PoW and outbound Nostr events

This document describes how Mostrix applies NIP-13 proof-of-work to events it publishes toward Mostro and related flows. It is intended for contributors and AI-assisted codegen so outbound signing behavior stays consistent with the Mostro instance policy.

Source of difficulty

• The Mostro instance status event (kind 38385) includes optional tags:
  • pow — unsigned integer; parsed into MostroInstanceInfo.pow (Option<u32>).
  • protocol_version — "1" or "2"; drives transport_from_instance → AppState.transport. Missing tag → legacy GiftWrap.
• There is no pow field in Settings or in the generated settings.toml template.
• Optional pow_first_contact on kind 38385 (when the daemon publishes it): parsed into MostroInstanceInfo.pow_first_contact. When absent, effective first-contact toll = base pow.
• Effective bits for signing: nostr_pow_from_instance maps base pow; nostr_pow_for_protocol_dm selects per-action bits for send_dm.

Cached instance info at runtime

• AppState.mostro_info holds the latest fetched MostroInstanceInfo.
• AppState.transport mirrors resolved Transport. Updated via set_mostro_info.
• EnterKeyContext threads mostro_info into async work without re-fetching per message.
• send_dm takes mostro_instance: Option<&MostroInstanceInfo> and computes pow = nostr_pow_for_protocol_dm(mostro_instance, action) once per send.

At startup (and on reload/reconnect via dm_transport_for_mostro), instance info is fetched before the DM listener spawns when relays are reachable.

Protocol v2 (NIP-44 direct) — outbound

send_dm uses wrap_message_with from mostro-core:

• v1 (GiftWrap): PoW on the outer kind-1059 envelope (via mostro-core nip59::wrap_message).
• v2 (Nip44Direct): PoW on the signed kind-14 event (WrapOptions.pow).
• NIP-40 expiration: default now + 30 days on v2 when the caller passes expiration: None (default_dm_expiration).

First-contact actions on strict v2 nodes may need higher PoW than instance pow (pow_first_contact on the daemon). Mostrix applies max(pow, pow_first_contact) on v2 for NewOrder, TakeBuy, and TakeSell via nostr_pow_for_protocol_dm. When the kind-38385 pow_first_contact tag is absent, the effective toll defaults to base pow (same as the daemon).

Chat vs protocol PoW

• Protocol DMs toward Mostro: instance PoW + transport from transport_from_instance + wrap_message_with.
• Shared-key chat (admin dispute, user order, observer): mostro_core::chat GiftWrap — no PoW.

Call sites (high level)

Order flows under src/util/order_utils/, admin actions in src/ui/key_handler/admin_handlers.rs, and rating handlers in src/ui/key_handler/message_handlers.rs pass cached mostro_instance into send_dm.

Related docs

• STARTUP_AND_CONFIG.md — instance info at boot and on reconnect
• MESSAGE_FLOW_AND_PROTOCOL.md — protocol overview and v2 status