cmd/w6c+selfhost/wcc+lib: route sizeof(str)/sizeof(slice) through SSoT

Audit §1.1/§1.2 cataloged 17 wwstage sites hardcoding 16 for sizeof(str)
and ~10 hardcoding 24 for sizeof(slice), plus 4 cstage str-size sites
and the cstage let_emit_size str/slice arms.  Each new size constant
required ~30 edits in both stages to bump cleanly — task #1 (str → 24B
{ptr,len,cap}) can't land until the literal sweep is done.

Track A — wwstage codegen (selfhost/cmd/wcc/*):

  - check.ww introduces two stateless helpers next to astsize:
    primtypesize(nm)  — primitive-name → byte size (i64; -1 unknown)
    tyslicesize()     — slice-header bytes (i64; 24 today)
    astsize now reads both for its N_TNAME-primitive and N_TSLICE arms,
    so the size(T) fold gets the SSoT for free.
  - cgen.ww, cgenutil.ww, cgenstmt.ww, cgendecl.ww: every `return 16`
    / `esz = 16` / `sz0 = 16` for str, every `return 24` /
    `localadd(c, _, 24, _)` for slice, plus the matching `sz == 16` /
    `sz == 24` / `for (i < 16/24)` gates in the global-let DATAW emit,
    route through primtypesize / tyslicesize.
  - Direct delegation slotsize→astsize would require restructuring
    astsize to drop its *checker dep (resolvealias) — the leaf
    primitive/slice cases factor out cleanly, the alias-chain leaves
    diverge because cgen's aliaslookup/structlookup tables and check's
    scope chain aren't unified yet (§1.8, task #50 follow-up).  Sharing
    the leaf table satisfies the SSoT promise without that refactor.

Track B — cstage (cmd/w6c/cgen.c):

  - let_emit_size's TY_STR/TY_SLICE arms drop the hardcoded 16/24 and
    fall to `(int)u->size` like the existing TY_STRUCT/TUPLE/TAGGED arms.
  - N_LET cgstmt's per-kind `sz` cascade collapses to a single
    `if (lu->kind ∈ {ARRAY,SLICE,STR,STRUCT,TUPLE,TAGGED}) sz = lu->size`.
  - N_LET cgexpr's match-bind primitive sizing: `bsz = (int)bu->size`
    drops the TY_STR/TY_SLICE special-cases (same outcome — ty_str/
    ty_slice already have ->size set by type.c).
  - Three `sz == 16` / `let_emit_size(d->type) != 16` gates against the
    str slot width route through ty_str->size.

  Cap-offset sites (cgen.c:2440/1994/3206/5517 `delta = 16` for
  slice's .cap field-write) intentionally NOT touched: 16 there is the
  *offset of .cap inside a slice header*, structurally always 16
  regardless of str.size.  #1 doesn't move the slice layout.

Track C — lib/ user code:

  - lib/strings.freeall + appendstr, lib/shlex.freepartial + appendstr:
    the four `16u64` literals (per-str-element stride for rt_ensure and
    os.free) become `size(str): u64`.  Check-time fold via #42's
    intercept resolves to 16 today; #1 reroutes via the bumped tinfo.

After this commit, bumping ty_str to 24B for task #1 requires editing
exactly two places (cmd/wcc/type.c:64 ty_str.size, plus check.ww
primtypesize's "str" arm) for the SSoT to propagate.

Verification:
  - 131/131 tests pass.  994_w6c_ww + 995_self_rebuild byte-identity
    holds — each replacement evaluates to the same constant the
    literal had today, so cgen output is unchanged.
  - selfhost source's `size(str): u64` folds at check time (cstage
    cmd/wcc/check.c:907-960 for the C-bootstrap of selfhost; wwstage
    check.ww:898-942 for the rebuild path), no runtime call introduced.

selfhost/cmd/w6c/main.combined.ww

@@ -1996,7 +1996,7 @@ export fn freeall(s: []str) void = {
 		i += 1;
 	};
 	if (s.cap > 0) {
-		os.free(s.ptr: *void, (s.cap: u64) * 16u64);
+		os.free(s.ptr: *void, (s.cap: u64) * size(str): u64);
 	};
 };
 
@@ -2599,7 +2599,7 @@ export fn remaining_tokens(s: *tokenizer) str = {
 fn appendstr(slice: *[]str, item: str) void = {
 	let newlen: i32 = slice.len + 1;
 	slice.len = newlen;
-	rtensure(slice: *void, 16u64);
+	rtensure(slice: *void, size(str): u64);
 	let dst: *str = &slice.ptr[newlen - 1];
 	dst.ptr = item.ptr;
 	dst.len = item.len;
@@ -7612,6 +7612,29 @@ fn mktname(c: *checker, nm: str) *node = {
 	return n;
 };
 
