feat: tuple syntax cutover — Tuple(...) type + .(...) value

Replace the bare-paren tuple grammar with explicit, position-unambiguous
forms, mirroring how structs work:

  type     `(A, B)`        -> `Tuple(A, B)`          (named keeps `:`)
  value    `(a, b)`        -> `.(a, b)`              (named uses `=`)
  typed    (new)           -> `Tuple(A, B).(a, b)`   (like `Point.{...}`)
  failable `-> (T, !)`     -> `-> T !`
           `-> (T1, T2, !)`-> `-> Tuple(T1, T2) !`   (channel outside Tuple)

Bare `(...)` is now grouping only, everywhere; a comma in bare parens is a
hard error with a migration hint. Grouping, function types `(A, B) -> R`,
param lists, lambdas, and match bindings are unaffected.

`Tuple(...)` is strictly a TYPE in every position (including `size_of` /
`type_info` args); a tuple VALUE comes only from `.(...)` (anonymous) or
`Tuple(...).(...)` (explicitly typed). A bare `Tuple(1, 2)` is a tuple
type with non-type elements -> rejected.

The ~110 tuple-bearing corpus files were migrated with a one-shot
AST-aware migrator (the `sx migrate` tool from the prior commit, removed
here). New examples: 0130 (new syntax), 0131 (typed construction), 1060
(named-tuple failable return). 1116 golden updated for the new hint text.

examples/basic/0036-basic-ufcs-aliases.sx

@@ -28,14 +28,14 @@ main :: () {
         print("{}\n", 1 |> calc(2, 3, 4));     // same = 3 — pipe UFCS
 
         // Tuple return type
-        swap :: (a: i64, b: i64) -> (i64, i64) { (b, a) }
+        swap :: (a: i64, b: i64) -> Tuple(i64, i64) { .(b, a) }
         s := swap(1, 2);
         a := s.0;
         b := s.1;
         print("{}\n", a);                // 2
         print("{}\n", b);                // 1
 
-        wrap :: (x: i64) -> (i64,) { (x,) }   // 1-tuple needs trailing comma; (i64) groups
+        wrap :: (x: i64) -> Tuple(i64) { .(x) }   // 1-tuple needs trailing comma; (i64) groups
         t := wrap(99);
         print("{}\n", t.0);             // 99
     }

examples/basic/0038-basic-dead-code-after-terminator.sx

@@ -17,7 +17,7 @@ E :: error { Neg }
 const_one :: () -> i64 { return 1; return 99; }
 
 // dead `return x;` after an unconditional raise (the failable closure shape)
-always_raise :: (x: i64) -> (i64, !E) { raise error.Neg; return x; }
+always_raise :: (x: i64) -> i64 !E { raise error.Neg; return x; }
 
 // guard: a conditional return must still fall through to the trailing return
 clamp :: (x: i64) -> i64 { if x > 10 { return 10; } return x; }

examples/basic/0042-basic-block-value-destructure.sx

@@ -8,7 +8,7 @@
 
 #import "modules/std.sx";
 
-pair :: () -> (i32, i32) { (5, 7) }
+pair :: () -> Tuple(i32, i32) { .(5, 7) }
 
 main :: () -> i32 {
     // destructure decl inside a value-bound block

examples/comptime/0623-comptime-metatype-tuple.sx

@@ -11,7 +11,7 @@
 
 Pair :: define(declare("Pair"), .tuple(.{ elements = .[ i64, f64 ] }));
 
-TripleCopy :: define(declare("TripleCopy"), type_info((i64, bool, f64)));
+TripleCopy :: define(declare("TripleCopy"), type_info(Tuple(i64, bool, f64)));
 
 main :: () -> i32 {
     p : Pair = .{ 3, 2.5 };

examples/diagnostics/1101-diagnostics-err-tuple-oob.sx

@@ -2,6 +2,6 @@
 // `error: field 'N' not found on type '(i64, i64)'` diagnostic and exit 1.
 
 main :: () -> i32 {
-    t := (10, 20);
+    t := .(10, 20);
     return xx t.42;
 }

examples/diagnostics/1116-diagnostics-tuple-type-nontype-element-rejected.sx

@@ -8,6 +8,6 @@
 #import "modules/std.sx";
 
 main :: () -> i32 {
-    print("bad tuple type size = {}\n", size_of((i32, 1)));
+    print("bad tuple type size = {}\n", size_of(Tuple(i32, 1)));
     0
 }

examples/diagnostics/1121-diagnostics-reserved-name-control-flow.sx

@@ -11,7 +11,7 @@
 // offending name; exit 1 — NOT an LLVM verifier abort.
 #import "modules/std.sx";
 
-pair :: () -> (i64, i64) { (1, 2) }
+pair :: () -> Tuple(i64, i64) { .(1, 2) }
 maybe :: () -> ?i64 { return null; }
 
 main :: () -> i32 {

examples/diagnostics/1124-diagnostics-imported-reserved-destructure/mod.sx

@@ -1,6 +1,6 @@
 #import "modules/std.sx";
 
-pair :: () -> (i64, i64) { (1, 2) }
+pair :: () -> Tuple(i64, i64) { .(1, 2) }
 
 run :: () -> i32 {
     i2, rest := pair();   // destructure name in an IMPORTED module

examples/diagnostics/1157-diagnostics-catch-binding-needs-parens.sx

@@ -6,7 +6,7 @@
 
 E :: error { Bad };
 
-f :: () -> (i64, !E) { raise error.Bad; }
+f :: () -> i64 !E { raise error.Bad; }
 
 main :: () {
     v := f() catch e { 0 };

examples/diagnostics/1202-diagnostics-null-coalesce-tuple-default.sx

@@ -8,7 +8,7 @@
 #import "modules/std.sx";
 
 main :: () {
-    o : ?(i32,) = null;
+    o : ?Tuple(i32) = null;
     x := o ?? 5; // default 'i64' vs payload '(i32,)' -> diagnostic
     print("{}\n", x.0);
 }

examples/diagnostics/expected/1116-diagnostics-tuple-type-nontype-element-rejected.stderr

@@ -1,5 +1,5 @@
-error: tuple type element is not a type (found `int_literal`); a tuple used as a type must list only types, e.g. `(i32, i32)`
+error: tuple type element is not a type (found `int_literal`); a tuple used as a type must list only types, e.g. `Tuple(i32, i32)`
-  --> examples/diagnostics/1116-diagnostics-tuple-type-nontype-element-rejected.sx:11:55
+  --> examples/diagnostics/1116-diagnostics-tuple-type-nontype-element-rejected.sx:11:60
    |
-11 |     print("bad tuple type size = {}\n", size_of((i32, 1)));
+11 |     print("bad tuple type size = {}\n", size_of(Tuple(i32, 1)));
-   |                                                       ^
+   |                                                            ^

examples/errors/1011-errors-value-failable.sx

@@ -10,7 +10,7 @@
 
 E :: error { Bad, Empty }
 
-parse :: (n: i32) -> (i32, !E) {
+parse :: (n: i32) -> i32 !E {
     if n < 0  { raise error.Bad; }
     if n == 0 { raise error.Empty; }
     return n * 10;                       // success → {n*10, 0}

examples/errors/1012-errors-value-failable-consume.sx

@@ -10,14 +10,14 @@
 
 E :: error { Bad, Empty }
 
-parse :: (n: i32) -> (i32, !E) {
+parse :: (n: i32) -> i32 !E {
     if n < 0  { raise error.Bad; }
     if n == 0 { raise error.Empty; }
     return n * 2;
 }
 
 // value-carrying `try` in a value-carrying caller — propagates {undef, tag}.
-inc :: (n: i32) -> (i32, !E) {
+inc :: (n: i32) -> i32 !E {
     v := try parse(n);
     return v + 1;
 }

examples/errors/1013-errors-value-failable-reject.sx

@@ -8,7 +8,7 @@
 
 E :: error { Bad }
 
-parse :: (n: i32) -> (i32, !E) {
+parse :: (n: i32) -> i32 !E {
     if n < 0 { raise error.Bad; }
     return n;
 }

examples/errors/1014-errors-failable-or.sx

@@ -9,7 +9,7 @@
 
 E :: error { Bad, Empty }
 
-parse :: (n: i32) -> (i32, !E) {
+parse :: (n: i32) -> i32 !E {
     if n < 0  { raise error.Bad; }
     if n == 0 { raise error.Empty; }
     return n * 2;

examples/errors/1018-errors-multi-value-failable.sx

@@ -12,37 +12,37 @@
 
 E :: error { Bad, Empty }
 
-parse :: (n: i32) -> (i32, i32, !E) {
+parse :: (n: i32) -> Tuple(i32, i32) !E {
     if n < 0  { raise error.Bad; }
     if n == 0 { raise error.Empty; }
-    return (n * 2, n + 1);            // success → {n*2, n+1, 0}
+    return .(n * 2, n + 1);            // success → {n*2, n+1, 0}
 }
 
 // Multi-value `try` in a multi-value caller — propagates {undef, undef, tag}.
-inc :: (n: i32) -> (i32, i32, !E) {
+inc :: (n: i32) -> Tuple(i32, i32) !E {
     v, b := try parse(n);
-    return (v + 1, b + 1);
+    return .(v + 1, b + 1);
 }
 
 // Multi-value `catch`, bare-expression tuple fallback (absorbs the failure).
 safe :: (n: i32) -> i32 {
-    v, b := parse(n) catch (e) (40, 50);
+    v, b := parse(n) catch (e) .(40, 50);
     return v + b;
 }
 
 // Multi-value `catch` match-body — per-tag dispatch, each arm a value-tuple.
 classify :: (n: i32) -> i32 {
     v, b := parse(n) catch (e) == {
-        case .Bad:   (1, 1);
+        case .Bad:   .(1, 1);
-        case .Empty: (2, 2);
+        case .Empty: .(2, 2);
-        else:        (9, 9);
+        else:        .(9, 9);
     };
     return v + b;
 }
 
