diff --git a/Makefile b/Makefile
index 54c5a186..6b062f57 100644
--- a/Makefile
+++ b/Makefile
@@ -308,6 +308,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_mixed_scalar_tuple_sret_run \
 	  $(BIN)/test_tuple_in_union_run \
 	  $(BIN)/test_tuple_slot_layout_run \
+	  $(BIN)/test_tagged_tuple_widen_run \
 	  $(BIN)/test_errtype_compare \
 	  $(BIN)/test_tuple_elem_slice_len_run \
 	  $(BIN)/test_str_forrange_loopvar_run \
@@ -1421,6 +1422,12 @@ $(BIN)/test_tuple_slot_layout_run: test/wcc/941_tuple_slot_layout_run.c \
 		$(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_tagged_tuple_widen_run: test/wcc/936_tagged_tuple_widen_run.c \
+		$(BIN)/ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
+		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
+		$(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_errtype_compare: test/wcc/949_errtype_compare.c \
 		$(BIN)/ww $(BIN)/w6c $(BIN)/w6a $(BIN)/w6l \
 		$(BIN)/ww_ww $(BIN)/w6c_ww $(BIN)/w6a_ww $(BIN)/w6l_ww \
diff --git a/cmd/w6c/cgen.c b/cmd/w6c/cgen.c
index c8f8ec38..36177eb8 100644
--- a/cmd/w6c/cgen.c
+++ b/cmd/w6c/cgen.c
@@ -2456,8 +2456,32 @@ cg_widen_tagged_store(Cg *c, Local **locals_p, Type *dst, Node *src,
 	 * (AX=tag, DX=word0, CX=word1, R8=word2) and the cgmlet receive
 	 * cursor. NOT the packed-by-size t.N field layout (#238). Mirror of
 	 * the struct-literal field-flow below, but 8B-slotted, not field-
-	 * offset. */
-	if (su && su->kind == TY_TUPLE && src->kind == N_TUPLE) {
+	 * offset.
+	 *
+	 * #66: the cast-wrapped tuple literal `((a, b): range_alias)` is
+	 * the spelling real code uses (regex.ha:213) — the cast targets the
+	 * CONCRETE variant, so the widen-cast peel above leaves it intact
+	 * and pre-#66 it fell to the scalar arm, silently dropping payload
+	 * slot 1+. Peel to the inner tuple here; st stays the CAST's type,
+	 * which resolves the variant tag by exact named match, so the #241
+	 * untyped-element un-matchability does not arise for this form. */
+	Node *tupsrc = NULL;
+	if (su && su->kind == TY_TUPLE) {
+		if (src->kind == N_TUPLE)
+			tupsrc = src;
+		else if (src->kind == N_CAST && src->lhs
+		    && src->lhs->kind == N_TUPLE)
+			tupsrc = src->lhs;
+		/* #72: any OTHER tuple-typed source (ident, call result,
+		 * match binding) would fall to the scalar arm below and
+		 * silently drop payload slot 1+ — loud-stop (rule 7) until
+		 * the word-copy / cursor-receive arms are wired. */
+		if (tupsrc == NULL)
+			fatal("cg_widen_tagged_store: tuple-typed source "
+			    "shape unwired (only the bare/cast tuple literal "
+			    "carries a full payload; see #72)");
+	}
+	if (tupsrc != NULL) {
 		int tag = cg_tag_for_variant(du, st);
 		/* #242: a tuple built from UNTYPED/literal elements (`(true,7)`)
 		 * leaves the src tuple type un-matchable by type_eq, so the
@@ -2478,7 +2502,7 @@ cg_widen_tagged_store(Cg *c, Local **locals_p, Type *dst, Node *src,
 		 * payload the slotted write assumes. Loud-stop (rule 7); the
 		 * SysV eightbyte tuple classification is a deferred follow-up. */
 		int total = 0;
-		for (Node *e = src->list; e; e = e->next)
+		for (Node *e = tupsrc->list; e; e = e->next)
 			total += (node_isstr(e) || node_isslice(e)) ? 24 : 8;
 		if (8 + total > sz)
 			fatal("cg_widen_tagged_store: tuple-in-union payload needs "
@@ -2489,7 +2513,7 @@ cg_widen_tagged_store(Cg *c, Local **locals_p, Type *dst, Node *src,
 			ins2(c, A_MOVQ, areg(D_AX),
 			    amem(D_BP, write_off + k));
 		int foff = 0;
-		for (Node *e = src->list; e; e = e->next) {
+		for (Node *e = tupsrc->list; e; e = e->next) {
 			int e_isf32 = 0;
 			int isflt = fld_isfloat(e->type, &e_isf32);
 			int wide = node_isstr(e) || node_isslice(e);
@@ -2702,11 +2726,17 @@ cg_widen_tagged_push(Cg *c, Local **locals_p, Type *dst, Node *src, int sz)
 	Type *su = (st && st->kind == TY_NAMED) ? st->under : st;
 	int src_is_struct = su && su->kind == TY_STRUCT;
 	int src_is_tagged = su && su->kind == TY_TAGGED;
+	/* #66: a tuple-typed source has no direct-push shape — the scalar
+	 * fast arm below would push word 0 only (payload slot 1+ dropped)
+	 * and coerce an unresolved tag to 0. Route through the scratch
+	 * store, whose #242/#66 tuple arm handles the literal/cast forms
+	 * and loud-stops the rest (#72). */
+	int src_is_tuple = su && su->kind == TY_TUPLE;
 	/* #38b: a MEMORY-class (>48B) dst slot always routes through the
 	 * scratch path — the str/slice fast arms push exactly 4 words,
 	 * short of the slot's msz/8 the mem pre-pass accounts for. */
 	int dst_is_mem = tagged_memarg_size(dst) > 0;
-	if (!src_is_struct && !src_is_tagged && !dst_is_mem) {
+	if (!src_is_struct && !src_is_tagged && !src_is_tuple && !dst_is_mem) {
 		/* Direct-push fast path: str / slice / scalar / pointer. */
 		cgexpr(c, src, *locals_p);
 		int tag = cg_tag_for_variant(du, st);
diff --git a/selfhost/cmd/w6c/main.combined.ww b/selfhost/cmd/w6c/main.combined.ww
index f54336ab..a21f269f 100644
--- a/selfhost/cmd/w6c/main.combined.ww
+++ b/selfhost/cmd/w6c/main.combined.ww
@@ -16228,8 +16228,24 @@ fn pushargsrev(c: *cgen, arg: *node, param: *node, memphase: bool) i32 = {
 		// then push slot words high → low). Scalar / str go via
 		// the direct push fast path below — keeps wwstage's asm
 		// byte-identical to cstage for selfhost source.
