diff --git a/src/core/Deal.Api/Endpoints/CardDetailsEndpoints.cs b/src/core/Deal.Api/Endpoints/CardDetailsEndpoints.cs
index 42894a2..e37d653 100644
--- a/src/core/Deal.Api/Endpoints/CardDetailsEndpoints.cs
+++ b/src/core/Deal.Api/Endpoints/CardDetailsEndpoints.cs
@@ -202,9 +202,7 @@ public static class CardDetailsEndpoints
             return EndpointResults.BadRequest(result.Error);
         }
 
-        return result.Card is null
-            ? EndpointResults.NotFound(CardNotFoundDetail)
-            : await ReadCardAsync(context, cardId, ct);
+        return await ReadCardAsync(context, cardId, ct);
     }
 
     // DELETE /api/cards/{cardId}/links/{linkId}: удалить ссылку. Ответ — карточка.
@@ -220,10 +218,8 @@ public static class CardDetailsEndpoints
         }
 
         CardsService service = context.RequestServices.GetRequiredService<CardsService>();
-        CardResultDto result = await service.RemoveLinkAsync(cardId, linkId, ct);
-        return result.Card is null
-            ? EndpointResults.NotFound(CardNotFoundDetail)
-            : await ReadCardAsync(context, cardId, ct);
+        await service.RemoveLinkAsync(cardId, linkId, ct);
+        return await ReadCardAsync(context, cardId, ct);
     }
 
     // POST /api/cards/{cardId}/files: загрузка вложений (multipart/form-data, поле files).
@@ -240,10 +236,7 @@ public static class CardDetailsEndpoints
         }
 
         CardsService cardsService = context.RequestServices.GetRequiredService<CardsService>();
-        if (await cardsService.GetCardAsync(cardId, ct) is null)
-        {
-            return EndpointResults.NotFound(CardNotFoundDetail);
-        }
+        await cardsService.GetCardAsync(cardId, ct);
 
         IFormCollection form;
         try
@@ -357,9 +350,7 @@ public static class CardDetailsEndpoints
             return EndpointResults.BadRequest(result.Error);
         }
 
-        return result.Card is null
-            ? EndpointResults.NotFound(CardNotFoundDetail)
-            : await ReadCardAsync(context, cardId, ct);
+        return await ReadCardAsync(context, cardId, ct);
     }
 
     // DELETE /api/cards/{cardId}/reminder: снять напоминание. Ответ — карточка.
@@ -374,9 +365,8 @@ public static class CardDetailsEndpoints
         }
 
         CardsService service = context.RequestServices.GetRequiredService<CardsService>();
-        return await service.ClearReminderAsync(cardId, ct)
-            ? await ReadCardAsync(context, cardId, ct)
-            : EndpointResults.NotFound(CardNotFoundDetail);
+        await service.ClearReminderAsync(cardId, ct);
+        return await ReadCardAsync(context, cardId, ct);
     }
 
     // POST /api/cards/{cardId}/reminder/snooze: «напомнить позже» (now + 24 ч). Ответ — карточка.
@@ -391,9 +381,8 @@ public static class CardDetailsEndpoints
         }
 
         CardsService service = context.RequestServices.GetRequiredService<CardsService>();
-        return await service.SnoozeReminderAsync(cardId, ct)
-            ? await ReadCardAsync(context, cardId, ct)
-            : EndpointResults.NotFound(CardNotFoundDetail);
+        await service.SnoozeReminderAsync(cardId, ct);
+        return await ReadCardAsync(context, cardId, ct);
     }
 
     // Читает карточку через единый сервис и возвращает её как ответ (404 — карточки нет).
@@ -412,11 +401,7 @@ public static class CardDetailsEndpoints
         CancellationToken ct)
     {
         CardsService cardsService = context.RequestServices.GetRequiredService<CardsService>();
-        CardDto? card = await cardsService.GetCardAsync(cardId, ct);
-        if (card is null)
-        {
-            return EndpointResults.NotFound(CardNotFoundDetail);
-        }
+        CardDto card = await cardsService.GetCardAsync(cardId, ct);
 
         SourceContent content = await cardsService.ResolveSourceAsync(card, ct);
         return Results.Ok(content);
@@ -428,10 +413,8 @@ public static class CardDetailsEndpoints
         CancellationToken ct)
     {
         CardsService cardsService = context.RequestServices.GetRequiredService<CardsService>();
-        CardDto? card = await cardsService.GetCardAsync(cardId, ct);
-        return card is null
-            ? EndpointResults.NotFound(CardNotFoundDetail)
-            : Results.Ok(card);
+        CardDto card = await cardsService.GetCardAsync(cardId, ct);
+        return Results.Ok(card);
     }
 