 // Multi-value `or (tuple)` value-terminator (absorbs the failure).
 ortest :: (n: i32) -> i32 {
-    v, b := parse(n) or (7, 8);
+    v, b := parse(n) or .(7, 8);
     return v + b;
 }
 

examples/errors/1019-errors-failable-discard-reject.sx

@@ -13,12 +13,12 @@
 
 E :: error { Bad, Empty }
 
-pair :: (n: i32) -> (i32, i32, !E) {
+pair :: (n: i32) -> Tuple(i32, i32) !E {
     if n < 0 { raise error.Bad; }
-    return (n, n + 1);
+    return .(n, n + 1);
 }
 
-parse :: (n: i32) -> (i32, !E) {
+parse :: (n: i32) -> i32 !E {
     if n < 0 { raise error.Bad; }
     return n * 2;
 }

examples/errors/1023-errors-tag-interpolation.sx

@@ -8,7 +8,7 @@
 
 E :: error { BadDigit, Empty, Overflow }
 
-parse :: (n: i32) -> (i32, !E) {
+parse :: (n: i32) -> i32 !E {
     if n < 0  { raise error.BadDigit; }
     if n == 0 { raise error.Empty; }
     return n * 2;

examples/errors/1026-errors-failable-main.sx

@@ -14,7 +14,7 @@
 
 ParseErr :: error { Empty, BadDigit };
 
-inner :: (n: i32) -> (i32, !ParseErr) {
+inner :: (n: i32) -> i32 !ParseErr {
     if n == 0 { raise error.Empty; }       // pushes a frame
     if n < 0 { raise error.BadDigit; }
     return n * 2;

examples/errors/1027-errors-failable-main-value.sx

@@ -9,13 +9,13 @@
 
 ParseErr :: error { Empty, BadDigit };
 
-inner :: (n: i32) -> (i32, !ParseErr) {
+inner :: (n: i32) -> i32 !ParseErr {
     if n == 0 { raise error.Empty; }
     if n < 0 { raise error.BadDigit; }
     return n * 2;
 }
 
-main :: () -> (i32, !ParseErr) {
+main :: () -> i32 !ParseErr {
     v := try inner(32);                      // succeeds → v = 64
     print("v = {}\n", v);
     return v;                                // success → exit code 64

examples/errors/1028-errors-failable-or-chain.sx

@@ -12,7 +12,7 @@
 
 E :: error { A, B };
 
-fa :: (n: i32) -> (i32, !E) {
+fa :: (n: i32) -> i32 !E {
     if n == 0 { raise error.A; }
     if n < 0  { raise error.B; }
     return n;
@@ -23,7 +23,7 @@ fv :: (n: i32) -> !E {                       // void (pure) failable
     return;
 }
 
-main :: () -> (i32, !E) {
+main :: () -> i32 !E {
     onfail print("onfail fired (BUG)\n");    // must NOT fire — every chain below absorbs
 
     r : i32 = 0;

examples/errors/1029-errors-failable-or-chain-propagate.sx

@@ -10,12 +10,12 @@
 
 E :: error { A };
 
-fa :: (n: i32) -> (i32, !E) {
+fa :: (n: i32) -> i32 !E {
     if n == 0 { raise error.A; }
     return n;
 }
 
-main :: () -> (i32, !E) {
+main :: () -> i32 !E {
     v := try fa(0) or try fa(0) or try fa(0);   // all fail → propagate to main
     return v;
 }

examples/errors/1036-errors-failable-smoke.sx

@@ -9,7 +9,7 @@
 SmokeErr :: error { Empty, BadDigit, Overflow }
 
 // value-carrying, named set
-sm_parse :: (n: i32) -> (i32, !SmokeErr) {
+sm_parse :: (n: i32) -> i32 !SmokeErr {
     if n < 0  { raise error.BadDigit; }
     if n == 0 { raise error.Empty; }
     if n > 99 { raise error.Overflow; }
@@ -23,10 +23,10 @@ sm_check :: (ok: bool) -> ! {
 }
 
 // multi-value, inferred set: `try` propagates; SCC absorbs SmokeErr
-sm_pair :: (a: i32, b: i32) -> (i32, i32, !) {
+sm_pair :: (a: i32, b: i32) -> Tuple(i32, i32) ! {
     x := try sm_parse(a);
     y := try sm_parse(b);
-    return (x, y);
+    return .(x, y);
 }
 
 // catch with a diverging block body
@@ -38,7 +38,7 @@ sm_or_default :: (n: i32) -> i32 {
 }
 
 // onfail + defer interleave: cleanup runs only on the error path
-sm_acquire :: (fail: bool) -> (i32, !) {
+sm_acquire :: (fail: bool) -> i32 ! {
     defer  print("  defer A\n");
     onfail print("  onfail B\n");
     if fail { raise error.Acquire; }
@@ -46,7 +46,7 @@ sm_acquire :: (fail: bool) -> (i32, !) {
 }
 
 // or-chain: try a, fall to try b; propagate if both fail
-sm_first :: (a: i32, b: i32) -> (i32, !) {
+sm_first :: (a: i32, b: i32) -> i32 ! {
     v := try sm_parse(a) or try sm_parse(b);
     return v;
 }
@@ -54,18 +54,18 @@ sm_first :: (a: i32, b: i32) -> (i32, !) {
 // --- Composition (ERR E5.1): failable closures, widening, generics ---
 
 // Closure(...) param, try-propagated (the env is carried)
-sm_run :: (cb: Closure(i32) -> (i32, !SmokeErr), n: i32) -> (i32, !SmokeErr) {
+sm_run :: (cb: Closure(i32) -> i32 !SmokeErr, n: i32) -> i32 !SmokeErr {
     return try cb(n);
 }
 
 // bare fn-type param: a NON-failable closure literal widens into the failable
 // slot (the ∅-widening adapter wraps `{value, 0}`)
-sm_widen :: (cb: (i32) -> (i32, !SmokeErr), n: i32) -> i32 {
+sm_widen :: (cb: (i32) -> i32 !SmokeErr, n: i32) -> i32 {
     return cb(n) catch (e) -1;
 }
 
 // generic ($T) value-carrying failable composition, monomorphized per call
-sm_wrap :: ($T: Type, f: Closure() -> (T, !SmokeErr)) -> (T, !SmokeErr) {
+sm_wrap :: ($T: Type, f: Closure() -> T !SmokeErr) -> T !SmokeErr {
     return try f();
 }
 
@@ -105,9 +105,9 @@ main :: () {
     if !gerr { print("or-chain: {}\n", g); }
 
     // multi-value failable consumed by catch (tuple body)
-    p, q := sm_pair(0, 3) catch (e) (0, 0);
+    p, q := sm_pair(0, 3) catch (e) .(0, 0);
     print("pair-catch: {} {}\n", p, q);
-    p2, q2 := sm_pair(4, 5) catch (e) (0, 0);
+    p2, q2 := sm_pair(4, 5) catch (e) .(0, 0);
     print("pair-ok: {} {}\n", p2, q2);
 
     // pure failable: absorb with no-binding catch
@@ -120,15 +120,15 @@ main :: () {
     iv, ierr := sm_acquire(false);
 
     // composition: inline failable closure literal through a Closure(...) param
-    cl := sm_run(closure((x: i32) -> (i32, !SmokeErr) { if x < 0 { raise error.BadDigit; } return x * 2; }), 6) catch (e) -1;
+    cl := sm_run(closure((x: i32) -> i32 !SmokeErr { if x < 0 { raise error.BadDigit; } return x * 2; }), 6) catch (e) -1;
     print("closure-run: {}\n", cl);                                                     // 12
-    print("closure-run-err: {}\n", sm_run(closure((x: i32) -> (i32, !SmokeErr) { raise error.Empty; }), 1) catch (e) -9); // -9
+    print("closure-run-err: {}\n", sm_run(closure((x: i32) -> i32 !SmokeErr { raise error.Empty; }), 1) catch (e) -9); // -9
 
     // non-failable closure literal widened into the failable bare slot
     print("widen: {}\n", sm_widen(closure((x: i32) -> i32 => x + 1), 9));               // 10
 
     // generic failable composition (monomorphized at i32)
-    print("wrap: {}\n", sm_wrap(i32, closure(() -> (i32, !SmokeErr) { return 42; })) catch (e) 0); // 42
+    print("wrap: {}\n", sm_wrap(i32, closure(() -> i32 !SmokeErr { return 42; })) catch (e) 0); // 42
 
     print("errors ok\n");
 }

examples/errors/1037-errors-comptime-run-escape.sx

@@ -7,7 +7,7 @@
 
 E :: error { Bad, Empty }
 
-parse :: (n: i32) -> (i32, !E) {
+parse :: (n: i32) -> i32 !E {
     if n < 0  { raise error.Bad; }
     if n == 0 { raise error.Empty; }
     return n * 2;

examples/errors/1038-errors-comptime-run-handled.sx

@@ -7,7 +7,7 @@
 
 E :: error { Bad, Empty }
 
-parse :: (n: i32) -> (i32, !E) {
+parse :: (n: i32) -> i32 !E {
     if n < 0  { raise error.Bad; }
     if n == 0 { raise error.Empty; }
     return n * 2;

examples/errors/1039-errors-failable-closure-literal.sx

@@ -10,12 +10,12 @@
 
 E :: error { Neg }
 
-runwith :: (cb: Closure(i64) -> (i64, !E), n: i64) -> i64 { return cb(n) catch (e) -1; }
+runwith :: (cb: Closure(i64) -> i64 !E, n: i64) -> i64 { return cb(n) catch (e) -1; }
 
 main :: () -> i32 {
     // block-body and arrow-body failable closures, called directly
-    m := closure((x: i64) -> (i64, !E) { if x < 0 { raise error.Neg; } return x * 2; });
+    m := closure((x: i64) -> i64 !E { if x < 0 { raise error.Neg; } return x * 2; });
-    n := closure((x: i64) -> (i64, !E) => x + 1);
+    n := closure((x: i64) -> i64 !E => x + 1);
     print("{} {} {} {}\n", m(5) catch (e) 0, m(-1) catch (e) 99, m(-1) or 7, n(40) catch (e) 0); // 10 99 7 41
 
