# ADR — Discovery mechanism (inbox-fed index, fan-out)

**Date:** 2026-06-16 · **Status:** mechanism accepted; target owner undecided.
Ported here for the discovery mechanism it defines — the piece this lib
realizes (`inbox.ts` post/materialize/watch; `store-registry.ts` fan-out). The
product intent (what a consumer application *should* surface) is the consumer
application's concern, not this lib's; only the mechanism is recorded here.

## Access is not discovery

- **Access**: may I read this document if I hold it? A public entity is
  world-readable with its NURI.
- **Discovery**: how do I learn it exists, in order to read it? This is the ADR's topic.

## The mechanism

1. A single global index, fed via its inbox. The creator does not edit
   the index directly: it deposits a reference into the index's inbox. The
   index is an owned document (public read), built up from its inbox (a
   watcher ingests deposits and adds entries).
2. Primary discovery is that global index.
3. Relational is a secondary axis, overlaid: a peer's participations,
   markers on the global list. It rests on existing per-item data (protected scope),
   with no new primitive.

## The 3-stage frame

`discovery → synchronization → query`

1. **Discovery**: the index gives the NURIs of the entity documents.
2. **Synchronization**: subscribe to those documents so they replicate locally
   (verifier: `self.repos` + oxigraph dataset).
3. **Query**: query what is now local (sort, limit, reactivity). SPARQL/ORM
   run on the local set only (`resolve_target_for_sparql` searches `self.repos`) —
   you cannot query what is not loaded.

**Corollary:** a reactive query does not replace the index — it runs at stage 3 on
the local union that stages 1-2 built. You don't sync what you didn't discover.

## Why one reused mechanism

- **No Group store.** The index is not open-write: it is an owned document
  (public read) plus a native inbox (a primitive present on every document). Nobody
  writes the index but its owner (by ingesting inbox deposits). So the model
  stays "3 stores + Dialog + inboxes, no Group store."
- **One mechanism, reused.** The inbox + ingest watcher serve both
  submitting an entity to the index and a registration/deposit in one consumer
  app — same `inbox.post` API, same handling. This is exactly `inbox.ts` in this
  lib (`post` / `read` / `materialize` / `watch`).
- **Natural dedup / moderation point:** the inbox → index ingest is where
  duplicates are detected / moderated before insertion.

## Index owner — target model undecided

NextGraph apps and services are mono-user with no global data
(see [`../nextgraph-current-state.md`](../nextgraph-current-state.md) § Apps &
services), so a dedicated service with its own wallet sharing a freely-readable
index is not a NextGraph shape. The only path glimpsed for a global document is a
singleton app bound to the developer-user — not implemented, uncertain, to explore
later. This is why a global-index package is a deferred separate package in this lib
(see the top-level README).

## Polyfill reality — the fan-out drift is now RESOLVED (special-account index)

The shared-wallet polyfill originally shipped a cross-account fan-out over
every account's public documents (`store-registry.ts` `listEntityDocs('public')`
/ `resolveReadGraphs`) — one account saw another's public entity without any
relationship to its creator. This ADR classified that per-account fan-out as a drift
to be replaced by the single global index.

That drift is now resolved in the polyfill. The inbox-fed global index of
this ADR is implemented on top of a reserved special account in the shim
(`discovery.ts`, `INDEX_ACCOUNT = reservedAccount("index")` — a sentinel-prefixed
key in the shim's reserved namespace that `normalizeId` can never produce, so it is
disjoint from any normalized user id, not the literal `"@index"`) that owns the
index document while
the target owner stays undecided: `submitToIndex(ref)` deposits into the index
document's inbox; `readIndex()` ingests (dedups) the entries. The app-facing
discovery path is now "read the index", exactly as this ADR prescribes — not
the fan-out. The cross-account fan-out survives only as an internal lib
fallback (it still powers per-scope listing like `resolveReadGraphs`), never
the discovery route. The special account is the provisional owner; at migration
it disappears and ownership moves to the decided global-index owner (see
[`../migration-guide.md`](../migration-guide.md)) with the consumer application's
surface (`submitToIndex` / `readIndex`) unchanged.

## Alternatives rejected (mechanism)

- **Open-write index** (creator writes the index directly): required a
  collaborative document (Group store, SDK-blocked) and exposed the index to
  corruption. Replaced by inbox deposit + owner-side ingest.
- **Purely relational discovery** (`social_query`): rejected as *primary* (a
  global list is wanted); kept as a secondary axis.
- **No index, direct reactive query**: impossible — SPARQL is local-only (stage 3).