+		// #66: a tuple-typed source has no direct-push shape — the
+		// scalar fast arm would push word 0 only (payload slot 1+
+		// dropped) and coerce an unresolved tag to 0. Route through
+		// the scratch store, whose #242/#66 tuple arm handles the
+		// literal/cast forms and loud-stops the rest (#72). Mirrors
+		// cstage cg_widen_tagged_push src_is_tuple.
+		let argtup: *tinfo = arg.type_: *tinfo;
+		for (argtup != nil && argtup.kind == tykind.TY_NAMED) {
+			argtup = argtup.under;
+		};
+		let argistuple: bool = false;
+		if (argtup != nil) {
+			if (argtup.kind == tykind.TY_TUPLE) {
+				argistuple = true;
+			};
+		};
 		let pname: str = rhsstructpayload(c, arg);
-		if (pname.len > 0) {
+		if (pname.len > 0 || argistuple) {
 			let ptype: *node = param.lhs;
 			let scroff: i32 = tagscradd(c, widensz);
 			emitline("\tXORQ\tAX, AX\n");
@@ -19221,7 +19237,46 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 	// (AX=tag, DX=word0, CX=word1, R8=word2) and the cgmlet receive
 	// cursor. NOT the packed-by-size t.N field layout (#238). Mirror of
 	// cstage cg_widen_tagged_store's TY_TUPLE arm.
-	if (src != nil) { if (src.kind == nkind.N_TUPLE) {
+	//
+	// #66: the cast-wrapped tuple literal `((a, b): range_alias)` is
+	// the spelling real code uses (regex.ha:213) — the cast targets the
+	// CONCRETE variant, so the widen-cast peel above leaves it intact
+	// and pre-#66 it fell to the scalar arm, silently dropping payload
+	// slot 1+. Peel to the inner tuple here; src.type_ stays the CAST's
+	// type, which resolves the variant tag by exact named match, so the
+	// #241 untyped-element un-matchability does not arise for this form.
+	let tupsrc: *node = nil;
+	let tupcast: bool = false;
+	if (src != nil) {
+		if (src.kind == nkind.N_TUPLE) { tupsrc = src; };
+		if (src.kind == nkind.N_CAST) {
+			if (src.lhs != nil) {
+				if (src.lhs.kind == nkind.N_TUPLE) {
+					tupsrc = src.lhs;
+					tupcast = true;
+				};
+			};
+		};
+		// #72: any OTHER tuple-typed source (ident, call result,
+		// match binding) would fall to the scalar arm below and
+		// silently drop payload slot 1+ — loud-stop (rule 7) until
+		// the word-copy / cursor-receive arms are wired. Mirrors
+		// cstage cg_widen_tagged_store.
+		if (tupsrc == nil) {
+			let stu72: *tinfo = src.type_: *tinfo;
+			for (stu72 != nil && stu72.kind == tykind.TY_NAMED) {
+				stu72 = stu72.under;
+			};
+			if (stu72 != nil) {
+				if (stu72.kind == tykind.TY_TUPLE) {
+					let m72: str = "cgwidentaggedstore: tuple-typed source shape unwired (only the bare/cast tuple literal carries a full payload; see #72)\n";
+					os.write(2, m72.ptr, m72.len: u64);
+					os.exit(1);
+				};
+			};
+		};
+	};
+	if (tupsrc != nil) {
 		let stu: *tinfo = src.type_: *tinfo;
 		for (stu != nil && stu.kind == tykind.TY_NAMED) { stu = stu.under; };
 		if (stu != nil) { if (stu.kind == tykind.TY_TUPLE) {
@@ -19235,9 +19290,11 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 			// cstage can't type: a bool literal (N_TRUE/N_FALSE) or a
 			// suffix-less numeric literal (untyped_int/untyped_float).
 			// LIFT BOTH stage guards together when #241 fixes cstage
-			// literal typing -> symmetric accept.
-			let bl: *node = src.list;
-			for (bl != nil) {
+			// literal typing -> symmetric accept. BARE form only (#66):
+			// the cast form resolves its tag from the cast's type on
+			// BOTH stages, so bare elements are fine there.
+			let bl: *node = tupsrc.list;
+			for (bl != nil && !tupcast) {
 				let bare: bool = false;
 				if (bl.kind == nkind.N_TRUE)  { bare = true; };
 				if (bl.kind == nkind.N_FALSE) { bare = true; };
@@ -19277,7 +19334,7 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 			// SysV eightbyte tuple classification is a deferred
 			// follow-up. Symmetric with cstage cg_widen_tagged_store.
 			let ttotal: i32 = 0;
-			let ce: *node = src.list;
+			let ce: *node = tupsrc.list;
 			for (ce != nil) {
 				if (nodeisstr(c, ce) || nodeisslice(c, ce)) {
 					ttotal += 24;
@@ -19298,7 +19355,7 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 				tzk += 8;
 			};
 			let tfoff: i32 = 0;
-			let te: *node = src.list;
+			let te: *node = tupsrc.list;
 			for (te != nil) {
 				let isflt: bool = isfloattype(c, te);
 				let wide: bool = nodeisstr(c, te) || nodeisslice(c, te);
@@ -19342,7 +19399,7 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 			emitline("(BP)\n");
 			return;
 		}; };
-	}; };
+	};
 	// Struct payload (literal or ident).
 	let sname: str = rhsstructpayload(c, src);
 	if (sname.len > 0) {
diff --git a/selfhost/cmd/wcc/cgenutil.ww b/selfhost/cmd/wcc/cgenutil.ww
index cd8c96c9..7d6e68a7 100644
--- a/selfhost/cmd/wcc/cgenutil.ww
+++ b/selfhost/cmd/wcc/cgenutil.ww
@@ -312,8 +312,24 @@ fn pushargsrev(c: *cgen, arg: *node, param: *node, memphase: bool) i32 = {
 		// then push slot words high → low). Scalar / str go via
 		// the direct push fast path below — keeps wwstage's asm
 		// byte-identical to cstage for selfhost source.
