fix(git): stop the blame statuscolumn leaking into new windows

lua/git/blame.lua

@@ -521,9 +521,21 @@ end
 ---@type table<integer, string>
 local saved_statuscolumn = {}
 
----Reconcile every window's `'statuscolumn'` with the overlay state: a
----window showing an overlay buffer gets the blame statuscolumn, and its
----previous value is saved so it can be restored on toggle-off.
+---Set a window's `'statuscolumn'` with `scope = "local"`, so the global
+---value stays clean and splits and new windows do not inherit the gutter.
+---@param win integer
+---@param value string
+local function set_statuscolumn(win, value)
+    vim.api.nvim_set_option_value(
+        "statuscolumn",
+        value,
+        { win = win, scope = "local" }
+    )
+end
+
+---Reconcile every window's `'statuscolumn'` with the overlay state.
+---Overlay windows get the blame statuscolumn, and a window that has it
+---but should not (a split inherits window options) is restored.
 local function refresh_overlay_columns()
     for win in pairs(saved_statuscolumn) do
         if not vim.api.nvim_win_is_valid(win) then
@@ -533,11 +545,16 @@ local function refresh_overlay_columns()
     for _, win in ipairs(vim.api.nvim_list_wins()) do
         local state = states[vim.api.nvim_win_get_buf(win)]
         local on = state ~= nil and state.overlay
-        if on and saved_statuscolumn[win] == nil then
-            saved_statuscolumn[win] = vim.wo[win].statuscolumn
-            vim.wo[win].statuscolumn = BLAME_EXPR .. native_items(win)
-        elseif not on and saved_statuscolumn[win] ~= nil then
-            vim.wo[win].statuscolumn = saved_statuscolumn[win]
+        local has_blame = vim.startswith(vim.wo[win].statuscolumn, BLAME_EXPR)
+        if on and not has_blame then
+            saved_statuscolumn[win] = saved_statuscolumn[win]
+                or vim.wo[win].statuscolumn
+            set_statuscolumn(win, BLAME_EXPR .. native_items(win))
+        elseif not on and has_blame then
+            set_statuscolumn(
+                win,
+                saved_statuscolumn[win] or vim.go.statuscolumn
+            )
             saved_statuscolumn[win] = nil
         end
     end
@@ -560,7 +577,7 @@ local function render(buf)
                 build_blame_text(state, win)
                 built = true
             end
-            vim.wo[win].statuscolumn = BLAME_EXPR .. native_items(win)
+            set_statuscolumn(win, BLAME_EXPR .. native_items(win))
         end
     end
 end