omnigraph/docs/server.md

# HTTP Server (`omnigraph-server`)

Axum 0.8 + tokio + utoipa-generated OpenAPI. Single repo per process; deploy multiple processes for multi-tenant.

## Endpoint inventory

| Method | Path | Auth | Action | Handler |
|---|---|---|---|---|
| GET | `/healthz` | none | — | `server_health` |
| GET | `/openapi.json` | none | — | `server_openapi` (strips security if auth disabled) |
| GET | `/snapshot?branch=` | bearer + `read` | snapshot of branch | `server_snapshot` |
| POST | `/read` | bearer + `read` | run named query | `server_read` |
| POST | `/export` | bearer + `export` | NDJSON stream | `server_export` |
| POST | `/change` | bearer + `change` | mutation | `server_change` |
| GET | `/schema` | bearer + `read` | get current `.pg` source | `server_schema_get` |
| POST | `/schema/apply` | bearer + `schema_apply` (target=`main`) | migrate | `server_schema_apply` |
| POST | `/ingest` | bearer + `branch_create` (if new) + `change` | bulk load | `server_ingest` (32 MB body limit) |
| GET | `/branches` | bearer + `read` | list branches | `server_branch_list` |
| POST | `/branches` | bearer + `branch_create` | create | `server_branch_create` |
| DELETE | `/branches/{branch}` | bearer + `branch_delete` | delete | `server_branch_delete` |
| POST | `/branches/merge` | bearer + `branch_merge` | merge `source → target` | `server_branch_merge` |
| GET | `/commits?branch=` | bearer + `read` | list | `server_commit_list` |
| GET | `/commits/{commit_id}` | bearer + `read` | show | `server_commit_show` |

## Streaming

Only `/export` streams (`application/x-ndjson`, MPSC channel + `Body::from_stream`). Everything else is buffered JSON.

## Error model

Uniform `ErrorOutput { error, code?, merge_conflicts[], manifest_conflict? }` with `code ∈ unauthorized | forbidden | bad_request | not_found | conflict | too_many_requests | service_unavailable | internal`. Merge conflicts attach structured `MergeConflictOutput { table_key, row_id?, kind, message }`.

`manifest_conflict` is set on **publisher CAS rejections** (HTTP 409): the
caller's pre-write view of one table's manifest version was stale.
`ManifestConflictOutput { table_key, expected, actual }` tells the client
which table to refresh and retry. This is the conflict shape produced by
concurrent `/change` or `/ingest` calls landing the same `(table, branch)`
race (MR-771 / MR-766).

HTTP status codes used: 200, 400, 401, 403, 404, 409, 429, 500, 503.

## Per-actor admission control (MR-686)

PR 2 (MR-686) removed the global server `RwLock<Omnigraph>`. Disjoint
`(table, branch)` writes from different actors now run concurrently,
guarded only by the engine's per-(table, branch) write queue. To keep
one heavy actor from exhausting shared capacity (Lance I/O, manifest
churn, network), the server gates mutating handlers through a
`WorkloadController` configured per-process from environment variables:

| Env var | Default | Purpose |
|---|---|---|
| `OMNIGRAPH_PER_ACTOR_INFLIGHT_MAX` | 16 | Concurrent in-flight mutations per actor |
| `OMNIGRAPH_PER_ACTOR_BYTES_MAX` | 4 GiB | In-flight estimated bytes per actor |
| `OMNIGRAPH_GLOBAL_REWRITE_MAX` | 4 | Concurrent compaction / index-build slots |

When an actor exceeds its in-flight count or byte budget, the server
returns **HTTP 429 Too Many Requests** with `code: too_many_requests`
and a `Retry-After` header (seconds). The actor should back off; other
actors are unaffected.

When the global rewrite pool is exhausted (compaction, index build),
the server returns **HTTP 503 Service Unavailable** with
`code: service_unavailable`. Clients can retry; the rewrite pool
empties as in-flight rewrites complete.

Cedar policy authorization runs **before** admission accounting so
denied requests don't consume admission slots.

Today admission gates the `/change` hot path. `/ingest`, `/branches/*`,
and `/schema/apply` flow through the unlocked engine handle without
admission gates — wiring those is mechanical follow-up work tracked
on MR-686.

## Body limits

- Default: 1 MB
- `/ingest`: 32 MB

## Auth model (`bearer + SHA-256`)

- Tokens are SHA-256 hashed on startup; plaintext is never persisted in memory.
- Constant-time comparison via `subtle::ConstantTimeEq`.
- Three sources, in precedence:
  1. `OMNIGRAPH_SERVER_BEARER_TOKENS_AWS_SECRET` — AWS Secrets Manager (build with `--features aws`)
  2. `OMNIGRAPH_SERVER_BEARER_TOKENS_FILE` or `OMNIGRAPH_SERVER_BEARER_TOKENS_JSON` — JSON `{actor_id: token, …}`
  3. `OMNIGRAPH_SERVER_BEARER_TOKEN` — single legacy token, actor `default`
- If no tokens configured, server runs unauthenticated (local dev) and `/openapi.json` strips the security scheme.

See [deployment.md](deployment.md) for token-source operational details.

## Tracing & observability

- `tower_http::TraceLayer::new_for_http()`
- Policy decisions logged at INFO level with actor, action, branch, decision, matched rule
- Startup logs: token source name, repo URI, bind address
- Graceful SIGINT shutdown

## Not implemented (by design or "TBD")

- CORS — not configured; add `tower_http::cors` if needed.
- Rate limiting — none.
- Pagination — none (commits/branches return everything; export streams).
- Multi-tenant routing — one repo per process.