check: populate fn-type params in the wwstage tinfo layer

The N_TFN arm stamped only size and return, so every fn tinfo carried
a nil param chain and typeeq judged any two same-return fn types
equal: tagged-union dedup collapsed (*fn(A) T | *fn(B) T) to a bare
8-byte pointer and match read the pointer word as a tag, falling
through every arm for a real second-variant value. Build the tparam
chain like cstage's N_TFN resolve (bare ... sets the FFI variadic
flag; a Hare T... param wraps to []T with a per-param variadic bit
that typeeq now compares, mirroring cstage type_eq). Graduates the
four r76_typeeq_fn pins; the DATABYTEID_DIVERGED ledger is empty.

Makefile

@@ -581,10 +581,9 @@ DATABYTEID_EXPECTED_MIN = 911
 # Known cs!=ww divergences (loud over blind, the 989_lib_byteid DIVERGE
 # discipline): each entry must still build on both stages AND still differ.
 # When a compiler fix lands the entry fails demanding graduation out of
-# this list rather than silently widening coverage.  Tracked with the #59
-# divergence family.
-DATABYTEID_DIVERGED = r76_typeeq_fn_diff_arity r76_typeeq_fn_diff_param_type \
-	  r76_typeeq_fn_io_vtable_shape r76_typeeq_fn_variadic_vs_fixed
+# this list rather than silently widening coverage.  Currently empty: the
+# 2026-08 drain closed all eight original entries.
+DATABYTEID_DIVERGED =
 $(if $(DATABYTEID_FILES),,$(error test-byteid: empty data corpus))
 test-data-byteid: $(BIN)/ww $(BIN)/w6c $(BIN)/w6c_ww
 	@work=$$(mktemp -d "$(CURDIR)/$(DATABYTEID_DIR).XXXXXX") || exit 1; \

lib/ww/syntax/typ.ww

@@ -88,6 +88,10 @@ export type tparam = struct {
 	// struct instead, matching cstage Type.iserror semantics.
 	// Faithful STORAGE_ERROR-node port filed as #62.
 	iserror: bool,
+	// Hare-style `T...` — type_ is []T when set. Mirrors cstage
+	// Tparam.variadic (cmd/wcc/ww.h); distinct from tinfo.variadic,
+	// the C-style FFI `...` marker.
+	variadic: bool,
 	tnext:  *tparam,
 };
 
@@ -547,6 +551,7 @@ export fn typeeq(a: *tinfo, b: *tinfo) bool = {
 		for (true) {
 			if (pa == nil) { if (pb == nil) { return true; }; return false; };
 			if (pb == nil) { return false; };
+			if (pa.variadic != pb.variadic) { return false; };
 			if (!typeeq(pa.type_, pb.type_)) { return false; };
 			pa = pa.tnext;
 			pb = pb.tnext;

selfhost/cmd/wcc/check.ww

@@ -2311,6 +2311,32 @@ fn tinfofornode(c: *checker, n: *syntax.node) *syntax.tinfo = {
 		r.slotsize = 8u64;
 		syntax.tinfocachebind(c.tc, n, r);
 		r.ret = tinfofornode(c, n.lhs);
+		// Params must be populated (cstage check.c N_TFN builds the
+		// Tparam chain): with params nil on every fn tinfo, typeeq saw
+		// any two same-return fn types equal, so tagged-union dedup
+		// collapsed `(*fn(A) T | *fn(B) T)` to a bare 8B pointer and
+		// match read the pointer word as a tag.
+		{
+			let fphead: *syntax.tparam = nil;
+			let fptail: *syntax.tparam = nil;
+			let fpn: *syntax.node = n.list;
+			for (fpn != nil) {
+				if (syntax.streq(fpn.str, "...")) {
+					r.variadic = 1;
+					fpn = fpn.next;
+					continue;
+				};
+				let fpt: *syntax.tinfo = tinfofornode(c, fpn.lhs);
+				let fpv: bool = fpn.op == syntax.tkind.TK_ELLIPSIS;
+				if (fpv) { fpt = syntax.typeslice(fpt); };
+				let ftp: *syntax.tparam = alloc(syntax.tparam{name=fpn.str, type_=fpt, iserror=false, variadic=fpv, tnext=nil})!;
+				if (fphead == nil) { fphead = ftp; }
+				else { fptail.tnext = ftp; };
+				fptail = ftp;
+				fpn = fpn.next;
+			};
+			r.params = fphead;
+		};
 	case syntax.nkind.N_TENUM:
 		// Cstage cmd/wcc/check.c:529-542: storage type's size/align
 		// (default i32 = 4B/4B). Cgen's slotsize-TENUM fallback pads
@@ -2546,7 +2572,7 @@ fn tinfofornode(c: *checker, n: *syntax.node) *syntax.tinfo = {
 						if (st.size > maxsz) { maxsz = st.size; };
 						if (st.align > al) { al = st.align; };
 					};
-					let tp: *syntax.tparam = alloc(syntax.tparam{name="", type_=src.type_, iserror=src.iserror, tnext=nil})!;
+					let tp: *syntax.tparam = alloc(syntax.tparam{name="", type_=src.type_, iserror=src.iserror, variadic=false, tnext=nil})!;
 					if (head == nil) { head = tp; } else { tail.tnext = tp; };
 					tail = tp;
 					nv += 1;
@@ -2564,7 +2590,7 @@ fn tinfofornode(c: *checker, n: *syntax.node) *syntax.tinfo = {
 					if (vt.align > al) { al = vt.align; };
 				};
 				let ve: bool = varianterr(c, v);
-				let tp: *syntax.tparam = alloc(syntax.tparam{name="", type_=vt, iserror=ve, tnext=nil})!;
+				let tp: *syntax.tparam = alloc(syntax.tparam{name="", type_=vt, iserror=ve, variadic=false, tnext=nil})!;
 				if (head == nil) { head = tp; } else { tail.tnext = tp; };
 				tail = tp;
 				nv += 1;