diff --git a/selfhost/cmd/w6c/main.combined.ww b/selfhost/cmd/w6c/main.combined.ww
index e3842bfc..20b1fc08 100644
--- a/selfhost/cmd/w6c/main.combined.ww
+++ b/selfhost/cmd/w6c/main.combined.ww
@@ -8369,12 +8369,36 @@ fn tinfofornode(c: *checker, n: *node) *tinfo = {
 		// sum-type shapes through NAMED variants).
 		r = newtype(tykind.TY_TAGGED);
 		tinfocachebind(c.tc, n, r);
+		// #50 / A.6.3f phase 1: populate ti.params as a tparam linked
+		// list (head=first source variant) in lock-step with the
+		// size/align accumulator. Mirrors cstage check.c:374-396 —
+		// same Tparam shape ww reuses across struct-fields / tuple-
+		// fields / fn-params / tagged-variants (sea-of-stars per rule
+		// 12). Phase 2 (#50b) retires cgenutil's AST-keyed
+		// nullableptrtag onto the chain.
+		let head: *tparam = nil;
+		let tail: *tparam = nil;
+		let maxsz: u64 = 0u64;
+		let al: u64 = 8u64;
+		let v: *node = n.list;
+		for (v != nil) {
+			let vt: *tinfo = tinfofornode(c, v);
+			let tp: *tparam = alloc(tparam{name="", type_=vt, tnext=nil})!;
+			if (head == nil) { head = tp; } else { tail.tnext = tp; };
+			tail = tp;
+			if (vt != nil) {
+				if (vt.size > maxsz) { maxsz = vt.size; };
+				if (vt.align > al) { al = vt.align; };
+			};
+			v = v.next;
+		};
+		r.params = head;
 		// #61 A.3 nullable fold: `(*T | void)` collapses to a single
 		// 8B pointer slot, null is the void variant. Mirrors
 		// cmd/wcc/check.c:412-426 — bare TNAME("void"), not `!void`,
-		// and not NAMED — so wwstage slotsize fast-path can graduate
-		// TY_TAGGED off the AST-walker fallback. Match before counting
-		// variants so the 8B fold lands in tinfo.size directly.
+		// and not NAMED. AST-kind discrimination retained: wwstage
+		// tinfo carries no `iserror` field, so cstage's tinfo-level
+		// (kind==TY_VOID && !iserror) check doesn't port symmetrically.
 		let a: *node = n.list;
 		if (a != nil) {
 			let b: *node = a.next;
@@ -8393,22 +8417,10 @@ fn tinfofornode(c: *checker, n: *node) *tinfo = {
 					r.align = 8u64;
 					r.nullable = 1;
 					r.slotsize = 8u64;
-					tinfocachebind(c.tc, n, r);
 					return r;
 				};
 			};
 		};
-		let maxsz: u64 = 0u64;
-		let al: u64 = 8u64;
-		let v: *node = n.list;
-		for (v != nil) {
-			let vt: *tinfo = tinfofornode(c, v);
-			if (vt != nil) {
-				if (vt.size > maxsz) { maxsz = vt.size; };
-				if (vt.align > al) { al = vt.align; };
-			};
-			v = v.next;
-		};
 		let pad: u64 = (maxsz + 7u64) & ~7u64;
 		r.size = 8u64 + pad;
 		r.align = al;
diff --git a/selfhost/cmd/wcc/check.ww b/selfhost/cmd/wcc/check.ww
index c6a39a79..711945ff 100644
--- a/selfhost/cmd/wcc/check.ww
+++ b/selfhost/cmd/wcc/check.ww
@@ -1299,12 +1299,36 @@ fn tinfofornode(c: *checker, n: *node) *tinfo = {
 		// sum-type shapes through NAMED variants).
 		r = newtype(tykind.TY_TAGGED);
 		tinfocachebind(c.tc, n, r);
+		// #50 / A.6.3f phase 1: populate ti.params as a tparam linked
+		// list (head=first source variant) in lock-step with the
+		// size/align accumulator. Mirrors cstage check.c:374-396 —
+		// same Tparam shape ww reuses across struct-fields / tuple-
+		// fields / fn-params / tagged-variants (sea-of-stars per rule
+		// 12). Phase 2 (#50b) retires cgenutil's AST-keyed
+		// nullableptrtag onto the chain.
+		let head: *tparam = nil;
+		let tail: *tparam = nil;
+		let maxsz: u64 = 0u64;
+		let al: u64 = 8u64;
+		let v: *node = n.list;
+		for (v != nil) {
+			let vt: *tinfo = tinfofornode(c, v);
+			let tp: *tparam = alloc(tparam{name="", type_=vt, tnext=nil})!;
+			if (head == nil) { head = tp; } else { tail.tnext = tp; };
+			tail = tp;
+			if (vt != nil) {
+				if (vt.size > maxsz) { maxsz = vt.size; };
+				if (vt.align > al) { al = vt.align; };
+			};
+			v = v.next;
+		};
+		r.params = head;
 		// #61 A.3 nullable fold: `(*T | void)` collapses to a single
 		// 8B pointer slot, null is the void variant. Mirrors
 		// cmd/wcc/check.c:412-426 — bare TNAME("void"), not `!void`,
-		// and not NAMED — so wwstage slotsize fast-path can graduate
-		// TY_TAGGED off the AST-walker fallback. Match before counting
-		// variants so the 8B fold lands in tinfo.size directly.
