Timeline

Introduces `edgesync hub serve` and extends the hub package so a hub can be named at the NATS level and optionally solicit a leaf connection upstream. This is the substrate piece; session/agent vocabulary lives in a consumer (sesh) above this layer.

hub.Config: - ServerName — sets opts.ServerName on the embedded NATS server; surfaces in leafnode handshakes, varz, gossip. Empty leaves nats-server's auto-generated random name. - LeafUpstream — optional URL to solicit a leafnode connection toward. Wired to opts.LeafNode.Remotes. Lets one hub act as a leaf of another, enabling multi-hub topologies. - NATSStoreDir default renamed `nats-store` → `messaging` — implementation- agnostic on disk; contents underneath are still NATS JetStream format. The config field name stays `NATSStoreDir` (Go code is honest about what it is).

hub.Hub.ServerName() — getter returning the live identity (Config.ServerName or the auto-generated name).

cmd: `edgesync hub serve --name=<server-name> --leaf-upstream=<url> ...` defaults --name to <hostname>-hub and repo path to ~/.edgesync/<name>/hub.repo.

docs/architecture/hub-package.md updated to reflect the new fields, the messaging/ default, and a generic repo-file naming convention (the package itself doesn't impose a filename; the CLI defaults to hub.repo).

Verified end-to-end: - Hub solicits a hub: bidirectional pub/sub flows across two hubs on this machine via the leafnode handshake. - 3-edge star: 1 root hub + 3 leaf processes — fan-in, cross-leaf, subject filter all behave as expected. - ServerName visible at server-side truth (h.server.Name()). - 31 tests pass, vet clean.

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