fix: restore x/X/D as modal debug keys, add quit_exits_mode config, track mapped keys exactly

tests/test_mode.lua

@@ -15,8 +15,8 @@ assert_eq(td.active(), false, "starts inactive")
 td.toggle()
 assert_eq(td.active(), true, "active after toggle")
 
--- keymaps are set
-for _, key in ipairs({ "c", "s", "d", "r", "q" }) do
+-- all modal keymaps are set (including breakpoint keys)
+for _, key in ipairs({ "c", "s", "d", "r", "q", "x", "X", "D" }) do
   assert_eq(has_buf_map(key), true, key .. " key mapped")
 end
 
@@ -24,9 +24,21 @@ end
 td.toggle()
 assert_eq(td.active(), false, "inactive after second toggle")
 
--- keymaps are removed
-for _, key in ipairs({ "c", "s", "d", "r", "q" }) do
+-- all modal keymaps are removed
+for _, key in ipairs({ "c", "s", "d", "r", "q", "x", "X", "D" }) do
   assert_eq(has_buf_map(key), false, key .. " key removed")
 end
 
+-- double exit is safe
+td.toggle() -- enter
+td.toggle() -- exit
+td.toggle() -- enter
+td.toggle() -- exit
+assert_eq(td.active(), false, "stable after multiple toggles")
+
+-- verify no leaked keymaps after rapid toggling
+for _, key in ipairs({ "c", "s", "d", "r", "q", "x", "X", "D" }) do
+  assert_eq(has_buf_map(key), false, key .. " clean after rapid toggle")
+end
+
 print("ALL MODE TESTS PASSED")