feat(acl): diploma upload stored in the ZGW Documenten API (S-10b, closes #103) (#108)

## What & why

S-10b: the self-service **diploma upload** is now real. After submitting, the citizen picks a PDF and
uploads it; the portal base64-encodes it client-side → BFF → domain → **ACL**, which stores it in the
ZGW **Documenten (DRC) API** as an `enkelvoudiginformatieobject` and relates it to the zaak, then the
`WachtOpDocumenten` wait completes and the case advances to beoordeling. Per §8.1 only the ACL talks to
ZGW.

Closes #103

Mechanism in **ADR-0018** (proposal #107). Builds on S-10a (#102). The zaak-close-on-expiry item is
carved to **#106 (S-10c)**.

## Definition of Done

- [x] Linked Gitea issue (above).
- [x] Failing test committed before the implementation (red→green per layer).
- [x] Conventional Commits referencing the issue (`refs #103`).
- [ ] CI green — all Gitea Actions jobs (pending on this PR).
- [x] `docker compose up` health unaffected (ACL boots on a placeholder informatieobjecttype URL; the real one is injected by verify-domain).
- [x] Docs updated (ADR-0018, demo-script, BACKLOG + S-10c).
- [x] ADR added (`docs/architecture/adr-0018-diploma-upload-via-acl-documenten.md`).
- [x] Demo note in `docs/demo-script.md`.

## Notes for reviewers

- **ACL** (`OpenZaakGateway.StoreDocumentAsync` + `AclService.StoreDiplomaAsync` + `POST /documenten`) reuses the existing gateway patterns (ZGW Bearer, buffered non-chunked body, **no CRS** — Documenten isn't geo). Unit-tested via the stub handler; an **integration test** stores a real document against live OpenZaak (verify-acl).
- **Transport:** base64 JSON on every hop (portal encodes client-side) — I deviated from proposal #107's multipart to keep one contract shape and avoid `IFormFile`/antiforgery/multipart-client plumbing; fine at diploma size (ADR-0018 §Alternatives).
- **Infra:** `seed_catalogus.py` seeds + publishes a "Diploma" `informatieobjecttype` and relates it to the zaaktype (while both concept); `verify-domain` injects its URL into the ACL. No new ZGW scopes (seed applicatie has `heeft_alle_autorisaties`).
- **e2e:** uploads a real PDF (`setInputFiles`) after the openbaar INGEDIEND row confirms the zaak is open (so storage doesn't race the OpenZaak worker).
- **Scope boundary:** the ZGW zaak is not set to a cancellation status on 30-day expiry — that's #106 (S-10c).

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Reviewed-on: #108

services/bff/Bff.Api/DownstreamClients.cs

@@ -27,10 +27,11 @@ public interface IDomainClient
     /// unknown or not the caller's (404), so the BFF can relay a 404 rather than a 500.</summary>
     Task<bool> WithdrawRegistrationAsync(string registrationId, string bsn, CancellationToken ct = default);
 
-    /// <summary>Provide the documents the caller's own registration is waiting for ("documenten
-    /// aanleveren"). Owner-scoped by <paramref name="bsn"/>. Returns <c>false</c> when the domain
-    /// reports the registration is unknown or not the caller's (404), so the BFF can relay a 404.</summary>
-    Task<bool> ProvideDocumentsAsync(string registrationId, string bsn, CancellationToken ct = default);
+    /// <summary>Provide (upload) the diploma the caller's own registration is waiting for ("documenten
+    /// aanleveren"). The file is carried base64-encoded. Owner-scoped by <paramref name="bsn"/>. Returns
+    /// <c>false</c> when the domain reports the registration is unknown or not the caller's (404).</summary>
+    Task<bool> ProvideDocumentsAsync(
+        string registrationId, string bsn, string contentBase64, string? fileName, string? contentType, CancellationToken ct = default);
 
     /// <summary>The behandelaar's werkbak — registrations awaiting beoordeling.</summary>
     Task<IReadOnlyList<WerkbakItem>> GetWerkbakAsync(CancellationToken ct = default);
@@ -68,10 +69,12 @@ public sealed class DomainClient(HttpClient http) : IDomainClient
         return true;
     }
 
-    public async Task<bool> ProvideDocumentsAsync(string registrationId, string bsn, CancellationToken ct = default)
+    public async Task<bool> ProvideDocumentsAsync(
+        string registrationId, string bsn, string contentBase64, string? fileName, string? contentType, CancellationToken ct = default)
     {
         using var response = await http.PostAsJsonAsync(
-            $"registrations/{registrationId}/documents", new { bsn }, ct);
+            $"registrations/{registrationId}/documents",
+            new { bsn, contentBase64, fileName, contentType }, ct);
         // The domain 404s an unknown or not-owned registration; relay that rather than fail hard.
         if (response.StatusCode == System.Net.HttpStatusCode.NotFound)
             return false;

services/bff/Bff.Api/Program.cs

@@ -109,13 +109,15 @@ app.MapPost("/self-service/registrations/{id}/withdraw", async (string id, Claim
 // forwarded to the domain, which owner-scopes the action and completes the WachtOpDocumenten task; a
 // registration that is unknown or not the caller's comes back 404. The real file upload + ZGW storage
 // is S-10b — this is the trigger that unblocks the process.
-app.MapPost("/self-service/registrations/{id}/documents", async (string id, ClaimsPrincipal user, IDomainClient domain, CancellationToken ct) =>
+app.MapPost("/self-service/registrations/{id}/documents", async (string id, ProvideDocumentsRequest body, ClaimsPrincipal user, IDomainClient domain, CancellationToken ct) =>
 {
     var bsn = user.FindFirstValue("bsn");
     if (string.IsNullOrWhiteSpace(bsn))
         return Results.BadRequest("The token carries no bsn claim.");
+    if (string.IsNullOrWhiteSpace(body?.ContentBase64))
+        return Results.BadRequest("A document is required.");
 
