Sync: oversized domains ride Blossom blobs — plus a coinos-hosted server.

A wallet with deep Ark coins had a 633KB ark sync domain against the relay's
40KB budget: the publish silently failed forever, the slot stayed stale,
and every boot retried. Relays can't carry it (64KB event cap) and neither
can NIP-44 (64KB plaintext), so a domain over budget now goes to Blossom
(nostr blob storage, BUD-01/02/06/11/12): sealed into an envelope
("CSB1" + xchacha20poly1305 under an HKDF of the wallet's NIP-44 self-key),
uploaded to the configured servers, and the kind-30078 event carries only
{ blob: { sha256, size, servers } }. Readers resolve pointers from their own
outbox copy first, else from the pointer's servers plus the configured
list, hash-verified. Small domains are unchanged.

The outbox uploads before it publishes (upload/delete authorizations are
kind-24242 events signed at enqueue time, so delivery after logout still
holds no key), keeps a local copy for recovery, and deletes superseded
blobs once the replacement is acknowledged.

Servers: Settings → Nostr → Sync storage (any Blossom server; a typed list
is kept), else the user's BUD-03 list (kind 10063) with the coinos server
as mirror, else blossom.coinos.io.

blossom/server.js is that default: a Bun Blossom server that stores ONLY
these envelopes (magic check → 415 for anything else), serves every blob as
an octet-stream attachment with nosniff, requires signed auth for
upload/list/delete, and enforces per-blob size, per-key quota (oldest
evicted), rate limits, a disk cap and unused-blob expiry — it cannot serve
as a file host. tools/sync-blob-test.js spawns it and covers the policy,
the outbox flow and a fresh device resolving a pointer.

Co-Authored-By: Claude Fable 5.1 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Nw1Dijik1tLVKRM1WkU7xE

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