# Federation Hub API

**Repository:** `reuse-surface`  
**Artifact:** `specs/FederationHubAPI.md`  
**Status:** Draft 0.1 (REUSE-WP-0011-T01)  
**Schema:** `schemas/hub-registration.schema.yaml`

---

## 1. Purpose

The federation hub is a hosted coordination service that records which
repositories publish capability indexes and serves a composed federated index
for agent discovery. It does **not** store capability entry Markdown bodies.

Companion deployment workplans: `railiance-apps` **RAILIANCE-WP-0007** (Helm
release), **RAILIANCE-WP-0008** (browser landing page).

### Browser vs API routing

Production ingress (owned by `railiance-apps`) splits paths:

| Path | Handler |
|---|---|
| `GET /` (HTTPS) | Static landing page (`reuse-surface-landing`) — humans only |
| `GET /health`, `GET /v1/*` | Hub API (`reuse-surface` service) |

The landing page does not implement registration or federation; clients and
agents should use `/health` and `/v1/*` only. See
`railiance-apps/docs/reuse-surface-on-railiance01.md`.

---

## 2. Base URL and formats

| Item | Value |
|---|---|
| Default production URL | `https://reuse.coulomb.social` (A → `92.205.62.239`) |
| API prefix | `/v1` |
| Read formats | JSON (default), YAML via `Accept: application/yaml` or `?format=yaml` |
| Write content type | `application/json` |

Environment variables for clients:

| Variable | Purpose |
|---|---|
| `REUSE_SURFACE_URL` | Service base URL (no trailing slash) |
| `REUSE_SURFACE_TOKEN` | Bearer token for write operations |

---

## 3. Authentication

| Endpoint class | Auth |
|---|---|
| `GET /health`, `GET /v1/repos`, `GET /v1/repos/{repo}`, `GET /v1/federated` | Public (read) |
| `POST /v1/repos`, `PATCH /v1/repos/{repo}`, `DELETE /v1/repos/{repo}`, `POST /v1/federated/compose` | Bearer token required |

Write requests must include:

```http
Authorization: Bearer <REUSE_SURFACE_TOKEN>
```

Missing or invalid token → `401 Unauthorized`.

---

## 4. Registration model

A registration mirrors federation `url` sources from
`schemas/federation.schema.yaml`, plus hub metadata:

| Field | Required | Notes |
|---|---|---|
| `repo` | yes | Slug `[a-z][a-z0-9-]*`; primary key |
| `url` | yes | HTTP(S) URL to `capabilities.yaml` |
| `enabled` | yes | Include in federated compose when true |
| `domain` | yes | e.g. `helix_forge` |
| `required` | no | Fail compose if fetch fails and no cache |
| `description` | no | Human-readable note |
| `cache_ttl_seconds` | no | Default `86400` |
| `auth_env` | no | Hub container env var for fetch auth (never returned in GET) |
| `auth_header` | no | Default `Authorization` |
| `registered_at` | hub | ISO-8601 UTC |
| `updated_at` | hub | ISO-8601 UTC |
| `registered_by` | no | Optional client-supplied actor label |

Local filesystem `index` paths are **not** accepted — registrations must use
published raw URLs.

---

## 5. Endpoints

### 5.1 `GET /health`

Liveness/readiness probe.

**Response `200`:**

```json
{
  "status": "ok",
  "service": "reuse-surface",
  "version": "0.1.0"
}
```

### 5.2 `GET /v1/repos`

List all registrations (including disabled).

**Response `200`:**

```json
{
  "count": 2,
  "repos": [
    {
      "repo": "reuse-surface",
      "url": "https://gitea.coulomb.social/coulomb/reuse-surface/raw/main/registry/indexes/capabilities.yaml",
      "enabled": true,
      "required": true,
      "domain": "helix_forge",
      "description": "Primary registry",
      "cache_ttl_seconds": 86400,
      "registered_at": "2026-06-15T12:00:00Z",
      "updated_at": "2026-06-15T12:00:00Z"
    }
  ]
}
```

`auth_env` is omitted from responses.

### 5.3 `POST /v1/repos`

Register a new repository. **Auth required.**

**Request body:** `registration_request` from schema.

**Response `201`:** Full registration object.

**Errors:**

| Code | Condition |
|---|---|
| `400` | Schema validation failure |
| `401` | Missing/invalid token |
| `409` | `repo` already registered |

### 5.4 `GET /v1/repos/{repo}`

Fetch one registration.

**Response `200`:** Registration object.  
**Response `404`:** Unknown repo.

### 5.5 `PATCH /v1/repos/{repo}`

Update fields on an existing registration. **Auth required.**

**Request body:** `registration_update` from schema (at least one field).

**Response `200`:** Updated registration.

**Errors:** `400`, `401`, `404`.

### 5.6 `DELETE /v1/repos/{repo}`

Remove a registration. **Auth required.**

**Response `204`:** No content.  
**Response `404`:** Unknown repo.

### 5.7 `GET /v1/federated`

Return the composed federated index from all **enabled** registrations.

Reuses WP-0010 remote fetch/cache logic server-side. Output shape matches
`registry/indexes/federated.yaml`:

```yaml
version: 1
updated: "2026-06-15"
domain: helix_forge
collision_policy: warn
sources:
  - repo: reuse-surface
    url: https://...
    count: 12
capabilities:
  - id: capability.registry.register
    source_repo: reuse-surface
    source_url: https://...
    # ... index fields ...
composed_at: "2026-07-07T16:22:09+00:00"  # REUSE-WP-0019-T02
stale: false                               # REUSE-WP-0019-T02
```

`composed_at`/`stale` (added REUSE-WP-0019-T02) track *forced* recomposes
only (`refresh=true`, the webhook, or the scheduled fallback) — a plain
`GET` still serves current best-effort data (per-source `cache_ttl_seconds`
still applies) but never silently clears a staleness signal nothing
actually refreshed. `composed_at` is `null` until the first forced
recompose since the hub process's SQLite DB was created. `stale: true`
means a `registry/indexes/` change was pushed (via webhook) since the last
forced recompose completed.

