# Client-Side Federation System

> **Companion spec:** This document covers the **client-side** multi-instance architecture. For server-to-server relay (HMAC auth, outbox pipeline, relay events, identity resolution), see [`federation.md`](federation.md). Both systems work together — S2S relay distributes data between servers, while this client system enables users to interact with multiple instances from a single app session.

Source files:
- `packages/web/src/stores/instanceStore.ts` — Core multi-instance connection management, token caching, topology sync
- `packages/web/src/hooks/useWebSocket.ts` — WebSocket multiplexing (one connection per instance), origin-aware event routing
- `packages/web/src/stores/spaceStore.ts` — Origin-aware space/channel store, `channelOriginMap`, `getChannelOrigin()`, `resolveUserOrigin()`, `getLayoutHomeOrigin()`, `getMyUserIdForOrigin()`, DM deduplication
- `packages/web/src/utils/crossStoreResolvers.ts` — Neutral module holding the cross-store resolver bindings (`_getApiForOrigin`, `_resolveOriginFromHostname`, `_getUserIdForOrigin`) + the WS-populated user-ID cache. Breaks a TDZ cycle between spaceStore and instanceStore; see "API Client Resolution" below
- `packages/web/src/utils/identity.ts` — Cross-instance user identity resolution (`isSelf`, `canonicalUserMatch`, self-ID registry)
- `packages/web/src/hooks/useInstanceConnect.ts` — Connection flow hook for the Connections UI
- `packages/web/src/components/modals/ConnectedInstances.tsx` — Connections settings panel

---

## Architecture Overview

**Client-side vs S2S federation by feature:**
- **Friend & DM relay are S2S.** Sending a friend request to `alice@orbit.tld` does not require having a federated account on `orbit.tld`; the sender's home server queues the relay (see `social.md` §6 outbound flow). DM messages are similarly relayed server-to-server once the initial channel exists.
- **Spaces are client-federated.** Joining a remote space still requires creating a federated account on that instance via the Connections UI.

Backspace supports **client-side federation**: a single app session (web or desktop — both are feature-identical) can connect to multiple Backspace instances simultaneously. The user has a **home instance** (their primary identity) and zero or more **connected remote instances**.

```
┌─────────────────────────────────────────────────┐
│               Electron / Web App                │
│                                                 │
│  ┌──────────────┐    ┌──────────────────────┐   │
│  │ Home Instance │    │ Remote Instance(s)   │   │
│  │ nova.ddns.net│    │ orbit.ddns.net│   │
│  │              │    │                      │   │
│  │ WS ──────────┤    │ WS ──────────────────┤   │
│  │ API ─────────┤    │ API ─────────────────┤   │
│  │ JWT ─────────┤    │ JWT ─────────────────┤   │
│  └──────────────┘    └──────────────────────┘   │
│                                                 │
│  instanceStore manages all connections          │
│  spaceStore merges data from all origins        │
│  channelOriginMap routes operations to origin   │
└─────────────────────────────────────────────────┘
```

**What this enables:**
- Join Spaces on any connected instance
- See friends across instances (friend discovery)
- DMs between users on different instances (via S2S relay — see [federation.md](federation.md))

**What each instance provides:**
- Its own JWT token and authenticated API client
- Its own WebSocket connection (heartbeat, events)
- Its own user identity (different Snowflake ID per instance)

---

## 1. Federated Account Creation

When a user adds a remote instance via the Connections settings to **join a space there**, the client creates (or logs into) an account on that instance. As of 2026-04-25, this is no longer required for friending or messaging users on a remote instance — those flows are fully S2S (see `social.md` §6 and `federation.md` §4 respectively). Federated accounts remain real loginable accounts and retain all capabilities (login, space membership, password sync, deletion).

This is a **real account with a real bcrypt password** — not a replicated stub.