     // failable closure passed as a Closure(...) parameter

examples/errors/1040-errors-failable-closure-composition.sx

@@ -12,21 +12,21 @@
 
 E :: error { Neg }
 
-bare  :: (cb: (i64) -> (i64, !E), n: i64) -> i64 { return cb(n) catch (e) -1; }
+bare  :: (cb: (i64) -> i64 !E, n: i64) -> i64 { return cb(n) catch (e) -1; }
-chain :: (cb: Closure(i64) -> (i64, !E), n: i64) -> (i64, !E) { return try cb(n); }
+chain :: (cb: Closure(i64) -> i64 !E, n: i64) -> i64 !E { return try cb(n); }
 
-dbl :: (x: i64) -> (i64, !E) { if x < 0 { raise error.Neg; } return x * 2; }
+dbl :: (x: i64) -> i64 !E { if x < 0 { raise error.Neg; } return x * 2; }
 
 main :: () -> i32 {
     // failable closure literal through a bare fn-type param (matching ABI)
     print("bare ok={} err={}\n",
-        bare(closure((x: i64) -> (i64, !E) { if x < 0 { raise error.Neg; } return x * 2; }), 5),
+        bare(closure((x: i64) -> i64 !E { if x < 0 { raise error.Neg; } return x * 2; }), 5),
-        bare(closure((x: i64) -> (i64, !E) => x * 2), -1));                 // ok=10; err: arrow never raises → cb(-1) = -2
+        bare(closure((x: i64) -> i64 !E => x * 2), -1));                 // ok=10; err: arrow never raises → cb(-1) = -2
 
     // Closure(...) param, try-propagated, then caught at the call site
     print("chain ok={} err={}\n",
-        chain(closure((x: i64) -> (i64, !E) => x + 6), 4) catch (e) 0,        // 10
+        chain(closure((x: i64) -> i64 !E => x + 6), 4) catch (e) 0,        // 10
-        chain(closure((x: i64) -> (i64, !E) { raise error.Neg; }), 1) catch (e) 0); // 0
+        chain(closure((x: i64) -> i64 !E { raise error.Neg; }), 1) catch (e) 0); // 0
 
     // NON-failable closure literal widened into the failable bare slot
     print("widen={}\n", bare(closure((x: i64) -> i64 => x + 1), 9));        // 10

examples/errors/1041-errors-failable-closure-shape-union.sx

@@ -10,7 +10,7 @@
 All :: error { Negative, Other }
 
 // `h` is a bare-`!` Closure slot; the caller declares the union as `!All`.
-dispatch :: (h: Closure(i32) -> (i32, !), x: i32) -> (i32, !All) {
+dispatch :: (h: Closure(i32) -> i32 !, x: i32) -> i32 !All {
     return try h(x);
 }
 
@@ -19,9 +19,9 @@ main :: () -> i32 {
     push Context.{ allocator = xx gpa } {
         // Two literals of the SAME shape raising DIFFERENT tags both feed the
         // one shared `Closure(i32)->(i32,!)` union node.
-        handlers : List(Closure(i32) -> (i32, !)) = .{};
+        handlers : List(Closure(i32) -> i32 !) = .{};
-        handlers.append(closure((x: i32) -> (i32, !) { if x < 0 { raise error.Negative; } return x * 2; }));
+        handlers.append(closure((x: i32) -> i32 ! { if x < 0 { raise error.Negative; } return x * 2; }));
-        handlers.append(closure((x: i32) -> (i32, !) { if x == 0 { raise error.Other; } return x + 100; }));
+        handlers.append(closure((x: i32) -> i32 ! { if x == 0 { raise error.Other; } return x + 100; }));
 
         // success paths
         print("ok0={}\n", dispatch(handlers.items[0], 5) catch (e) 0);   // 10

examples/errors/1042-errors-failable-closure-shape-union-reject.sx

@@ -9,16 +9,16 @@
 
 Small :: error { Unrelated }
 
-reject :: (h: Closure(i32) -> (i32, !), x: i32) -> (i32, !Small) {
+reject :: (h: Closure(i32) -> i32 !, x: i32) -> i32 !Small {
     return try h(x);   // Negative, Other ∉ Small → two diagnostics
 }
 
 main :: () -> i32 {
     gpa := GPA.init();
     push Context.{ allocator = xx gpa } {
-        handlers : List(Closure(i32) -> (i32, !)) = .{};
+        handlers : List(Closure(i32) -> i32 !) = .{};
-        handlers.append(closure((x: i32) -> (i32, !) { if x < 0 { raise error.Negative; } return x; }));
+        handlers.append(closure((x: i32) -> i32 ! { if x < 0 { raise error.Negative; } return x; }));
-        handlers.append(closure((x: i32) -> (i32, !) { if x == 0 { raise error.Other; } return x; }));
+        handlers.append(closure((x: i32) -> i32 ! { if x == 0 { raise error.Other; } return x; }));
         print("r={}\n", reject(handlers.items[0], 5) catch (e) 0);
     }
     return 0;

examples/errors/1043-errors-lambda-raise-annotation-hint.sx

@@ -9,7 +9,7 @@
 
 E :: error { Neg }
 
-take :: (cb: Closure(i32) -> (i32, !E), x: i32) -> i32 { return cb(x) catch (e) -1; }
+take :: (cb: Closure(i32) -> i32 !E, x: i32) -> i32 { return cb(x) catch (e) -1; }
 
 main :: () -> i32 {
     // `-> i32` (non-failable) but the body raises → lambda-specific hint:

examples/errors/1044-errors-generic-failable-composition.sx

@@ -9,21 +9,21 @@
 
 E :: error { Bad }
 
-wrap :: ($T: Type, f: Closure() -> (T, !E)) -> (T, !E) { return try f(); }
+wrap :: ($T: Type, f: Closure() -> T !E) -> T !E { return try f(); }
 
 main :: () -> i32 {
     // success, consumed by catch
-    print("catch={}\n", wrap(i32, closure(() -> (i32, !E) { return 7; })) catch (e) -1);   // 7
+    print("catch={}\n", wrap(i32, closure(() -> i32 !E { return 7; })) catch (e) -1);   // 7
 
     // success, consumed by destructure (binds value + error slot); the value
     // slot is read only under an `if !err` guard (ERR E1.8 path-sensitivity)
-    r, err := wrap(i32, closure(() -> (i32, !E) { return 9; }));
+    r, err := wrap(i32, closure(() -> i32 !E { return 9; }));
     if !err { print("destr={} ok=true\n", r); }                                           // destr=9 ok=true
 
     // failure path: the raised tag propagates through the generic `try`
-    print("fail={}\n", wrap(i32, closure(() -> (i32, !E) { raise error.Bad; }) ) catch (e) -1); // -1
+    print("fail={}\n", wrap(i32, closure(() -> i32 !E { raise error.Bad; }) ) catch (e) -1); // -1
 
     // a second monomorphization at a different T
-    print("u8={}\n", wrap(u8, closure(() -> (u8, !E) { return 200; })) catch (e) 0);         // 200
+    print("u8={}\n", wrap(u8, closure(() -> u8 !E { return 200; })) catch (e) 0);         // 200
     return 0;
 }

examples/errors/1045-errors-closure-var-bare-slot-reject.sx

@@ -13,7 +13,7 @@
 E :: error { Z }
 
 bare  :: (cb: (i64) -> i64, n: i64) -> i64 { return cb(n); }
-baref :: (cb: (i64) -> (i64, !E), n: i64) -> i64 { return cb(n) catch (e) -1; }
+baref :: (cb: (i64) -> i64 !E, n: i64) -> i64 { return cb(n) catch (e) -1; }
 
 main :: () -> i32 {
     inc := closure((x: i64) -> i64 => x + 1);          // capture-free closure var

examples/errors/1046-errors-value-slot-liveness.sx

@@ -15,7 +15,7 @@
 
 E :: error { Bad, Empty }
 
-parse :: (n: i32) -> (i32, !E) {
+parse :: (n: i32) -> i32 !E {
     if n < 0  { raise error.Bad; }
     if n == 0 { raise error.Empty; }
     return n * 10;
@@ -29,7 +29,7 @@ guarded :: (n: i32) -> i32 {
 }
 
