Function dispatch_mark_pc_key 

pub fn dispatch_mark_pc_key(schedule_id: &str, pc_id: &str) -> String

Per-pc dispatch-mark key (OncePerPc).

The pc. / target. kind prefix keeps the two namespaces apart, and each component is length-prefixed (<len>.<value>) so no two distinct (schedule_id, pc_id) pairs can ever collide — even when an id contains the . separator: ("a.b", "c") → pc.3.a.b.1.c, ("a", "b.c") → pc.1.a.3.b.c. (Percent-/base64-encoding isn’t an option: NATS KV keys only allow [-/_=.a-zA-Z0-9], so the self-delimiting length prefix is the cheapest injective encoding that stays in-charset.)