Per CLAUDE.md rule 10, align cstage down to wwstage — when every
variant in a `?` propagation maps to itself, the remap loop emits
zero JMPs and the propret label is dead. Lazy-allocate it so the
label-counter ID is only consumed when at least one JMP fires.
Smoke test selfhost/test/trypromote.ww exercises same-shape
(i64|nomem)→(i64|nomem) propagation; cstage and wwstage now emit
byte-identical asm for the TRYPROP region.
Hojun-Cho
58e6d349a2