### Username Format

| Account type | Username | passwordHash | homeInstance | Can log in? |
|---|---|---|---|---|
| Local (native) | `erin` | bcrypt hash | `NULL` | Yes |
| Federated (client-created) | `erin@nova.ddns.net` | bcrypt hash | `nova.ddns.net` | Yes |
| Replicated stub (S2S-created) | `erin@nova.ddns.net` | `!federation-replicated` | `nova.ddns.net` | No |

Key distinction: **Federated accounts** and **replicated stubs** can have the same username format (`user@instance`), but federated accounts have real passwords and can log in. Replicated stubs are server-created placeholders for identity resolution and cannot log in.

The merge migration in `migrate.ts` detects when both exist for the same remote user and merges them (real account always wins).

### Connection Flow (`connectToRemote`)

When a user adds a remote instance via the Connections settings:

1. **Verify home password** — client confirms the user's password against the home instance
2. **Compute federated username** — `{bareUsername}@{homeHost}` (e.g., `erin@nova.ddns.net`)
3. **Try registration** on remote instance with:
   - Username: `erin@nova.ddns.net`
   - Password: same as home instance password
   - `homeInstance`: `nova.ddns.net` (bare domain)
   - `homeUserId`: user's Snowflake ID on home instance
4. **If registration fails** (account already exists) — fall back to login
5. **On success** — store JWT token, create API client, open WebSocket, sync profile

The same password is used across all instances. Password changes on the home instance are synced to remote instances automatically.

### API Client Error Contract

The shared API client (`packages/web/src/api/client.ts:298`) throws `new Error(body.error)` for non-2xx responses. The server's structured error code is on `err.message`; there is **no** `err.body` or `err.code` property. Catch handlers that need to map codes to UI messages should read `err.message` and pass it as both the code and the fallback to `mapServerErrorToMessage` (see `packages/web/src/utils/friendErrors.ts`).

This was documented after T19/T20 catch blocks initially read the wrong shape and surfaced raw codes as toast text — fixed in commit `d207af4`. The same pattern applies to any new client-side code that catches API errors from the home or remote instances.

---

## 2. Instance Store (`instanceStore.ts`)

The central store for multi-instance state.

### State

```typescript
interface ConnectedInstance {
  origin: string;           // 'https://orbit.ddns.net'
  label: string;            // Instance display name
  token: string;            // JWT for this instance
  user: User;               // User record on this instance
  username: string;         // e.g., 'erin@nova.ddns.net'
  status: 'connected' | 'connecting' | 'disconnected' | 'error';
  error?: string;
  api: BackspaceApiClient;  // Authenticated API client
}

interface InstanceState {
  instances: ConnectedInstance[];
  _autoConnectDone: boolean;    // Has startup reconnection finished?
  pendingSyncOrigins: string[]; // Instances needing password sync
}
```

### Token Caching

Tokens are persisted to `localStorage` keyed by `backspace_instances_${userId}`. This allows automatic reconnection on app restart without re-entering passwords.

### Auto-Connect on Startup (`autoConnectAll`)

Called once per session after login:

1. Read `currentUser.replicatedInstances` from the home server (list of known remote origins)
2. Load cached tokens from `localStorage`
3. For instances **with cached tokens**: attempt reconnection in parallel — verify token, open WebSocket, sync profile
4. For instances **without cached tokens**: create error placeholders (visible in Connections UI with "re-authenticate" prompt)
5. Set `_autoConnectDone = true` to unblock topology sync

### Topology Sync (`syncInstanceList`)

After connections change, the client notifies all instances of the current topology. Each instance receives a perspective-correct list:
- **Home instance** gets: list of all remote origins
- **Remote instances** get: home origin + all other remote origins (excluding self)

This allows S2S federation to know which peers to relay to.

---

## 3. Origin-Aware Routing

### Origin String Convention

- `''` (empty string) = home instance
- `'https://domain.com'` = remote instance (full URL with protocol)

### channelOriginMap

Every channel (space channels and DM channels) is tagged with its origin instance:

```typescript
// In spaceStore:
channelOriginMap: Map<string, string>  // channelId → origin

// Usage:
getChannelOrigin(channelId): string    // Returns '' for home, origin URL for remote
```

Built during `populateFromReady()` when WS ready events arrive from each instance.