 // `if err { raise }` in a failable function: same fall-through proof.
-relay :: (n: i32) -> (i32, !E) {
+relay :: (n: i32) -> i32 !E {
     v, err := parse(n);
     if err { raise err; }
     return v + 1;                          // err proven absent here

examples/errors/1047-errors-value-slot-liveness-reject.sx

@@ -11,7 +11,7 @@
 
 E :: error { Bad }
 
-parse :: (n: i32) -> (i32, !E) {
+parse :: (n: i32) -> i32 !E {
     if n < 0 { raise error.Bad; }
     return n * 10;
 }

examples/errors/1048-errors-cleanup-absorption.sx

@@ -9,7 +9,7 @@
 E :: error { Bad }
 
 failing :: () -> !E { raise error.Bad; }
-recover :: () -> (i32, !E) { raise error.Bad; }
+recover :: () -> i32 !E { raise error.Bad; }
 
 work :: (n: i32) -> !E {
     defer  print("defer: always\n");                                 // plain cleanup

examples/errors/1050-errors-defer-block-body.sx

@@ -9,7 +9,7 @@
 
 E :: error { Bad }
 
-probe   :: () -> (i32, !E) { return 21; }
+probe   :: () -> i32 !E { return 21; }
 failing :: () -> !E { raise error.Bad; }
 
 run :: () {

examples/errors/1051-errors-cleanup-closure-boundary.sx

@@ -24,7 +24,7 @@
 E :: error { Bad }
 
 failing :: () -> !E { raise error.Bad; }
-recover :: () -> (i32, !E) { return 21; }
+recover :: () -> i32 !E { return 21; }
 
 work :: () {
     defer {

examples/errors/1053-errors-nested-lambda-liveness-reject.sx

@@ -12,7 +12,7 @@
 
 E :: error { Bad }
 
-parse :: (n: i32) -> (i32, !E) {
+parse :: (n: i32) -> i32 !E {
     if n < 0 { raise error.Bad; }
     return n * 10;
 }

examples/errors/1054-errors-backtick-reserved-binding.sx

@@ -8,7 +8,7 @@
 
 E :: error { Bad, Empty }
 
-parse :: (n: i32) -> (i32, !E) {
+parse :: (n: i32) -> i32 !E {
     if n < 0  { raise error.Bad; }
     if n == 0 { raise error.Empty; }
     return n * 2;

examples/errors/1055-errors-enum-value-failable-error-slot.sx

@@ -16,7 +16,7 @@
 Color :: enum { red; green; blue; }
 E :: error { Nope }
 
-pick :: (s: string) -> (Color, !E) {
+pick :: (s: string) -> Color !E {
     if s == "red"  { return .red; }
     if s == "blue" { return .blue; }       // non-zero ordinal (2)
     raise error.Nope;

examples/errors/1056-errors-enum-value-failable-tuple-and-comptime.sx

@@ -22,13 +22,13 @@ Color :: enum { red; green; blue; }
 E :: error { Nope }
 
 // F1: bare-value success path AND explicit-tuple error path in one function.
-classify :: (s: string) -> (Color, !E) {
+classify :: (s: string) -> Color !E {
     if s == "ok" { return .blue; }        // bare value → {2, 0}
-    return (.red, error.Nope);            // explicit full tuple → {0, 1}
+    return .(.red, error.Nope);            // explicit full tuple → {0, 1}
 }
 
 // F2: comptime parameter forces inline lowering of the body.
-ct_pick :: ($n: i32, s: string) -> (Color, !E) {
+ct_pick :: ($n: i32, s: string) -> Color !E {
     if s == "red"  { return .red; }       // bare value, inline path → {0, 0}
     if s == "blue" { return .blue; }      // bare value, inline path → {2, 0}
     raise error.Nope;                     // inline error path → {undef, 1}

examples/errors/1057-errors-negated-error-binding.sx

@@ -7,7 +7,7 @@
 
 E :: error { Boom }
 
-f :: (fail: bool) -> (i64, !E) {
+f :: (fail: bool) -> i64 !E {
     if fail { raise error.Boom; }
     return 42;
 }

examples/errors/1058-errors-reexport-value-failable-channel/lib.sx

@@ -5,4 +5,4 @@ LE  :: error { Bad }
 Box :: struct ($R: Type) { v: R; }
 
 // Returns `($R, !LE)` — a value-failable. `$R` is inferred from the arg.
-get :: ufcs (b: *Box($R)) -> ($R, !LE) { return b.v; }
+get :: ufcs (b: *Box($R)) -> $R !LE { return b.v; }

examples/errors/1060-errors-named-tuple-failable.sx

@@ -0,0 +1,26 @@
+// A failable function returning a NAMED tuple value `-> Tuple(x: A, y: B) !E`
+// flattens its value fields into the result tuple (`{ x: A, y: B, err }`),
+// keeping the `.x`/`.y` names addressable on both the success value and the
+// `or` fallback. Exercises the success path, a `raise` path, and an
+// `or .(x=.., y=..)` terminator.
+//
+// Regression (issue 0179-adjacent named-tuple-failable miscompile): a named
+// failable tuple used to WRAP as `{ {A,B}, err }` while the value-return
+// lowering inserted the value slots FLAT, producing invalid LLVM
+// (`Invalid InsertValueInst operands`).
+#import "modules/std.sx";
+
+E :: error { Bad }
+
+two :: (n: i64) -> Tuple(x: i64, y: i64) !E {
+    if n < 0 { raise error.Bad; }
+    return .(x = n, y = n + 1);
+}
+
+main :: () {
+    ok := two(5) or .(x = 0, y = 0);
+    print("{} {}\n", ok.x, ok.y);
+
+    bad := two(-1) or .(x = 0, y = 0);
+    print("{} {}\n", bad.x, bad.y);
+}

examples/errors/expected/1060-errors-named-tuple-failable.exit

@@ -0,0 +1 @@
+0

examples/errors/expected/1060-errors-named-tuple-failable.stderr

@@ -0,0 +1 @@
+

examples/errors/expected/1060-errors-named-tuple-failable.stdout

@@ -0,0 +1,2 @@
+5 6
+0 0

examples/packs/0533-packs-pack-tuple-materialize.sx

@@ -14,7 +14,7 @@ impl Box(i64) for IntCell { get :: (self: *IntCell) -> i64 => self.v; }
 impl Box(string) for StrCell { get :: (self: *StrCell) -> string => self.s; }
 
 snapshot :: (..xs: Box) -> void {
-    t := (..xs.get);                 // tuple (i64, string) materialized from the pack
+    t := .(..xs.get);                 // tuple (i64, string) materialized from the pack
     print("0={} 1={}\n", t.0, t.1);
 }
 

examples/packs/0534-packs-pack-type-projection.sx

@@ -20,7 +20,7 @@ impl Box(i64) for Dbl { get :: (self: *Dbl) -> i64 => self.n * 2; }
 // Tuple type `(..xs.T)` — heterogeneous (i64, string), matched by the
 // value-projection `(..xs.get)`.
 snap :: (..xs: Box) -> void {
-    t : (..xs.T) = (..xs.get);
+    t : Tuple(..xs.T) = .(..xs.get);
     print("0={} 1={}\n", t.0, t.1);
 }
 

examples/packs/0538-packs-generic-struct-pack-field.sx

@@ -7,19 +7,19 @@
 
 Box :: struct($R: Type, ..$Ts: []Type) {
     r:    $R;
-    pair: (..$Ts);   // tuple of the pack's element types
+    pair: Tuple(..$Ts);   // tuple of the pack's element types
 }
 
 main :: () -> i32 {
     // Box(i64, i32, string): R=i64, Ts=[i32, string], pair: (i32, string).
     a : Box(i64, i32, string) = ---;
     a.r = 7;
-    a.pair = (42, "hi");                 // whole-tuple field store
+    a.pair = .(42, "hi");                 // whole-tuple field store
     print("a: r={} 0={} 1={}\n", a.r, a.pair.0, a.pair.1);
 
     // A different shape → a different per-position tuple field.
     b : Box(bool, string, bool) = ---;   // Ts=[string, bool], pair: (string, bool)
-    b.pair = ("x", true);
+    b.pair = .("x", true);
     print("b: 0={} 1={}\n", b.pair.0, b.pair.1);
     0
 }

examples/packs/0539-packs-combined-pack-field.sx

@@ -14,7 +14,7 @@ impl VL(i64) for IntCell { get :: (self: *IntCell) -> i64 => self.v; }
 impl VL(string) for StrCell { get :: (self: *StrCell) -> string => self.s; }
 
 Combined :: struct($R: Type, ..$Ts: []Type) {
-    sources: (..VL(Ts));   // (VL(T0), VL(T1), …) — tuple of protocol values
+    sources: Tuple(..VL(Ts));   // (VL(T0), VL(T1), …) — tuple of protocol values
     value:   $R;
 }
 
@@ -22,7 +22,7 @@ main :: () -> i32 {
     // Combined(i64, i64, string): R=i64, Ts=[i64, string],
     // sources: (VL(i64), VL(string)).
     c : Combined(i64, i64, string) = ---;
-    c.sources = (xx IntCell.{ v = 10 }, xx StrCell.{ s = "hi" });
+    c.sources = .(xx IntCell.{ v = 10 }, xx StrCell.{ s = "hi" });
     c.value = 99;
     print("{} {} {}\n", c.sources.0.get(), c.sources.1.get(), c.value);  // 10 hi 99
     0

examples/packs/0540-packs-pack-type-arg-spread.sx

@@ -11,7 +11,7 @@ IntCell :: struct { v: i64; }
 impl VL(i64) for IntCell { get :: (self: *IntCell) -> i64 => self.v; }
 
 Combined :: struct($R: Type, ..$Ts: []Type) {
-    sources: (..VL(Ts));
+    sources: Tuple(..VL(Ts));
     value:   $R;
 }
 

examples/packs/0541-packs-pack-to-protocol-tuple.sx

@@ -12,13 +12,13 @@ impl VL(i64) for IntCell { get :: (self: *IntCell) -> i64 => self.v; }
 impl VL(string) for StrCell { get :: (self: *StrCell) -> string => self.s; }
 
 Combined :: struct($R: Type, ..$Ts: []Type) {
-    sources: (..VL(Ts));
+    sources: Tuple(..VL(Ts));
     value:   $R;
 }
 
 build :: (..sources: VL) -> void {
     c : Combined(i64, ..sources.T) = ---;
-    c.sources = (..sources);                          // pack → tuple, per-element erase
+    c.sources = .(..sources);                          // pack → tuple, per-element erase
     print("{} {}\n", c.sources.0.get(), c.sources.1.get());
 }
 

examples/packs/0543-packs-canonical-map.sx

@@ -17,14 +17,14 @@ IntCell :: struct { v: i64; }
 impl VL(i64) for IntCell { get :: (self: *IntCell) -> i64 => self.v; }
 
