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/boot.fth

@@ -310,3 +310,39 @@
 \   State-smart string literal for the next whitespace-delimited token.
 \   Handled in Rust (outer.rs interpret_token_immediate / compile_token)
 \   so the string survives REFILL in interpret mode.
+
+\ ---------------------------------------------------------------
+\ Structures (Forth 2012 Facility-ext 10.6.2.0935 family)
+\ ---------------------------------------------------------------
+\ Usage:
+\   BEGIN-STRUCTURE POINT  FIELD: P.X  FIELD: P.Y  END-STRUCTURE
+\   CREATE ORIGIN POINT ALLOT
+\   1 ORIGIN P.X !   2 ORIGIN P.Y !
+
+\ Each defining word factored inline (CREATE .. DOES>). WAFER dispatches
+\ DOES>-defining words only at the outer interpreter, so they can't be
+\ factored through other compiled words (FIELD: -> +FIELD would no-op).
+
+: BEGIN-STRUCTURE  ( "name" -- struct-sys 0 )
+  CREATE HERE 0 0 , DOES> @ ;
+
+: END-STRUCTURE  ( struct-sys +n -- )
+  SWAP ! ;
+
+: +FIELD   ( n1 "name" n2 -- n3 )
+  CREATE OVER , + DOES> @ + ;
+
+: FIELD:   ( n1 "name" -- n2 )
+  CREATE ALIGNED DUP , 1 CELLS + DOES> @ + ;
+
+: CFIELD:  ( n1 "name" -- n2 )
+  CREATE DUP , 1 CHARS + DOES> @ + ;
+
+: FFIELD:  ( n1 "name" -- n2 )
+  CREATE FALIGNED DUP , 1 FLOATS + DOES> @ + ;
+
+: SFFIELD: ( n1 "name" -- n2 )
+  CREATE SFALIGNED DUP , 1 SFLOATS + DOES> @ + ;
+
+: DFFIELD: ( n1 "name" -- n2 )
+  CREATE DFALIGNED DUP , 1 DFLOATS + DOES> @ + ;

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
     // ===================================================================