class-v6: the acceptance's class v4 shape predicate and the draw's source rule set the window and layer 8 off aside (lane D's finding: a +nowin or +reg64c program was judged by the class v2 parts on the chain's path); test: every v6 flag keeps the shape and the attempt cap

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

igneum-pow/src/accept.rs

@@ -489,7 +489,9 @@ pub fn is_class_v4_shape(class: &LoadClass) -> bool {
         // class v5 (docs/design/class-v5-stored-state.md) is judged under the same rules: its state flag is set aside;
         // class v6 lane 1's index fold and re-weight table are set aside too (the address path and the op table are
         // not the shape)
-        && LoadClass { era: None, shadow: None, state: false, fold: false, rw: 0, ..*class } == LoadClass { shadow: None, ..V4_CLASS }
+        // the window and layer 8 off are set aside too (lane D's finding of 8 October 2026, 19:1x UK: a +nowin or +reg64c
+        // program was judged by the class v2 parts alone on the chain's path; the harness's own predicate hid it)
+        && LoadClass { era: None, shadow: None, state: false, fold: false, rw: 0, nowin: false, reg64: false, reg64_chain: false, ..*class } == LoadClass { shadow: None, ..V4_CLASS }
 }
 
 /// One pass of the dataflow freshness over the base program then the shadow block (the order of one iteration),

igneum-pow/src/generator.rs

@@ -1705,7 +1705,7 @@ pub fn candidate_from_words_class(
     // class v6 lane 1: the index fold and the re-weight table are set aside too (the address path and the table are not
     // the shape; a +fold or +rw program draws its sources under the same rule)
     let source_rule_v4 = matches!(class.shadow, Some(ShadowClass { instrs: V4_SHADOW_INSTRS, .. }))
-        && LoadClass { era: None, shadow: None, state: false, fold: false, rw: 0, nowin: false, ..class } == LoadClass { shadow: None, ..V4_CLASS };
+        && LoadClass { era: None, shadow: None, state: false, fold: false, rw: 0, nowin: false, reg64: false, reg64_chain: false, ..class } == LoadClass { shadow: None, ..V4_CLASS };
     // the op table and the roll's range: the plain table at 75 for every class without the re-weight flag
     let (weights, weights_sum) = class.nonload_weights();
     let mut fresh = [false; 8];

igneum-pow/tests/v6fold.rs

@@ -247,6 +247,23 @@ fn v6_draw_connects_all_lanes_and_keeps_mad_bijective_by_construction() {
     assert_ne!(a.program_id(), b.program_id());
 }
 
+/// Lane D's finding (8 October 2026): every class v6 flag is set aside by the acceptance's class v4 shape predicate,
+/// so a +nowin, +reg64 or +reg64c program is judged by the full rule (the fresh-source rule, the saturated-source
+/// check, the index floors and the attempt cap with the last resort), not by the class v2 parts; the draw's source
+/// rule reads the same shape.
+#[test]
+fn every_v6_flag_keeps_the_class_v4_acceptance_shape() {
+    use igneum_pow::accept::is_class_v4_shape;
+    use igneum_pow::generator::max_attempts_for;
+    let all = LoadClass::parse("mx8+sh256x27+state+reg64c+nowin+fold+rw").unwrap();
+    for c in [V5_CLASS, V5_CLASS.with_nowin(), V5_CLASS.with_reg64(), V5_CLASS.with_reg64().with_reg64_chain(), V5_CLASS.with_fold(), all] {
+        assert!(is_class_v4_shape(&c), "{}", c.name());
+        assert!(is_class_v4_shape(&LoadClass::era(c, &f8_bytes("era", 4), &V3_ALLOWED)), "{} under an era", c.name());
+        assert_eq!(max_attempts_for(&c), max_attempts_for(&V5_CLASS), "{}: the same attempt cap and last resort", c.name());
+    }
+    assert!(!is_class_v4_shape(&V3_CLASS) && !is_class_v4_shape(&LoadClass::V2));
+}
+
 /// 2. The fold's form: `y = x * M; y ^= y >> 16; y = rotl(y, R)`, and nothing else moves. The plain era's stride is
 /// `rotl(x * M, R)` byte for byte.
 #[test]