> **DM channels** are mapped to the origin of the instance that delivered them in the `ready` event. For 1-on-1 DMs created locally this is typically `''` (home), but federated DMs may arrive from any connected instance. DM read/write operations are routed to the channel's origin via `getApiForOrigin(getChannelOrigin(channelId))`. S2S relay then propagates changes to all other instances that have the same channel.

### DM Origin Failover

When a remote instance's WebSocket drops mid-session, every DM pinned to that origin is re-keyed to a connected sibling that mirrors the same federated DM (via S2S replication). This keeps DM operations working through a transient disconnect, at the cost of a brief message-cache flush on the rekeyed DMs.

**Mechanism:**

- `dmAlternatives: Map<federatedId, Map<origin, localChannelId>>` on `spaceStore` records every origin's local channel ID observed in any `ready` payload, regardless of whether the dedup pass kept that copy in `dmChannels`.
- `failoverDmOriginsFromDisconnected(origin)` in `utils/dmOriginFailover.ts` walks DMs pinned to the disconnected origin, looks up a connected alternate in `dmAlternatives` (preference: home first, then any connected remote in insertion order), and calls `rekeyDmChannel` to atomically rename the DM across `spaceStore`, `chatStore`, and the URL.
- `chatStore.rekeyChannelState(oldId, newId)` deletes all channel-keyed entries for `oldId` (messages, hasMore, scrollPositions, channelAccessTimes, typingUsers, readStates) without seeding `newId` — subscribers re-fetch from the new origin. `unreadChannels` membership transfers only if `oldId` was already unread. `currentChannelId` updates when it matches `oldId`.
- URL: `history.replaceState` swaps the path segment in place when the user is viewing the rekeyed DM — no router navigation.

**Triggers:** `instanceStore.setInstanceStatus` on `connected → disconnected|error`; `disconnectInstance` and `forceRemoveEntry` call failover before `removeInstanceSpaces` so DMs with connected alternatives survive user-initiated disconnect.

**Intentional UX trade-off:** on failover, the active DM's message cache is flushed (origin-local message IDs don't match the new origin's responses). A brief "loading" state appears while the chat view re-fetches. Documented intentionally — failover is a recovery path, not the hot path.

**Voice is out of scope.** LiveKit rooms are bound to the hosting origin and cannot migrate. `voiceStore.activeDmCall` / `outgoingCall` / `incomingCall` are not rewritten by failover; voice state clears through existing LiveKit disconnect paths.

**No re-home on reconnect:** when the originally pinned origin comes back, its `ready` re-adds its local id to `dmAlternatives` but leaves the new primary in place. Avoids flapping.

**WS event routing contract:** every DM WS event handler either routes via the primary `dmChannels` id (using `resolveDmChannelId(rawId)`) or silently no-ops on unknown ids. Only `dm_channel_created` creates new `dmChannels` entries — and it dedups by `federatedId` first.

Source: `utils/dmOriginFailover.ts` + extensions in `stores/spaceStore.ts`, `stores/chatStore.ts`, `stores/instanceStore.ts`, `hooks/useWebSocket.ts`. Design spec: `docs/superpowers/specs/2026-04-23-dm-origin-failover-design.md`.

### User View Cache

The DM dedup pass at `populateFromReady` is first-wins by `federatedId` and skips the duplicate channel **as a whole**, including its `members` array. When a user is connected to multiple instances and a sibling instance's `ready` arrives first, the home instance's view of the same federated DM is dropped. Without further machinery, render sites would only ever see the sibling-stub view of every member — wrong username (`name@homeHost`), stale or 404-ing avatar URL, wrong `avatarColor`, and a globe icon for users whose home IS our currently-logged-in instance.

`userViews` is a parallel cache that mirrors the philosophy of `dmAlternatives`: information from skipped ready payloads is still load-bearing — for rendering, not for routing. Render sites read through it to surface the home view of every user the client has ever heard about, regardless of which carrying channel survived dedup.