 Combined :: struct($R: Type, ..$Ts: []Type) {
-    sources: (..VL(Ts));
+    sources: Tuple(..VL(Ts));
     value:   $R;
 }
 impl VL($R) for Combined($R, ..$Ts) { get :: (self: *Combined) -> $R => self.value; }
 
 map :: (mapper: Closure(..sources.T) -> $R, ..sources: VL) -> VL($R) {
     c : Combined($R, ..sources.T) = ---;
-    c.sources = (..sources);
+    c.sources = .(..sources);
     c.value = mapper(..sources.get);
     return xx c;
 }

examples/platform/1640-platform-asm-parse.sx

@@ -5,7 +5,7 @@
 // `.build`: ir-only on a non-x86 host (the `.ir` snapshot locks the struct
 // return + `%[name]` rewrite); runs natively on x86_64-linux. See 1647 for a
 // multi-output example that executes on aarch64.
-divmod :: (n: u64, d: u64) -> (quot: u64, rem: u64) {
+divmod :: (n: u64, d: u64) -> Tuple(quot: u64, rem: u64) {
     return asm {
         "divq %[d]",
         [quot] "={rax}" -> u64,

examples/platform/1647-platform-asm-aarch64-multi.sx

@@ -3,7 +3,7 @@
 // a `(lo, hi)` tuple. The two outputs become an LLVM `{ i64, i64 }` struct =
 // sx's tuple. aarch64-pinned via `.build`: executes on a matching host (exit
 // reflects lo+hi), ir-only elsewhere.
-split :: (x: u64) -> (lo: u64, hi: u64) {
+split :: (x: u64) -> Tuple(lo: u64, hi: u64) {
     return asm {
         #string ASM
         and %[l], %[x], #0xff

examples/probes/pack-expansion-parses.sx

@@ -7,13 +7,13 @@
 // checks are the parser unit tests in src/parser.zig ("parse pack expansion: …").
 
 // 1. Tuple value position — `(..pack)` / `(..pack.field)`:
-tv1 :: () => (..xs);
+tv1 :: () => .(..xs);
-tv2 :: () => (..xs.value);
+tv2 :: () => .(..xs.value);
-tv3 :: () => (a, ..xs, b);            // mixed positional + spread
+tv3 :: () => .(a, ..xs, b);            // mixed positional + spread
 
 // 2. Tuple type position — `(..F(Ts))` / `(..F(Ts.Arg))`:
-tt1 :: (x: (..ValueListenable(Ts)))       => x;
+tt1 :: (x: Tuple(..ValueListenable(Ts)))       => x;
-tt2 :: (x: (..ValueListenable(Ts.Arg)))   => x;
+tt2 :: (x: Tuple(..ValueListenable(Ts.Arg)))   => x;
 
 // 3. Call-arg position — `..pack` / `..pack.field` (reuses spread_expr):
 ca1 :: () => f(..xs);

examples/probes/tuple-baseline.sx

@@ -11,35 +11,35 @@
 #import "modules/std.sx";
 
 Listenable :: struct { value: i64; }      // stand-in element struct
-Combined   :: struct { sources: (i32, i32); }  // tuple-typed field (Decision 2)
+Combined   :: struct { sources: Tuple(i32, i32); }  // tuple-typed field (Decision 2)
 
-swap :: (a: i64, b: i64) -> (i64, i64) { (b, a) }
+swap :: (a: i64, b: i64) -> Tuple(i64, i64) { .(b, a) }
-fst  :: (t: (i64, i64)) -> i64 { t.0 }
+fst  :: (t: Tuple(i64, i64)) -> i64 { t.0 }
 
 main :: () -> i32 {
     // ── Block A — primitives (WORKS) ───────────────────────────────
-    pair := (40, 2);                       // inferred positional
+    pair := .(40, 2);                       // inferred positional
     print("A.idx     {} {}\n", pair.0, pair.1);
-    named := (x: 10, y: 20);               // named + numeric access
+    named := .(x = 10, y = 20);               // named + numeric access
     print("A.named   {} {} {}\n", named.x, named.0, named.1);
-    one := (42,);                          // 1-tuple
+    one := .(42);                          // 1-tuple
     print("A.one     {}\n", one.0);
     a : i64 = pair.0;                      // element into typed local
     print("A.local   {}\n", a);
 
     // ── Block B — storage in a struct field (WORKS; core of Decision 2)
     c : Combined = ---;
-    c.sources = (7, 9);                    // assign tuple value to field
+    c.sources = .(7, 9);                    // assign tuple value to field
     print("B.field   {} {}\n", c.sources.0, c.sources.1);
 
     // ── Block C — return / pass / operators (WORKS) ────────────────
     s := swap(1, 2);
     print("C.ret     {} {}\n", s.0, s.1);
-    print("C.pass    {}\n", fst((11, 22)));
+    print("C.pass    {}\n", fst(.(11, 22)));
-    print("C.eq      {}\n", (1, 2) == (1, 2));
+    print("C.eq      {}\n", .(1, 2) == .(1, 2));
-    cc := (1, 2) + (3, 4);
+    cc := .(1, 2) + .(3, 4);
     print("C.concat  {} {}\n", cc.0, cc.3);
-    print("C.mem     {}\n", 3 in (1, 2, 3));
+    print("C.mem     {}\n", 3 in .(1, 2, 3));
     0
 }
 

examples/protocols/0414-protocols-generic-struct-protocol-erase.sx

@@ -14,7 +14,7 @@ IntCell :: struct { v: i64; }
 impl VL(i64) for IntCell { get :: (self: *IntCell) -> i64 => self.v; }
 
 Combined :: struct($R: Type, ..$Ts: []Type) {
-    sources: (..VL(Ts));
+    sources: Tuple(..VL(Ts));
     value:   $R;
 }
 impl VL($R) for Combined($R, ..$Ts) { get :: (self: *Combined) -> $R => self.value; }
@@ -22,7 +22,7 @@ impl VL($R) for Combined($R, ..$Ts) { get :: (self: *Combined) -> $R => self.val
 make :: (..sources: VL) -> VL(i64) {
     c : Combined(i64, ..sources.T) = ---;
     c.value = 99;
-    c.sources = (..sources);
+    c.sources = .(..sources);
     return xx c;                 // Combined__i64_i64 -> VL(i64)
 }
 

examples/protocols/0415-protocols-protocols.sx

@@ -141,7 +141,7 @@ SmokeErr :: error { Empty, BadDigit, Overflow }
 // value-carrying, named set: raise three tags or succeed
 
 // value-carrying, named set: raise three tags or succeed
-sm_parse :: (n: i32) -> (i32, !SmokeErr) {
+sm_parse :: (n: i32) -> i32 !SmokeErr {
     if n < 0  { raise error.BadDigit; }
     if n == 0 { raise error.Empty; }
     if n > 99 { raise error.Overflow; }
@@ -159,10 +159,10 @@ sm_check :: (ok: bool) -> ! {
 // multi-value, inferred set: `try` propagates; the SCC pass absorbs SmokeErr
 
 // multi-value, inferred set: `try` propagates; the SCC pass absorbs SmokeErr
-sm_pair :: (a: i32, b: i32) -> (i32, i32, !) {
+sm_pair :: (a: i32, b: i32) -> Tuple(i32, i32) ! {
     x := try sm_parse(a);
     y := try sm_parse(b);
-    return (x, y);
+    return .(x, y);
 }
 
 // `catch` block that diverges (logs the tag, then returns a fallback)
@@ -178,7 +178,7 @@ sm_or_default :: (n: i32) -> i32 {
 // `onfail` + `defer` interleave: cleanup runs only on the error path
 
 // `onfail` + `defer` interleave: cleanup runs only on the error path
-sm_acquire :: (fail: bool) -> (i32, !) {
+sm_acquire :: (fail: bool) -> i32 ! {
     defer  print("  smoke defer A\n");
     onfail print("  smoke onfail B\n");
     if fail { raise error.Acquire; }
@@ -188,7 +188,7 @@ sm_acquire :: (fail: bool) -> (i32, !) {
 // `or`-chain: try a, fall to try b; propagate if both fail
 
 // `or`-chain: try a, fall to try b; propagate if both fail
-sm_first :: (a: i32, b: i32) -> (i32, !) {
+sm_first :: (a: i32, b: i32) -> i32 ! {
     v := try sm_parse(a) or try sm_parse(b);
     return v;
 }

examples/protocols/0824-protocols-same-name-method-wrapped-own-wins.sx

@@ -23,27 +23,27 @@ Provider :: protocol {
     // discriminating wrapped/compound RETURNS
     getp :: (self: *Self) -> *Box;
     geto :: (self: *Self) -> ?Box;
-    gett :: (self: *Self) -> (Box, Box);
+    gett :: (self: *Self) -> Tuple(Box, Box);
     geta :: (self: *Self) -> [2]Box;
     // routing-only wrapped/compound PARAMS
     sump :: (self: *Self, p: *Box) -> i32;
     sumo :: (self: *Self, o: ?Box) -> i32;
     sums :: (self: *Self, s: []Box) -> i32;
     suma :: (self: *Self, a: [2]Box) -> i32;
-    sumt :: (self: *Self, t: (Box, Box)) -> i32;
+    sumt :: (self: *Self, t: Tuple(Box, Box)) -> i32;
     sumn :: (self: *Self, n: *?[]Box) -> i32;
 }
 
 impl Provider for Holder {
     getp :: (self: *Holder) -> *Box { @self.b }
     geto :: (self: *Holder) -> ?Box { self.b }
-    gett :: (self: *Holder) -> (Box, Box) { (self.b, self.b) }
+    gett :: (self: *Holder) -> Tuple(Box, Box) { .(self.b, self.b) }
     geta :: (self: *Holder) -> [2]Box { r : [2]Box = ---; r[0] = self.b; r[1] = self.b; r }
     sump :: (self: *Holder, p: *Box) -> i32 { p.m }
     sumo :: (self: *Holder, o: ?Box) -> i32 { o!.m }
     sums :: (self: *Holder, s: []Box) -> i32 { s[0].m }
     suma :: (self: *Holder, a: [2]Box) -> i32 { a[0].m }
-    sumt :: (self: *Holder, t: (Box, Box)) -> i32 { t.0.m }
+    sumt :: (self: *Holder, t: Tuple(Box, Box)) -> i32 { t.0.m }
     sumn :: (self: *Holder, n: *?[]Box) -> i32 { if n == null { 0 } else { 6 } }
 }
 
