boot: add structure words (Facility-ext 10.6.2.0935)

BEGIN-STRUCTURE, END-STRUCTURE, +FIELD, FIELD:, CFIELD:, FFIELD:,
SFFIELD:, DFFIELD: — the Forth 2012 structure-definition family plus
the float-typed variants for symmetry with WAFER's float wordset.

Each defining word carries its own inline CREATE .. DOES> — factoring
through a shared +FIELD helper doesn't work in WAFER, because DOES>-
defining words only dispatch at the outer interpreter, not from compiled
IR. So FIELD: can't call +FIELD and have the DOES> action fire; each
FIELD:/CFIELD:/... repeats the pattern directly.

Three tests cover size computation, field offsets, and mixed cell + char
fields with alignment.

crates/core/src/outer.rs

@@ -7675,6 +7675,42 @@ mod tests {
         assert_eq!(vm.take_output(), "test");
     }
 
+    // ===================================================================
+    // Structures (BEGIN-STRUCTURE / +FIELD / FIELD: / CFIELD: / END-STRUCTURE)
+    // ===================================================================
+
+    #[test]
+    fn test_struct_basic_point() {
+        let mut vm = ForthVM::<NativeRuntime>::new().unwrap();
+        vm.evaluate("BEGIN-STRUCTURE POINT FIELD: P.X FIELD: P.Y END-STRUCTURE")
+            .unwrap();
+        vm.evaluate("POINT").unwrap();
+        assert_eq!(vm.pop_data_stack().unwrap(), 8);
+
+        vm.evaluate("CREATE ORIGIN POINT ALLOT").unwrap();
+        vm.evaluate("1 ORIGIN P.X !  2 ORIGIN P.Y !").unwrap();
+        vm.evaluate("ORIGIN P.X @  ORIGIN P.Y @").unwrap();
+        assert_eq!(vm.data_stack(), vec![2, 1]);
+    }
+
+    #[test]
+    fn test_struct_field_offsets() {
+        let mut vm = ForthVM::<NativeRuntime>::new().unwrap();
+        vm.evaluate("BEGIN-STRUCTURE REC FIELD: A FIELD: B FIELD: C END-STRUCTURE")
+            .unwrap();
+        vm.evaluate("REC 0 A 0 B 0 C").unwrap();
+        assert_eq!(vm.data_stack(), vec![8, 4, 0, 12]);
+    }
+
+    #[test]
+    fn test_struct_mixed_cfield() {
+        let mut vm = ForthVM::<NativeRuntime>::new().unwrap();
+        vm.evaluate("BEGIN-STRUCTURE MIX CFIELD: TAG FIELD: VAL END-STRUCTURE")
+            .unwrap();
+        vm.evaluate("MIX 0 TAG 0 VAL").unwrap();
+        assert_eq!(vm.data_stack(), vec![4, 0, 8]);
+    }
+
     // ===================================================================
     // New words: RANDOM / RND-SEED
     // ===================================================================