**State:**

- `userViews: Map<canonicalUserKey, UserViewEntry>` on `spaceStore`. Each entry is `{ user: User, deliveredBy: string, isHome: boolean, updatedAt: number }`.
- `canonicalUserKey(user)` (in `utils/identity.ts`) returns `<homeInstanceHost>:<homeUserId>` for federated users and `:<id>` for purely-local users — same key across instances for the same person.
- `isDeliveryFromHome(user, deliveringOrigin)` (in `utils/identity.ts`) decides whether a delivery is "home view" or "stub view": the user is delivered from their home iff their `homeInstance` matches the delivering origin's host (with `''` resolving to `window.location.host`).

**Preference rule on upsert (`upsertUserView(user, deliveringOrigin)`):**

- If no entry exists: insert.
- If existing is home view and incoming is stub: ignore.
- If existing is stub and incoming is home view: overwrite (upgrade).
- Same tier (both home or both stub): freshness wins; incoming overwrites.

`deliveringOrigin` is a REQUIRED parameter — never default it. The user's declared `homeInstance` is NOT a substitute, because a stub view delivered by orbit has `homeInstance=nova`; pruning by declared home would evict the wrong entries.

**Wire surfaces that upsert** (every place a `User` lands on the client from a connection):

- `populateFromReady` walks `incomingDms[].members` BEFORE the `federatedId` dedup pass — load-bearing — and walks every space's `members[].user`. `loadSpaceDetail` upserts each member after asset normalization.
- WS handlers in `useWebSocket.ts`: `ready` (space members), `dm_message_created` / `dm_message_updated` / `message_created` / `message_updated` (`message.user` and `message.replyTo?.user`), `user_updated`, `member_joined`, `friend_request_received` / `friend_request_sent` / `friend_request_accepted`, `dm_channel_created`, `dm_member_added`.
- REST hydrators: `socialStore.loadFriends` / `loadRequests` / `searchUsers`, `discoverStore.fetchUsers`, `utils/mutuals.loadFederatedMutuals`. Each upserts with the load's origin.
- Modals that fetch a profile via REST (`UserProfileModal`, `TransferOwnershipModal`) call `useSpaceStore.getState().upsertUserView(fetchedUser, fetchOrigin)` after the fetch returns.

**Render-side lookup:**

- `useCanonicalUserView(user)` in `utils/userViewLookup.ts` is a Zustand selector hook that subscribes to the cache entry for `canonicalUserKey(user)`. Render sites call this before reading `username` / `displayName` / `avatar` / `avatarColor` / `homeInstance` / `homeUserId`. The hook returns the input on cache miss; the component falls back to current best information until the cache fills.
- `getCanonicalUserView(user)` is the synchronous getter for non-React paths (event handlers, helpers like `useVoiceParticipantMeta`).
- `isFederationGlobeApplicable(user)` in `utils/identity.ts` is the predicate used at three globe-icon sites (`DmListItem`, `MainContent`, `MobileDmsScreen`). It gates the globe on `parseFederatedUsername(username).domain && domain !== window.location.host` — no globe for users whose home is us, even when only a stub is loaded.

**Render reactivity is structural, not coincidental.** Subscribers receive cache updates via the Zustand selector, regardless of whether legacy update paths (`updateUserEverywhere`, `updateFriendProfile`) also fired. That coupling was deliberately avoided so that future contributors who add a new wire surface and only call `upsertUserView` do not silently break render propagation.

**Composition with `isSelf` / `resolveDisplayIdentity`.** Self-rendering continues to flow through the existing identity helpers — `isSelf` for filtering, `resolveDisplayIdentity` for substituting the home identity into a replicated alias of self. The cache lookup composes alongside, not inside: render sites filter via `isSelf`, then pass non-self users through `useCanonicalUserView`. Self-as-member (e.g. in a group DM) goes through the cache like any other member; the cache holds the home view of self anyway.

**Lifecycle:**

- Pruned in `removeInstanceSpaces(origin)` — drops every entry whose `deliveredBy === origin`. Mirrors the `dmAlternatives` prune in the same function.
- `reset()` clears the cache.
- **NOT pruned on transient WS disconnect.** Last-known view persists across blips, matching `dmAlternatives`' no-flapping invariant. If the surviving cache no longer holds a home view for some user (because the home origin was fully removed), render falls back to whatever the carrying payload supplies — degrades to the stub view, no crash.