+// #43: SSoT for primitive type byte sizes. astsize's N_TNAME-primitive
+// arm and every wwstage cgen size walker (slotsize/fieldsize/letemit-
+// size/elemsizeof/paramfieldsize) consult this table so a future
+// ty_str.size bump (#1) lands in one place. Returns -1 for non-prim
+// names; callers fall back to alias/struct/enum lookup. Cstage's
+// equivalent SSoT is cmd/wcc/type.c:46-79 (ty_void/ty_bool/.../ty_str).
+fn primtypesize(nm: str) i64 = {
+	if (streq(nm, "void")) { return 0i64; };
+	if (streq(nm, "bool")) { return 1i64; };
+	if (streq(nm, "i8") || streq(nm, "u8")) { return 1i64; };
+	if (streq(nm, "i16") || streq(nm, "u16")) { return 2i64; };
+	if (streq(nm, "i32") || streq(nm, "u32") || streq(nm, "f32") || streq(nm, "rune")) { return 4i64; };
+	if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64")) { return 8i64; };
+	if (streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr")) { return 8i64; };
+	if (streq(nm, "str")) { return 16i64; };
+	return -1i64;
+};
+
+// #43: SSoT for slice header size (ptr+len+cap = 24B today). Mirrors
+// cstage cmd/wcc/type.c:103 (ty_slice->size = 24). Bumping a slice's
+// header layout in #34 touches only this constant.
+fn tyslicesize() i64 = { return 24i64; };
+
 // #42: AST-level layout helpers for the size(T)/align(T)/offset(e.f)
 // fold. Mirror cstage resolve_type's size/align computation
 // (cmd/wcc/check.c:286-528) on AST nodes — wwstage check.ww never
@@ -7673,7 +7696,7 @@ fn astsize(c: *checker, t: *node) i64 = {
 	let k: nkind = t.kind;
 	if (k == nkind.N_TBANG) { return astsize(c, t.lhs); };
 	if (k == nkind.N_TPTR)   { return 8i64; };
-	if (k == nkind.N_TSLICE) { return 24i64; };
+	if (k == nkind.N_TSLICE) { return tyslicesize(); };
 	if (k == nkind.N_TCHAN)  { return 8i64; };
 	if (k == nkind.N_TFN)    { return 8i64; };
 	if (k == nkind.N_TARRAY) {
@@ -7725,13 +7748,8 @@ fn astsize(c: *checker, t: *node) i64 = {
 	};
 	if (k == nkind.N_TNAME) {
 		let nm: str = t.str;
-		if (streq(nm, "void")) { return 0i64; };
-		if (streq(nm, "bool")) { return 1i64; };
-		if (streq(nm, "i8") || streq(nm, "u8")) { return 1i64; };
-		if (streq(nm, "i16") || streq(nm, "u16")) { return 2i64; };
-		if (streq(nm, "i32") || streq(nm, "u32") || streq(nm, "f32") || streq(nm, "rune")) { return 4i64; };
-		if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64") || streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr")) { return 8i64; };
-		if (streq(nm, "str")) { return 16i64; };
+		let ps: i64 = primtypesize(nm);
+		if (ps >= 0i64) { return ps; };
 		let resolved: *node = resolvealias(c, t);
 		if (resolved != nil && resolved != t) {
 			return astsize(c, resolved);
@@ -9854,7 +9872,7 @@ fn indexbaseesz(c: *cgen, base: *node) i32 = {
 				let elem: *node = ft.lhs;
 				if (elem != nil) {
 					if (elem.kind == nkind.N_TNAME) {
-						if (streq(elem.str, "str")) { return 16; };
+						if (streq(elem.str, "str")) { return primtypesize("str"): i32; };
 						let ps: i32 = primsize(elem.str);
 						if (ps > 0) { return ps; };
 						// Pointer to named struct: indexing
@@ -9962,11 +9980,11 @@ fn elemsizeof(t: *node) i32 = {
 	// `*[]T`: stride is the slice header (24B). Hare-faithful — a
 	// pointer-to-slice is a 1D array of slices, not of T. Mirrors the
 	// cstage check.c default `*U → U` path for U=[]T (slice element).
-	if (elem.kind == nkind.N_TSLICE) { return 24; };
+	if (elem.kind == nkind.N_TSLICE) { return tyslicesize(): i32; };
 	if (elem.kind == nkind.N_TNAME) {
 		let nm: str = elem.str;
 		// str element is 16B (ptr+len). primsize returns 0 for it.
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let ps: i32 = primsize(nm);
 		if (ps > 0) { return ps; };
 	};
@@ -10561,7 +10579,7 @@ export fn letslotsize(c: *cgen, n: *node) i32 = {
 								// (ptr+len) — primsize returns 0 for
 								// it, so it'd slot 8B without this.
 								if (streq(elemn.str, "str")) {
-									esz = 16;
+									esz = primtypesize("str"): i32;
 								} else {
 									let ps: i32 = primsize(elemn.str);
 									if (ps > 0) { esz = ps; };
@@ -10610,7 +10628,7 @@ fn slotsize(c: *cgen, typn: *node) i32 = {
 	if (k == nkind.N_TPTR)   { return 8; };
 	if (k == nkind.N_TFN)    { return 8; };
 	if (k == nkind.N_TCHAN)  { return 8; };
-	if (k == nkind.N_TSLICE) { return 24; };
+	if (k == nkind.N_TSLICE) { return tyslicesize(): i32; };
 	if (k == nkind.N_TTUPLE) {
 		// Sum element sizes. Mirrors C cgen which uses raw type
 		// sizes; padding to 8 happens inside slotsize for primitives,
@@ -10650,7 +10668,7 @@ fn slotsize(c: *cgen, typn: *node) i32 = {
 		// slot+8 picking up the callee's stale-DX. Bypassing primsize's
 		// `> 0` guard keeps the rest of the prim-pad-to-8 contract intact.
 		if (streq(nm, "void")) { return 0; };
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let ps: i32 = primsize(nm);
 		if (ps > 0) {
 			// Pad to 8 for stack slots — matches C cgen which spills
@@ -10691,7 +10709,7 @@ fn slotsize(c: *cgen, typn: *node) i32 = {
 				// explicit case a `[N]str` would slot 8B/elem,
 				// collapsing the per-element stride and losing
 				// every .len half.
-				if (streq(en, "str")) { esz = 16; };
+				if (streq(en, "str")) { esz = primtypesize("str"): i32; };
 				let ps: i32 = primsize(en);
