issues: file 0060 — closure-literal composition miscompiles (blocks ERR/E5.1)

Probing ERR/E5.1 (composition with closures) surfaced pre-existing closure-
literal lowering bugs: a closure literal passed as a function-type argument and
called inside the callee returns wrong values (block-body 192, arrow-body 20,
want 10 — non-failable too; the working contrast passes the value as a separate
arg, examples/0302). On top of that, failable closure returns don't parse
(isLambda omits .bang — one-line fix in the issue) and arrow-body failable
closures miscompile (return 0); block-body failable closures called directly
work. Runnable repro + parser patch + investigation prompt in the issue.

E5.1 paused per the impassable rule rather than built on miscompiling closures;
the parser fix + a regression example were reverted to avoid landing silently-
miscompiling failable closures on master.

src/parser.zig

@@ -3304,7 +3304,8 @@ pub const Parser = struct {
                     self.current.tag == .l_bracket or self.current.tag == .r_bracket or
                     self.current.tag == .l_paren or self.current.tag == .r_paren or
                     self.current.tag == .comma or self.current.tag == .int_literal or
-                    self.current.tag == .star or self.current.tag == .question)
+                    self.current.tag == .star or self.current.tag == .question or
+                    self.current.tag == .bang)
                 {
                     self.advance();
                 } else break;