fix(git): refresh the gutter after staging a hunk

lua/git/hunks.lua

@@ -599,7 +599,7 @@ end
 
 ---@param buf? integer
 function M.stage_hunk(buf)
-    local _, state, h = cursor_hunk(buf)
+    local target, state, h = cursor_hunk(buf)
     if not state then
         return
     end
@@ -616,6 +616,12 @@ function M.stage_hunk(buf)
                     "git apply failed: %s",
                     vim.trim(res.stderr or "")
                 )
+                return
+            end
+            local s = states[target]
+            if s then
+                s.index_sha = nil
+                schedule(target)
             end
         end,
     })

test/git/hunks_test.lua

@@ -296,6 +296,23 @@ t.test("stage_hunk stages a deletion", function()
     t.eq(h.git(dir, "show", ":0:a.txt").stdout, "a\nc")
 end)
 
+t.test("stage_hunk refreshes the gutter when status stays modified", function()
+    local _, buf = setup("a\nb\nc\nd\ne\n", "A\nb\nC\nd\nE\n")
+    t.eq(#assert(hunks.state(buf)).hunks, 3)
+
+    vim.api.nvim_win_set_cursor(0, { 1, 0 })
+    hunks.stage_hunk(buf)
+    t.wait_for(function()
+        return #assert(hunks.state(buf)).hunks == 2
+    end, "gutter to drop the first staged hunk")
+
+    vim.api.nvim_win_set_cursor(0, { 3, 0 })
+    hunks.stage_hunk(buf)
+    t.wait_for(function()
+        return #assert(hunks.state(buf)).hunks == 1
+    end, "gutter to drop the middle staged hunk")
+end)
+
 t.test("reset_hunk restores the index content for a change", function()
     local _, buf, state = setup("a\nb\nc\n", "a\nB\nc\n")
     vim.api.nvim_win_set_cursor(0, { 2, 0 })