 				if (esz == 8) { if (ps > 0) { esz = ps; }
 				else {
@@ -10749,7 +10767,7 @@ fn fieldsize(c: *cgen, tnode: *node) i32 = {
 	if (k == nkind.N_TTAGGED){ return slotsize(c, tnode); };
 	if (k == nkind.N_TNAME) {
 		let nm: str = tnode.str;
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let ps: i32 = primsize(nm);
 		if (ps > 0) { return ps; };
 		let si: *structinfo = structlookup(c, nm);
@@ -10776,7 +10794,7 @@ fn fieldsize(c: *cgen, tnode: *node) i32 = {
 		return 8;
 	};
 	if (k == nkind.N_TPTR)   { return 8; };
-	if (k == nkind.N_TSLICE) { return 24; };
+	if (k == nkind.N_TSLICE) { return tyslicesize(): i32; };
 	if (k == nkind.N_TARRAY) {
 		// Same shape as slotsize's TARRAY branch.
 		let lenn: *node = tnode.rhs;
@@ -19139,7 +19157,7 @@ fn cglet(c: *cgen, n: *node) void = {
 			if (elemn != nil) {
 				if (elemn.kind == nkind.N_TNAME) {
 					if (streq(elemn.str, "str")) {
-						esz = 16;
+						esz = primtypesize("str"): i32;
 						isstrel = true;
 					} else {
 						let ps: i32 = primsize(elemn.str);
@@ -19624,8 +19642,8 @@ fn cgmlet(c: *cgen, n: *node) void = {
 			if (s0_is_str != s1_is_str) {
 				let sz0: i32 = 8;
 				let sz1: i32 = 8;
-				if (s0_is_str) { sz0 = 16; };
-				if (s1_is_str) { sz1 = 16; };
+				if (s0_is_str) { sz0 = primtypesize("str"): i32; };
+				if (s1_is_str) { sz1 = primtypesize("str"): i32; };
 				let off0: i32 = localadd(c, l0.str, sz0, t0);
 				let off1: i32 = localadd(c, l1.str, sz1, t1);
 				if (s0_is_str) {
@@ -19682,7 +19700,7 @@ fn paramfieldsize(t: *node) i32 = {
 	if (k == nkind.N_TCHAN)  { return 8; };
 	if (k == nkind.N_TNAME)  {
 		let nm: str = t.str;
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let ps: i32 = primsize(nm);
 		if (ps > 0) { return ps; };
 	};
@@ -20054,7 +20072,7 @@ fn cgfnparams(c: *cgen, params: *node) void = {
 			if (p.op == tkind.TK_ELLIPSIS) {
 				let tn: *node = slicewrap(c, p.lhs);
 				if (idx + 3 <= 6) {
-					let off: i32 = localadd(c, nm, 24, tn);
+					let off: i32 = localadd(c, nm, tyslicesize(): i32, tn);
 					emitline("\tMOVQ\t");
 					emitline(argregname(idx));
 					emitline(", ");
@@ -20078,7 +20096,7 @@ fn cgfnparams(c: *cgen, params: *node) void = {
 					// at the ABI boundary (the call site synthesises a
 					// 24B descriptor and pushes ptr/len/cap), so this
 					// mirrors the slice branch at cgendecl.ww:518.
-					let off: i32 = localadd(c, nm, 24, tn);
+					let off: i32 = localadd(c, nm, tyslicesize(): i32, tn);
 					let regs_left: i32 = 6 - idx;
 					let w: i32 = 0;
 					for (w < regs_left) {
@@ -20178,7 +20196,7 @@ fn cgfnparams(c: *cgen, params: *node) void = {
 				};};
 			} else { if (isslicetype(c, p.lhs)) {
 				if (idx + 3 <= 6) {
-					let off: i32 = localadd(c, nm, 24, p.lhs);
+					let off: i32 = localadd(c, nm, tyslicesize(): i32, p.lhs);
 					emitline("\tMOVQ\t");
 					emitline(argregname(idx));
 					emitline(", ");
@@ -20202,7 +20220,7 @@ fn cgfnparams(c: *cgen, params: *node) void = {
 					// 440-469. Caller's pushargsrev greedy-fills the
 					// remaining argregs (ptr,len,cap order), the tail
 					// spills to +16+stkcursor*8(BP).
-					let off: i32 = localadd(c, nm, 24, p.lhs);
+					let off: i32 = localadd(c, nm, tyslicesize(): i32, p.lhs);
 					let regs_left: i32 = 6 - idx;
 					let w: i32 = 0;
 					for (w < regs_left) {
@@ -21426,7 +21444,7 @@ fn letemitsize(c: *cgen, d: *node) i32 = {
 	let t: *node = d.lhs;
 	for (t != nil) {
 		if (t.kind == nkind.N_TPTR) { return 8; };
-		if (t.kind == nkind.N_TSLICE) { return 24; };
+		if (t.kind == nkind.N_TSLICE) { return tyslicesize(): i32; };
 		if (t.kind == nkind.N_TARRAY) {
 			let lenn: *node = t.rhs;
 			let elemn: *node = t.lhs;
@@ -21448,7 +21466,7 @@ fn letemitsize(c: *cgen, d: *node) i32 = {
 		if (letscalarprim(nm)) { return 8; };
 		let fsz: i32 = letfloatprim(nm);
 		if (fsz > 0) { return fsz; };
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let si: *structinfo = structlookup(c, nm);
 		if (si != nil) { return si.totsize; };
 		let next: *node = aliaslookup(c, nm);
@@ -21774,7 +21792,7 @@ fn emitletdataw(c: *cgen, file: *node) void = {
 						emitline("\"\n");
 					};
 				};
-				if (sz == 16 && !issg) {
+				if (sz == primtypesize("str"): i32 && !issg) {
 					let r: *node = d.rhs;
 					for (r != nil) {
 						if (r.kind != nkind.N_CAST) { break; };
@@ -21830,7 +21848,8 @@ fn emitletdataw(c: *cgen, file: *node) void = {
 							emitsymname(c, nm);
 							emitline("(SB),\"");
 							let i: i32 = 0;
-							for (i < 16) {
+							let szstr: i32 = primtypesize("str"): i32;
+							for (i < szstr) {
 								emitdatawbyte(0u8);
 								i += 1;
 							};
@@ -21838,7 +21857,7 @@ fn emitletdataw(c: *cgen, file: *node) void = {
 						};
 					};
 				};
-				if (sz == 24 && !issg) {
+				if (sz == tyslicesize(): i32 && !issg) {
 					// Slice: zero-init only (no slice-literal
 					// syntax to honour). Any rhs other than
 					// `nil` is skipped → undefined symbol at
@@ -21860,7 +21879,8 @@ fn emitletdataw(c: *cgen, file: *node) void = {
 						emitsymname(c, nm);
 						emitline("(SB),\"");
 						let i: i32 = 0;
-						for (i < 24) {
+						let szsl: i32 = tyslicesize(): i32;
+						for (i < szsl) {
 							emitdatawbyte(0u8);
 							i += 1;
 						};

