudecode/cwd.lua
 file lua/claudecode/cwd.lua 55d26ea362173afa
 == lua/claudecode/diff.lua
-file lua/claudecode/diff.lua b437f6282811538e
+file lua/claudecode/diff.lua ab11e592a3f2c13d
 block resolve_saved          46d5f3f732711fe1
 block resolve_rejected       c7a620816abff9a1
 block open_blocking          92067df7f9d4d4d9
-block setup_blocking         b45a7bfd5203a085
+block setup_blocking         257189386f7b6147
 block close_by_name          cc40c0d2ffdf7946
 block close_pending          31bc827d1065da70
 block close_for_client       330cc91666bc7884

lua/claudecode/diff.lua

@@ -1867,6 +1867,13 @@ function M._setup_blocking_diff(params, resolution_callback)
       end
     end
 
+    -- A raising handler of the user (autocmd callback) makes the cleanup above fail inside Neovim API calls. Neovim
+    -- 0.8.0 bundles a LuaJIT that then keeps pointing at the main Lua thread, while this code runs in the coroutine
+    -- of tools.handle_invoke. The next JIT trace exit corrupts the stack of the main thread and Neovim aborts or
+    -- crashes, exit 134 or 139 (LuaJIT issue #1066, fixed in September 2023). An API call that returns normally points
+    -- LuaJIT at the running coroutine again. Make one before the error leaves the coroutine.
+    vim.api.nvim_get_current_tabpage()
+
     -- Re-throw the error for MCP compliance
     error({
       code = -32000,

tests/integration/diff_failed_setup_guards_spec.lua

@@ -1,6 +1,6 @@
 -- Real-Neovim guards for openDiff with `diff_opts.open_in_new_tab`: when the diff setup fails after `:tabnew` and a
 -- handler of the user raises while the plugin cleans up, openDiff still answers "Diff setup failed", closes the tab
--- it opened and goes back to the tab it left. Under busted's mock vim this is pending;
+-- it opened and goes back to the tab it left, and Neovim keeps running. Under busted's mock vim this is pending;
 -- scripts/run_integration_tests_individually.sh runs it in Neovim, including CI's oldest supported version.
 if vim == nil or vim.fn.has("nvim") ~= 1 then
   describe("openDiff when the setup fails in a new tab", function()
@@ -101,32 +101,67 @@ describe("openDiff when the setup fails in a new tab", function()
     _G.claude_deferred_responses = {}
   end)
 
-  after_each(function()
+  local function reset()
     pcall(vim.api.nvim_del_augroup_by_name, group)
     diff._cleanup_all_active_diffs("test cleanup")
     vim.cmd("silent! tabonly!")
     vim.cmd("silent! only!")
     vim.cmd("silent! %bwipeout!")
+  end
+
+  after_each(function()
+    reset()
     vim.fn.delete(dir, "rf")
     _G.claude_deferred_responses = nil
+    if jit then
+      jit.opt.start("hotloop=56", "hotexit=10", "tryside=4") -- LuaJIT's defaults
+    end
   end)
 
+  local function a_WinClosed_handler_raises()
+    wipe_the_proposal_when_shown()
+    raise_when_a_window_closes()
+  end
+
+  local function a_WinLeave_handler_raises_during_the_cleanup()
+    fail_the_setup_and_then_raise_when("WinLeave")
+  end
+
+  local function a_BufLeave_handler_raises_during_the_cleanup()
+    fail_the_setup_and_then_raise_when("BufLeave")
+  end
+
   it("closes the new tab and goes back to the tab it left when a WinClosed handler raises", function()
-    closes_the_new_tab_and_goes_back(function()
-      wipe_the_proposal_when_shown()
-      raise_when_a_window_closes()
-    end)
+    closes_the_new_tab_and_goes_back(a_WinClosed_handler_raises)
   end)
 
   it("closes the new tab and goes back when a WinLeave handler raises during the cleanup", function()
-    closes_the_new_tab_and_goes_back(function()
-      fail_the_setup_and_then_raise_when("WinLeave")
-    end)
+    closes_the_new_tab_and_goes_back(a_WinLeave_handler_raises_during_the_cleanup)
   end)
 
   it("closes the new tab and goes back when a BufLeave handler raises during the cleanup", function()
-    closes_the_new_tab_and_goes_back(function()
-      fail_the_setup_and_then_raise_when("BufLeave")
-    end)
+    closes_the_new_tab_and_goes_back(a_BufLeave_handler_raises_during_the_cleanup)
+  end)
+
+  -- Neovim 0.8.0 bundles a LuaJIT with a bug (LuaJIT issue #1066, fixed in September 2023). When a Neovim API call
+  -- raises inside a coroutine because a handler it ran raised, LuaJIT keeps pointing at the main Lua thread, and the
+  -- next JIT trace exit corrupts the stack of that thread. Neovim then aborts (exit 134, "bad stack slot") or crashes
+  -- (exit 139), and plenary prints no summary. openDiff runs in a coroutine (tools.handle_invoke). The three cases
+  -- above hit the bug in a few of 100 runs. A JIT that compiles at once makes the passes below hit it in most runs,
+  -- so this case fails on Neovim 0.8.0 when diff.lua leaves the bug in place.
+  it("keeps Neovim running when handlers raise on repeated failed setups under an eager JIT", function()
+    if jit then
+      jit.opt.start("hotloop=1", "hotexit=1", "tryside=1")
+    end
+    local arrangements = {
+      a_WinClosed_handler_raises,
+      a_WinLeave_handler_raises_during_the_cleanup,
+      a_BufLeave_handler_raises_during_the_cleanup,
+    }
+    for pass = 1, 6 do
+      vim.api.nvim_create_augroup(group, { clear = true })
+      closes_the_new_tab_and_goes_back(arrangements[pass % #arrangements + 1])
+      reset()
+    end
   end)
 end)