+		// #66: a tuple-typed source has no direct-push shape — the
+		// scalar fast arm would push word 0 only (payload slot 1+
+		// dropped) and coerce an unresolved tag to 0. Route through
+		// the scratch store, whose #242/#66 tuple arm handles the
+		// literal/cast forms and loud-stops the rest (#72). Mirrors
+		// cstage cg_widen_tagged_push src_is_tuple.
+		let argtup: *tinfo = arg.type_: *tinfo;
+		for (argtup != nil && argtup.kind == tykind.TY_NAMED) {
+			argtup = argtup.under;
+		};
+		let argistuple: bool = false;
+		if (argtup != nil) {
+			if (argtup.kind == tykind.TY_TUPLE) {
+				argistuple = true;
+			};
+		};
 		let pname: str = rhsstructpayload(c, arg);
-		if (pname.len > 0) {
+		if (pname.len > 0 || argistuple) {
 			let ptype: *node = param.lhs;
 			let scroff: i32 = tagscradd(c, widensz);
 			emitline("\tXORQ\tAX, AX\n");
@@ -3305,7 +3321,46 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 	// (AX=tag, DX=word0, CX=word1, R8=word2) and the cgmlet receive
 	// cursor. NOT the packed-by-size t.N field layout (#238). Mirror of
 	// cstage cg_widen_tagged_store's TY_TUPLE arm.
-	if (src != nil) { if (src.kind == nkind.N_TUPLE) {
+	//
+	// #66: the cast-wrapped tuple literal `((a, b): range_alias)` is
+	// the spelling real code uses (regex.ha:213) — the cast targets the
+	// CONCRETE variant, so the widen-cast peel above leaves it intact
+	// and pre-#66 it fell to the scalar arm, silently dropping payload
+	// slot 1+. Peel to the inner tuple here; src.type_ stays the CAST's
+	// type, which resolves the variant tag by exact named match, so the
+	// #241 untyped-element un-matchability does not arise for this form.
+	let tupsrc: *node = nil;
+	let tupcast: bool = false;
+	if (src != nil) {
+		if (src.kind == nkind.N_TUPLE) { tupsrc = src; };
+		if (src.kind == nkind.N_CAST) {
+			if (src.lhs != nil) {
+				if (src.lhs.kind == nkind.N_TUPLE) {
+					tupsrc = src.lhs;
+					tupcast = true;
+				};
+			};
+		};
+		// #72: any OTHER tuple-typed source (ident, call result,
+		// match binding) would fall to the scalar arm below and
+		// silently drop payload slot 1+ — loud-stop (rule 7) until
+		// the word-copy / cursor-receive arms are wired. Mirrors
+		// cstage cg_widen_tagged_store.
+		if (tupsrc == nil) {
+			let stu72: *tinfo = src.type_: *tinfo;
+			for (stu72 != nil && stu72.kind == tykind.TY_NAMED) {
+				stu72 = stu72.under;
+			};
+			if (stu72 != nil) {
+				if (stu72.kind == tykind.TY_TUPLE) {
+					let m72: str = "cgwidentaggedstore: tuple-typed source shape unwired (only the bare/cast tuple literal carries a full payload; see #72)\n";
+					os.write(2, m72.ptr, m72.len: u64);
+					os.exit(1);
+				};
+			};
+		};
+	};
+	if (tupsrc != nil) {
 		let stu: *tinfo = src.type_: *tinfo;
 		for (stu != nil && stu.kind == tykind.TY_NAMED) { stu = stu.under; };
 		if (stu != nil) { if (stu.kind == tykind.TY_TUPLE) {
@@ -3319,9 +3374,11 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 			// cstage can't type: a bool literal (N_TRUE/N_FALSE) or a
 			// suffix-less numeric literal (untyped_int/untyped_float).
 			// LIFT BOTH stage guards together when #241 fixes cstage
-			// literal typing -> symmetric accept.
-			let bl: *node = src.list;
-			for (bl != nil) {
+			// literal typing -> symmetric accept. BARE form only (#66):
+			// the cast form resolves its tag from the cast's type on
+			// BOTH stages, so bare elements are fine there.
+			let bl: *node = tupsrc.list;
+			for (bl != nil && !tupcast) {
 				let bare: bool = false;
 				if (bl.kind == nkind.N_TRUE)  { bare = true; };
 				if (bl.kind == nkind.N_FALSE) { bare = true; };
@@ -3361,7 +3418,7 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 			// SysV eightbyte tuple classification is a deferred
 			// follow-up. Symmetric with cstage cg_widen_tagged_store.
 			let ttotal: i32 = 0;
-			let ce: *node = src.list;
+			let ce: *node = tupsrc.list;
 			for (ce != nil) {
 				if (nodeisstr(c, ce) || nodeisslice(c, ce)) {
 					ttotal += 24;
@@ -3382,7 +3439,7 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 				tzk += 8;
 			};
 			let tfoff: i32 = 0;
-			let te: *node = src.list;
+			let te: *node = tupsrc.list;
 			for (te != nil) {
 				let isflt: bool = isfloattype(c, te);
 				let wide: bool = nodeisstr(c, te) || nodeisslice(c, te);
@@ -3426,7 +3483,7 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 			emitline("(BP)\n");
 			return;
 		}; };
-	}; };
+	};
 	// Struct payload (literal or ident).