selfhost/cmd/wcc/cgen.ww

@@ -965,7 +965,7 @@ fn letemitsize(c: *cgen, d: *node) i32 = {
 	let t: *node = d.lhs;
 	for (t != nil) {
 		if (t.kind == nkind.N_TPTR) { return 8; };
-		if (t.kind == nkind.N_TSLICE) { return 24; };
+		if (t.kind == nkind.N_TSLICE) { return tyslicesize(): i32; };
 		if (t.kind == nkind.N_TARRAY) {
 			let lenn: *node = t.rhs;
 			let elemn: *node = t.lhs;
@@ -987,7 +987,7 @@ fn letemitsize(c: *cgen, d: *node) i32 = {
 		if (letscalarprim(nm)) { return 8; };
 		let fsz: i32 = letfloatprim(nm);
 		if (fsz > 0) { return fsz; };
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let si: *structinfo = structlookup(c, nm);
 		if (si != nil) { return si.totsize; };
 		let next: *node = aliaslookup(c, nm);
@@ -1313,7 +1313,7 @@ fn emitletdataw(c: *cgen, file: *node) void = {
 						emitline("\"\n");
 					};
 				};
-				if (sz == 16 && !issg) {
+				if (sz == primtypesize("str"): i32 && !issg) {
 					let r: *node = d.rhs;
 					for (r != nil) {
 						if (r.kind != nkind.N_CAST) { break; };
@@ -1369,7 +1369,8 @@ fn emitletdataw(c: *cgen, file: *node) void = {
 							emitsymname(c, nm);
 							emitline("(SB),\"");
 							let i: i32 = 0;
-							for (i < 16) {
+							let szstr: i32 = primtypesize("str"): i32;
+							for (i < szstr) {
 								emitdatawbyte(0u8);
 								i += 1;
 							};
@@ -1377,7 +1378,7 @@ fn emitletdataw(c: *cgen, file: *node) void = {
 						};
 					};
 				};
-				if (sz == 24 && !issg) {
+				if (sz == tyslicesize(): i32 && !issg) {
 					// Slice: zero-init only (no slice-literal
 					// syntax to honour). Any rhs other than
 					// `nil` is skipped → undefined symbol at
@@ -1399,7 +1400,8 @@ fn emitletdataw(c: *cgen, file: *node) void = {
 						emitsymname(c, nm);
 						emitline("(SB),\"");
 						let i: i32 = 0;
-						for (i < 24) {
+						let szsl: i32 = tyslicesize(): i32;
+						for (i < szsl) {
 							emitdatawbyte(0u8);
 							i += 1;
 						};

selfhost/cmd/wcc/cgendecl.ww

@@ -46,7 +46,7 @@ fn cgfnparams(c: *cgen, params: *node) void = {
 			if (p.op == tkind.TK_ELLIPSIS) {
 				let tn: *node = slicewrap(c, p.lhs);
 				if (idx + 3 <= 6) {
-					let off: i32 = localadd(c, nm, 24, tn);
+					let off: i32 = localadd(c, nm, tyslicesize(): i32, tn);
 					emitline("\tMOVQ\t");
 					emitline(argregname(idx));
 					emitline(", ");
@@ -70,7 +70,7 @@ fn cgfnparams(c: *cgen, params: *node) void = {
 					// at the ABI boundary (the call site synthesises a
 					// 24B descriptor and pushes ptr/len/cap), so this
 					// mirrors the slice branch at cgendecl.ww:518.
-					let off: i32 = localadd(c, nm, 24, tn);
+					let off: i32 = localadd(c, nm, tyslicesize(): i32, tn);
 					let regs_left: i32 = 6 - idx;
 					let w: i32 = 0;
 					for (w < regs_left) {
@@ -170,7 +170,7 @@ fn cgfnparams(c: *cgen, params: *node) void = {
 				};};
 			} else { if (isslicetype(c, p.lhs)) {
 				if (idx + 3 <= 6) {
-					let off: i32 = localadd(c, nm, 24, p.lhs);
+					let off: i32 = localadd(c, nm, tyslicesize(): i32, p.lhs);
 					emitline("\tMOVQ\t");
 					emitline(argregname(idx));
 					emitline(", ");
@@ -194,7 +194,7 @@ fn cgfnparams(c: *cgen, params: *node) void = {
 					// 440-469. Caller's pushargsrev greedy-fills the
 					// remaining argregs (ptr,len,cap order), the tail
 					// spills to +16+stkcursor*8(BP).
-					let off: i32 = localadd(c, nm, 24, p.lhs);
+					let off: i32 = localadd(c, nm, tyslicesize(): i32, p.lhs);
 					let regs_left: i32 = 6 - idx;
 					let w: i32 = 0;
 					for (w < regs_left) {

selfhost/cmd/wcc/cgenstmt.ww

@@ -759,7 +759,7 @@ fn cglet(c: *cgen, n: *node) void = {
 			if (elemn != nil) {
 				if (elemn.kind == nkind.N_TNAME) {
 					if (streq(elemn.str, "str")) {
-						esz = 16;
+						esz = primtypesize("str"): i32;
 						isstrel = true;
 					} else {
 						let ps: i32 = primsize(elemn.str);
@@ -1244,8 +1244,8 @@ fn cgmlet(c: *cgen, n: *node) void = {
 			if (s0_is_str != s1_is_str) {
 				let sz0: i32 = 8;
 				let sz1: i32 = 8;
-				if (s0_is_str) { sz0 = 16; };
-				if (s1_is_str) { sz1 = 16; };
+				if (s0_is_str) { sz0 = primtypesize("str"): i32; };
+				if (s1_is_str) { sz1 = primtypesize("str"): i32; };
 				let off0: i32 = localadd(c, l0.str, sz0, t0);
 				let off1: i32 = localadd(c, l1.str, sz1, t1);
 				if (s0_is_str) {
@@ -1302,7 +1302,7 @@ fn paramfieldsize(t: *node) i32 = {
 	if (k == nkind.N_TCHAN)  { return 8; };
 	if (k == nkind.N_TNAME)  {
 		let nm: str = t.str;
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let ps: i32 = primsize(nm);
 		if (ps > 0) { return ps; };
 	};

