Function matches 

pub fn matches(topic: &str, filter: &str) -> bool

Does topic match filter?

The segmented grammar of docs/PROTOCOL.md §6.4: segments split on ., * for exactly one whole segment, a trailing # for zero or more, every other byte literal, and the empty filter matching everything.

The objection this function used to carry was that treating * as a wildcard “would make topics with a literal * unaddressable and would put a matching language in the hot path”. Both halves were true and both are accepted deliberately (decisions/0007 §4.6): a filter can no longer select a segment containing ., * or # literally — there is no escape character, and no sheet reports a use for one — while a byte prefix could not express a boundary at all, so sensors.temp also selected sensors.temperature. The hot-path half is answered by the shape rather than by the choice: # is legal only as the final segment, so this is one left-to-right walk with no backtracking, no allocation and work bounded by the 256 B filter cap.

A topic is never a pattern: * and # in a published topic are literal bytes here, exactly like any other.