 	let sname: str = rhsstructpayload(c, src);
 	if (sname.len > 0) {
diff --git a/selfhost/cmd/wwdump/main.combined.ww b/selfhost/cmd/wwdump/main.combined.ww
index 0ba2fed1..de3a0656 100644
--- a/selfhost/cmd/wwdump/main.combined.ww
+++ b/selfhost/cmd/wwdump/main.combined.ww
@@ -16228,8 +16228,24 @@ fn pushargsrev(c: *cgen, arg: *node, param: *node, memphase: bool) i32 = {
 		// then push slot words high → low). Scalar / str go via
 		// the direct push fast path below — keeps wwstage's asm
 		// byte-identical to cstage for selfhost source.
+		// #66: a tuple-typed source has no direct-push shape — the
+		// scalar fast arm would push word 0 only (payload slot 1+
+		// dropped) and coerce an unresolved tag to 0. Route through
+		// the scratch store, whose #242/#66 tuple arm handles the
+		// literal/cast forms and loud-stops the rest (#72). Mirrors
+		// cstage cg_widen_tagged_push src_is_tuple.
+		let argtup: *tinfo = arg.type_: *tinfo;
+		for (argtup != nil && argtup.kind == tykind.TY_NAMED) {
+			argtup = argtup.under;
+		};
+		let argistuple: bool = false;
+		if (argtup != nil) {
+			if (argtup.kind == tykind.TY_TUPLE) {
+				argistuple = true;
+			};
+		};
 		let pname: str = rhsstructpayload(c, arg);
-		if (pname.len > 0) {
+		if (pname.len > 0 || argistuple) {
 			let ptype: *node = param.lhs;
 			let scroff: i32 = tagscradd(c, widensz);
 			emitline("\tXORQ\tAX, AX\n");
@@ -19221,7 +19237,46 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 	// (AX=tag, DX=word0, CX=word1, R8=word2) and the cgmlet receive
 	// cursor. NOT the packed-by-size t.N field layout (#238). Mirror of
 	// cstage cg_widen_tagged_store's TY_TUPLE arm.
-	if (src != nil) { if (src.kind == nkind.N_TUPLE) {
+	//
+	// #66: the cast-wrapped tuple literal `((a, b): range_alias)` is
+	// the spelling real code uses (regex.ha:213) — the cast targets the
+	// CONCRETE variant, so the widen-cast peel above leaves it intact
+	// and pre-#66 it fell to the scalar arm, silently dropping payload
+	// slot 1+. Peel to the inner tuple here; src.type_ stays the CAST's
+	// type, which resolves the variant tag by exact named match, so the
+	// #241 untyped-element un-matchability does not arise for this form.
+	let tupsrc: *node = nil;
+	let tupcast: bool = false;
+	if (src != nil) {
+		if (src.kind == nkind.N_TUPLE) { tupsrc = src; };
+		if (src.kind == nkind.N_CAST) {
+			if (src.lhs != nil) {
+				if (src.lhs.kind == nkind.N_TUPLE) {
+					tupsrc = src.lhs;
+					tupcast = true;
+				};
+			};
+		};
+		// #72: any OTHER tuple-typed source (ident, call result,
+		// match binding) would fall to the scalar arm below and
+		// silently drop payload slot 1+ — loud-stop (rule 7) until
+		// the word-copy / cursor-receive arms are wired. Mirrors
+		// cstage cg_widen_tagged_store.
+		if (tupsrc == nil) {
+			let stu72: *tinfo = src.type_: *tinfo;
+			for (stu72 != nil && stu72.kind == tykind.TY_NAMED) {
+				stu72 = stu72.under;
+			};
+			if (stu72 != nil) {
+				if (stu72.kind == tykind.TY_TUPLE) {
+					let m72: str = "cgwidentaggedstore: tuple-typed source shape unwired (only the bare/cast tuple literal carries a full payload; see #72)\n";
+					os.write(2, m72.ptr, m72.len: u64);
+					os.exit(1);
+				};
+			};
+		};
+	};
+	if (tupsrc != nil) {
 		let stu: *tinfo = src.type_: *tinfo;
 		for (stu != nil && stu.kind == tykind.TY_NAMED) { stu = stu.under; };
 		if (stu != nil) { if (stu.kind == tykind.TY_TUPLE) {
@@ -19235,9 +19290,11 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 			// cstage can't type: a bool literal (N_TRUE/N_FALSE) or a
 			// suffix-less numeric literal (untyped_int/untyped_float).
 			// LIFT BOTH stage guards together when #241 fixes cstage
-			// literal typing -> symmetric accept.
-			let bl: *node = src.list;
-			for (bl != nil) {
+			// literal typing -> symmetric accept. BARE form only (#66):
+			// the cast form resolves its tag from the cast's type on
+			// BOTH stages, so bare elements are fine there.
+			let bl: *node = tupsrc.list;
+			for (bl != nil && !tupcast) {
 				let bare: bool = false;
 				if (bl.kind == nkind.N_TRUE)  { bare = true; };
 				if (bl.kind == nkind.N_FALSE) { bare = true; };
@@ -19277,7 +19334,7 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 			// SysV eightbyte tuple classification is a deferred
 			// follow-up. Symmetric with cstage cg_widen_tagged_store.
 			let ttotal: i32 = 0;
-			let ce: *node = src.list;
+			let ce: *node = tupsrc.list;
 			for (ce != nil) {
 				if (nodeisstr(c, ce) || nodeisslice(c, ce)) {
 					ttotal += 24;
@@ -19298,7 +19355,7 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 				tzk += 8;
 			};
 			let tfoff: i32 = 0;
-			let te: *node = src.list;
+			let te: *node = tupsrc.list;
 			for (te != nil) {
 				let isflt: bool = isfloattype(c, te);
 				let wide: bool = nodeisstr(c, te) || nodeisslice(c, te);
@@ -19342,7 +19399,7 @@ fn cgwidentaggedstorebp(c: *cgen, dst: *tinfo, src: *node, slot_off: i32, slot_s
 			emitline("(BP)\n");
 			return;
 		}; };
-	}; };
+	};
 	// Struct payload (literal or ident).