**Out of scope by design:**

- The cache is render-only. It does NOT feed identity-resolution or write paths. API write payloads (e.g. `api.dm.create`, `api.friend.add`) continue to source identity from the original prop or click-site state, where the user explicitly nominated `homeUserId`/`homeInstance`.
- The cache stores `User`-shaped fields. Extended profile data (`bio`, `banner`, `pronouns`) fetched via REST in profile modals lives in those modals' local state; `upsertUserView` is called from modals only to seed the home view of the cache, not to mirror extended profile data.

Source: `stores/spaceStore.ts` (state, `upsertUserView`, prune in `removeInstanceSpaces`), `utils/identity.ts` (`normalizeOriginToHost`, `canonicalUserKey`, `isDeliveryFromHome`, `isFederationGlobeApplicable`), `utils/userViewLookup.ts` (`getCanonicalUserView`, `useCanonicalUserView`).

### API Client Resolution

```typescript
getApiForOrigin(origin: string): BackspaceApiClient
```

Returns the correct API client for the given origin. Uses a resolver pattern to break circular dependencies between stores:

- The resolver backing, its setter (`setApiForOriginResolver`), and the getter (`getApiForOrigin`) live in `packages/web/src/utils/crossStoreResolvers.ts` — a neutral module with no store imports
- `instanceStore` imports the setter from the utility directly (not from `spaceStore`) and registers the resolver at module init
- `spaceStore` re-exports `getApiForOrigin` (and its sibling setters) from the utility for backward compatibility with existing import sites
- Consumers call `getApiForOrigin(getChannelOrigin(channelId))` to get the right client

The same pattern covers `resolveOriginFromHostname` (for `resolveUserOrigin`), the user-ID resolver (`resolveUserIdFromInstances`), and the WS-populated user-ID cache (`setMyUserIdForOrigin` / `getCachedUserIdForOrigin` / `clearMyUserIdCache`).

**Why the utility exists:** `instanceStore` runs top-level `setXResolver` calls at module load. If spaceStore holds the backing `let _getApiForOrigin` declaration AND the import chain reaches instanceStore while spaceStore is mid-load (e.g. via `JoinSpaceModal` importing `useInstanceStore` directly), the setter crashes with TDZ: `Cannot access '_getApiForOrigin' before initialization`. Hoisting the mutable bindings into a module that has no back-edges into the stores eliminates the cycle. Do NOT add imports from `./stores/*` into `crossStoreResolvers.ts` — doing so re-creates the exact cycle that module was carved out to break.

### User Origin Resolution

```typescript
resolveUserOrigin(user: { homeInstance?: string | null }): string
```

Determines which connected instance a user belongs to, based on their `homeInstance` field. Returns the origin string or `''` for local users.

---

## 4. WebSocket Multiplexing (`useWebSocket.ts`)

The client maintains **one WebSocket connection per instance** (home + each remote). Each connection has:
- Independent heartbeat (15-second ping via Web Worker)
- Exponential backoff reconnection
- Origin-aware event dispatching

### Sending

```typescript
wsSend(event, origin)    // Send to specific instance
wsSendAll(event)         // Broadcast to all instances
```

### Receiving

All incoming WS events pass through `handleEvent(origin, event)`. The `origin` parameter identifies which instance sent the event, enabling origin-aware state updates.