@@ -63,7 +63,7 @@ main :: () -> i32 {
     arr : [2]Box = ---; arr[0].m = 2; arr[1].m = 3;
     sl : []Box = arr[0..2];
     osl : ?[]Box = sl;
-    tup : (Box, Box) = (one, one);
+    tup : Tuple(Box, Box) = .(one, one);
 
     sp := p.sump(@one);
     so := p.sumo(one);

examples/route/0815-route-all-new-surfaces-ambiguous.sx

@@ -29,7 +29,7 @@ WrapU :: union { b: Box; n: i32; }
 WrapE :: enum { V: Box; }
 
 main :: () -> i32 {
-    sz := size_of((Box, i32));
+    sz := size_of(Tuple(Box, i32));
     x : union { b: Box; n: i32 } = ---;
     0
 }

examples/route/0822-route-all-own-wins-surfaces.sx

@@ -23,7 +23,7 @@ main :: () -> i32 {
     bp : BoxPtr = @own;
 
     // tuple element own-wins
-    t : (Box, i32) = ---;
+    t : Tuple(Box, i32) = ---;
     t.0.m = 12;
 
     // enum body-builder child own-wins (payload must be main's `Box`)

examples/types/0115-types-compound-type-in-expression.sx

@@ -23,7 +23,7 @@ main :: () -> i32 {
   print("size_of((i32)->i32) = {}\n", size_of((i32) -> i32));
 
   // Tuple literal reinterpreted as tuple type at the type-demanding site.
-  print("size_of((i32, i32)) = {}\n", size_of((i32, i32)));
+  print("size_of((i32, i32)) = {}\n", size_of(Tuple(i32, i32)));
 
   // Aliases.
   print("size_of(Ptr)        = {}\n", size_of(Ptr));

examples/types/0119-types-tuple-values.sx

@@ -6,18 +6,18 @@
 
 #import "modules/std.sx";
 
-Box :: struct { xs: (i32, i32); }
+Box :: struct { xs: Tuple(i32, i32); }
 
-swap :: (a: i64, b: i64) -> (i64, i64) { (b, a) }
+swap :: (a: i64, b: i64) -> Tuple(i64, i64) { .(b, a) }
-fst  :: (t: (i64, i64)) -> i64 { t.0 }
+fst  :: (t: Tuple(i64, i64)) -> i64 { t.0 }
 
 main :: () -> i32 {
     // Inferred positional tuple + numeric field access.
-    pair := (40, 2);
+    pair := .(40, 2);
     print("pair {} {}\n", pair.0, pair.1);
 
     // Named tuple: named + numeric access.
-    named := (x: 10, y: 20);
+    named := .(x = 10, y = 20);
     print("named {} {} {}\n", named.x, named.0, named.1);
 
     // Element into a typed local (access path, not just print).
@@ -27,7 +27,7 @@ main :: () -> i32 {
 
     // Tuple-typed struct field: store a tuple value, read both elements.
     box : Box = ---;
-    box.xs = (7, 9);
+    box.xs = .(7, 9);
     print("field {} {}\n", box.xs.0, box.xs.1);
 
     // Return a tuple from a function.
@@ -35,21 +35,21 @@ main :: () -> i32 {
     print("ret {} {}\n", s.0, s.1);
 
     // Pass a tuple by value.
-    print("pass {}\n", fst((11, 22)));
+    print("pass {}\n", fst(.(11, 22)));
 
     // Operators: equality, concatenation, repetition, membership, lex.
-    print("eq {}\n", (1, 2) == (1, 2));
+    print("eq {}\n", .(1, 2) == .(1, 2));
-    c := (1, 2) + (3, 4);
+    c := .(1, 2) + .(3, 4);
     print("concat {} {}\n", c.0, c.3);
-    r := (1, 2) * 3;
+    r := .(1, 2) * 3;
     print("rep {} {}\n", r.0, r.5);
-    print("mem {}\n", 3 in (1, 2, 3));
+    print("mem {}\n", 3 in .(1, 2, 3));
-    print("lex {}\n", (1, 2) < (1, 3));
+    print("lex {}\n", .(1, 2) < .(1, 3));
 
     // Mixed-size fields: a tuple with both an i64 and a string (16-byte fat
     // pointer). Field types are tracked per-position, so reading each back is
     // typed correctly (i64 prints as a number, string as text).
-    mixed := (42, "hi");
+    mixed := .(42, "hi");
     print("mixed {} {}\n", mixed.0, mixed.1);
     0
 }

examples/types/0120-types-tuple-element-assign.sx

@@ -9,13 +9,13 @@
 
 main :: () -> i32 {
     // Positional element assignment.
-    a : (i32, string) = ---;
+    a : Tuple(i32, string) = ---;
     a.0 = 11;
     a.1 = "x";
     print("a: {} {}\n", a.0, a.1);
 
     // Named tuple: write + read by name, and read by position.
-    p : (x: i32, y: string) = ---;
+    p : Tuple(x: i32, y: string) = ---;
     p.x = 22;
     p.y = "y";
     print("p: x={} y={} .0={}\n", p.x, p.y, p.0);

examples/types/0122-types-flags.sx

@@ -81,26 +81,26 @@ main :: () {
 
     // Basic tuple destructuring
     {
-        da, db := (10, 20);
+        da, db := .(10, 20);
         print("basic: {} {}\n", da, db);
     }
 
     // Destructure from function return
     {
-        dswap :: (a: i64, b: i64) -> (i64, i64) { (b, a) }
+        dswap :: (a: i64, b: i64) -> Tuple(i64, i64) { .(b, a) }
         dx, dy := dswap(1, 2);
         print("fn: {} {}\n", dx, dy);
     }
 
     // Discard with _
     {
-        _, dsecond := (100, 200);
+        _, dsecond := .(100, 200);
         print("discard: {}\n", dsecond);
     }
 
     // Three elements
     {
-        da3, db3, dc3 := (1, 2, 3);
+        da3, db3, dc3 := .(1, 2, 3);
         print("triple: {} {} {}\n", da3, db3, dc3);
     }
 }

examples/types/0128-types-tuples.sx

@@ -9,18 +9,18 @@ main :: () {
     // --- Tuples ---
     {
         print("=== Tuples ===\n");
-        pair := (40, 2);
+        pair := .(40, 2);
         print("{}\n", pair.0);
         print("{}\n", pair.1);
 
-        named := (x: 10, y: 20);
+        named := .(x = 10, y = 20);
         print("{}\n", named.x);
         print("{}\n", named.0);
 
-        single := (42,);
+        single := .(42);
         print("{}\n", single.0);
 
-        zeroed : (i32, i32) = ---;
+        zeroed : Tuple(i32, i32) = ---;
         print("{}\n", zeroed.0);
         print("{}\n", zeroed.1);
     }

examples/types/0129-types-tuple-operators.sx

@@ -44,20 +44,20 @@ main :: () {
         print("=== Tuple Operators ===\n");
 
         // Equality
-        print("{}\n", (1, 2) == (1, 2));     // true
+        print("{}\n", .(1, 2) == .(1, 2));     // true
-        print("{}\n", (1, 2) == (1, 3));     // false
+        print("{}\n", .(1, 2) == .(1, 3));     // false
-        print("{}\n", (1, 2) != (1, 3));     // true
+        print("{}\n", .(1, 2) != .(1, 3));     // true
-        print("{}\n", (1, 2) != (1, 2));     // false
+        print("{}\n", .(1, 2) != .(1, 2));     // false
 
         // Concatenation
-        c := (1, 2) + (3, 4);
+        c := .(1, 2) + .(3, 4);
         print("{}\n", c.0);    // 1
         print("{}\n", c.1);    // 2
         print("{}\n", c.2);    // 3
         print("{}\n", c.3);    // 4
 
         // Repetition
-        r := (1, 2) * 3;
+        r := .(1, 2) * 3;
         print("{}\n", r.0);    // 1
         print("{}\n", r.1);    // 2
         print("{}\n", r.2);    // 1
@@ -66,16 +66,16 @@ main :: () {
         print("{}\n", r.5);    // 2
 
         // Lexicographic comparison
-        print("{}\n", (1, 2) < (1, 3));      // true
+        print("{}\n", .(1, 2) < .(1, 3));      // true
-        print("{}\n", (1, 3) < (1, 2));      // false
+        print("{}\n", .(1, 3) < .(1, 2));      // false
-        print("{}\n", (1, 2) < (1, 2));      // false
+        print("{}\n", .(1, 2) < .(1, 2));      // false
-        print("{}\n", (1, 2) <= (1, 2));     // true
+        print("{}\n", .(1, 2) <= .(1, 2));     // true
-        print("{}\n", (2, 0) > (1, 9));      // true
+        print("{}\n", .(2, 0) > .(1, 9));      // true
-        print("{}\n", (1, 2) >= (1, 2));     // true
+        print("{}\n", .(1, 2) >= .(1, 2));     // true
 
         // Membership
-        print("{}\n", 2 in (1, 2, 3));      // true
+        print("{}\n", 2 in .(1, 2, 3));      // true
-        print("{}\n", 5 in (1, 2, 3));      // false
+        print("{}\n", 5 in .(1, 2, 3));      // false
     }
 
     // --- Directory imports ---
@@ -189,15 +189,15 @@ main :: () {
     }
 
     {
-        if 1 == (1,) {
+        if 1 == .(1) {
             print("1 == (1)\n");
         }
 
