u2: add cancel fast option that discards the fast without saving to history

Adds fast_cancel() in fastforge_core.c which clears the running fast and
saves state without appending to history. Wires a new "Cancel Current Fast"
main menu item (index 3) that calls it, showing a confirmation placeholder.
Updates sync_main_menu_state() to reflect cancel availability dynamically.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

4 files changed, 56 insertions, 12 deletions

diff --git a/PLAN.md b/PLAN.md
index e0efab3..545f1d5 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -209,12 +209,13 @@ On phone side (minimal companion app or Rebble tools) receive the data as CSV.
 
 1. Start New Fast → Presets submenu  
 2. Current Timer  
-3. Stop Current Fast (if running)  
-4. History  
-5. Statistics  
-6. Settings  
-7. Backup to Phone  
-8. About  
+3. Stop Current Fast (if running) — saves to history  
+4. Cancel Current Fast (if running) — discards, not saved to history  
+5. History  
+6. Statistics  
+7. Settings  
+8. Backup to Phone  
+9. About  
 
 ---
 
diff --git a/src/c/fastforge.c b/src/c/fastforge.c
index 623765e..2dc7cf0 100644
--- a/src/c/fastforge.c
+++ b/src/c/fastforge.c
@@ -9,12 +9,13 @@ enum {
   MAIN_MENU_INDEX_START_NEW = 0,
   MAIN_MENU_INDEX_CURRENT_TIMER = 1,
   MAIN_MENU_INDEX_STOP_CURRENT = 2,
-  MAIN_MENU_INDEX_HISTORY = 3,
-  MAIN_MENU_INDEX_STATS = 4,
-  MAIN_MENU_INDEX_SETTINGS = 5,
-  MAIN_MENU_INDEX_BACKUP = 6,
-  MAIN_MENU_INDEX_ABOUT = 7,
-  MAIN_MENU_ITEM_COUNT = 8
+  MAIN_MENU_INDEX_CANCEL_CURRENT = 3,
+  MAIN_MENU_INDEX_HISTORY = 4,
+  MAIN_MENU_INDEX_STATS = 5,
+  MAIN_MENU_INDEX_SETTINGS = 6,
+  MAIN_MENU_INDEX_BACKUP = 7,
+  MAIN_MENU_INDEX_ABOUT = 8,
+  MAIN_MENU_ITEM_COUNT = 9
 };
 
 enum {
@@ -96,6 +97,7 @@ static char s_settings_target_text[32];
 static char s_settings_dev_text[32];
 #endif
 static char s_menu_stop_subtitle[32];
+static char s_menu_cancel_subtitle[32];
 static char s_placeholder_title_text[24];
 static char s_placeholder_body_text[160];
 static char s_placeholder_hint_text[24];
@@ -655,10 +657,13 @@ static void refresh_goal_window_content(void) {
 static void sync_main_menu_state(void) {
   if (fast_is_running()) {
     snprintf(s_menu_stop_subtitle, sizeof(s_menu_stop_subtitle), "End now and save");
+    snprintf(s_menu_cancel_subtitle, sizeof(s_menu_cancel_subtitle), "Discard, no history");
   } else {
     snprintf(s_menu_stop_subtitle, sizeof(s_menu_stop_subtitle), "No fast running");
+    snprintf(s_menu_cancel_subtitle, sizeof(s_menu_cancel_subtitle), "No fast running");
   }
   s_main_menu_items[MAIN_MENU_INDEX_STOP_CURRENT].subtitle = s_menu_stop_subtitle;
+  s_main_menu_items[MAIN_MENU_INDEX_CANCEL_CURRENT].subtitle = s_menu_cancel_subtitle;
 
   if (s_main_menu_layer) {
     menu_layer_reload_data(simple_menu_layer_get_menu_layer(s_main_menu_layer));
@@ -1087,6 +1092,18 @@ static void menu_stop_current_callback(int index, void *context) {
   refresh_all_ui_state();
 }
 
+/* Cancel discards the running fast without saving it to history. */
+static void menu_cancel_current_callback(int index, void *context) {
+  (void)index;
+  (void)context;
+  if (!fast_cancel()) {
+    show_placeholder_window("NOT RUNNING", "There is no active fast to cancel.", "BACK Menu");
+    return;
+  }
+  show_placeholder_window("FAST CANCELLED", "Fast discarded. Not in history.", "BACK Menu");
+  refresh_all_ui_state();
+}
+
 static void menu_history_callback(int index, void *context) {
   (void)index;
   (void)context;
@@ -1740,6 +1757,11 @@ static void configure_main_menu_items(void) {
     .subtitle = "",
     .callback = menu_stop_current_callback
   };
+  s_main_menu_items[MAIN_MENU_INDEX_CANCEL_CURRENT] = (SimpleMenuItem) {
+    .title = "Cancel Current Fast",
+    .subtitle = "",
+    .callback = menu_cancel_current_callback
+  };
   s_main_menu_items[MAIN_MENU_INDEX_HISTORY] = (SimpleMenuItem) {
     .title = "History",
     .subtitle = "Completed fasts",
diff --git a/src/c/fastforge.h b/src/c/fastforge.h
index 6c24e75..263a75b 100644
--- a/src/c/fastforge.h
+++ b/src/c/fastforge.h
@@ -28,5 +28,6 @@ void load_all_data(void);
 bool fast_is_running(void);
 bool fast_start(uint16_t preset_target_minutes);
 bool fast_stop(void);
+bool fast_cancel(void);
 
 #endif
diff --git a/src/c/fastforge_core.c b/src/c/fastforge_core.c
index a9bec03..cde224f 100644
--- a/src/c/fastforge_core.c
+++ b/src/c/fastforge_core.c
@@ -297,6 +297,26 @@ bool fast_stop(void) {
   return true;
 }
 
+/* Cancel discards the running fast without recording it in history. */
+bool fast_cancel(void) {
+  if (!fast_is_running()) {
+    return false;
+  }
+
+  memset(&current_fast, 0, sizeof(current_fast));
+#ifdef DEBUG
+  s_current_fast_origin_offset_seconds = 0;
+#endif
+  if (alarm_timer) {
+    app_timer_cancel(alarm_timer);
+    alarm_timer = NULL;
+  }
+  target_time = 0;
+  save_all_data();
+  APP_LOG(APP_LOG_LEVEL_INFO, "Cancelled fast (not saved to history)");
+  return true;
+}
+
 static void alarm_callback(void *data) {
   (void)data;
   alarm_timer = NULL;