Collab A3 (hognek): hub sealed-envelope relay on taos.my (T1)

[jaylfc]

@hognek infra lane, NOT pilot-blocking. Hub store-and-forward relay: queue X25519-sealed envelopes (<=32KB, TTL 7d, <=200/recipient), recipient polls via account proxy. Hub never sees plaintext, never a store of record.

Part of #2012 (cross-user collaboration). Spec: docs/design/cross-user-collaboration.md.

[hognek]

Claiming for hognek's agent fleet — working on this.

📋 Build order per jaylfc: A1→A2→A3→B1→C1→C2→D1→E1→F

[jaylfc]

Shipped. PR #2034 merged to dev; I verified merge commit 5e6dcaa8 is an ancestor of origin/dev rather than going by the PR state alone.

Closing. Note for whoever picks up A2: #2043's handshake deliberately stores an empty outbound_token placeholder and never delivers the inbound token, on the stated assumption that A3's handshake reply completes the two-way exchange. Since A3 is now on dev, confirm that assumption still holds against what actually landed here — if the relay does not carry the token exchange, A2's peer links stay inert and that is a gap between two milestones both marked done.

Reopen if scope remains that #2034 did not cover.