     // Имя файла для Content-Disposition без кавычек «"».
diff --git a/src/core/Deal.Api/Endpoints/CardsEndpoints.cs b/src/core/Deal.Api/Endpoints/CardsEndpoints.cs
index a000360..68856da 100644
--- a/src/core/Deal.Api/Endpoints/CardsEndpoints.cs
+++ b/src/core/Deal.Api/Endpoints/CardsEndpoints.cs
@@ -128,10 +128,8 @@ public static class CardsEndpoints
         }
 
         CardsService cardsService = context.RequestServices.GetRequiredService<CardsService>();
-        CardDto? card = await cardsService.GetCardAsync(cardId, ct);
-        return card is null
-            ? EndpointResults.NotFound(CardNotFoundDetail)
-            : Results.Ok(card);
+        CardDto card = await cardsService.GetCardAsync(cardId, ct);
+        return Results.Ok(card);
     }
 
     private static async Task<IResult> MarkAllSeenAsync(HttpContext context, CancellationToken ct)
@@ -184,18 +182,11 @@ public static class CardsEndpoints
             return EndpointResults.BadRequest(outcome.Error);
         }
 
-        if (!outcome.Exists)
-        {
-            return EndpointResults.NotFound(CardNotFoundDetail);
-        }
-
         await AuditAppender.AppendTenantAsync(context, AuditEvents.CardMoved, new { cardId, to = body.To }, ct);
 
         CardsService cardsService = context.RequestServices.GetRequiredService<CardsService>();
-        CardDto? unified = await cardsService.GetCardAsync(cardId, ct);
-        return unified is null
-            ? EndpointResults.NotFound(CardNotFoundDetail)
-            : Results.Ok(unified);
+        CardDto unified = await cardsService.GetCardAsync(cardId, ct);
+        return Results.Ok(unified);
     }
 
     private static async Task<IResult> TrashAsync(
@@ -353,11 +344,7 @@ public static class CardsEndpoints
         }
 
         CardsService cardsService = context.RequestServices.GetRequiredService<CardsService>();
-        CardDto? card = await cardsService.GetCardAsync(cardId, ct);
-        if (card is null)
-        {
-            return EndpointResults.NotFound(CardNotFoundDetail);
-        }
+        CardDto card = await cardsService.GetCardAsync(cardId, ct);
 
         CardReclassifier reclassifier = context.RequestServices.GetRequiredService<CardReclassifier>();
         ReclassifyResultDto result = await reclassifier.ReclassifyCardAsync(card, ct);
diff --git a/src/core/Deal.Api/Endpoints/DiscoveryEndpoints.cs b/src/core/Deal.Api/Endpoints/DiscoveryEndpoints.cs
index f46981d..d17eeaa 100644
--- a/src/core/Deal.Api/Endpoints/DiscoveryEndpoints.cs
+++ b/src/core/Deal.Api/Endpoints/DiscoveryEndpoints.cs
@@ -55,9 +55,6 @@ public static class DiscoveryEndpoints
     // Путь лога задачи (GET).
     private const string TaskLogPath = "/tasks/{task_id}/log";
 
-    // 404: кандидат не найден.
-    private const string CandidateNotFoundDetail = "Кандидат не найден";
-
     private const string AlreadyJoinedDetail = "Уже вступили в этот источник";
 
     private const string JoinedRejectDetail = "Уже вступили — удалите источник из каналов";
@@ -281,11 +278,7 @@ public static class DiscoveryEndpoints
         }
 
         DiscoveryCandidatesService candidates = context.RequestServices.GetRequiredService<DiscoveryCandidatesService>();
-        DiscoveryCandidateDto? row = await candidates.GetAsync(dialog_id, ct);
-        if (row is null)
-        {
-            return EndpointResults.NotFound(CandidateNotFoundDetail);
-        }
+        DiscoveryCandidateDto row = await candidates.GetAsync(dialog_id, ct);
 
         if (row.Status == DiscoveryCandidateStatuses.Joined)
         {
@@ -314,8 +307,8 @@ public static class DiscoveryEndpoints
 
         try
         {
-            DiscoveryCandidateDto? joined = await candidates.MarkJoinedAsync(dialog_id, auto: false, ct);
-            return joined is null ? EndpointResults.NotFound(CandidateNotFoundDetail) : Results.Ok(joined);
+            DiscoveryCandidateDto joined = await candidates.MarkJoinedAsync(dialog_id, auto: false, ct);
+            return Results.Ok(joined);
         }
         catch (DiscoveryValidationException exception)
         {
@@ -334,11 +327,7 @@ public static class DiscoveryEndpoints
         }
 