 	let sname: str = rhsstructpayload(c, src);
 	if (sname.len > 0) {
diff --git a/test/wcc/936_tagged_tuple_widen_run.c b/test/wcc/936_tagged_tuple_widen_run.c
new file mode 100644
index 00000000..0210e73c
--- /dev/null
+++ b/test/wcc/936_tagged_tuple_widen_run.c
@@ -0,0 +1,525 @@
+/*
+ * 936_tagged_tuple_widen_run — #66 (fold-4 prereq): the cast-wrapped
+ * tuple literal `((a, b): variant_alias)` widened into a tagged-union
+ * payload. Pre-#66 the #242 tuple arm of the widen choke-point
+ * (cg_widen_tagged_store / cgwidentaggedstorebp) gated on a BARE
+ * N_TUPLE source; the cast-to-CONCRETE-VARIANT wrapper — the only
+ * spelling real code uses (ref/hare/regex/regex.ha:213
+ * `(start_b, end_b): charset_range_item`) — was not peeled (it is not
+ * a widen-cast: its destination is the variant, not the union), fell
+ * to the SCALAR arm and silently stored cursor word 0 only, zero-
+ * filling payload slot 1+ (both stages, byte-id — gate-blind). The
+ * read side (match-extract slot walk) was always correct.
+ *
+ *   row                    | shape                                | want
+ *   -----------------------+--------------------------------------+-----
+ *   cast_let_packed        | let v: item = ((65,90): rng); .0/.1  | 0
+ *   cast_let_3member       | + (str,*fn) member present, never    |
+ *                          | constructed (layout-neutral pin)     | 0
+ *   cast_append_local      | append(xs, cast) → index → extract   | 0
+ *   cast_append_indexplace | append(cs[len-1], cast), [][]item    | 0
+ *   cast_append_derefplace | through *[][]item param (via_outer)  | 0
+ *   cast_append_ptrfield   | append(p.cs[len-1], cast) — ptr-     |
+ *                          | FIELD-rooted place                   | 0
+ *   cast_ident_elems       | (start_b, end_b) u32 LOCALS — the    |
+ *                          | handle_bracket shape                 | 0
+ *   cast_float_elem        | (u32, f64) — MOVSD element store     | 0
+ *   cast_str_elem          | (i64, str) — 3-word wide element     | 0
+ *   cast_arg_direct        | cast tuple as a DIRECT tagged ARG —  |
+ *                          | cg_widen_tagged_push routes tuple    |
+ *                          | srcs to the scratch store (the fast  |
+ *                          | scalar push dropped slot 1+)         | 0
+ *   bare_ident_arg         | bare (a, b) typed idents as a tagged |
+ *                          | ARG — same push routing, tag from    |
+ *                          | the typed tuple                      | 0
+ *   bare_ident_no_regress  | bare (a, b) typed-ident return into  |
+ *                          | tagged — the strconv parseint shape  | 0
+ *   bare_literal_reject    | bare (5, 6) literal-element tuple    |
+ *                          | into tagged stays the #242/#241 loud |
+ *                          | stop (the cast form lifts it; the    |
+ *                          | bare form must NOT silently change)  | err
+ *   tuple_ident_reject     | tuple-typed IDENT into tagged stays  |
+ *                          | LOUD (#72) — was a silent slot-1+    |
+ *                          | drop through the scalar arm          | err
+ *
+ * Every K_RUN row also asserts cstage/wwstage asm byte-id. NNN<950,
+ * self-contained (/tmp, no imports) — rule-14's selfhost-sibling race
+ * does not apply (941 precedent).
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+
+static int
+runwait(const char *cmd)
+{
+	int rc = system(cmd);
+	if (rc == -1) return -1;
+	if (WIFEXITED(rc)) return WEXITSTATUS(rc);
+	return -1;
+}
+
+static int
+slurp_eq(const char *a, const char *b)
+{
+	FILE *fa = fopen(a, "rb");
+	FILE *fb = fopen(b, "rb");
+	if (!fa || !fb) { if (fa) fclose(fa); if (fb) fclose(fb); return -1; }
+	int rc = 0;
+	for (;;) {
+		int ca = fgetc(fa), cb = fgetc(fb);
+		if (ca != cb) { rc = -1; break; }
+		if (ca == EOF) break;
+	}
+	fclose(fa); fclose(fb);
+	return rc;
+}
+
+#define K_RUN      0	/* build+run both drivers, exit==want, + cs==ww byte-id */
+#define K_BUILDERR 1	/* build must FAIL with experr on BOTH drivers (rule 7) */
+
+struct row { const char *label; const char *src; int want;
+             int kind; const char *experr; };
+
+/* errlog_has — a BUILDERR row must fail WITH its diagnostic; any other
+ * failure (parse error, crash) is a vacuous reject (940 precedent). */
+static int
+errlog_has(const char *path, const char *needle)
+{
+	FILE *f = fopen(path, "rb");
