host_keymap: a present-but-empty / "None" [KeyMap] line is an explicit unbind

host_keymap_load zeroed an action's binds when its line was present and then
apply_defaults() put the built-in key straight back, so "Turbo = None" (or
an empty value) silently re-armed Tab. Track explicit_unbound per action:
set when the line is present but yields no binds, and honoured by
apply_defaults through want_default(). A missing line still receives the
default, so existing config.ini files are unaffected.

Pairs with the launcher's Backspace-to-clear (recomp-ui
feat/additional-ui-functionality), which writes "None" for that reason.
README documents the rule; test_rewind_toggle_combo.py guards it.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

README.md

@@ -746,6 +746,10 @@ acceleration is **opt-in**, per game, so the accurate path is never compromised:
   speed until pressed again. Controller host shortcuts bound to a single
   button or trigger are chords with Select — the launcher shows them as
   `select + …`; only a two-button capture replaces the implicit Select.
+  Backspace while the launcher is listening clears a shortcut; in the files
+  that is `0` for a `[hotkeys]` pad value and `None` for a `[KeyMap]` key (a
+  present-but-empty or `None` line is an explicit unbind, a missing line
+  keeps the built-in default).
 - **The "Fast Loading (host pacing)" and "CD Speed" mods** — automatic
   acceleration during load waits, shipped with every title and **off by
   default**, with `turbo_audio_sink` keeping the SPU timeline coherent through

runtime/src/host_keymap.c

@@ -25,10 +25,19 @@ typedef struct HostKeyBind {
 typedef struct HostKeyAction {
     HostKeyBind binds[HOST_KEYMAP_MAX_BINDS];
     int count;
+    /* 1 when [KeyMap] names this action with an empty / "None" / "(unbound)"
+     * value: the user cleared it, so apply_defaults must NOT put the built-in
+     * key back. A MISSING line still gets the default. */
+    int explicit_unbound;
 } HostKeyAction;
 
+
 static HostKeyAction s_actions[HOST_KEYMAP_ACTION_COUNT];
 
+static int want_default(HostKeymapAction action) {
+    return s_actions[action].count == 0 && !s_actions[action].explicit_unbound;
+}
+
 static int ieq(const char *a, const char *b) {
     if (!a || !b) return 0;
     while (*a && *b) {
@@ -79,27 +88,27 @@ static void add_bind(HostKeymapAction action, int keycode, int scancode, int mod
 }
 
 static void apply_defaults(void) {
-    if (s_actions[HOST_KEYMAP_FULLSCREEN].count == 0) {
+    if (want_default(HOST_KEYMAP_FULLSCREEN)) {
         add_bind(HOST_KEYMAP_FULLSCREEN, (int)SDLK_RETURN, (int)SDL_SCANCODE_RETURN, KMOD_ALT);
         add_bind(HOST_KEYMAP_FULLSCREEN, (int)SDLK_f, (int)SDL_SCANCODE_F, KMOD_CTRL);
     }
-    if (s_actions[HOST_KEYMAP_TURBO].count == 0)
+    if (want_default(HOST_KEYMAP_TURBO))
         add_bind(HOST_KEYMAP_TURBO, (int)SDLK_TAB, (int)SDL_SCANCODE_TAB, 0);
-    if (s_actions[HOST_KEYMAP_VOLUME_UP].count == 0)
+    if (want_default(HOST_KEYMAP_VOLUME_UP))
         add_bind(HOST_KEYMAP_VOLUME_UP, (int)SDLK_KP_PLUS, (int)SDL_SCANCODE_KP_PLUS, 0);
-    if (s_actions[HOST_KEYMAP_VOLUME_DOWN].count == 0)
+    if (want_default(HOST_KEYMAP_VOLUME_DOWN))
         add_bind(HOST_KEYMAP_VOLUME_DOWN, (int)SDLK_KP_MINUS, (int)SDL_SCANCODE_KP_MINUS, 0);
-    if (s_actions[HOST_KEYMAP_DISPLAY_PERF].count == 0)
+    if (want_default(HOST_KEYMAP_DISPLAY_PERF))
         add_bind(HOST_KEYMAP_DISPLAY_PERF, (int)SDLK_f, (int)SDL_SCANCODE_F, 0);
 #if defined(PSX_HAS_RBENGINE_SNAP)
-    if (s_actions[HOST_KEYMAP_REWIND].count == 0)
+    if (want_default(HOST_KEYMAP_REWIND))
         add_bind(HOST_KEYMAP_REWIND, (int)SDLK_F8, (int)SDL_SCANCODE_F8, 0);
 #endif
-    if (s_actions[HOST_KEYMAP_SAVE_STATE_MENU].count == 0)
+    if (want_default(HOST_KEYMAP_SAVE_STATE_MENU))
         add_bind(HOST_KEYMAP_SAVE_STATE_MENU, (int)SDLK_F7, (int)SDL_SCANCODE_F7, 0);
-    if (s_actions[HOST_KEYMAP_SCANLINES].count == 0)
+    if (want_default(HOST_KEYMAP_SCANLINES))
         add_bind(HOST_KEYMAP_SCANLINES, (int)SDLK_F6, (int)SDL_SCANCODE_F6, 0);
-    if (s_actions[HOST_KEYMAP_TURBO_TOGGLE].count == 0)
+    if (want_default(HOST_KEYMAP_TURBO_TOGGLE))
         add_bind(HOST_KEYMAP_TURBO_TOGGLE, (int)SDLK_F9, (int)SDL_SCANCODE_F9, 0);
 }
 
@@ -202,10 +211,13 @@ void host_keymap_load(const char *config_ini_path) {
         trim_inplace(val);
         act = action_for_key(key);
         if (act == HOST_KEYMAP_ACTION_COUNT) continue;
-        /* Explicit empty unbinds (no keypad fallback for that action until
-         * apply_defaults — empty means user cleared it; still fall back). */
+        /* Explicit empty / "None" unbinds: the user cleared it, so no
+         * default fallback for that action (explicit_unbound). */
         s_actions[act].count = 0;
+        s_actions[act].explicit_unbound = 0;
         parse_value(act, val);
+        if (s_actions[act].count == 0)
+            s_actions[act].explicit_unbound = 1;
     }
     fclose(f);
     apply_defaults();

runtime/tests/test_rewind_toggle_combo.py

@@ -75,5 +75,11 @@ KEYMAP_C = (ROOT / "runtime" / "src" / "host_keymap.c").read_text(encoding="utf-
 assert "HOST_KEYMAP_TURBO_TOGGLE," in KEYMAP_H
 assert 'ieq(name, "TurboToggle")' in KEYMAP_C
 assert "add_bind(HOST_KEYMAP_TURBO_TOGGLE, (int)SDLK_F9" in KEYMAP_C
+# A present-but-empty / "None" [KeyMap] line is an explicit unbind: no
+# built-in default is re-applied for that action (launcher Backspace-to-clear).
+assert "int explicit_unbound;" in KEYMAP_C
+assert "static int want_default(HostKeymapAction action)" in KEYMAP_C
+assert "s_actions[HOST_KEYMAP_TURBO].count == 0" not in KEYMAP_C
+assert "if (want_default(HOST_KEYMAP_TURBO))" in KEYMAP_C
 
 print("host shortcut guard passed")