         DiscoveryCandidatesService candidates = context.RequestServices.GetRequiredService<DiscoveryCandidatesService>();
-        DiscoveryCandidateDto? row = await candidates.GetAsync(dialog_id, ct);
-        if (row is null)
-        {
-            return EndpointResults.NotFound(CandidateNotFoundDetail);
-        }
+        DiscoveryCandidateDto row = await candidates.GetAsync(dialog_id, ct);
 
         if (row.Status == DiscoveryCandidateStatuses.Joined)
         {
@@ -347,8 +336,8 @@ public static class DiscoveryEndpoints
 
         try
         {
-            DiscoveryCandidateDto? rejected = await candidates.MarkRejectedAsync(dialog_id, ManualRejectReason, ct);
-            return rejected is null ? EndpointResults.NotFound(CandidateNotFoundDetail) : Results.Ok(rejected);
+            DiscoveryCandidateDto rejected = await candidates.MarkRejectedAsync(dialog_id, ManualRejectReason, ct);
+            return Results.Ok(rejected);
         }
         catch (DiscoveryValidationException exception)
         {
diff --git a/src/core/Deal.Api/Endpoints/MlEndpoints.cs b/src/core/Deal.Api/Endpoints/MlEndpoints.cs
index 64a4a4d..b7d816a 100644
--- a/src/core/Deal.Api/Endpoints/MlEndpoints.cs
+++ b/src/core/Deal.Api/Endpoints/MlEndpoints.cs
@@ -37,8 +37,6 @@ public static class MlEndpoints
 
     private const string EnterTextDetail = "Введите текст";
 
-    private const string MessageNotFoundDetail = "Исходное сообщение не найдено";
-
     /// <summary>
     /// Регистрирует группу /api/ml
     /// </summary>
@@ -141,12 +139,7 @@ public static class MlEndpoints
         }
 
         MlReviewService review = context.RequestServices.GetRequiredService<MlReviewService>();
-        MlApplyResult? result = await review.ApplyAsync(body.DialogId, body.MsgId, body.Action, ct);
-        if (result is null)
-        {
-            return EndpointResults.NotFound(MessageNotFoundDetail);
-        }
-
+        MlApplyResult result = await review.ApplyAsync(body.DialogId, body.MsgId, body.Action, ct);
         if (result.Error is not null)
         {
             return EndpointResults.BadRequest(result.Error);
diff --git a/src/core/Deal.Api/Endpoints/OperatorTenantsEndpoints.cs b/src/core/Deal.Api/Endpoints/OperatorTenantsEndpoints.cs
index bafc30c..73f8f05 100644
--- a/src/core/Deal.Api/Endpoints/OperatorTenantsEndpoints.cs
+++ b/src/core/Deal.Api/Endpoints/OperatorTenantsEndpoints.cs
@@ -144,12 +144,7 @@ public static class OperatorTenantsEndpoints
             return EndpointResults.Unauthorized(AuthHelpers.OperatorUnauthorizedDetail);
         }
 
-        TenantDetailDto? tenant = await tenantAdminService.GetAsync(id, ct);
-        if (tenant is null)
-        {
-            return EndpointResults.NotFound(TenantNotFoundDetail);
-        }
-
+        TenantDetailDto tenant = await tenantAdminService.GetAsync(id, ct);
         return Results.Ok(tenant);
     }
 
diff --git a/src/core/Deal.Api/Endpoints/PipelineEndpoints.cs b/src/core/Deal.Api/Endpoints/PipelineEndpoints.cs
index f7ea7cb..24166af 100644
--- a/src/core/Deal.Api/Endpoints/PipelineEndpoints.cs
+++ b/src/core/Deal.Api/Endpoints/PipelineEndpoints.cs
@@ -33,8 +33,6 @@ public static class PipelineEndpoints
     // Путь возврата записи отсева в обработку (POST).
     private const string RejectedReturnPath = "/rejected/{rejId}/return";
 
-    private const string RejectedNotFoundDetail = "Запись не найдена";
-
     private const int DefaultPageSize = 100;
 