+	if (!f) return 0;
+	char buf[8192];
+	size_t got = fread(buf, 1, sizeof buf - 1, f);
+	fclose(f);
+	buf[got] = '\0';
+	return strstr(buf, needle) != NULL;
+}
+
+static const struct row rows[] = {
+	{ "cast_let_packed",
+	  "package main;\n"
+	  "type lit = rune;\n"
+	  "type rng = (u32, u32);\n"
+	  "type item = (lit | rng);\n"
+	  "export fn main() i32 = {\n"
+	  "	let v: item = ((65, 90): rng);\n"
+	  "	match (v) {\n"
+	  "	case let r: rng => {\n"
+	  "		if (r.0 != 65) { return 1; };\n"
+	  "		if (r.1 != 90) { return 2; };\n"
+	  "	};\n"
+	  "	case => return 3;\n"
+	  "	};\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* the real charset element: the (str,*fn) class member is PRESENT
+	 * IN THE TYPE but never constructed — its presence must not alter
+	 * the lit/range slot layout or walks (fold-4 PF1 caveat). */
+	{ "cast_let_3member",
+	  "package main;\n"
+	  "type lit = rune;\n"
+	  "type rng = (u32, u32);\n"
+	  "type cls = (str, *fn(c: rune) bool);\n"
+	  "type item = (lit | rng | cls);\n"
+	  "export fn main() i32 = {\n"
+	  "	let v: item = ((65, 90): rng);\n"
+	  "	match (v) {\n"
+	  "	case let r: rng => {\n"
+	  "		if (r.0 != 65) { return 1; };\n"
+	  "		if (r.1 != 90) { return 2; };\n"
+	  "	};\n"
+	  "	case => return 3;\n"
+	  "	};\n"
+	  "	let w: item = ('a': lit);\n"
+	  "	match (w) {\n"
+	  "	case let l: lit => { if ((l: rune) != 'a') { return 4; }; };\n"
+	  "	case => return 5;\n"
+	  "	};\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	{ "cast_append_local",
+	  "package main;\n"
+	  "type lit = rune;\n"
+	  "type rng = (u32, u32);\n"
+	  "type item = (lit | rng);\n"
+	  "export fn main() i32 = {\n"
+	  "	let xs: []item;\n"
+	  "	append(xs, ('a': lit));\n"
+	  "	append(xs, ((65, 90): rng));\n"
+	  "	if (len(xs) != 2) { return 1; };\n"
+	  "	let e: item = xs[1];\n"
+	  "	match (e) {\n"
+	  "	case let r: rng => {\n"
+	  "		if (r.0 != 65) { return 2; };\n"
+	  "		if (r.1 != 90) { return 3; };\n"
+	  "	};\n"
+	  "	case => return 4;\n"
+	  "	};\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* append place = indexed inner slice — the handle_bracket
+	 * `append(charsets[len(charsets)-1], ...)` route. */
+	{ "cast_append_indexplace",
+	  "package main;\n"
+	  "type lit = rune;\n"
+	  "type rng = (u32, u32);\n"
+	  "type item = (lit | rng);\n"
+	  "export fn main() i32 = {\n"
+	  "	let charsets: [][]item;\n"
+	  "	let empty: []item;\n"
+	  "	append(charsets, empty);\n"
+	  "	append(charsets[len(charsets) - 1], ((7, 9): rng));\n"
+	  "	if (len(charsets[0]) != 1) { return 1; };\n"
+	  "	let e: item = charsets[0][0];\n"
+	  "	match (e) {\n"
+	  "	case let r: rng => {\n"
+	  "		if (r.0 != 7) { return 2; };\n"
+	  "		if (r.1 != 9) { return 3; };\n"
+	  "	};\n"
+	  "	case => return 4;\n"
+	  "	};\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* append place behind a *[][]item param — the via_outer
+	 * (pointer-rooted) widen route. */
+	{ "cast_append_derefplace",
+	  "package main;\n"
+	  "type lit = rune;\n"
+	  "type rng = (u32, u32);\n"
+	  "type item = (lit | rng);\n"
+	  "fn addrange(cs: *[][]item, a: u32, b: u32) void = {\n"
+	  "	if (len(*cs) == 0) {\n"
+	  "		let empty: []item;\n"
+	  "		append(*cs, empty);\n"
+	  "	};\n"
+	  "	append((*cs)[len(*cs) - 1], ((a, b): rng));\n"
+	  "};\n"
+	  "export fn main() i32 = {\n"
+	  "	let charsets: [][]item;\n"
+	  "	addrange(&charsets, 5, 8);\n"
+	  "	if (len(charsets) != 1) { return 1; };\n"
+	  "	if (len(charsets[0]) != 1) { return 2; };\n"
+	  "	let e: item = charsets[0][0];\n"
+	  "	match (e) {\n"
+	  "	case let r: rng => {\n"
+	  "		if (r.0 != 5) { return 3; };\n"
+	  "		if (r.1 != 8) { return 4; };\n"
+	  "	};\n"
+	  "	case => return 5;\n"
+	  "	};\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* append place rooted at a ptr-FIELD ([][]item field through
+	 * *struct) — the re.charsets-style place spelling. */
+	{ "cast_append_ptrfield",
+	  "package main;\n"
+	  "type lit = rune;\n"
+	  "type rng = (u32, u32);\n"
+	  "type item = (lit | rng);\n"
+	  "type holder = struct { cs: [][]item, n: i64 };\n"
+	  "export fn main() i32 = {\n"
+	  "	let h: holder = holder { n = 0, ... };\n"
+	  "	let p: *holder = &h;\n"
+	  "	let empty: []item;\n"
+	  "	append(p.cs, empty);\n"
+	  "	append(p.cs[len(p.cs) - 1], ((7, 9): rng));\n"
+	  "	if (len(h.cs[0]) != 1) { return 1; };\n"
+	  "	match (h.cs[0][0]) {\n"
+	  "	case let r: rng => {\n"
+	  "		if (r.0 != 7) { return 2; };\n"
