Add for to the compiler. Emit block/loop/br_if/br with auto-init and auto-increment. Store the end bound in $__for_end:

        if (streq(word, "for")) {
            if (cur() == '(') { pos += 1; skip(); }
            c_expression();          // start
            if (cur() == '.') { pos += 1; }
            if (cur() == '.') { pos += 1; }
            skip();
            c_expression();          // end
            emit_str("  local.set $__for_end\n");
            if (cur() == ')') { pos += 1; skip(); }
            if (cur() == '|') { pos += 1; skip(); }
            const loop_var: []const u8 = read_name();
            if (cur() == '|') { pos += 1; skip(); }
            // init
            emit_str("  local.set $"); emit_str(loop_var); emit_byte('\n');
            emit_op("block");
            emit_op("loop");
            // condition: i >= end -> exit
            emit_str("  local.get $"); emit_str(loop_var); emit_byte('\n');
            emit_str("  local.get $__for_end\n");
            emit_op("i64.ge_s");
            emit_op("br_if 1");
            c_block();
            emit_op("drop");
            // increment
            emit_str("  local.get $"); emit_str(loop_var); emit_byte('\n');
            emit_op("i64.const 1");
            emit_op("i64.add");
            emit_str("  local.set $"); emit_str(loop_var); emit_byte('\n');
            emit_op("br 0");
            emit_op("end");
            emit_op("end");
            return false;
        }

Add (local $__for_end i64) to emit_locals(). Update scan_for_locals to detect |name| in for statements and register the capture as a local.

Agreement tests:

    check_both("var s: i64 = 0; for (0..5) |i| { s += i; } s", 10);
    check_both("var s: i64 = 0; for (0..3) |i| { for (0..4) |j| { s += 1; } } s", 12);