     /// <summary>
@@ -140,11 +138,7 @@ public static class PipelineEndpoints
         }
 
         PipelineProcessingService processing = context.RequestServices.GetRequiredService<PipelineProcessingService>();
-        RejectReturnResultDto? result = await processing.ReturnAsync(rejId, body.Reason ?? string.Empty, ct);
-        if (result is null)
-        {
-            return EndpointResults.NotFound(RejectedNotFoundDetail);
-        }
+        RejectReturnResultDto result = await processing.ReturnAsync(rejId, body.Reason ?? string.Empty, ct);
 
         return result.Error is not null
             ? EndpointResults.BadRequest(result.Error)
diff --git a/src/core/Deal.Infrastructure/Services/CardMover.cs b/src/core/Deal.Infrastructure/Services/CardMover.cs
index 5739095..1f59b4c 100644
--- a/src/core/Deal.Infrastructure/Services/CardMover.cs
+++ b/src/core/Deal.Infrastructure/Services/CardMover.cs
@@ -22,8 +22,6 @@ public sealed class CardMover(CardsService cardsService) : ICardMover
         CardResultDto result = CardsDefaultContainers.Contains(toContainerId)
             ? await cardsService.MoveStageCardAsync(cardId, toContainerId, ct)
             : await cardsService.MoveDashboardCardAsync(cardId, toContainerId, ct);
-        return result.Error is not null
-            ? new CardMoveResultDto(result.Error, Exists: true)
-            : new CardMoveResultDto(null, Exists: result.Card is not null);
+        return new CardMoveResultDto(result.Error);
     }
 }
diff --git a/src/core/Deal.Modules.Cards/Application/Abstractions/ICardMover.cs b/src/core/Deal.Modules.Cards/Application/Abstractions/ICardMover.cs
index 904ae3f..21f1a26 100644
--- a/src/core/Deal.Modules.Cards/Application/Abstractions/ICardMover.cs
+++ b/src/core/Deal.Modules.Cards/Application/Abstractions/ICardMover.cs
@@ -1,5 +1,6 @@
 using Deal.Modules.Cards.Application.Dtos;
 using Deal.Modules.Cards.Application.Models;
+using Deal.SharedKernel.Errors;
 
 namespace Deal.Modules.Cards.Application.Abstractions;
 
@@ -14,7 +15,8 @@ public interface ICardMover
     /// <param name="cardId">Id карточки.</param>
     /// <param name="toContainerId">Id контейнера назначения (стадия «Выбранных» либо дашборд-контейнер).</param>
     /// <param name="ctx">Контекст перехода (инициатор, причина, обучение).</param>
-    /// <returns>Результат: Error (400-текст отказа) | Exists=false (карточки нет, 404) | успех (Exists=true).</returns>
+    /// <returns>Результат: Error (400-текст отказа) либо null (успех).</returns>
+    /// <exception cref="NotFoundException">Карточка не найдена.</exception>
     public Task<CardMoveResultDto> MoveAsync(
         string cardId,
         string toContainerId,
diff --git a/src/core/Deal.Modules.Cards/Application/Dtos/CardMoveResultDto.cs b/src/core/Deal.Modules.Cards/Application/Dtos/CardMoveResultDto.cs
index 166419e..06bfa6a 100644
--- a/src/core/Deal.Modules.Cards/Application/Dtos/CardMoveResultDto.cs
+++ b/src/core/Deal.Modules.Cards/Application/Dtos/CardMoveResultDto.cs
@@ -5,6 +5,5 @@ namespace Deal.Modules.Cards.Application.Dtos;
 /// <summary>
 /// Результат перехода карточки единым механизмом <see cref="ICardMover"/>.
 /// </summary>
-/// <param name="Error">Текст 400-ошибки либо null.</param>
-/// <param name="Exists">True — карточка найдена и переход выполнен (либо перенос был no-op).</param>
-public sealed record CardMoveResultDto(string? Error, bool Exists);
+/// <param name="Error">Текст 400-ошибки либо null (успех).</param>
+public sealed record CardMoveResultDto(string? Error);
diff --git a/src/core/Deal.Modules.Discovery/Application/Services/DiscoveryCandidatesService.cs b/src/core/Deal.Modules.Discovery/Application/Services/DiscoveryCandidatesService.cs
index ecabc16..6115bad 100644
--- a/src/core/Deal.Modules.Discovery/Application/Services/DiscoveryCandidatesService.cs
+++ b/src/core/Deal.Modules.Discovery/Application/Services/DiscoveryCandidatesService.cs
@@ -2,6 +2,7 @@ using Deal.Contracts.Integrations.Models;
 using Deal.Modules.Discovery.Application.Abstractions;
 using Deal.Modules.Discovery.Application.Exceptions;
 using Deal.Modules.Discovery.Application.Models;
+using Deal.SharedKernel.Errors;
 
 namespace Deal.Modules.Discovery.Application.Services;
 