-    var provided = await domain.ProvideDocumentsAsync(id, bsn, ct);
+    var provided = await domain.ProvideDocumentsAsync(id, bsn, body.ContentBase64, body.FileName, body.ContentType, ct);
     return provided ? Results.NoContent() : Results.NotFound();
 })
     .RequireAuthorization()
@@ -163,6 +165,10 @@ app.Run();
 /// <summary>The behandelaar's decision on a registration.</summary>
 public sealed record DecideRequest(string Besluit);
 
+/// <summary>A diploma upload from the self-service portal — the file base64-encoded client-side, with
+/// its name and MIME type. The bsn is taken from the DigiD token, not this body.</summary>
+public sealed record ProvideDocumentsRequest(string ContentBase64, string? FileName = null, string? ContentType = null);
+
 // Behandel (medewerker-realm) authentication + authorization wiring (ADR-0013).
 internal static class BehandelAuth
 {

services/bff/Bff.Tests/BffFactory.cs

@@ -94,15 +94,15 @@ internal sealed class FakeDomainClient : IDomainClient
         return Task.FromResult(WithdrawSucceeds);
     }
 
-    public (string RegistrationId, string Bsn)? DocumentsProvidedFor { get; private set; }
+    public (string RegistrationId, string Bsn, string ContentBase64, string? FileName, string? ContentType)? DocumentsProvidedFor { get; private set; }
 
     /// <summary>Whether the fake domain reports the provide-documents as done (true → 204) or
     /// not-found/not-owned (false → 404). Tests set this to exercise the relay.</summary>
     public bool ProvideDocumentsSucceeds { get; set; } = true;
 
-    public Task<bool> ProvideDocumentsAsync(string registrationId, string bsn, CancellationToken ct = default)
+    public Task<bool> ProvideDocumentsAsync(string registrationId, string bsn, string contentBase64, string? fileName, string? contentType, CancellationToken ct = default)
     {
-        DocumentsProvidedFor = (registrationId, bsn);
+        DocumentsProvidedFor = (registrationId, bsn, contentBase64, fileName, contentType);
         return Task.FromResult(ProvideDocumentsSucceeds);
     }
 

services/bff/Bff.Tests/SelfServiceEndpointTests.cs

@@ -114,7 +114,17 @@ public class SelfServiceEndpointTests
 
     private static HttpRequestMessage ProvideDocuments(string? bearer, string id = "reg-123")
     {
-        var request = new HttpRequestMessage(HttpMethod.Post, $"/self-service/registrations/{id}/documents");
+        var request = new HttpRequestMessage(HttpMethod.Post, $"/self-service/registrations/{id}/documents")
+        {
+            // The portal base64-encodes the file client-side and posts it as JSON (S-10b); the bsn is
+            // never in the body — it comes from the DigiD token.
+            Content = JsonContent.Create(new
+            {
+                contentBase64 = Convert.ToBase64String([1, 2, 3]),
+                fileName = "diploma.pdf",
+                contentType = "application/pdf",
+            }),
+        };
         if (bearer is not null)
             request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", bearer);
         return request;
@@ -132,14 +142,19 @@ public class SelfServiceEndpointTests
     }
 
     [Fact]
-    public async Task Provides_documents_for_the_callers_registration_forwarding_the_id_and_bsn()
+    public async Task Provides_documents_for_the_callers_registration_forwarding_id_bsn_and_file()
     {
         using var factory = new BffFactory();
 
         var response = await factory.CreateClient().SendAsync(ProvideDocuments(TestTokens.Valid("123456782"), "reg-9"));
 
         Assert.Equal(HttpStatusCode.NoContent, response.StatusCode);
-        Assert.Equal(("reg-9", "123456782"), factory.Domain.DocumentsProvidedFor);
+        var provided = factory.Domain.DocumentsProvidedFor;
+        Assert.NotNull(provided);
+        Assert.Equal("reg-9", provided!.Value.RegistrationId);
+        Assert.Equal("123456782", provided.Value.Bsn);
+        Assert.Equal(Convert.ToBase64String([1, 2, 3]), provided.Value.ContentBase64);
+        Assert.Equal("diploma.pdf", provided.Value.FileName);
     }
 
     [Fact]

services/bff/openapi.json

@@ -76,6 +76,16 @@
             }
           }
         ],
+        "requestBody": {
+          "content": {
+            "application/json": {
+              "schema": {
+                "$ref": "#/components/schemas/ProvideDocumentsRequest"
+              }
+            }
+          },
+          "required": true
+        },
         "responses": {
           "204": {
             "description": "No Content"
@@ -228,6 +238,29 @@
           }
         }
       },
+      "ProvideDocumentsRequest": {
+        "required": [
+          "contentBase64"
+        ],
+        "type": "object",
+        "properties": {
+          "contentBase64": {
+            "type": "string"
+          },
+          "fileName": {
+            "type": [
+              "null",
+              "string"
+            ]
+          },
+          "contentType": {
+            "type": [
+              "null",
+              "string"
+            ]
+          }
+        }
+      },
       "SubmitAccepted": {
         "required": [
           "registrationId",