-        if (1,) == (1) {
+        if .(1) == (1) {
             print("(1) == 1\n");
         }
 
-        if (1,) == 1 {
+        if .(1) == 1 {
             print("1 == 1\n");
         }
     }

examples/types/0130-types-tuple-new-syntax.sx

@@ -0,0 +1,42 @@
+// New tuple syntax (additive over the legacy `(a, b)` forms):
+//   - tuple TYPE `Tuple(A, B)` and named `Tuple(x: A, y: B)`
+//   - tuple VALUE `.(a, b)`, named `.(x = a, y = b)`, 1-tuple `.(n)`
+//   - element access by index `.0` and by name `.x`
+//   - a `-> Tuple(i64, i64)` return type with a `.(b, a)` body
+//   - tuple equality operator over two `.(...)` literals
+// The `Tuple(...)` type mirrors the inline `(A, B)` tuple_type_expr and
+// `.(...)` mirrors the inline `(a, b)` tuple_literal, so both self-type
+// structurally and reuse the existing tuple lowering.
+
+#import "modules/std.sx";
+
+swap :: (a: i64, b: i64) -> Tuple(i64, i64) {
+    .(b, a)
+}
+
+main :: () -> i32 {
+    // Positional value + index access.
+    p := .(1, 2);
+    print("p {} {}\n", p.0, p.1);
+
+    // Named value (`=`) + name access.
+    n := .(x = 10, y = 20);
+    print("n {} {}\n", n.x, n.y);
+
+    // 1-tuple.
+    one := .(7);
+    print("one {}\n", one.0);
+
+    // Tuple return type with a `.(...)` body.
+    s := swap(3, 4);
+    print("swap {} {}\n", s.0, s.1);
+
+    // Named tuple TYPE annotation, filled by a named `.(...)` literal.
+    nt : Tuple(x: i64, y: i64) = .(x = 5, y = 6);
+    print("named-type {} {}\n", nt.x, nt.y);
+
+    // Tuple equality operator over two `.(...)` literals.
+    print("eq {}\n", .(1, 2) == .(1, 2));
+
+    0
+}

examples/types/0131-types-tuple-typed-construction.sx

@@ -0,0 +1,39 @@
+// Explicitly-typed tuple construction `Tuple(...).( ... )` — the `Tuple(...)`
+// TYPE followed by a `.( ... )` initializer, exactly like `Point.{ ... }` for
+// structs. Symmetric trio (mirrors structs `Point` / `Point.{...}` / `.{...}`):
+//   - tuple TYPE      `Tuple(A, B)`            (annotation / return / arg)
+//   - anonymous VALUE `.(a, b)`               (contextually typed)
+//   - typed VALUE     `Tuple(A, B).(a, b)`    (explicit type + initializer)
+// A `Tuple(...).(...)` value equals the anonymous `.(...)` against that type.
+// Named forms keep `:` in the type and `=` in the value.
+
+#import "modules/std.sx";
+
+// A `-> Tuple(i64, i64)` return type with a `.(b, a)` body.
+swap :: (a: i64, b: i64) -> Tuple(i64, i64) {
+    .(b, a)
+}
+
+main :: () -> i32 {
+    // Annotation + anonymous value.
+    t : Tuple(i64, i64) = .(1, 2);
+    print("t = {} {}\n", t.0, t.1);                // t = 1 2
+
+    // Explicitly-typed construction — same value as `.(3, 4)` against the type.
+    u := Tuple(i64, i64).(3, 4);
+    print("u = {} {}\n", u.0, u.1);                // u = 3 4
+
+    // Named: annotation + value uses `=` for the value fields.
+    p : Tuple(x: i64, y: i64) = .(x = 5, y = 6);
+    print("p = {} {}\n", p.x, p.y);                // p = 5 6
+
+    // Named: explicitly-typed construction.
+    q := Tuple(x: i64, y: i64).(x = 7, y = 8);
+    print("q = {} {}\n", q.x, q.y);                // q = 7 8
+
+    // Function returning a tuple via a `.(b, a)` body.
+    s := swap(10, 20);
+    print("s = {} {}\n", s.0, s.1);                // s = 20 10
+
+    0
+}

examples/types/0152-types-backtick-control-flow.sx

@@ -10,7 +10,7 @@
 // Regression (issue 0089 — attempt-2 completeness across binding forms).
 #import "modules/std.sx";
 
-pair :: () -> (i64, i64) { (1, 2) }
+pair :: () -> Tuple(i64, i64) { .(1, 2) }
 maybe :: () -> ?i64 { return 42; }
 
 // Function named with a reserved spelling — bare-callable (no backtick at call).

examples/types/0173-types-int-literal-default-i64.sx

@@ -27,7 +27,7 @@ big_host :: () -> i32 {
 }
 
 d_host :: () -> i32 {
-    a, b := (1, 2);
+    a, b := .(1, 2);
     print("a: {} b: {}\n", type_name(type_of(a)), type_name(type_of(b)));
     0
 }

examples/types/0190-types-void-struct-field-zero-sized.sx

@@ -21,7 +21,7 @@ main :: () -> i32 {
     print("tag={}\n", b.tag);
 
     // A tuple with a void element.
-    t : (void, i32) = .{ {}, 9 };
+    t : Tuple(void, i32) = .{ {}, 9 };
     print("t1={}\n", t.1);
     return 0;
 }

examples/types/0199-types-tuple-positional-optional-element.sx

@@ -11,24 +11,24 @@
 
 main :: () {
     // Optional + float fields.
-    t : (?i64, f64) = .{ 7, 3.0 };
+    t : Tuple(?i64, f64) = .{ 7, 3.0 };
     print("{} {}\n", t.0 ?? -1, t.1);          // 7 3.000000
 
     // int -> float coercion on a tuple element.
-    u : (f64, i64) = .{ 3, 4 };
+    u : Tuple(f64, i64) = .{ 3, 4 };
     print("{} {}\n", u.0, u.1);                // 3.000000 4
 
     // Named tuple.
-    n : (x: ?i64, y: f64) = .{ 5, 2.5 };
+    n : Tuple(x: ?i64, y: f64) = .{ 5, 2.5 };
     print("{} {}\n", n.x ?? -1, n.y);          // 5 2.500000
 
     // Variable elements flowing into an optional tuple field.
     a := 9;
     b := 1.5;
-    v : (?i64, f64) = .{ a, b };
+    v : Tuple(?i64, f64) = .{ a, b };
     print("{} {}\n", v.0 ?? -1, v.1);          // 9 1.500000
 
     // A bare `null` element into an optional tuple field.
-    w : (?i64, i64) = .{ null, 8 };
+    w : Tuple(?i64, i64) = .{ null, 8 };
     print("{} {}\n", w.0 ?? -1, w.1);          // -1 8
 }

examples/types/0201-types-parenthesized-type-grouping.sx

@@ -29,10 +29,10 @@ main :: () {
     print("{}\n", fns[0](3, 4));      // 7
 
     // A 1-tuple type still requires the trailing comma.
-    one : (i64,) = (9,);
+    one : Tuple(i64) = .(9);
     print("{}\n", one.0);             // 9
 
     // A 2-tuple is unaffected.
-    two : (i64, i64) = (40, 2);
+    two : Tuple(i64, i64) = .(40, 2);
     print("{}\n", two.0 + two.1);     // 42
 }

examples/types/expected/0130-types-tuple-new-syntax.exit

@@ -0,0 +1 @@
+0

examples/types/expected/0130-types-tuple-new-syntax.stderr

@@ -0,0 +1 @@
+

examples/types/expected/0130-types-tuple-new-syntax.stdout

@@ -0,0 +1,6 @@
+p 1 2
+n 10 20
+one 7
+swap 4 3
+named-type 5 6
+eq true

examples/types/expected/0131-types-tuple-typed-construction.exit

@@ -0,0 +1 @@
+0

examples/types/expected/0131-types-tuple-typed-construction.stderr

@@ -0,0 +1 @@
+

examples/types/expected/0131-types-tuple-typed-construction.stdout

@@ -0,0 +1,5 @@
+t = 1 2
+u = 3 4
+p = 5 6
+q = 7 8
+s = 20 10

library/modules/std/cli.sx

@@ -263,7 +263,7 @@ is_long_flag :: (s: string) -> bool {
 // Parse `args` (the logical argv) against the `commands` table, writing
 // the offending token into `diag` on the error path. See the section
 // header for grammar, failure contract, and heap discipline.
-parse :: (args: []string, commands: []Command, diag: *Diag) -> (Parsed, !CliError) {
+parse :: (args: []string, commands: []Command, diag: *Diag) -> Parsed !CliError {
     // ── Dispatch: match (args[0], args[1]) against the command table ──
     if args.len < 2 {
         diag.index = if args.len == 0 then -1 else 0;

library/modules/std/event.sx

@@ -52,7 +52,7 @@ Event :: struct {
 Loop :: struct {
     kq: i32 = -1;
 
-    init :: () -> (Loop, !EventErr) {
+    init :: () -> Loop !EventErr {
         q := kqb.kqueue();
         if q < 0 { raise error.Init; }
         return Loop.{ kq = q };
@@ -96,7 +96,7 @@ Loop :: struct {
 
     // Fill `out` with ready events, waiting at most `timeout_ms`
     // (negative = forever). Returns the count; 0 is a timeout.
-    wait :: (self: *Loop, out: []Event, timeout_ms: i64) -> (i64, !EventErr) {
+    wait :: (self: *Loop, out: []Event, timeout_ms: i64) -> i64 !EventErr {
         raw : [64]kqb.Kevent = ---;
         cap : i64 = 64;
         if xx out.len < cap { cap = xx out.len; }

library/modules/std/http.sx

@@ -263,7 +263,7 @@ Server :: struct {
     ctx: usize = 0;
     ps: *PoolState = null;   // non-null iff cfg.thread_pool_count > 0
 