### Ready Event Processing

When a WS connection opens and authenticates, the server sends a `ready` event containing spaces, DM channels, voice states, etc. The client processes this via `populateFromReady()`:

1. Tag all spaces with `_instanceOrigin`
2. Merge into the unified space list (replacing stale data from same origin)
3. Build/update `channelOriginMap`, `channelToSpaceMap`
4. Normalize remote asset URLs to absolute paths
5. Merge DM channels from all origins — DMs are accepted regardless of which instance sends the `ready` event. Channels are deduplicated by `federatedId`: if a DM channel with the same `federatedId` is already loaded (from a previous `ready` event on another connection), the second copy is skipped (first-loaded copy wins). Channels without a `federatedId` are always accepted.
6. Last-write-wins layout merge for sidebar order

---

## 5. Cross-Instance Identity (`identity.ts`)

Users have **different Snowflake IDs on each instance**. The identity system resolves these:

### Self-ID Registry

```typescript
registerSelfId(id)   // Called on each WS ready event
isSelf(user)         // Checks all registered IDs
```

Tracks all IDs belonging to the current user across instances.

### Display Identity Resolution

```typescript
resolveDisplayIdentity(user, homeUser): User
```

If a user is `isSelf()`, returns the home user for consistent avatar/display name rendering. Prevents the same person appearing with different profiles across instances.

### Canonical User Match

```typescript
canonicalUserMatch(a, b): boolean
```

Determines if two user records represent the same person across instances. Cascade: same local ID → same homeUserId → username+homeInstance match.

---

## 6. Connections Settings UI

The **Connections** panel (in user settings) allows managing remote instance connections:

- **Home Instance** — always shown, cannot be removed. Desktop app has a "Change" button.
- **Remote Instances** — each shows status (connected/disconnected/error), hostname, username. Actions: Reconnect, Re-authenticate, Sync Password, Disconnect.
- **Add Instance** — multi-step form: enter hostname → verify password → register/login → connected.

### Add-Instance Pre-Flight: `federatedRegistrationOpen`

The hostname-probe step calls `GET /api/instance/info` on the target. The response carries two registration fields:

```typescript
{ name, version, registrationOpen: boolean, federatedRegistrationOpen: boolean, sourceCodeUrl: string, commit: string | null }
```

`sourceCodeUrl` / `commit` are the AGPL § 13 source offer (see `api.md`). `probeInstance` returns the whole payload, and the connect/login/reconnect/autoConnect paths persist `version`, `sourceCodeUrl`, and `commit` onto each `ConnectedInstance` so the client can surface the source link per instance.

`federatedRegistrationOpen` is the gate for **creating a federated `username@thisInstance` account** via the Connections flow. When the probe returns `federatedRegistrationOpen === false`, `ConnectedInstances.tsx` (the AddInstanceFlow's password step) renders an amber-tinted banner above the password input:

> "This instance has disabled new federated registrations. Existing accounts can still sign in."

**The submit button stays enabled.** This is the [login-unaffected invariant](auth.md#3-registration-flow) made operational on the client. The flow runs through `instanceStore`'s register-then-login fall-through:
- A user **without** an existing federated account on the target — register attempts 403 with `Federated registration is closed on this instance`; login attempts then fail with the existing "no account" error; the user sees the post-error toast.
- A user **with** an existing federated account on the target — register 403s, then login succeeds against their existing credentials. Working path preserved for legitimate re-login.

Disabling submit would extend the gate into login territory and soft-lock users with existing accounts on a closed instance — exactly the failure mode the invariant prevents. The 403 server-side stays as the security boundary; the banner is a UX hint.

The probe response is not cached client-side beyond the in-flight request, so toggle flips on the target are observed on the next add-instance attempt without explicit invalidation.

### Identity Deletion

Each remote instance row exposes an identity deletion flow with three modes:

| Mode | Label | Behavior |
|------|-------|----------|
| `leave` | Leave quietly | Client-only disconnect; no server call. Registry entry removed locally. |
| `soft` | Delete User | S2S soft delete — anonymizes the remote account and removes memberships; message history is retained. |
| `full` | Nuke everything | S2S full tombstone — soft delete plus purge of DM data and reactions. |

A scope selector controls which remotes are targeted: **This instance** (single remote) or **All remote instances** (fans out to every connected remote). A "Select instances" option is planned for future multi-select.