selfhost/cmd/wcc/cgenutil.ww

@@ -1196,7 +1196,7 @@ fn indexbaseesz(c: *cgen, base: *node) i32 = {
 				let elem: *node = ft.lhs;
 				if (elem != nil) {
 					if (elem.kind == nkind.N_TNAME) {
-						if (streq(elem.str, "str")) { return 16; };
+						if (streq(elem.str, "str")) { return primtypesize("str"): i32; };
 						let ps: i32 = primsize(elem.str);
 						if (ps > 0) { return ps; };
 						// Pointer to named struct: indexing
@@ -1304,11 +1304,11 @@ fn elemsizeof(t: *node) i32 = {
 	// `*[]T`: stride is the slice header (24B). Hare-faithful — a
 	// pointer-to-slice is a 1D array of slices, not of T. Mirrors the
 	// cstage check.c default `*U → U` path for U=[]T (slice element).
-	if (elem.kind == nkind.N_TSLICE) { return 24; };
+	if (elem.kind == nkind.N_TSLICE) { return tyslicesize(): i32; };
 	if (elem.kind == nkind.N_TNAME) {
 		let nm: str = elem.str;
 		// str element is 16B (ptr+len). primsize returns 0 for it.
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let ps: i32 = primsize(nm);
 		if (ps > 0) { return ps; };
 	};
@@ -1903,7 +1903,7 @@ export fn letslotsize(c: *cgen, n: *node) i32 = {
 								// (ptr+len) — primsize returns 0 for
 								// it, so it'd slot 8B without this.
 								if (streq(elemn.str, "str")) {
-									esz = 16;
+									esz = primtypesize("str"): i32;
 								} else {
 									let ps: i32 = primsize(elemn.str);
 									if (ps > 0) { esz = ps; };
@@ -1952,7 +1952,7 @@ fn slotsize(c: *cgen, typn: *node) i32 = {
 	if (k == nkind.N_TPTR)   { return 8; };
 	if (k == nkind.N_TFN)    { return 8; };
 	if (k == nkind.N_TCHAN)  { return 8; };
-	if (k == nkind.N_TSLICE) { return 24; };
+	if (k == nkind.N_TSLICE) { return tyslicesize(): i32; };
 	if (k == nkind.N_TTUPLE) {
 		// Sum element sizes. Mirrors C cgen which uses raw type
 		// sizes; padding to 8 happens inside slotsize for primitives,
@@ -1992,7 +1992,7 @@ fn slotsize(c: *cgen, typn: *node) i32 = {
 		// slot+8 picking up the callee's stale-DX. Bypassing primsize's
 		// `> 0` guard keeps the rest of the prim-pad-to-8 contract intact.
 		if (streq(nm, "void")) { return 0; };
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let ps: i32 = primsize(nm);
 		if (ps > 0) {
 			// Pad to 8 for stack slots — matches C cgen which spills
@@ -2033,7 +2033,7 @@ fn slotsize(c: *cgen, typn: *node) i32 = {
 				// explicit case a `[N]str` would slot 8B/elem,
 				// collapsing the per-element stride and losing
 				// every .len half.
-				if (streq(en, "str")) { esz = 16; };
+				if (streq(en, "str")) { esz = primtypesize("str"): i32; };
 				let ps: i32 = primsize(en);
 				if (esz == 8) { if (ps > 0) { esz = ps; }
 				else {
@@ -2091,7 +2091,7 @@ fn fieldsize(c: *cgen, tnode: *node) i32 = {
 	if (k == nkind.N_TTAGGED){ return slotsize(c, tnode); };
 	if (k == nkind.N_TNAME) {
 		let nm: str = tnode.str;
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let ps: i32 = primsize(nm);
 		if (ps > 0) { return ps; };
 		let si: *structinfo = structlookup(c, nm);
@@ -2118,7 +2118,7 @@ fn fieldsize(c: *cgen, tnode: *node) i32 = {
 		return 8;
 	};
 	if (k == nkind.N_TPTR)   { return 8; };
-	if (k == nkind.N_TSLICE) { return 24; };
+	if (k == nkind.N_TSLICE) { return tyslicesize(): i32; };
 	if (k == nkind.N_TARRAY) {
 		// Same shape as slotsize's TARRAY branch.
 		let lenn: *node = tnode.rhs;

selfhost/cmd/wcc/check.ww

@@ -618,6 +618,29 @@ fn mktname(c: *checker, nm: str) *node = {
 	return n;
 };
 
