fix(gen-zig): @intCast runtime shift amounts; pin bare-literal shift LHS

NOW.md

@@ -2,6 +2,13 @@
 
 Last updated: 2026-08-08
 
+## gen-zig: runtime shift amounts get @intCast; literal shift LHS pinned (Closes #1932)
+
+- `x << k` with a runtime amount emitted a raw u32/usize RHS (Zig wants u5 for u32) and `1 << family` left a comptime_int LHS; runtime amounts now emit `@intCast(rhs)` and a bare-literal LHS pins `@as(u32, lit)` (u64 above u32 range)
+- Literal amounts untouched -- existing gens byte-identical
+- tri-net corpus: both shift error classes gone (13 specs); 6 newly pass zig test end-to-end, 7 advance to their runtime layer (checked-add overflow in hash mixing, the spec-side +% idiom)
+- FROZEN_HASH resealed
+
 ## gen-zig: invariant marker is a comment; untyped literal-init mutables pinned to u32 (Closes #1930)
 
 - Empty invariant blocks emitted `@compileLog(...)` -- a hard error under `zig test`; the marker is now a comment

bootstrap/src/compiler.rs

@@ -4151,9 +4151,31 @@ impl Codegen {
             }
             NodeKind::ExprBinary => {
                 if node.children.len() >= 2 {
-                    self.gen_expr_maybe_paren(&node.children[0]);
-                    self.write(&format!(" {} ", node.extra_op));
-                    self.gen_expr_maybe_paren(&node.children[1]);
+                    let op = node.extra_op.as_str();
+                    // Zig shift RHS must be Log2(LHS-width)-typed (u5 for u32);
+                    // a runtime u32/usize amount needs @intCast, and a bare
+                    // integer-literal LHS (comptime_int) needs a pinned width
+                    // once the amount is not comptime-known. Literal amounts
+                    // are left untouched so existing gens stay byte-identical.
+                    let shift_runtime_rhs = matches!(op, "<<" | ">>")
+                        && !matches!(node.children[1].kind, NodeKind::ExprLiteral);
+                    if shift_runtime_rhs {
+                        if let Some(ty) = Self::zig_int_literal_default_type(&node.children[0]) {
+                            self.write(&format!("@as({}, ", ty));
+                            self.gen_expr_maybe_paren(&node.children[0]);
+                            self.write(")");
+                        } else {
+                            self.gen_expr_maybe_paren(&node.children[0]);
+                        }
+                        self.write(&format!(" {} ", op));
+                        self.write("@intCast(");
+                        self.gen_expr(&node.children[1]);
+                        self.write(")");
+                    } else {
+                        self.gen_expr_maybe_paren(&node.children[0]);
+                        self.write(&format!(" {} ", op));
+                        self.gen_expr_maybe_paren(&node.children[1]);
+                    }
                 }
             }
             NodeKind::ExprUnary => {

bootstrap/stage0/FROZEN_HASH

@@ -1 +1 @@
-34b8bad47530199936ab793a6596c8e3589a30baf5ebb159c10d57c1299062b8
+f084381976dca390adfa048d03c70c62c58d335de8ac68790ccd93acd4f72caa

docs/NOW.md

@@ -2,6 +2,13 @@
 
 Last updated: 2026-08-08
 
+## gen-zig: runtime shift amounts get @intCast; literal shift LHS pinned (Closes #1932)
+
+- `x << k` with a runtime amount emitted a raw u32/usize RHS (Zig wants u5 for u32) and `1 << family` left a comptime_int LHS; runtime amounts now emit `@intCast(rhs)` and a bare-literal LHS pins `@as(u32, lit)` (u64 above u32 range)
+- Literal amounts untouched -- existing gens byte-identical
+- tri-net corpus: both shift error classes gone (13 specs); 6 newly pass zig test end-to-end, 7 advance to their runtime layer (checked-add overflow in hash mixing, the spec-side +% idiom)
+- FROZEN_HASH resealed
+
 ## gen-zig: invariant marker is a comment; untyped literal-init mutables pinned to u32 (Closes #1930)
 
 - Empty invariant blocks emitted `@compileLog(...)` -- a hard error under `zig test` ("found compile log statement"), so every spec with an empty invariant failed before one test ran; the marker is now a comment