Query parameters:

| Param | Default | Meaning |
|---|---|---|
| `format` | `json` | `json` or `yaml` |
| `refresh` | `false` | Bypass remote cache when `true`; also updates `composed_at` and clears `stale` |

Warnings from compose (duplicate IDs, fetch fallbacks) are returned in response
header `X-Federation-Warnings` (semicolon-separated) for MVP; JSON envelope
extension is a future option. `composed_at` is also echoed as response header
`X-Composed-At` when set.

**Response `200`:** Federated index document.  
**Response `502`:** Required source unavailable with no cache.

### 5.8 `POST /v1/federated/compose`

Trigger federated index refresh (same as `GET /v1/federated?refresh=true`).
**Auth required.** Useful for operators after bulk registration changes.
This is the hub's recompose endpoint referenced elsewhere as "trigger a
recompose" — there is no separate `/v1/recompose` route; this one already
does that job.

**Response `200`:** Federated index document (with `composed_at` updated,
`stale` cleared).

### 5.9 `POST /v1/webhooks/forgejo`

Forgejo (or Gitea, during the transition) push-event webhook receiver.
Added REUSE-WP-0019-T02. Design: **webhook triggers, compose stays
pull-based** — the webhook never parses pushed file content into registry
state; it only decides whether to trigger a pull-based recompose from the
already-registered raw URLs.

**Signature verification (required, not optional):** HMAC-SHA256 over the
raw request body, hex-encoded, in `X-Forgejo-Signature` (or
`X-Gitea-Signature` — both accepted, since Forgejo is Gitea-compatible and
repos migrate independently). Secret from `REUSE_SURFACE_FORGEJO_WEBHOOK_SECRET`
(never in code or committed config — route via the standard credential
mechanism for this deployment). A missing/wrong signature is `401`; an
unconfigured secret is `503` (fails closed, not open).

**Behavior:**

1. Verify signature (raw body, constant-time compare).
2. Parse the push-event payload; check every commit's `added`/`modified`/`removed`
   lists for any path under `registry/indexes/`.
3. If none match: `200 {"accepted": false, "reason": "no registry/indexes/ change"}` — no-op.
4. If a match: mark the compose state stale, run a real recompose
   (`refresh=true` equivalent) under the same lock used by
   `POST /v1/federated/compose` (concurrent triggers coalesce rather than
   overlap), record `composed_at`, clear `stale`.

**Response `200`:** `{"accepted": true|false, ...}`.  
**Response `401`:** Missing or invalid signature.  
**Response `503`:** Webhook secret not configured.  
**Response `502`:** Recompose failed (stale is deliberately left set so the
next check reports the failure honestly, not silently).

Org-level webhook rollout (single config covering all repos, T03) and the
Forgejo Actions scheduled fallback for when webhooks are unavailable are
separate, deployment-side follow-ups — this section covers the receiver
contract only.

---

## 6. Error envelope

Non-2xx responses use:

```json
{
  "error": "validation_error",
  "message": "Human-readable summary",
  "details": ["optional field-level messages"]
}
```

| `error` code | HTTP |
|---|---|
| `validation_error` | 400 |
| `unauthorized` | 401 |
| `not_found` | 404 |
| `conflict` | 409 |
| `misconfigured` | 503 |
| `compose_error` | 502 |

---

## 7. Hub service configuration

| Env var | Required | Purpose |
|---|---|---|
| `REUSE_SURFACE_TOKEN` | yes | Write API bearer token |
| `REUSE_SURFACE_DB` | no | SQLite path (default `/data/reuse.db`) |
| `REUSE_SURFACE_CACHE_DIR` | no | Remote index cache (default `/data/cache`) |
| `REUSE_SURFACE_DOMAIN` | no | Default federated `domain` (default `helix_forge`) |
| `REUSE_SURFACE_FORGEJO_WEBHOOK_SECRET` | for webhook | HMAC secret for `POST /v1/webhooks/forgejo` (REUSE-WP-0019-T02) |
| `REUSE_SURFACE_FORGE_BASE_URL` | no | Default target host for `reuse-surface federation migrate-host` (REUSE-WP-0019-T01), e.g. `https://forgejo.coulomb.social` |

---

## 8. CLI mapping

| CLI command | API call |
|---|---|
| `reuse-surface hub status` | `GET /health` |
| `reuse-surface hub list` | `GET /v1/repos` |
| `reuse-surface hub show --repo X` | `GET /v1/repos/X` |
| `reuse-surface hub register ...` | `POST /v1/repos` |
| `reuse-surface hub update ...` | `PATCH /v1/repos/{repo}` |

Run locally: `reuse-surface serve`. Global client flags: `--base-url`, env
`REUSE_SURFACE_URL`, `REUSE_SURFACE_TOKEN`.

---

## 9. Deployment reference

- Image: `gitea.coulomb.social/coulomb/reuse-surface:<tag>`
- Public URL: `https://reuse.coulomb.social`
- Secret: `reuse-surface-env` with `REUSE_SURFACE_TOKEN`
- Probe path: `/health`
- Persistence: PVC at `/data` (SQLite + fetch cache)
- Helm release: `railiance-apps` RAILIANCE-WP-0007
- Landing page at `/`: `railiance-apps` RAILIANCE-WP-0008 (disable via
  `landing.enabled: false` in Helm values)