+// #43: SSoT for primitive type byte sizes. astsize's N_TNAME-primitive
+// arm and every wwstage cgen size walker (slotsize/fieldsize/letemit-
+// size/elemsizeof/paramfieldsize) consult this table so a future
+// ty_str.size bump (#1) lands in one place. Returns -1 for non-prim
+// names; callers fall back to alias/struct/enum lookup. Cstage's
+// equivalent SSoT is cmd/wcc/type.c:46-79 (ty_void/ty_bool/.../ty_str).
+fn primtypesize(nm: str) i64 = {
+	if (streq(nm, "void")) { return 0i64; };
+	if (streq(nm, "bool")) { return 1i64; };
+	if (streq(nm, "i8") || streq(nm, "u8")) { return 1i64; };
+	if (streq(nm, "i16") || streq(nm, "u16")) { return 2i64; };
+	if (streq(nm, "i32") || streq(nm, "u32") || streq(nm, "f32") || streq(nm, "rune")) { return 4i64; };
+	if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64")) { return 8i64; };
+	if (streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr")) { return 8i64; };
+	if (streq(nm, "str")) { return 16i64; };
+	return -1i64;
+};
+
+// #43: SSoT for slice header size (ptr+len+cap = 24B today). Mirrors
+// cstage cmd/wcc/type.c:103 (ty_slice->size = 24). Bumping a slice's
+// header layout in #34 touches only this constant.
+fn tyslicesize() i64 = { return 24i64; };
+
 // #42: AST-level layout helpers for the size(T)/align(T)/offset(e.f)
 // fold. Mirror cstage resolve_type's size/align computation
 // (cmd/wcc/check.c:286-528) on AST nodes — wwstage check.ww never
@@ -679,7 +702,7 @@ fn astsize(c: *checker, t: *node) i64 = {
 	let k: nkind = t.kind;
 	if (k == nkind.N_TBANG) { return astsize(c, t.lhs); };
 	if (k == nkind.N_TPTR)   { return 8i64; };
-	if (k == nkind.N_TSLICE) { return 24i64; };
+	if (k == nkind.N_TSLICE) { return tyslicesize(); };
 	if (k == nkind.N_TCHAN)  { return 8i64; };
 	if (k == nkind.N_TFN)    { return 8i64; };
 	if (k == nkind.N_TARRAY) {
@@ -731,13 +754,8 @@ fn astsize(c: *checker, t: *node) i64 = {
 	};
 	if (k == nkind.N_TNAME) {
 		let nm: str = t.str;
-		if (streq(nm, "void")) { return 0i64; };
-		if (streq(nm, "bool")) { return 1i64; };
-		if (streq(nm, "i8") || streq(nm, "u8")) { return 1i64; };
-		if (streq(nm, "i16") || streq(nm, "u16")) { return 2i64; };
-		if (streq(nm, "i32") || streq(nm, "u32") || streq(nm, "f32") || streq(nm, "rune")) { return 4i64; };
-		if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64") || streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr")) { return 8i64; };
-		if (streq(nm, "str")) { return 16i64; };
+		let ps: i64 = primtypesize(nm);
+		if (ps >= 0i64) { return ps; };
 		let resolved: *node = resolvealias(c, t);
 		if (resolved != nil && resolved != t) {
 			return astsize(c, resolved);

selfhost/cmd/wwdump/main.combined.ww

@@ -1996,7 +1996,7 @@ export fn freeall(s: []str) void = {
 		i += 1;
 	};
 	if (s.cap > 0) {
-		os.free(s.ptr: *void, (s.cap: u64) * 16u64);
+		os.free(s.ptr: *void, (s.cap: u64) * size(str): u64);
 	};
 };
 
@@ -2599,7 +2599,7 @@ export fn remaining_tokens(s: *tokenizer) str = {
 fn appendstr(slice: *[]str, item: str) void = {
 	let newlen: i32 = slice.len + 1;
 	slice.len = newlen;
-	rtensure(slice: *void, 16u64);
+	rtensure(slice: *void, size(str): u64);
 	let dst: *str = &slice.ptr[newlen - 1];
 	dst.ptr = item.ptr;
 	dst.len = item.len;
@@ -7612,6 +7612,29 @@ fn mktname(c: *checker, nm: str) *node = {
 	return n;
 };
 