+	  "		if (r.1 != 9) { return 3; };\n"
+	  "	};\n"
+	  "	case => return 4;\n"
+	  "	};\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* typed u32 LOCALS as the tuple elements — handle_bracket's
+	 * exact `(start_b, end_b): charset_range_item` shape. */
+	{ "cast_ident_elems",
+	  "package main;\n"
+	  "type lit = rune;\n"
+	  "type rng = (u32, u32);\n"
+	  "type item = (lit | rng);\n"
+	  "export fn main() i32 = {\n"
+	  "	let start_b: u32 = 97;\n"
+	  "	let end_b: u32 = 122;\n"
+	  "	let v: item = ((start_b, end_b): rng);\n"
+	  "	match (v) {\n"
+	  "	case let r: rng => {\n"
+	  "		if (r.0 != 97) { return 1; };\n"
+	  "		if (r.1 != 122) { return 2; };\n"
+	  "	};\n"
+	  "	case => return 3;\n"
+	  "	};\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* float element rides the MOVSD store branch under the cast form */
+	{ "cast_float_elem",
+	  "package main;\n"
+	  "type mf = (u32, f64);\n"
+	  "type item = (rune | mf);\n"
+	  "export fn main() i32 = {\n"
+	  "	let a: u32 = 9;\n"
+	  "	let x: f64 = 2.5;\n"
+	  "	let v: item = ((a, x): mf);\n"
+	  "	match (v) {\n"
+	  "	case let m: mf => {\n"
+	  "		if (m.0 != 9) { return 1; };\n"
+	  "		if (m.1 != 2.5) { return 2; };\n"
+	  "	};\n"
+	  "	case => return 3;\n"
+	  "	};\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* str element rides the 3-word wide branch under the cast form */
+	{ "cast_str_elem",
+	  "package main;\n"
+	  "type ms = (i64, str);\n"
+	  "type item = (rune | ms);\n"
+	  "export fn main() i32 = {\n"
+	  "	let n: i64 = 12;\n"
+	  "	let s: str = \"wxyz\";\n"
+	  "	let v: item = ((n, s): ms);\n"
+	  "	match (v) {\n"
+	  "	case let m: ms => {\n"
+	  "		if (m.0 != 12) { return 1; };\n"
+	  "		if (len(m.1) != 4) { return 2; };\n"
+	  "	};\n"
+	  "	case => return 3;\n"
+	  "	};\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* cast tuple passed DIRECTLY as a tagged call arg — pre-fix
+	 * cg_widen_tagged_push's scalar fast path pushed word 0 only
+	 * (and coerced an unresolved tag to 0); tuple-typed sources now
+	 * route through the scratch store choke-point. */
+	{ "cast_arg_direct",
+	  "package main;\n"
+	  "type lit = rune;\n"
+	  "type rng = (u32, u32);\n"
+	  "type item = (lit | rng);\n"
+	  "fn check(v: item) i32 = {\n"
+	  "	match (v) {\n"
+	  "	case let r: rng => {\n"
+	  "		if (r.0 != 65) { return 1; };\n"
+	  "		if (r.1 != 90) { return 2; };\n"
+	  "		return 0;\n"
+	  "	};\n"
+	  "	case => return 3;\n"
+	  "	};\n"
+	  "};\n"
+	  "export fn main() i32 = {\n"
+	  "	return check(((65, 90): rng));\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* bare typed-ident tuple as a tagged call arg — the strconv
+	 * `(neg, n)` shape at a CALL boundary; rides the same push
+	 * routing, tag resolved from the typed tuple. */
+	{ "bare_ident_arg",
+	  "package main;\n"
+	  "type item = (rune | (i64, i64));\n"
+	  "fn check(v: item) i32 = {\n"
+	  "	match (v) {\n"
+	  "	case let r: (i64, i64) => {\n"
+	  "		if (r.0 != 5) { return 1; };\n"
+	  "		if (r.1 != 6) { return 2; };\n"
+	  "		return 0;\n"
+	  "	};\n"
+	  "	case => return 3;\n"
+	  "	};\n"
+	  "};\n"
+	  "export fn main() i32 = {\n"
+	  "	let a: i64 = 5;\n"
+	  "	let b: i64 = 6;\n"
+	  "	return check((a, b));\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* bare N_TUPLE of TYPED idents (the strconv parseint `(neg, n)`
+	 * return shape) must keep working — no-regress on the bare arm. */
+	{ "bare_ident_no_regress",
+	  "package main;\n"
+	  "fn mk() ((i64, i64) | nomem) = {\n"
+	  "	let a: i64 = 5;\n"
+	  "	let b: i64 = 6;\n"
+	  "	return (a, b);\n"
+	  "};\n"
+	  "export fn main() i32 = {\n"
+	  "	match (mk()) {\n"
+	  "	case let t: (i64, i64) => {\n"
+	  "		if (t.0 != 5) { return 1; };\n"
+	  "		if (t.1 != 6) { return 2; };\n"
+	  "	};\n"
+	  "	case => return 3;\n"
+	  "	};\n"
+	  "	return 0;\n"
+	  "};\n", 0, K_RUN, NULL },
+	/* bare literal-element tuple into tagged stays the #242/#241
+	 * loud-stop — the cast form lifts it (the cast supplies the
+	 * variant type), the bare form must not silently change. */
+	{ "bare_literal_reject",
+	  "package main;\n"
+	  "fn mk() ((i64, i64) | nomem) = {\n"
+	  "	return (5, 6);\n"
+	  "};\n"
+	  "export fn main() i32 = {\n"
+	  "	match (mk()) {\n"
+	  "	case let t: (i64, i64) => { if (t.0 != 5) { return 1; }; };\n"
+	  "	case => return 2;\n"
+	  "	};\n"
+	  "	return 0;\n"
+	  "};\n", 0,
+	  K_BUILDERR, "tuple-in-union variant tag unresolved" },