@@ -13,6 +14,10 @@ public sealed class DiscoveryCandidatesService(
     DiscoveryLogService log,
     DiscoveryBlacklistService blacklist)
 {
+    private const string CandidateEntityName = "Кандидат";
+
+    private const string TaskEntityName = "Задача поиска";
+
     /// <summary>
     /// 400 mark_rejected
     /// </summary>
@@ -53,10 +58,12 @@ public sealed class DiscoveryCandidatesService(
     /// Кандидат по dialog_id.
     /// </summary>
     /// <param name="dialogId">Подписанный id источника.</param>
-    /// <returns>Кандидат или null (404 «Кандидат не найден»).</returns>
-    public Task<DiscoveryCandidateDto?> GetAsync(string dialogId, CancellationToken ct)
+    /// <returns>Кандидат.</returns>
+    /// <exception cref="NotFoundException">Кандидат не найден.</exception>
+    public async Task<DiscoveryCandidateDto> GetAsync(string dialogId, CancellationToken ct)
     {
-        return store.GetCandidateAsync(dialogId, ct);
+        return await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false)
+            ?? throw new NotFoundException(CandidateEntityName, dialogId);
     }
 
     /// <summary>
@@ -78,11 +85,8 @@ public sealed class DiscoveryCandidatesService(
         string hue,
         CancellationToken ct)
     {
-        DiscoveryTaskDto? task = await store.GetTaskAsync(taskId, ct).ConfigureAwait(false);
-        if (task is null)
-        {
-            return null;
-        }
+        DiscoveryTaskDto task = await store.GetTaskAsync(taskId, ct).ConfigureAwait(false)
+            ?? throw new NotFoundException(TaskEntityName, taskId);
 
         if (await store.IsDialogMonitoredAsync(dialogId, ct).ConfigureAwait(false))
         {
@@ -125,7 +129,8 @@ public sealed class DiscoveryCandidatesService(
         };
         await store.CreateCandidateAsync(row, ct).ConfigureAwait(false);
         await store.BumpTaskCounterAsync(taskId, DiscoveryCounterField.Found, 1, ct).ConfigureAwait(false);
-        return await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false);
+        return await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false)
+            ?? throw new NotFoundException(CandidateEntityName, dialogId);
     }
 
     /// <summary>
@@ -134,18 +139,21 @@ public sealed class DiscoveryCandidatesService(
     /// <param name="taskId">Id задачи.</param>
     /// <param name="dialogId">Подписанный id источника.</param>
     /// <param name="patch">Изменяемые поля (null — не менять).</param>
-    /// <returns>Обновлённый кандидат либо null — задачи/кандидата нет (или кандидат другой задачи).</returns>
-    public async Task<DiscoveryCandidateDto?> SetAsync(
+    /// <returns>Обновлённый кандидат.</returns>
+    /// <exception cref="NotFoundException">Задача или кандидат не найдены.</exception>
+    public async Task<DiscoveryCandidateDto> SetAsync(
         string taskId,
         string dialogId,
         DiscoveryCandidatePatch patch,
         CancellationToken ct)
     {
-        DiscoveryTaskDto? task = await store.GetTaskAsync(taskId, ct).ConfigureAwait(false);
-        DiscoveryCandidateDto? current = await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false);
-        if (task is null || current is null || current.TaskId != taskId)
+        _ = await store.GetTaskAsync(taskId, ct).ConfigureAwait(false)
+            ?? throw new NotFoundException(TaskEntityName, taskId);
+        DiscoveryCandidateDto current = await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false)
+            ?? throw new NotFoundException(CandidateEntityName, dialogId);
+        if (current.TaskId != taskId)
         {
-            return null;
+            throw new NotFoundException(CandidateEntityName, dialogId);
         }
 