+// #43: SSoT for primitive type byte sizes. astsize's N_TNAME-primitive
+// arm and every wwstage cgen size walker (slotsize/fieldsize/letemit-
+// size/elemsizeof/paramfieldsize) consult this table so a future
+// ty_str.size bump (#1) lands in one place. Returns -1 for non-prim
+// names; callers fall back to alias/struct/enum lookup. Cstage's
+// equivalent SSoT is cmd/wcc/type.c:46-79 (ty_void/ty_bool/.../ty_str).
+fn primtypesize(nm: str) i64 = {
+	if (streq(nm, "void")) { return 0i64; };
+	if (streq(nm, "bool")) { return 1i64; };
+	if (streq(nm, "i8") || streq(nm, "u8")) { return 1i64; };
+	if (streq(nm, "i16") || streq(nm, "u16")) { return 2i64; };
+	if (streq(nm, "i32") || streq(nm, "u32") || streq(nm, "f32") || streq(nm, "rune")) { return 4i64; };
+	if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64")) { return 8i64; };
+	if (streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr")) { return 8i64; };
+	if (streq(nm, "str")) { return 16i64; };
+	return -1i64;
+};
+
+// #43: SSoT for slice header size (ptr+len+cap = 24B today). Mirrors
+// cstage cmd/wcc/type.c:103 (ty_slice->size = 24). Bumping a slice's
+// header layout in #34 touches only this constant.
+fn tyslicesize() i64 = { return 24i64; };
+
 // #42: AST-level layout helpers for the size(T)/align(T)/offset(e.f)
 // fold. Mirror cstage resolve_type's size/align computation
 // (cmd/wcc/check.c:286-528) on AST nodes — wwstage check.ww never
@@ -7673,7 +7696,7 @@ fn astsize(c: *checker, t: *node) i64 = {
 	let k: nkind = t.kind;
 	if (k == nkind.N_TBANG) { return astsize(c, t.lhs); };
 	if (k == nkind.N_TPTR)   { return 8i64; };
-	if (k == nkind.N_TSLICE) { return 24i64; };
+	if (k == nkind.N_TSLICE) { return tyslicesize(); };
 	if (k == nkind.N_TCHAN)  { return 8i64; };
 	if (k == nkind.N_TFN)    { return 8i64; };
 	if (k == nkind.N_TARRAY) {
@@ -7725,13 +7748,8 @@ fn astsize(c: *checker, t: *node) i64 = {
 	};
 	if (k == nkind.N_TNAME) {
 		let nm: str = t.str;
-		if (streq(nm, "void")) { return 0i64; };
-		if (streq(nm, "bool")) { return 1i64; };
-		if (streq(nm, "i8") || streq(nm, "u8")) { return 1i64; };
-		if (streq(nm, "i16") || streq(nm, "u16")) { return 2i64; };
-		if (streq(nm, "i32") || streq(nm, "u32") || streq(nm, "f32") || streq(nm, "rune")) { return 4i64; };
-		if (streq(nm, "i64") || streq(nm, "u64") || streq(nm, "f64") || streq(nm, "int") || streq(nm, "uint") || streq(nm, "uintptr")) { return 8i64; };
-		if (streq(nm, "str")) { return 16i64; };
+		let ps: i64 = primtypesize(nm);
+		if (ps >= 0i64) { return ps; };
 		let resolved: *node = resolvealias(c, t);
 		if (resolved != nil && resolved != t) {
 			return astsize(c, resolved);
@@ -9854,7 +9872,7 @@ fn indexbaseesz(c: *cgen, base: *node) i32 = {
 				let elem: *node = ft.lhs;
 				if (elem != nil) {
 					if (elem.kind == nkind.N_TNAME) {
-						if (streq(elem.str, "str")) { return 16; };
+						if (streq(elem.str, "str")) { return primtypesize("str"): i32; };
 						let ps: i32 = primsize(elem.str);
 						if (ps > 0) { return ps; };
 						// Pointer to named struct: indexing
@@ -9962,11 +9980,11 @@ fn elemsizeof(t: *node) i32 = {
 	// `*[]T`: stride is the slice header (24B). Hare-faithful — a
 	// pointer-to-slice is a 1D array of slices, not of T. Mirrors the
 	// cstage check.c default `*U → U` path for U=[]T (slice element).
-	if (elem.kind == nkind.N_TSLICE) { return 24; };
+	if (elem.kind == nkind.N_TSLICE) { return tyslicesize(): i32; };
 	if (elem.kind == nkind.N_TNAME) {
 		let nm: str = elem.str;
 		// str element is 16B (ptr+len). primsize returns 0 for it.
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let ps: i32 = primsize(nm);
 		if (ps > 0) { return ps; };
 	};
@@ -10561,7 +10579,7 @@ export fn letslotsize(c: *cgen, n: *node) i32 = {
 								// (ptr+len) — primsize returns 0 for
 								// it, so it'd slot 8B without this.
 								if (streq(elemn.str, "str")) {
-									esz = 16;
+									esz = primtypesize("str"): i32;
 								} else {
 									let ps: i32 = primsize(elemn.str);
 									if (ps > 0) { esz = ps; };
@@ -10610,7 +10628,7 @@ fn slotsize(c: *cgen, typn: *node) i32 = {
 	if (k == nkind.N_TPTR)   { return 8; };
 	if (k == nkind.N_TFN)    { return 8; };
 	if (k == nkind.N_TCHAN)  { return 8; };
-	if (k == nkind.N_TSLICE) { return 24; };
+	if (k == nkind.N_TSLICE) { return tyslicesize(): i32; };
 	if (k == nkind.N_TTUPLE) {
 		// Sum element sizes. Mirrors C cgen which uses raw type
 		// sizes; padding to 8 happens inside slotsize for primitives,
@@ -10650,7 +10668,7 @@ fn slotsize(c: *cgen, typn: *node) i32 = {
 		// slot+8 picking up the callee's stale-DX. Bypassing primsize's
 		// `> 0` guard keeps the rest of the prim-pad-to-8 contract intact.
 		if (streq(nm, "void")) { return 0; };
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let ps: i32 = primsize(nm);
 		if (ps > 0) {
 			// Pad to 8 for stack slots — matches C cgen which spills
@@ -10691,7 +10709,7 @@ fn slotsize(c: *cgen, typn: *node) i32 = {
 				// explicit case a `[N]str` would slot 8B/elem,
 				// collapsing the per-element stride and losing
 				// every .len half.
-				if (streq(en, "str")) { esz = 16; };
+				if (streq(en, "str")) { esz = primtypesize("str"): i32; };
 				let ps: i32 = primsize(en);
 				if (esz == 8) { if (ps > 0) { esz = ps; }
 				else {
@@ -10749,7 +10767,7 @@ fn fieldsize(c: *cgen, tnode: *node) i32 = {
 	if (k == nkind.N_TTAGGED){ return slotsize(c, tnode); };
 	if (k == nkind.N_TNAME) {
 		let nm: str = tnode.str;
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let ps: i32 = primsize(nm);
