channelSubId
Derive a 2-byte wire sub-id from a channel name.
The derivation is:
Compute a stable polynomial hash of the UTF-8 bytes of name.
Fold the result into a Short (the low 16 bits of the hash).
Collision probability is ~1/65536 per distinct pair of channel names. For typical deployments (< 100 channels), the probability of any collision is negligible. Colliding channels receive each other's frames; name collisions are documented as application-level responsibility.
The algorithm is not cryptographic — it exists solely for deterministic, coordination-free tag assignment.