         DiscoveryCandidatePatch normalized = NormalizePatch(patch, current);
@@ -159,7 +167,8 @@ public sealed class DiscoveryCandidatesService(
         }
 
         await store.PatchCandidateAsync(dialogId, normalized, ct).ConfigureAwait(false);
-        return await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false);
+        return await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false)
+            ?? throw new NotFoundException(CandidateEntityName, dialogId);
     }
 
     /// <summary>
@@ -167,9 +176,10 @@ public sealed class DiscoveryCandidatesService(
     /// </summary>
     /// <param name="dialogId">Подписанный id источника.</param>
     /// <param name="status">Новый статус: new|review.</param>
-    /// <returns>Обновлённый кандидат либо null (кандидата нет).</returns>
+    /// <returns>Обновлённый кандидат.</returns>
+    /// <exception cref="NotFoundException">Кандидат не найден.</exception>
     /// <exception cref="DiscoveryValidationException">Статус не new/review.</exception>
-    public async Task<DiscoveryCandidateDto?> SetStatusAsync(
+    public async Task<DiscoveryCandidateDto> SetStatusAsync(
         string dialogId,
         string status,
         CancellationToken ct)
@@ -179,11 +189,8 @@ public sealed class DiscoveryCandidatesService(
             throw new DiscoveryValidationException(string.Format(TransitionNotAllowedFormat, status));
         }
 
-        DiscoveryCandidateDto? current = await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false);
-        if (current is null)
-        {
-            return null;
-        }
+        DiscoveryCandidateDto current = await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false)
+            ?? throw new NotFoundException(CandidateEntityName, dialogId);
 
         await store.SetCandidateStatusAsync(dialogId, status, ct).ConfigureAwait(false);
         if (status == DiscoveryCandidateStatuses.Review)
@@ -195,7 +202,8 @@ public sealed class DiscoveryCandidatesService(
                 ct).ConfigureAwait(false);
         }
 
-        return await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false);
+        return await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false)
+            ?? throw new NotFoundException(CandidateEntityName, dialogId);
     }
 
     /// <summary>
@@ -203,17 +211,15 @@ public sealed class DiscoveryCandidatesService(
     /// </summary>
     /// <param name="dialogId">Подписанный id источника.</param>
     /// <param name="auto">True — авто-вступление воркера; false — ручное.</param>
-    /// <returns>Кандидат в joined либо null (кандидата нет). Повторный вызов для joined — идемпотентен.</returns>
-    public async Task<DiscoveryCandidateDto?> MarkJoinedAsync(
+    /// <returns>Кандидат в joined. Повторный вызов для joined — идемпотентен.</returns>
+    /// <exception cref="NotFoundException">Кандидат не найден.</exception>
+    public async Task<DiscoveryCandidateDto> MarkJoinedAsync(
         string dialogId,
         bool auto,
         CancellationToken ct)
     {
-        DiscoveryCandidateDto? current = await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false);
-        if (current is null)
-        {
-            return null;
-        }
+        DiscoveryCandidateDto current = await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false)
+            ?? throw new NotFoundException(CandidateEntityName, dialogId);
 
         if (current.Status == DiscoveryCandidateStatuses.Joined)
         {
@@ -224,7 +230,8 @@ public sealed class DiscoveryCandidatesService(
         await store.BumpTaskCounterAsync(current.TaskId, DiscoveryCounterField.Joined, 1, ct).ConfigureAwait(false);
         string logEvent = auto ? DiscoveryLogEvents.JoinAuto : DiscoveryLogEvents.JoinManual;
         await log.AddAsync(current.TaskId, logEvent, string.Format(JoinedLogFormat, dialogId), ct).ConfigureAwait(false);
-        return await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false);
+        return await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false)
+            ?? throw new NotFoundException(CandidateEntityName, dialogId);
     }
 
     /// <summary>
@@ -232,18 +239,16 @@ public sealed class DiscoveryCandidatesService(
     /// </summary>
     /// <param name="dialogId">Подписанный id источника.</param>
     /// <param name="reason">Причина отклонения (в лог/чёрный список; «отклонено вручную» — эндпоинт reject).</param>
-    /// <returns>Кандидат в rejected либо null (кандидата нет). Повторный вызов для rejected — идемпотентен.</returns>
+    /// <returns>Кандидат в rejected. Повторный вызов для rejected — идемпотентен.</returns>
+    /// <exception cref="NotFoundException">Кандидат не найден.</exception>
     /// <exception cref="DiscoveryValidationException">Источник уже joined — отклонить нельзя.</exception>
-    public async Task<DiscoveryCandidateDto?> MarkRejectedAsync(
+    public async Task<DiscoveryCandidateDto> MarkRejectedAsync(
         string dialogId,
         string reason,
         CancellationToken ct)
     {
-        DiscoveryCandidateDto? current = await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false);
-        if (current is null)
-        {
-            return null;
-        }
+        DiscoveryCandidateDto current = await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false)
+            ?? throw new NotFoundException(CandidateEntityName, dialogId);
 