Deletion is triggered via `POST /api/users/@me/federation-identity/delete` on the home instance (rate-limited 5/15 min). The home instance fans out HMAC-signed `DELETE /api/federation/identity` requests to each target remote in parallel and returns a per-origin results map `{ [origin]: { success, error?, ownedSpaces? } }`. If a remote reports owned spaces (`409`), the UI surfaces the space list so the user can resolve ownership before retrying.

---

## 7. Federation Registry

The federation registry is a persistent server-side record of all instances a user has federated with. Unlike the `replicatedInstances` field (which serves S2S topology relay), the registry tracks the full lifecycle of each connection.

### Storage

- **Server:** `user_federation_registry` table — composite PK `(userId, origin)`
- **Client:** `registry` Map in `instanceStore` (Zustand)
- **LWW timestamp:** `federationRegistryUpdatedAt` on `users` table

### Lifecycle States

| State | Meaning |
|-------|---------|
| `connected` | Active WebSocket, valid token |
| `disconnected` | User intentionally disconnected; account exists on remote |
| `unreachable` | Remote is down/unresponsive |
| `auth_expired` | Token invalid; needs re-authentication |

### Sync Pattern

Client-driven LWW whole-registry push (same pattern as `profileSync.ts`):
1. User mutates registry → `registryUpdatedAt = Date.now()`
2. Client calls `PUT /api/users/@me/federation-registry` on all connected instances
3. Server rejects if `updatedAt <= stored` (409 Conflict)
4. On startup, client fetches registry from home via `GET`, merges with localStorage tokens, and seeds any `replicatedInstances` entries that aren't yet in the registry (with status `auth_expired`) so users with pre-feature data — or whose initial GET failed — still see their connections in the UI

### Sync-Ready Gate

`PUT` is gated behind an in-memory `_registrySyncReady` flag that is set true **only after a successful initial GET** in `autoConnectAll`. Until that flag flips, `syncRegistry()` is a no-op (and `autoConnectAll` does not call it).

**Why:** without this gate, a transient GET failure would leave the local Map empty/incomplete, but `set()` would still compute `registryUpdatedAt = Date.now()` (since `serverRegistryUpdatedAt = 0`). The trailing `syncRegistry()` would PUT the empty payload with a fresh-now timestamp; the server's LWW guard (`updatedAt > stored`) accepts it, and legitimate registry rows are wiped — including remote-instance entries the user never explicitly removed.

**Degraded mode (GET failed):**
- Registry Map is populated locally from `replicatedInstances` synthesis (display-only) so the UI still shows the user's known remotes as `auth_expired`.
- Mutations (`connectToRemote`, `disconnectInstance`, `reconnectInstance`, etc.) still update the local Map but **do not push** to home — `syncRegistry()` short-circuits.
- On the next session where GET succeeds, `localStorage` cached tokens reseed the registry and `syncRegistry()` pushes the merged authoritative state. No data is lost; sync is just deferred until we have a complete picture to merge against.

`reset()` (logout/account switch) clears `_registrySyncReady` along with the registry Map.

### API

- `GET /api/users/@me/federation-registry` — fetch registry + updatedAt
- `PUT /api/users/@me/federation-registry` — LWW whole-registry push

### Relationship to replicatedInstances

`replicatedInstances` continues to serve S2S topology relay — it tells the federation layer which peers to relay events to. The registry is a superset that also includes disconnected, unreachable, and auth-expired entries. The two are maintained independently.

---

## 8. Outbound Peering Gate (client surfaces)

When the local instance has `autoAcceptPeering=0`, every outbound new-peer attempt funnels through the centralized [Outbound Peering Gate](federation.md#outbound-peering-gate) on the server. The client surfaces three things: a new error code on the friend-add path, a new peering-status value on `/peer/ensure`, and two new Connections-settings panels (pending and outcomes).

### Peering-status taxonomy (`/peer/ensure` response)

`peeringStatus` returned from `POST /api/federation/peer/ensure` now includes `'admin_required'` alongside the existing `'active' | 'pending' | 'awaiting_approval' | 'rejected' | 'unreachable' | 'revoked'`. `'admin_required'` means: gate fired locally, your own admin must approve before any traffic reaches the wire. The user's request becomes admin-approvable rather than auto-firing.

