feat(behandelportal): WP-66 wire the decision into OpenZaak

Extends IZaakSource with RecordBesluit, mirroring WP-50's CreateZaak write
pattern: OpenZaakZaakSource POSTs a new Statussen entry (highest-volgnummer
statustype, since the harness catalogus has no per-outcome besluittype),
carrying the besluit + toelichting in statustoelichting; LocalZaakSource
no-ops. The beoordeling endpoint calls it after the local decision commits,
flagging a failure via RecordZgwDivergence the same way submit's
create-zaak/document writes do — closing WP-60's "second write pair" gap.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/src/BigRegister.Api/Program.cs

@@ -442,13 +442,14 @@ api.MapGet("/beoordeling/{id}", (string id, HttpContext ctx, IZaakSource zaken)
 .ProducesProblem(StatusCodes.Status403Forbidden)
 .Produces(StatusCodes.Status404NotFound);
 
-// --- Besluit (WP-65b): record a behandelaar's decision, advancing the WP-63 status
-// lifecycle. Runs against ApplicationStore directly (not the IZaakSource seam) — same
-// reasoning as the GET above: a new seam method would force an OpenZaakZaakSource
-// write now, which is WP-66's surface, not this one's. The transition-legality check
+// --- Besluit (WP-65b/66): record a behandelaar's decision, advancing the WP-63 status
+// lifecycle. The local write runs against ApplicationStore directly (not the IZaakSource
+// seam) — same reasoning as the GET above. The transition-legality check
 // (BeoordelingRules.CanDecide) is the SAME function the GET's canBesluiten flag uses,
-// so the two can never drift.
-api.MapPost("/beoordeling/{id}/besluit", (string id, RecordBesluitRequest req, HttpContext ctx) =>
+// so the two can never drift. WP-66: once the local decision has committed, IZaakSource
+// also gets a chance to advance the ZGW-side zaak status — LocalZaakSource no-ops,
+// OpenZaakZaakSource POSTs a new Statussen entry (see its RecordBesluit).
+api.MapPost("/beoordeling/{id}/besluit", (string id, RecordBesluitRequest req, HttpContext ctx, IZaakSource zaken) =>
     Beoordelen(ctx, $"aanvraag/{id}/besluit", () =>
     {
       if (!Enum.TryParse<Besluit>(req.Besluit, out var besluit))
@@ -468,6 +469,19 @@ api.MapPost("/beoordeling/{id}/besluit", (string id, RecordBesluitRequest req, H
 
       var updated = ApplicationStore.RecordBesluit(id, besluit, req.Toelichting)!;
       app.Logger.LogInformation("aanvraag besluit id={Id} besluit={Besluit}", id, besluit);
+
+      // WP-60: the local decision above already committed — a ZGW failure here is caught and
+      // flagged rather than allowed to diverge silently, same handling as submit's create-zaak
+      // and document-link writes.
+      try
+      {
+        zaken.RecordBesluit(updated, besluit, req.Toelichting, now, ctx.Caller());
+      }
+      catch (Exception ex)
+      {
+        RecordZgwDivergence(ctx, id, updated.Referentie ?? id, ex);
+      }
+
       return Results.Ok(new RecordBesluitResponse(updated.ToStatusDto(now)));
     }))
 .Produces<RecordBesluitResponse>()