# ADR-012: Registry backing, write surface, and the two-op-kind shape

## Status
Accepted (resolves OQ-06, OQ-07; amends ADR-010's feature story; §3 gate
table replaced by ADR-015)

## Context

With OQ-08's model fixed (ADR-011: grants in repo records, policy in
core), three decisions remained, tangled together:

1. **Backing store for the gix feature's `GitRegistry` impl** (OQ-06,
   deferred on "metadata-scale requirements"). The deferral assumed the
   backing choice gated something; under the alknet repo/adapter pattern
   (traits + in-memory/config default in-crate, persistence adapters
   additive in separate crates — alknet ADR-033/035), the default's
   choice never depended on scale. Scale only ever gates a *persistence
   adapter*, which is additive by construction.
2. **Registry mutation ops** (OQ-07): whether the gix feature ships
   repo create/delete/visibility/grant management as reusable alkcall
   ops, or leaves all mutation to downstream assembly. The user-session
   resolution: CRUD is wanted, with a two-tier shape — a global admin
   has the scopes for most things, while a user who creates a repo
   administers *their own* repos.
3. **Op-kind classification** (user session, 2026-09-21): git is the
   first family payload that naturally wants both alkcall op kinds —
   call ops (JSON RPC, schema-validated) for record management, an open
   op (channels, `BiStream`) for git sessions. The alkcall registry
   already supports this (openable ALPNs are operations — alkcall
   ADR-047; `ChannelOpenSpec` + `OperationSpec` in one
   `OperationRegistry`); alktty/alktunnels ship only open ops, and the
   coming docker crate will ship only call ops (bollard management)
   plus consume alk/tty's open op. Git supplying both kinds from one
   crate is new for the family but classification-only — no new
   registry machinery.

Also carried: the "gix feature" name conflated the gitoxide engine
components with the `gix` facade crate (a client-oriented entry point)
and with the registry store (which needs no gitoxide at all).

## Decision

### 1. Read/write split on the record family

```
pub trait GitRegistry: Send + Sync {
    async fn resolve(&self, repo_id: &str) -> Result<RepoRecord, RegistryError>;
}

pub trait GitRegistryStore: GitRegistry {
    async fn put_repo(&self, record: &RepoRecord) -> Result<(), RegistryError>;
    async fn update_repo(&self, record: &RepoRecord) -> Result<(), RegistryError>;
    async fn remove_repo(&self, repo_id: &str) -> Result<(), RegistryError>;
}
```

- The write supertrait follows alknet ADR-035's shape (read on the wire
  hot path, write on the management path; `ConfigIdentityProvider` does
  not implement the write trait there, and the config-backed default
  here follows the same posture — its write path is record files, §2).
- Grants ride `RepoRecord` (ADR-011); grant mutation is `update_repo`.
  Convenience wrappers (grant/revoke as named methods) are additive
  later, two-way.
- The `git/repo/*` ops are thin wrappers over `Arc<dyn
  GitRegistryStore>`. An embedder with a DB registry registers the same
  ops over their own store.

### 2. Default backing: per-repo record files, in-memory index (`registry-file` feature)

- One small record file per repo (repo id, storage root, visibility,
  grants), plus an in-memory index (the resolve path reads the index,
  never the file). Config-seeded at boot; op-mutable at runtime.
- Writes are atomic (write-temp + rename) and update the index on
  change. Reload-on-change via file watching is the file-scale analog
  of alknet's honker NOTIFY story (alknet ADR-035) — adequate at
  repo-record scale; if multi-process sharing ever matters, that is a
  persistence-adapter concern, not a trait change.
- Storage roots are derived by the store's own naming rules at create
  time. Wire names never touch paths (ADR-008 unchanged): creation is
  not a wire-input-to-path operation, and resolution returns the
  configured root.
- Feature: **`registry-file`**, default-on, **no gitoxide
  dependency**. Persistence adapters (SQLite et al.) are future,
  separate, additive — built when a deployment with dynamic repo
  management at persistence scale exists.

### 3. CRUD ops shipped in-crate, always-on, External with scope+grant ACL

*(Gate table amended by ADR-015 — the original "scope OR ownership"
formulation was not expressible in alkcall's `AccessControl` (review 001
A-1); the two-tier rule below is the ADR-015 shape.)*

Ops (names indicative, schema-stable once published):

| Op | Acts on | Gate |
|---|---|---|
| `git/repo/create` | store: mint id, allocate root, seed record | scope `git:repo:create` (static registry gate) |
| `git/repo/delete` | store: remove record | scope `git:admin` **or** `manage` grant (ADR-015) |
| `git/repo/update` | store: visibility/grants/root | scope `git:admin` **or** `manage` grant (ADR-015) |
| `git/repo/get` (list/read) | registry reads | scope `git:admin` **or** `manage` grant (ADR-015) |