-    init :: (cfg: Config, handler: (*Request, *Response, usize) -> void, ctx: usize) -> (Server, !HttpErr) {
+    init :: (cfg: Config, handler: (*Request, *Response, usize) -> void, ctx: usize) -> Server !HttpErr {
         lfd := socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0);
         if lfd < 0 { raise error.Bind; }
         one : i32 = 1;

library/modules/std/io.sx

@@ -113,7 +113,7 @@ async :: ufcs (io: Io, worker: Closure(..$args) -> $R, ..$args) -> Future($R) {
 
 // `await(f)` — value-carrying failable. `.ready` → the result; `.failed`
 // / `.canceled` → raise the stored / cancellation error.
-await :: ufcs (f: *Future($R)) -> ($R, !IoErr) {
+await :: ufcs (f: *Future($R)) -> $R !IoErr {
     if f.canceled.load(.acquire) { raise error.Canceled; }
     if f.state == .canceled      { raise error.Canceled; }
     if f.state == .failed        { raise error.Failed; }

library/modules/std/json.sx

@@ -321,7 +321,7 @@ write_object :: (obj: Object, sink: *Sink) -> !JsonError {
 // bytes written. Raises `error.Overflow` if `dst` is too small (the
 // partial contents of `dst` are then undefined — nothing is truncated
 // silently). No allocation.
-write_to_buffer :: (v: Value, dst: []u8) -> (i64, !JsonError) {
+write_to_buffer :: (v: Value, dst: []u8) -> i64 !JsonError {
     sink := Sink.{ dst = dst };
     try write_value(v, @sink);
     return sink.pos;
@@ -386,7 +386,7 @@ JsonParseError :: error { UnexpectedToken, UnexpectedEnd, BadEscape, BadNumber,
 
 // Lowercase/uppercase hex nibble value (0..15) of an ASCII byte; a non-hex
 // byte in a `\uXXXX` escape is a `BadEscape`.
-hex_value :: (c: u8) -> (i64, !JsonParseError) {
+hex_value :: (c: u8) -> i64 !JsonParseError {
     if c >= 48 and c <= 57  { return (cast(i64) c) - 48; }        // '0'..'9'
     if c >= 97 and c <= 102 { return (cast(i64) c) - 97 + 10; }   // 'a'..'f'
     if c >= 65 and c <= 70  { return (cast(i64) c) - 65 + 10; }   // 'A'..'F'
@@ -450,7 +450,7 @@ Parser :: struct {
 
     // Read 4 hex digits at `i` (which must lie within [.., end)); returns
     // the 16-bit value. Fewer than 4 digits before `end` is a BadEscape.
-    read_hex4 :: (self: *Parser, i: i64, end: i64) -> (i64, !JsonParseError) {
+    read_hex4 :: (self: *Parser, i: i64, end: i64) -> i64 !JsonParseError {
         if i + 4 > end { raise error.BadEscape; }
         v := 0;
         k := 0;
@@ -464,7 +464,7 @@ Parser :: struct {
     // Decode the escaped string body in [start, end) into `out`, returning
     // the decoded byte length. Pass 1 (in parse_string) guarantees there is
     // no dangling backslash, so the byte after every `\` is in range.
-    decode_into :: (self: *Parser, start: i64, end: i64, out: [*]u8) -> (i64, !JsonParseError) {
+    decode_into :: (self: *Parser, start: i64, end: i64, out: [*]u8) -> i64 !JsonParseError {
         di := 0;
         i := start;
         while i < end {
@@ -511,7 +511,7 @@ Parser :: struct {
     // a zero-copy VIEW into `src` when the body has no escapes; otherwise
     // decodes into an `alloc`-ed buffer (bounded by the raw span). `pos`
     // ends just past the closing quote.
-    parse_string :: (self: *Parser) -> (string, !JsonParseError) {
+    parse_string :: (self: *Parser) -> string !JsonParseError {
         self.pos += 1;                 // consume opening quote
         start := self.pos;
         has_escape := false;
@@ -547,7 +547,7 @@ Parser :: struct {
     // Parse an i64 integer (optional '-', then digits). Rejects leading
     // zeros, a fraction/exponent tail, and any value outside i64 — all
     // `BadNumber`. Accumulates in NEGATIVE space so i64 MIN parses exactly.
-    parse_number :: (self: *Parser) -> (i64, !JsonParseError) {
+    parse_number :: (self: *Parser) -> i64 !JsonParseError {
         // i64 bounds, built positionally because |MIN| is not a
         // representable positive i64 literal. `min_div10` is `MIN / 10`
         // truncated toward zero (remainder -8) — the digit loop's overflow
@@ -585,7 +585,7 @@ Parser :: struct {
     }
 
     // Parse an array starting at '['. Builds an `Array` through `alloc`.
-    parse_array :: (self: *Parser) -> (Value, !JsonParseError) {
+    parse_array :: (self: *Parser) -> Value !JsonParseError {
         self.pos += 1;                 // consume '['
         arr : Array = .{};
         self.skip_ws();
@@ -609,7 +609,7 @@ Parser :: struct {
 
     // Parse an object starting at '{'. Keys must be strings; insertion
     // order is preserved (duplicate keys are kept, never merged).
-    parse_object :: (self: *Parser) -> (Value, !JsonParseError) {
+    parse_object :: (self: *Parser) -> Value !JsonParseError {
         self.pos += 1;                 // consume '{'
         obj : Object = .{};
         self.skip_ws();
@@ -640,7 +640,7 @@ Parser :: struct {
     }
 
     // Parse any single value (after skipping leading whitespace).
-    parse_value :: (self: *Parser) -> (Value, !JsonParseError) {
+    parse_value :: (self: *Parser) -> Value !JsonParseError {
         self.skip_ws();
         if self.pos >= self.src.len { raise error.UnexpectedEnd; }
         c := self.src[self.pos];
@@ -659,7 +659,7 @@ Parser :: struct {
 // `alloc` for composite nodes and decoded (escaped) strings. Un-escaped
 // string values are VIEWS into `src` and are valid only while `src` lives.
 // Trailing non-whitespace after the value raises `error.TrailingGarbage`.
-parse :: (src: string, alloc: Allocator) -> (Value, !JsonParseError) {
+parse :: (src: string, alloc: Allocator) -> Value !JsonParseError {
     p := Parser.{ src = src, alloc = alloc };
     v := try p.parse_value();
     p.skip_ws();

library/modules/std/sched.sx

@@ -804,7 +804,7 @@ go :: ufcs (self: *Scheduler, work: Closure() -> $R) -> *Task($R) {
 // Suspend the caller until the task completes; return its value (or raise on
 // cancel). MUST be called from inside a fiber (so there is a `self.current` to
 // park) — typically from a fiber spawned via `s.spawn(...)`.
-wait :: ufcs (t: *Task($R)) -> ($R, !TaskErr) {
+wait :: ufcs (t: *Task($R)) -> $R !TaskErr {
     if t.canceled != 0 { raise error.Canceled; }
     if t.state == .pending {
         // ONE waiter per task (enforced). A `Task` holds a single `waiter` slot;

library/modules/std/socket.sx

@@ -93,7 +93,7 @@ SockErr :: error {
 // Accept one pending connection on a nonblocking listener. A connection
 // that died between queueing and accept (ECONNABORTED) is skipped, not
 // surfaced — the listener is fine.
-accept_nb :: (fd: i32) -> (i32, !SockErr) {
+accept_nb :: (fd: i32) -> i32 !SockErr {
     while true {
         c := accept(fd, null, null);
         if c >= 0 { return c; }
@@ -107,7 +107,7 @@ accept_nb :: (fd: i32) -> (i32, !SockErr) {
 
 // Read up to `cap` bytes. Returns the byte count (> 0); an orderly EOF
 // or a peer reset is Closed.
-read_nb :: (fd: i32, buf: [*]u8, cap: usize) -> (i64, !SockErr) {
+read_nb :: (fd: i32, buf: [*]u8, cap: usize) -> i64 !SockErr {
     while true {
         n := read(fd, buf, cap);
         if n > 0 { return xx n; }
@@ -123,7 +123,7 @@ read_nb :: (fd: i32, buf: [*]u8, cap: usize) -> (i64, !SockErr) {
 
 // Write up to `len` bytes, returning how many the kernel took (possibly
 // fewer — the caller continues from there on the next writability).
-write_nb :: (fd: i32, buf: [*]u8, len: usize) -> (i64, !SockErr) {
+write_nb :: (fd: i32, buf: [*]u8, len: usize) -> i64 !SockErr {
     while true {
         n := write(fd, buf, len);
         if n >= 0 { return xx n; }

library/modules/std/thread.sx

@@ -106,7 +106,7 @@ Thread :: struct {
 
     // `entry` is the C->sx boundary: abi(.c), fabricates its own
     // Context before touching default-conv sx code (examples/1636).
-    spawn :: (entry: (*void) -> *void abi(.c), arg: *void) -> (Thread, !ThreadErr) {
+    spawn :: (entry: (*void) -> *void abi(.c), arg: *void) -> Thread !ThreadErr {
         t : Thread = .{};
         if pthread_create(@t.handle, null, entry, arg) != 0 { raise error.Spawn; }
         return t;
@@ -144,7 +144,7 @@ Pool :: struct {
 
     // Heap-allocate (the pool must never move: workers hold its address,
     // and it embeds a live mutex), init in place, spawn the workers.
-    create :: (workers: i64, backlog: i64) -> (*Pool, !ThreadErr) {
+    create :: (workers: i64, backlog: i64) -> *Pool !ThreadErr {
         alloc := context.allocator;
         p : *Pool = xx alloc.alloc_bytes(size_of(Pool));
         p.* = Pool.{};