+	/* tuple-typed IDENT source into a tagged slot: the widen
+	 * choke-point has no word-copy arm for it — pre-#72 it fell to
+	 * the scalar arm and SILENTLY dropped payload slot 1+; now loud
+	 * (rule 7) until #72 wires ident/call/match-binding sources. */
+	{ "tuple_ident_reject",
+	  "package main;\n"
+	  "type lit = rune;\n"
+	  "type rng = (u32, u32);\n"
+	  "type item = (lit | rng);\n"
+	  "export fn main() i32 = {\n"
+	  "	let t: rng = ((65, 90): rng);\n"
+	  "	let v: item = t;\n"
+	  "	match (v) {\n"
+	  "	case let r: rng => { if (r.0 != 65) { return 1; }; };\n"
+	  "	case => return 2;\n"
+	  "	};\n"
+	  "	return 0;\n"
+	  "};\n", 0,
+	  K_BUILDERR, "tuple-typed source shape unwired" },
+};
+
+/* build+run via a driver (ww / ww_ww); returns 0 pass, nonzero fail. */
+static int
+run_driver(const char *driver, const struct row *r, int i)
+{
+	char src[96], tmpdir[96], errf[96], cmd[1024];
+	snprintf(src, sizeof src, "/tmp/ttw_%d_%d.ww", getpid(), i);
+	snprintf(tmpdir, sizeof tmpdir, "/tmp/ttw_%d_d_%d", getpid(), i);
+	snprintf(errf, sizeof errf, "/tmp/ttw_%d_e_%d", getpid(), i);
+
+	FILE *f = fopen(src, "wb");
+	if (!f) return -1;
+	fputs(r->src, f);
+	fclose(f);
+
+	mkdir(tmpdir, 0755);
+	snprintf(cmd, sizeof cmd, "cd %s && %s build %s >/dev/null 2>%s",
+	    tmpdir, driver, src, errf);
+	int brc = runwait(cmd);
+	if (r->kind == K_BUILDERR) {
+		int ok = (brc != 0)
+		    && (r->experr == NULL || errlog_has(errf, r->experr));
+		if (!ok)
+			fprintf(stderr, "row[%s]: %s expected loud builderr "
+			    "\"%s\" (brc=%d)\n", r->label, driver,
+			    r->experr ? r->experr : "", brc);
+		unlink(src); unlink(errf); rmdir(tmpdir);
+		return ok ? 0 : 1;
+	}
+	if (brc != 0) {
+		fprintf(stderr, "row[%s]: build via %s failed\n",
+		    r->label, driver);
+		unlink(src); unlink(errf); rmdir(tmpdir);
+		return -1;
+	}
+
+	const char *base = strrchr(src, '/');
+	base = base ? base + 1 : src;
+	char outbin[256];
+	snprintf(outbin, sizeof outbin, "%s/%s", tmpdir, base);
+	char *dot = strrchr(outbin, '.');
+	if (dot && strcmp(dot, ".ww") == 0) *dot = '\0';
+	int got = runwait(outbin);
+
+	unlink(src); unlink(outbin); unlink(errf); rmdir(tmpdir);
+	if (got != r->want) {
+		fprintf(stderr, "row[%s]: %s exit %d, want %d\n",
+		    r->label, driver, got, r->want);
+		return 1;
+	}
+	return 0;
+}
+
+/* cs==ww .s byte-id (rule 10). */
+static int
+asm_byte_identical(const char *bin, const struct row *r, int i)
+{
+	char src[96], cs[96], ws[96], cmd[1024];
+	snprintf(src, sizeof src, "/tmp/ttw_asm_%d_%d.ww", getpid(), i);
+	snprintf(cs,  sizeof cs,  "/tmp/ttw_asm_%d_%d_c.s", getpid(), i);
+	snprintf(ws,  sizeof ws,  "/tmp/ttw_asm_%d_%d_w.s", getpid(), i);
+
+	FILE *f = fopen(src, "wb");
+	if (!f) return -1;
+	fputs(r->src, f);
+	fclose(f);
+
+	snprintf(cmd, sizeof cmd, "%s/w6c -o %s %s 2>/dev/null", bin, cs, src);
+	if (runwait(cmd) != 0) {
+		fprintf(stderr, "row[%s]: w6c errored\n", r->label);
+		unlink(src);
+		return -1;
+	}
+	snprintf(cmd, sizeof cmd, "%s/w6c_ww -o %s %s 2>/dev/null",
+	    bin, ws, src);
+	if (runwait(cmd) != 0) {
+		fprintf(stderr, "row[%s]: w6c_ww errored\n", r->label);
+		unlink(src); unlink(cs);
+		return -1;
+	}
+	int rc = slurp_eq(cs, ws);
+	if (rc != 0)
+		fprintf(stderr, "row[%s]: cstage vs wwstage asm differs\n",
+		    r->label);
+	unlink(src); unlink(cs); unlink(ws);
+	return rc;
+}
+
+int
+main(void)
+{
+	const char *bin = getenv("BIN");
+	if (!bin) bin = "out/bin";
+	char absbin[2080];
+	if (bin[0] != '/') {
+		char cwd[1024];
+		if (getcwd(cwd, sizeof cwd) == NULL) return 1;
+		snprintf(absbin, sizeof absbin, "%s/%s", cwd, bin);
+		bin = absbin;
+	}
+
+	char cdrv[2120], wdrv[2120];
+	snprintf(cdrv, sizeof cdrv, "%s/ww", bin);
+	snprintf(wdrv, sizeof wdrv, "%s/ww_ww", bin);
+
+	int n = (int)(sizeof rows / sizeof rows[0]);
+	int total = 0, fail = 0;
+
+	for (int i = 0; i < n; i++) {
+		total++;
+		if (run_driver(cdrv, &rows[i], i) != 0) fail++;
+	}
+	if (access(wdrv, X_OK) == 0) {
+		for (int i = 0; i < n; i++) {
+			total++;
+			if (run_driver(wdrv, &rows[i], i) != 0) fail++;
+		}
+		for (int i = 0; i < n; i++) {
+			if (rows[i].kind == K_BUILDERR)
+				continue;
+			total++;
+			if (asm_byte_identical(bin, &rows[i], i) != 0) fail++;
+		}
+	}
+
+	if (fail) {
+		fprintf(stderr, "tagged_tuple_widen: %d/%d checks failed\n",
+		    fail, total);
+		return 1;
+	}
+	printf("tagged_tuple_widen: %d/%d ok\n", total, total);
+	return 0;
+}