Second installment from @zicklag.dev
At @roomy.space we've been cooking up the design for the next, ATProto-native iteration of Roomy, and that includes private data on protocol!
The first component that we're working on is a group membership service that we're calling the...
The permissioned data proposal has the concept of membership, but leaves it to the app to orchestrate it. The arbiter is our idea for a general-purpose, interoperable ATProto group membership service.
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From @zicklag.dev
So far the short addendum to the arbiter doc should be at least:
Having a special $publish space that allows writing to public records under the arbiter’s DID, if the arbiter has a public repo setup.
Making a note about syncing, that it could go either way, and that we might need to experiment with different solutions. The core implementation is agnostic to sync specifics, and if you don’t use remote space delegation, then you don’t need syncing at all.
Mentioning “adopting” a DID as an option.
Mention that I think when it comes to publishing records to permissioned spaces or a public repo that is an extra feature that isn’t required for all arbiter implementations.
Edit: Also we could have a $labeler role that lets you create / edit / delete labels if you have the ConfigureSpace permission in that space.
A preliminary version of this is being sketched out in @flo-bit.dev ’s contrail .
# Communities
Group-controlled atproto DIDs. A community is a DID whose signing/rotation keys are held by the appview on behalf of multiple members, with tiered access levels. Built on top of [spaces](./05-spaces.md).
## When to use this
When you want atproto records published under a *shared* identity — a team, a project, a channel — not a single user. Think: a group's published calendar events, a community's published posts.
## Two modes
- **Minted** — contrail creates a fresh `did:plc` for the community, holds the signing key plus one rotation key (a second rotation key is returned to the creator once for recovery), and publishes from it.
- **Adopted** — contrail takes over an existing account by holding an **app password** issued from its PDS. The owner's identity, signing key, and rotation keys are unchanged; contrail just gets PDS write access via the app password.
Either way, the result is the same: a DID that multiple members can act through, gated by access levels.
## Access levels
Each member has a level (ranked). Levels map to write permissions. Owners can grant/revoke levels. Two reserved levels exist: `owner` and `member`. Your deployment defines the rest:
```ts
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# Spaces
Auth-gated store for records that can't live on public PDSes — private events, invite-only groups, members-only chat. Opt-in; zero cost if you don't enable it.
## Mental model
> A **space** is a bag of records with one lock. The **member list** says who has the key.
- One owner (DID), one type (NSID), one key. Identified by `ats://<owner>/<type>/<key>` — distinct scheme from atproto record URIs (`at://`) so the two can't be confused at any layer.
- Every member (including owner) has read + write inside the space. Delete is scoped to your own records — no one can remove records they didn't author, owner included. To wipe everything, delete the space.
- Optional **app policy** gates which OAuth clients can act in the space.
Every permission boundary is its own space. No nested ACLs. Richer roles = more spaces or app-layer checks.
## Enable
```ts
import type { ContrailConfig } from "@atmo-dev/contrail";
const config: ContrailConfig = {
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