git.stella-ops.org/docs/aoc/guard-library.md

# Aggregation-Only Guard Library Reference

> **Packages:** `StellaOps.Aoc`, `StellaOps.Aoc.AspNetCore`  
> **Related tasks:** `WEB-AOC-19-001`, `WEB-AOC-19-003`, `DEVOPS-AOC-19-001`  
> **Audience:** Concelier/Excititor service owners, Platform guild, QA

The Aggregation-Only Contract (AOC) guard library enforces the canonical ingestion
rules described in `docs/ingestion/aggregation-only-contract.md`. Service owners
should use the guard whenever raw advisory or VEX payloads are accepted so that
forbidden fields are rejected long before they reach MongoDB.

## Packages

### `StellaOps.Aoc`
- `IAocGuard` / `AocWriteGuard` — validate JSON payloads and emit `AocGuardResult`.
- `AocGuardOptions` — toggles for signature enforcement, tenant requirements, and required top-level fields.
- `AocViolation` / `AocViolationCode` — structured violations surfaced to callers.
- `AocError` — canonical error DTO (`code`, `message`, `violations[]`) re-used by HTTP helpers, CLI tooling, and telemetry.
- `ServiceCollectionExtensions.AddAocGuard()` — DI helper that registers the singleton guard.
- `AocGuardExtensions.ValidateOrThrow()` — throws `AocGuardException` when validation fails.

### `StellaOps.Aoc.AspNetCore`
- `AocGuardEndpointFilter<TRequest>` — Minimal API endpoint filter that evaluates request payloads through the guard before invoking handlers.
- `AocHttpResults.Problem()` — Produces a RFC 7807 payload that includes violation codes, suitable for API responses.

## Minimal API integration

```csharp
using StellaOps.Aoc;
using StellaOps.Aoc.AspNetCore.Routing;
using StellaOps.Aoc.AspNetCore.Results;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddAocGuard();
builder.Services.Configure<AocGuardOptions>(options =>
{
    options.RequireSignatureMetadata = true;
    options.RequireTenant = true;
});

var app = builder.Build();

app.MapPost("/ingest", async (IngestionRequest request, IAocGuard guard, ILogger<Program> logger) =>
    {
        // additional application logic
        return Results.Accepted();
    })
    .AddEndpointFilter(new AocGuardEndpointFilter<IngestionRequest>(
        request => new object?[] { request.Payload },
        serializerOptions: null,
        guardOptions: null))
    .ProducesProblem(StatusCodes.Status400BadRequest)
    .WithTags("AOC");

app.UseExceptionHandler(errorApp =>
{
    errorApp.Run(async context =>
    {
        var exceptionHandler = context.Features.Get<IExceptionHandlerFeature>();
        if (exceptionHandler?.Error is AocGuardException guardException)
        {
            var result = AocHttpResults.Problem(context, guardException);
            await result.ExecuteAsync(context);
            return;
        }

        context.Response.StatusCode = StatusCodes.Status500InternalServerError;
    });
});
```

Key points:
- Register the guard singleton before wiring repositories or worker services.
- Use `AocGuardEndpointFilter<TRequest>` to protect Minimal API endpoints. The `payloadSelector`
  can yield multiple payloads (e.g. batch ingestion) and the filter will validate each one.
- Prefer the `RequireAocGuard` extension when wiring endpoints; it wraps `AddEndpointFilter`
  and handles single-payload scenarios without additional boilerplate.
- Wrap guard exceptions with `AocHttpResults.Problem` to ensure clients receive machine-readable codes (`ERR_AOC_00x`). The helper now emits the serialized `AocError` under the `error` extension for consumers that want a typed payload.

### Allowed top-level fields

`AocWriteGuard` enforces the contract’s top-level allowlist: `_id`, `tenant`, `source`, `upstream`,
`content`, `identifiers`, `linkset`, `supersedes`, `createdAt`/`created_at`, `ingestedAt`/`ingested_at`, and `attributes`.
Unknown fields produce `ERR_AOC_007` violations. When staging schema changes, extend the allowlist through
`AocGuardOptions.AllowedTopLevelFields`:

```csharp
builder.Services.Configure<AocGuardOptions>(options =>
{
    options.AllowedTopLevelFields =
        options.AllowedTopLevelFields.Add("experimental_field");
});
```

## Worker / repository usage

Inject `IAocGuard` (or a module-specific wrapper such as `IVexRawWriteGuard`) anywhere documents
are persisted. Call `ValidateOrThrow` before writes to guarantee fail-fast behaviour, for example:

```csharp
public sealed class AdvisoryRawRepository
{
    private readonly IAocGuard _guard;

    public AdvisoryRawRepository(IAocGuard guard) => _guard = guard;

    public Task WriteAsync(JsonDocument document, CancellationToken cancellationToken)
    {
        _guard.ValidateOrThrow(document.RootElement);
        // proceed with storage logic
    }
}
```

## Configuration tips

- Adjust `AocGuardOptions.RequiredTopLevelFields` when staging new schema changes. All configured names are case-insensitive.
- Extend `AllowedTopLevelFields` for temporary schema experiments so that guard runs stay clean while the contract is updated.
- Set `RequireSignatureMetadata = false` for legacy feeds that do not provide signature envelopes yet; track the waiver in the module backlog.
- Use module-specific wrappers (`AddConcelierAocGuards`, `AddExcititorAocGuards`) to combine guard registration with domain exceptions and metrics.

## Testing guidance

- Unit-test guard behaviour with fixture payloads (see `src/Aoc/__Tests`).
- Service-level tests should assert that ingestion endpoints return `ERR_AOC_*` codes via `AocHttpResults`.
- CI must run `stella aoc verify` once CLI support lands (`DEVOPS-AOC-19-002`).
- Roslyn analyzer enforcement (`WEB-AOC-19-003`) will ensure the guard is registered; keep services wired through the shared extensions to prepare for that gate.

For questions or updates, coordinate with the BE‑Base Platform guild and reference `WEB-AOC-19-001`.