### Friend-add error mapping (`peer_pending_local_admin`)

`POST /api/social/requests` returns 409 `peer_pending_local_admin` when the gate fires for a never-peered remote target (the user's request is queued + subscriber-tracked on the server; admin must approve).

`packages/web/src/utils/friendErrors.ts` maps `peer_pending_local_admin` to:

> "Your admin needs to approve federation with this instance. You'll see your request in Connections settings."

The catch handler reads `err.message` (per the API client error contract documented in §1) and passes it to `mapServerErrorToMessage`. Distinct from `peer_pending_approval` ("the *remote* admin must approve") — this one is local-admin gating.

### Connections settings — Pending peering approvals

A new section in the Connections settings UI (alongside the federation registry) lists the calling user's rows from `peer_approval_subscribers`, joined to parent `peer_approval_requests`. Each row renders:

- "Awaiting your admin's approval to federate with `{peerOrigin}` so you can `friend_add → alice@orbit`."
- A Cancel button. Cancel calls `DELETE /api/federation/peering-subscriptions/:id`. If the cancelled row was the last subscriber for the parent, the parent cascades and disappears from the admin's queue too.

Live updates: a `peering_subscription_changed` WebSocket event refetches the list.

### Connections settings — Recent peering outcomes

A second new section above the pending list shows unread `peer_approval_notifications` rows ordered by `createdAt DESC`. Each row's copy branches on `kind`:

- **`approved`** — "Your peering request to `{peerOrigin}` was approved — retry your friend-add to `{triggerTarget}`?" `[Retry]` `[Dismiss]`. Retry deep-links to the friend-add UI prefilled with the original target. Today only the `friend_add` reason produces a retry deep-link; future trigger reasons add their own deep-link flows. Dismiss POSTs to `/peering-notifications/:id/read`.
- **`denied`** — "Your peering request to `{peerOrigin}` was denied by your admin." `[Dismiss]`.
- **`expired`** — "Your peering request to `{peerOrigin}` expired without admin action." `[Dismiss]`.

A "Mark all as read" action POSTs to `/peering-notifications/read-all`. Read rows hide from view (soft-delete preserves audit; the storage janitor cleans up read rows older than 30 days).

Live updates: a `peering_notification_received` WebSocket event refetches the list and may surface a transient toast for the matching `kind` (online users only).

### Federation store slice

A new `federationStore.ts` slice (separate from `instanceStore`) holds:

- `peeringSubscriptions: PeeringSubscriptionSummary[]`
- `peeringNotifications: PeeringNotificationSummary[]`
- `pendingFriendAddPrefill?: { username: string }` — side-channel populated by the Retry button on `kind='approved'` notifications, consumed by the friend-add modal on next open.

This slice is intentionally separate from `instanceStore` because the data is per-user (not per-instance) and lives on the home server only. WebSocket handlers route `peering_subscription_changed` and `peering_notification_received` events into this slice's refetch actions.

---

## 9. Relationship to S2S Federation

Client-side and S2S federation serve different purposes:

| Aspect | Client-Side Federation | S2S Federation |
|---|---|---|
| **Purpose** | User interacts with multiple instances | Instances exchange data automatically |
| **Scope** | Spaces, DM access, friend discovery | DM relay, friend relay, file replication, read state sync |
| **Authentication** | Per-user JWT on each instance | Per-peer HMAC shared secret |
| **Initiated by** | User (Connections settings) | Admin (peer handshake) |
| **Connection** | Client → each server directly | Server → server via outbox |

**How they work together:**
1. User adds a remote instance via Connections (client-side)
2. The client triggers S2S peering between the two servers (automatic)
3. User joins Spaces on the remote instance (client-side — API calls go directly to remote)
4. User sends DMs — DM writes go to whichever instance delivered the channel (determined by `channelOriginMap`). S2S relay distributes messages, reactions, read states, and membership changes to all peer instances. DM calls remain home-only (gated for federated users).
5. Friend requests and discovery work across instances (client loads friends from all connected instances, S2S relays friend events)