- **Shape:** ordinary alkcall call ops (`OperationSpec`, JSON,
  schema-validated), `Visibility::External`, registered by the
  assembler wherever it wants them exposed. They are **not**
  feature-gated (thin over the store trait, no gitoxide) and not
  Internal: ops an end user must call are wire-callable by definition;
  the gitea lesson is served by the ACL (visible-surface =
  authorized-surface), not by hiding the ops. OQ-07's old
  "Internal ops over an admin listener" framing had the right mechanism
  and the wrong axis.
- **Two-tier authorization** *(superseded by ADR-015's shape: `create`
  keeps a pure-scope `AccessControl`; `delete`/`update`/`get` carry an
  empty `AccessControl` and the handler evaluates "admin scope OR
  `authorize(record, identity, manage)`" as one tested function in
  alkgit core, with the generic FORBIDDEN denial and the unknown-repo ≡
  unauthorized rule (ADR-008) at the op layer. Repo create mints
  ownership via `OwnershipStore::record` *and seeds the creator's
  `{read, write, manage}` grants* — "creator administers their own
  repos" is now the `manage` grant path.)*
- **Grants govern access; scopes govern platform capability.** Repo
  create seeds the creator's `{read, write, manage}` grants in the
  record explicitly (ADR-015: administration is the `manage` grant —
  the record is the single per-repo authz surface; op scopes and record
  grants remain distinct *sources*, platform capability vs per-repo
  capability).

### 4. Feature split (amends ADR-010's single-`gix` feature story)

| Feature | Default | Contents | Needs gitoxide |
|---|---|---|---|
| `gix` | yes | `GitRefs` / `GitPackGen` / `GitPackIngest` impls (the local-disk object-storage engine: odb/pack/ref/object/fsck components) | yes |
| `registry-file` | yes | `GitRegistry`/`GitRegistryStore` default impl + the record store | no |
| neither | — | wire/protocol-only embed (`default-features = false`) | — |

- Two features, not one: independent seams (backend.md's full-family
  rationale) — a downstream with a DB registry still wants the gix
  engine; a downstream with S3 object storage still wants a simple
  registry. Batteries-included unchanged (both default-on).
- **The `gix` facade crate is dropped from the dependency list.** POC-2
  drove `gix-odb`/`gix-pack` at the component level; the backend needs
  `gix-discover` + `gix-odb::Store::at` from a registry-resolved root,
  not facade machinery. Verified at implementation; the facade comes
  back only if a concrete need appears.
- `gix-protocol`/`gix-transport` (client-side) remain in the wire
  layer's dependency set only pending the consumer-half decision
  (`GitSession` may reuse `gix-protocol`'s response parsing or
  hand-roll the small client surface; `gix-transport` is almost
  certainly droppable). Implementation-time call, recorded, not an
  architecture commitment.

### 5. The recorded future trigger for a crate split

If the op set ever grows past repo records — users, orgs, cross-repo
permission management — that is a platform application, and it is
downstream's crate, not alkgit's. The ops stay minimal ("ops wrap a
method on the repo"); the trait family and the one-crate shape are
unpublished, so the split remains a two-way door.

## Consequences

- **Positive:** OQ-06 resolves without its deferred "scale
  requirements" ever arriving (the trait is the boundary; the default
  is file-scale by design; persistence adapters stay additive); OQ-07
  resolves with a shipped, small, reusable op set; the docker-crate
  comparison (call ops / open op separation) lands as a classification,
  not a structural change; the feature story now matches what the
  features actually contain.
- **Negative:** the op set is public API before any downstream exists
  (names + schemas become compat surface at first publish — OQ-03's
  freeze inventory). Grant-convenience methods deferred means grant
  edits go through full-record `update_repo` in v1 (last-writer races
  are the assembler's concern; acceptable at record scale, and the
  additive path exists).
- **Neutral:** the registry-file store's watch/reload loop is an
  implementation detail; its failure mode (watch loss) degrades to
  "records update on next process start," never to wrong-path or
  wrong-authz behavior (the index is authoritative per record file
  content, re-verified on reload).

## References

- OQ-06, OQ-07 (resolved by this ADR), OQ-03 (the publish freeze this
  op set enters)
- ADR-010 (superseded sub-parts: single `gix` feature story), ADR-008
  (registry-resolved ids), ADR-007 (enforcement order), ADR-011
  (grants in records, two-data-sources rule)
- alkcall ADR-047 (openable ALPNs are operations — the classification),
  ADR-017 (visibility + handler identity), ADR-011 (ownership model —
  repo-create mint-and-own), alkcall `AccessControl` (scope + resource
  composition)
- alknet ADR-033/035 (repo/adapter pattern; read-sync/write-async split;
  honker NOTIFY — the pattern this ADR's file-watch analog follows)
- alktty (open-op-only posture), alknet-docker (planned call-op-only
  posture — the two siblings this ADR's dual-kind shape sits between)
- backend.md (trait family, feature model), doors.md (registration
  surface), vision.md §"Registry management ops" (amended by §3)