         if (current.Status == DiscoveryCandidateStatuses.Joined)
         {
@@ -260,7 +265,8 @@ public sealed class DiscoveryCandidatesService(
         string text = string.IsNullOrEmpty(reason) ? string.Format(RejectedLogFormat, dialogId) : reason;
         await log.AddAsync(current.TaskId, DiscoveryLogEvents.Reject, text, ct).ConfigureAwait(false);
         await blacklist.AddAsync(dialogId, current.Name, reason ?? string.Empty, ct).ConfigureAwait(false);
-        return await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false);
+        return await store.GetCandidateAsync(dialogId, ct).ConfigureAwait(false)
+            ?? throw new NotFoundException(CandidateEntityName, dialogId);
     }
 
     /// <summary>
diff --git a/src/core/Deal.Modules.Kanban/Application/Services/CardsService.Operations.cs b/src/core/Deal.Modules.Kanban/Application/Services/CardsService.Operations.cs
index 1378c99..d24c6a8 100644
--- a/src/core/Deal.Modules.Kanban/Application/Services/CardsService.Operations.cs
+++ b/src/core/Deal.Modules.Kanban/Application/Services/CardsService.Operations.cs
@@ -27,9 +27,16 @@ public sealed partial class CardsService
     /// </summary>
     /// <param name="cardId">Id карточки (<c>c_...</c>).</param>
     /// <returns>Карточка или null — строки нет (эндпоинт отвечает 404 «Карточка не найдена»).</returns>
-    public Task<CardDto?> GetCardAsync(string cardId, CancellationToken ct)
+    /// <summary>
+    /// Одна карточка по id.
+    /// </summary>
+    /// <param name="cardId">Id карточки (<c>c_...</c>).</param>
+    /// <returns>Карточка.</returns>
+    /// <exception cref="NotFoundException">Карточка не найдена.</exception>
+    public async Task<CardDto> GetCardAsync(string cardId, CancellationToken ct)
     {
-        return _store.GetCardAsync(cardId, ct);
+        return await _store.GetCardAsync(cardId, ct)
+            ?? throw new NotFoundException(CardEntityName, cardId);
     }
 
 
@@ -57,7 +64,7 @@ public sealed partial class CardsService
         CardDto? card = await _store.GetCardAsync(cardId, ct);
         if (card is null)
         {
-            return new CardResultDto(null, null);
+            throw new NotFoundException(CardEntityName, cardId);
         }
 
         if (card.Col == CardIds.Archive || card.Col == CardIds.Trash)
@@ -81,7 +88,10 @@ public sealed partial class CardsService
             await _mlClient.PushAsync(text, toCol, PushWeightUser, ct);
         }
 
-        return new CardResultDto(null, await _store.GetCardAsync(cardId, ct));
+        return new CardResultDto(
+            null,
+            await _store.GetCardAsync(cardId, ct)
+                ?? throw new NotFoundException(CardEntityName, cardId));
     }
 
     /// <summary>
diff --git a/src/core/Deal.Modules.Kanban/Application/Services/CardsService.Reminders.cs b/src/core/Deal.Modules.Kanban/Application/Services/CardsService.Reminders.cs
index c1c6b56..f4214ff 100644
--- a/src/core/Deal.Modules.Kanban/Application/Services/CardsService.Reminders.cs
+++ b/src/core/Deal.Modules.Kanban/Application/Services/CardsService.Reminders.cs
@@ -1,5 +1,6 @@
 using Deal.Modules.Kanban.Application.Models;
 using Deal.Modules.Settings.Application.Models;
+using Deal.SharedKernel.Errors;
 
 namespace Deal.Modules.Kanban.Application.Services;
 
