Implement EDIT statement and ON TIMER/ON KEY event trapping, update to v0.9.0

Add event-driven programming: ON TIMER(n) GOSUB with TIMER ON/OFF/STOP,
ON KEY(n) GOSUB with KEY(n) ON/OFF/STOP for F1-F10. Fix F-key escape
sequence parser (F9/F10 detection, push back consumed bytes on unmatched
sequences). Add EDIT statement for TUI line editing. Guard key trap
polling so keystrokes aren't consumed when no traps are configured.

include/gwbasic.h

@@ -10,7 +10,7 @@
 #include "gw_math.h"
 #include "strings.h"
 
-#define GW_VERSION "0.8.0"
+#define GW_VERSION "0.9.0"
 #define GW_BANNER "GW-BASIC " GW_VERSION
 
 /* Tokenizer */

include/interp.h

@@ -76,6 +76,10 @@ typedef struct {
     /* COMMON variable list for CHAIN */
     int common_count;
     struct { char name[2]; gw_valtype_t type; } common_vars[64];
+
+    /* Event trapping */
+    timer_trap_t timer_trap;
+    event_trap_t key_traps[10];  /* KEY(1)-KEY(10) */
 } interp_state_t;
 
 extern interp_state_t gw;

include/tui.h

@@ -45,6 +45,9 @@ typedef struct {
 #define TK_CTRL_C   0x03
 #define TK_CTRL_BREAK 0x200
 
+/* Key buffer for event trapping (keys consumed from HAL but not yet processed) */
+#define TUI_KEYBUF_SIZE 16
+
 /* TUI state */
 typedef struct {
     tui_cell_t *screen;             /* dynamically allocated [rows * cols] */
@@ -60,6 +63,9 @@ typedef struct {
     volatile bool break_flag;       /* set by SIGINT handler */
     int view_top;                   /* top of scrollable area */
     int view_bottom;                /* bottom row (rows-1 normally, rows-2 with key bar) */
+    int keybuf[TUI_KEYBUF_SIZE];   /* ring buffer for pushed-back keys */
+    int keybuf_head;
+    int keybuf_tail;
 } tui_state_t;
 
 extern tui_state_t tui;
@@ -93,6 +99,14 @@ void tui_key_on(void);
 void tui_key_off(void);
 void tui_key_list(void);
 
+/* EDIT statement */
+void tui_edit_line(const char *prefill);
+
+/* Key buffer for event trapping */
+void tui_push_key(int key);
+int  tui_pop_key(void);
+bool tui_keybuf_empty(void);
+
 /* Ctrl+Break */
 void tui_check_break(void);
 void tui_install_break_handler(void);

include/types.h

@@ -64,11 +64,30 @@ typedef struct {
     uint16_t line_num;
 } for_entry_t;
 
+/* Event trap mode */
+typedef enum { TRAP_OFF = 0, TRAP_ON = 1, TRAP_STOP = 2 } trap_mode_t;
+
+/* Event trap state (shared by TIMER/KEY traps) */
+typedef struct event_trap {
+    trap_mode_t mode;
+    uint16_t gosub_line;
+    bool pending;
+    bool in_handler;
+} event_trap_t;
+
+/* ON TIMER trap */
+typedef struct {
+    event_trap_t trap;
+    float interval;        /* seconds */
+    double last_fire;      /* monotonic timestamp */
+} timer_trap_t;
+
 /* GOSUB stack entry */
 typedef struct {
     uint8_t *ret_text;
     struct program_line *ret_line;
     uint16_t line_num;
+    struct event_trap *event_source;  /* non-NULL for event handler GOSUB */
 } gosub_entry_t;
 
 /* WHILE stack entry */