docs: ADR-0001 nostr event model

Records the decision to compose standard NIPs (99 listing, 78 reservation,
52 calendar, 17/59 DMs) and reserve aiolabs kind:22000/22001 only for the
ephemeral availability RPC. Documents rejected alternatives (bespoke 2200x
booking record, RSVP-as-booking, deprecated NIP-15) and flags the 22000/1
allocation to register in workspace CLAUDE.md.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019VUQCfdqiLSsFS2jcGnaFD

docs/adr-0001-nostr-event-model.md

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+# ADR-0001 — Nostr event model for room rentals
+
+**Status:** accepted (design phase) · **Date:** 2026-07-19
+
+## Context
+
+Chatelet needs a Nostr representation for: a room listing, a private booking
+negotiation, a durable reservation record for the guest, public
+availability, and a live "is it free?" query. No single NIP defines a
+rental-booking protocol. We must decide whether to invent a bespoke set of
+kinds or compose existing NIPs.
+
+Constraints from the workspace:
+
+- **Respect protocol semantics over friction reduction** — pick the kind a
+  primitive is *for*, not whatever listener happens to exist.
+- **CLINK band `21001–21099` is OFF-LIMITS.** Aiolabs custom band is
+  `22000–22099`; document each allocation.
+- **No nsec at rest** — all signing/encryption via `resolve_signer`.
+
+## Decision
+
+Compose standard NIPs; reach into the aiolabs band only for the one case no
+standard kind fits.
+
+| Concern | Choice | Why |
+|---|---|---|
+| Room listing | **NIP-99 `kind:30402`** | Purpose-built for listings; the NIP names *rentals* explicitly. Has `price` with a `frequency` (`night`), `location`, `g` geohash, images. Addressable (`d`=room id) so edits replace. |
+| Guest reservation record | **NIP-78 `kind:30078`** | App-specific replaceable data; workspace already endorses 30078 for app state. Addressable (`d`=booking id) so status transitions replace in place. NIP-44 encrypted to the guest. |
+| Public availability | **NIP-52 `kind:31923/31924`** | Calendar events are exactly "these dates are occupied". Published without PII, gated by `settings.publish_availability`, so third-party clients can render open dates without querying us. |
+| Private request → quote → confirm → check-in | **NIP-17/59 giftwrap (`kind:1059`)** | The private-messaging standard. Relays store them (survives operator downtime), metadata-private, no bespoke transport to maintain. |
+| Live availability query + response | **aiolabs `kind:22000` / `kind:22001`** (ephemeral) | A live ping/pong; no standard kind fits, and it *should* be ephemeral (no need to persist a stale "free?" check). Mirrors how CLINK uses the ephemeral range for payment RPC. |
+
+## Rejected alternatives
+
+- **A single bespoke `kind:2200x` for the whole booking (request + record).**
+  Rejected: the `20000–29999` range is *ephemeral* — relays don't store it,
+  so a booking request would be lost if the operator were briefly offline.
+  Persistent booking state belongs in stored kinds (giftwrap DMs + `30078`),
+  not the ephemeral band. Using ephemeral only for the genuinely-transient
+  availability ping is the semantically honest split.
+- **NIP-52 RSVP (`kind:31925`) as the booking request.** Rejected: RSVP means
+  "attendance intent for a calendar event" — a commercial reservation with
+  money and a hold is a different relationship. Repurposing it would conflate
+  attendance with booking (the exact anti-pattern the workspace CLINK/kind
+  rule warns against).
+- **NIP-15 marketplace order flow (`kind:30017–30019`).** Rejected: the NIP
+  is deprecated ("too complicated, use NIP-99") and its stall/product/order
+  model is a poor fit for date-ranged, single-inventory lodging.
+
+## Kind allocation register (action required before ship)
+
+`22000` (availability query) and `22001` (availability response) are hereby
+claimed for Chatelet in the aiolabs `22000–22099` band. **Follow-up:**
+record this allocation in the workspace `CLAUDE.md` kind-allocation section
+so a future extension doesn't reuse the numbers. Ephemeral, so on-wire
+collisions would be transient — but still worth registering.
+
+## Consequences
+
+- The heavy lifting stays in standard NIPs → third-party Nostr clients get
+  listings + availability for free; less bespoke code to maintain.
+- Exactly one custom, low-stakes (ephemeral) kind pair to own.
+- Booking *authority* stays in LNbits regardless of event choices — the
+  events are the interop skin over a DB-arbitrated flow (see
+  [`event-flow.md`](event-flow.md)).