 		if (ps > 0) { return ps; };
 		let si: *structinfo = structlookup(c, nm);
@@ -10776,7 +10794,7 @@ fn fieldsize(c: *cgen, tnode: *node) i32 = {
 		return 8;
 	};
 	if (k == nkind.N_TPTR)   { return 8; };
-	if (k == nkind.N_TSLICE) { return 24; };
+	if (k == nkind.N_TSLICE) { return tyslicesize(): i32; };
 	if (k == nkind.N_TARRAY) {
 		// Same shape as slotsize's TARRAY branch.
 		let lenn: *node = tnode.rhs;
@@ -19139,7 +19157,7 @@ fn cglet(c: *cgen, n: *node) void = {
 			if (elemn != nil) {
 				if (elemn.kind == nkind.N_TNAME) {
 					if (streq(elemn.str, "str")) {
-						esz = 16;
+						esz = primtypesize("str"): i32;
 						isstrel = true;
 					} else {
 						let ps: i32 = primsize(elemn.str);
@@ -19624,8 +19642,8 @@ fn cgmlet(c: *cgen, n: *node) void = {
 			if (s0_is_str != s1_is_str) {
 				let sz0: i32 = 8;
 				let sz1: i32 = 8;
-				if (s0_is_str) { sz0 = 16; };
-				if (s1_is_str) { sz1 = 16; };
+				if (s0_is_str) { sz0 = primtypesize("str"): i32; };
+				if (s1_is_str) { sz1 = primtypesize("str"): i32; };
 				let off0: i32 = localadd(c, l0.str, sz0, t0);
 				let off1: i32 = localadd(c, l1.str, sz1, t1);
 				if (s0_is_str) {
@@ -19682,7 +19700,7 @@ fn paramfieldsize(t: *node) i32 = {
 	if (k == nkind.N_TCHAN)  { return 8; };
 	if (k == nkind.N_TNAME)  {
 		let nm: str = t.str;
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let ps: i32 = primsize(nm);
 		if (ps > 0) { return ps; };
 	};
@@ -20054,7 +20072,7 @@ fn cgfnparams(c: *cgen, params: *node) void = {
 			if (p.op == tkind.TK_ELLIPSIS) {
 				let tn: *node = slicewrap(c, p.lhs);
 				if (idx + 3 <= 6) {
-					let off: i32 = localadd(c, nm, 24, tn);
+					let off: i32 = localadd(c, nm, tyslicesize(): i32, tn);
 					emitline("\tMOVQ\t");
 					emitline(argregname(idx));
 					emitline(", ");
@@ -20078,7 +20096,7 @@ fn cgfnparams(c: *cgen, params: *node) void = {
 					// at the ABI boundary (the call site synthesises a
 					// 24B descriptor and pushes ptr/len/cap), so this
 					// mirrors the slice branch at cgendecl.ww:518.
-					let off: i32 = localadd(c, nm, 24, tn);
+					let off: i32 = localadd(c, nm, tyslicesize(): i32, tn);
 					let regs_left: i32 = 6 - idx;
 					let w: i32 = 0;
 					for (w < regs_left) {
@@ -20178,7 +20196,7 @@ fn cgfnparams(c: *cgen, params: *node) void = {
 				};};
 			} else { if (isslicetype(c, p.lhs)) {
 				if (idx + 3 <= 6) {
-					let off: i32 = localadd(c, nm, 24, p.lhs);
+					let off: i32 = localadd(c, nm, tyslicesize(): i32, p.lhs);
 					emitline("\tMOVQ\t");
 					emitline(argregname(idx));
 					emitline(", ");
@@ -20202,7 +20220,7 @@ fn cgfnparams(c: *cgen, params: *node) void = {
 					// 440-469. Caller's pushargsrev greedy-fills the
 					// remaining argregs (ptr,len,cap order), the tail
 					// spills to +16+stkcursor*8(BP).
-					let off: i32 = localadd(c, nm, 24, p.lhs);
+					let off: i32 = localadd(c, nm, tyslicesize(): i32, p.lhs);
 					let regs_left: i32 = 6 - idx;
 					let w: i32 = 0;
 					for (w < regs_left) {
@@ -21426,7 +21444,7 @@ fn letemitsize(c: *cgen, d: *node) i32 = {
 	let t: *node = d.lhs;
 	for (t != nil) {
 		if (t.kind == nkind.N_TPTR) { return 8; };
-		if (t.kind == nkind.N_TSLICE) { return 24; };
+		if (t.kind == nkind.N_TSLICE) { return tyslicesize(): i32; };
 		if (t.kind == nkind.N_TARRAY) {
 			let lenn: *node = t.rhs;
 			let elemn: *node = t.lhs;
@@ -21448,7 +21466,7 @@ fn letemitsize(c: *cgen, d: *node) i32 = {
 		if (letscalarprim(nm)) { return 8; };
 		let fsz: i32 = letfloatprim(nm);
 		if (fsz > 0) { return fsz; };
-		if (streq(nm, "str")) { return 16; };
+		if (streq(nm, "str")) { return primtypesize("str"): i32; };
 		let si: *structinfo = structlookup(c, nm);
 		if (si != nil) { return si.totsize; };
 		let next: *node = aliaslookup(c, nm);
@@ -21774,7 +21792,7 @@ fn emitletdataw(c: *cgen, file: *node) void = {
 						emitline("\"\n");
 					};
 				};
-				if (sz == 16 && !issg) {
+				if (sz == primtypesize("str"): i32 && !issg) {
 					let r: *node = d.rhs;
 					for (r != nil) {
 						if (r.kind != nkind.N_CAST) { break; };
@@ -21830,7 +21848,8 @@ fn emitletdataw(c: *cgen, file: *node) void = {
 							emitsymname(c, nm);
 							emitline("(SB),\"");
 							let i: i32 = 0;
-							for (i < 16) {
+							let szstr: i32 = primtypesize("str"): i32;
+							for (i < szstr) {
 								emitdatawbyte(0u8);
 								i += 1;
 							};
@@ -21838,7 +21857,7 @@ fn emitletdataw(c: *cgen, file: *node) void = {
 						};
 					};
 				};
-				if (sz == 24 && !issg) {
+				if (sz == tyslicesize(): i32 && !issg) {
 					// Slice: zero-init only (no slice-literal
 					// syntax to honour). Any rhs other than
 					// `nil` is skipped → undefined symbol at
@@ -21860,7 +21879,8 @@ fn emitletdataw(c: *cgen, file: *node) void = {
 						emitsymname(c, nm);
 						emitline("(SB),\"");
 						let i: i32 = 0;
-						for (i < 24) {
+						let szsl: i32 = tyslicesize(): i32;
+						for (i < szsl) {
 							emitdatawbyte(0u8);
 							i += 1;
 						};

selfhost/test/smoke.combined.ww

@@ -1887,7 +1887,7 @@ export fn freeall(s: []str) void = {
 		i += 1;
 	};
 	if (s.cap > 0) {
-		os.free(s.ptr: *void, (s.cap: u64) * 16u64);
+		os.free(s.ptr: *void, (s.cap: u64) * size(str): u64);
 	};
 };
 
@@ -2490,7 +2490,7 @@ export fn remaining_tokens(s: *tokenizer) str = {
 fn appendstr(slice: *[]str, item: str) void = {
 	let newlen: i32 = slice.len + 1;
 	slice.len = newlen;
-	rtensure(slice: *void, 16u64);
+	rtensure(slice: *void, size(str): u64);
 	let dst: *str = &slice.ptr[newlen - 1];
 	dst.ptr = item.ptr;
 	dst.len = item.len;