fix: qdup/tuck/2swap bugs, getline, and cached word pointers

Co-authored-by: aider (openrouter/moonshotai/kimi-k2.6) <aider@aider.chat>

forth.h

@@ -7,10 +7,14 @@
 #include <ctype.h>
 #include <stdint.h>
 #include <inttypes.h>
+#include <sys/types.h>
 
 // Configuration (all hard limits removed)
 #define MAX_NAME_LEN 31
 
+#define F_IMMEDIATE (1 << 7)
+#define F_HIDDEN    (1 << 6)
+
 // Core types
 typedef struct Word Word;
 typedef union Cell {
@@ -45,7 +49,8 @@ extern int32_t compile_idx;
 extern int32_t compile_cap;
 extern char compiling_name[MAX_NAME_LEN + 1];
 
-extern char input_buf[1024];      // fixed for line input
+extern char* input_buf;           // line buffer (dynamic, managed by getline)
+extern size_t input_buf_cap;
 extern char* input_ptr;
 
 extern int64_t *compile_stack;    // holds indices into compile_buf
@@ -56,6 +61,14 @@ extern Cell *user_mem;
 extern int64_t user_mem_size;     // in cells
 extern Cell* here;
 
+// Pointers to critical hidden/primitive words (set during init)
+extern Word* w_exit;
+extern Word* w_docolon;
+extern Word* w_lit;
+extern Word* w_branch;
+extern Word* w_zbranch;
+extern Word* w_dot_quote_inner;
+
 // Core function prototypes
 void data_push(int64_t val);
 int64_t data_pop(void);