+		// and not NAMED. AST-kind discrimination retained: wwstage
+		// tinfo carries no `iserror` field, so cstage's tinfo-level
+		// (kind==TY_VOID && !iserror) check doesn't port symmetrically.
 		let a: *node = n.list;
 		if (a != nil) {
 			let b: *node = a.next;
@@ -1323,22 +1347,10 @@ fn tinfofornode(c: *checker, n: *node) *tinfo = {
 					r.align = 8u64;
 					r.nullable = 1;
 					r.slotsize = 8u64;
-					tinfocachebind(c.tc, n, r);
 					return r;
 				};
 			};
 		};
-		let maxsz: u64 = 0u64;
-		let al: u64 = 8u64;
-		let v: *node = n.list;
-		for (v != nil) {
-			let vt: *tinfo = tinfofornode(c, v);
-			if (vt != nil) {
-				if (vt.size > maxsz) { maxsz = vt.size; };
-				if (vt.align > al) { al = vt.align; };
-			};
-			v = v.next;
-		};
 		let pad: u64 = (maxsz + 7u64) & ~7u64;
 		r.size = 8u64 + pad;
 		r.align = al;
diff --git a/selfhost/cmd/wwdump/main.combined.ww b/selfhost/cmd/wwdump/main.combined.ww
index c6a3e8a4..5ac78ace 100644
--- a/selfhost/cmd/wwdump/main.combined.ww
+++ b/selfhost/cmd/wwdump/main.combined.ww
@@ -8369,12 +8369,36 @@ fn tinfofornode(c: *checker, n: *node) *tinfo = {
 		// sum-type shapes through NAMED variants).
 		r = newtype(tykind.TY_TAGGED);
 		tinfocachebind(c.tc, n, r);
+		// #50 / A.6.3f phase 1: populate ti.params as a tparam linked
+		// list (head=first source variant) in lock-step with the
+		// size/align accumulator. Mirrors cstage check.c:374-396 —
+		// same Tparam shape ww reuses across struct-fields / tuple-
+		// fields / fn-params / tagged-variants (sea-of-stars per rule
+		// 12). Phase 2 (#50b) retires cgenutil's AST-keyed
+		// nullableptrtag onto the chain.
+		let head: *tparam = nil;
+		let tail: *tparam = nil;
+		let maxsz: u64 = 0u64;
+		let al: u64 = 8u64;
+		let v: *node = n.list;
+		for (v != nil) {
+			let vt: *tinfo = tinfofornode(c, v);
+			let tp: *tparam = alloc(tparam{name="", type_=vt, tnext=nil})!;
+			if (head == nil) { head = tp; } else { tail.tnext = tp; };
+			tail = tp;
+			if (vt != nil) {
+				if (vt.size > maxsz) { maxsz = vt.size; };
+				if (vt.align > al) { al = vt.align; };
+			};
+			v = v.next;
+		};
+		r.params = head;
 		// #61 A.3 nullable fold: `(*T | void)` collapses to a single
 		// 8B pointer slot, null is the void variant. Mirrors
 		// cmd/wcc/check.c:412-426 — bare TNAME("void"), not `!void`,
-		// and not NAMED — so wwstage slotsize fast-path can graduate
-		// TY_TAGGED off the AST-walker fallback. Match before counting
-		// variants so the 8B fold lands in tinfo.size directly.
+		// and not NAMED. AST-kind discrimination retained: wwstage
+		// tinfo carries no `iserror` field, so cstage's tinfo-level
+		// (kind==TY_VOID && !iserror) check doesn't port symmetrically.
 		let a: *node = n.list;
 		if (a != nil) {
 			let b: *node = a.next;
@@ -8393,22 +8417,10 @@ fn tinfofornode(c: *checker, n: *node) *tinfo = {
 					r.align = 8u64;
 					r.nullable = 1;
 					r.slotsize = 8u64;
-					tinfocachebind(c.tc, n, r);
 					return r;
 				};
 			};
 		};
-		let maxsz: u64 = 0u64;
-		let al: u64 = 8u64;
-		let v: *node = n.list;
-		for (v != nil) {
-			let vt: *tinfo = tinfofornode(c, v);
-			if (vt != nil) {
-				if (vt.size > maxsz) { maxsz = vt.size; };
-				if (vt.align > al) { al = vt.align; };
-			};
-			v = v.next;
-		};
 		let pad: u64 = (maxsz + 7u64) & ~7u64;
 		r.size = 8u64 + pad;
 		r.align = al;