@@ -22,17 +23,15 @@ public sealed partial class CardsService
     /// </summary>
     /// <param name="cardId">Id карточки (<c>c_...</c>).</param>
     /// <param name="atMs">Время напоминания, epoch-ms.</param>
-    /// <returns>Результат: Error <see cref="RemindersDisabledDetail"/> (400) | Card=null без Error (404) | Card — карточка с напоминанием.</returns>
+    /// <returns>Результат: Error <see cref="RemindersDisabledDetail"/> (400) | Card — карточка с напоминанием.</returns>
+    /// <exception cref="NotFoundException">Карточка не найдена.</exception>
     public async Task<CardResultDto> SetReminderAsync(
         string cardId,
         long atMs,
         CancellationToken ct)
     {
-        CardDto? card = await _store.GetCardAsync(cardId, ct);
-        if (card is null)
-        {
-            return new CardResultDto(null, null);
-        }
+        CardDto card = await _store.GetCardAsync(cardId, ct)
+            ?? throw new NotFoundException(CardEntityName, cardId);
 
         if (!await ReadRemindersEnabledAsync(ct))
         {
@@ -41,7 +40,7 @@ public sealed partial class CardsService
 
         await _store.SetReminderAsync(cardId, atMs, ct);
         CardDto saved = await _store.GetCardAsync(cardId, ct)
-            ?? throw new InvalidOperationException("Карточка не прочиталась после установки напоминания: " + cardId);
+            ?? throw new NotFoundException(CardEntityName, cardId);
         return new CardResultDto(null, saved);
     }
 
@@ -49,35 +48,27 @@ public sealed partial class CardsService
     /// Снимает напоминание карточки.
     /// </summary>
     /// <param name="cardId">Id карточки (<c>c_...</c>).</param>
-    /// <returns>True — карточка есть и напоминание снято; false — карточки нет (404).</returns>
-    public async Task<bool> ClearReminderAsync(string cardId, CancellationToken ct)
+    /// <exception cref="NotFoundException">Карточка не найдена.</exception>
+    public async Task ClearReminderAsync(string cardId, CancellationToken ct)
     {
-        CardDto? card = await _store.GetCardAsync(cardId, ct);
-        if (card is null)
-        {
-            return false;
-        }
+        _ = await _store.GetCardAsync(cardId, ct)
+            ?? throw new NotFoundException(CardEntityName, cardId);
 
         await _store.ClearReminderAsync(cardId, ct);
-        return true;
     }
 
     /// <summary>
     /// «Напомнить позже»
     /// </summary>
     /// <param name="cardId">Id карточки (<c>c_...</c>).</param>
-    /// <returns>True — карточка есть и напоминание отложено; false — карточки нет (404).</returns>
-    public async Task<bool> SnoozeReminderAsync(string cardId, CancellationToken ct)
+    /// <exception cref="NotFoundException">Карточка не найдена.</exception>
+    public async Task SnoozeReminderAsync(string cardId, CancellationToken ct)
     {
-        CardDto? card = await _store.GetCardAsync(cardId, ct);
-        if (card is null)
-        {
-            return false;
-        }
+        _ = await _store.GetCardAsync(cardId, ct)
+            ?? throw new NotFoundException(CardEntityName, cardId);
 
         long snoozedAtMs = DateTimeOffset.UtcNow.ToUnixTimeMilliseconds() + ReminderSnoozeMs;
         await _store.SetReminderAsync(cardId, snoozedAtMs, ct);
-        return true;
     }
 
     /// <summary>
diff --git a/src/core/Deal.Modules.Kanban/Application/Services/CardsService.Selected.cs b/src/core/Deal.Modules.Kanban/Application/Services/CardsService.Selected.cs
index 69899fd..34b97ab 100644
--- a/src/core/Deal.Modules.Kanban/Application/Services/CardsService.Selected.cs
+++ b/src/core/Deal.Modules.Kanban/Application/Services/CardsService.Selected.cs
@@ -12,6 +12,9 @@ namespace Deal.Modules.Kanban.Application.Services;
 /// </summary>
 public sealed partial class CardsService
 {
+    // Имя сущности для текста ошибки «не найдено».
+    private const string CardLinkEntityName = "Ссылка карточки";
+
     /// <summary>
     /// 400 перенос по стадии
     /// </summary>
@@ -159,18 +162,16 @@ public sealed partial class CardsService
     /// <param name="cardId">Id карточки (<c>c_...</c>).</param>
     /// <param name="name">Название ссылки; пустое после Trim → name = url.</param>
     /// <param name="url">URL ссылки (без схемы — добавится https://).</param>
-    /// <returns>Результат: Error (400 «Пустая ссылка») | Card=null без Error (404) | Card — карточка со ссылкой.</returns>
+    /// <returns>Результат: Error (400 «Пустая ссылка») | Card — карточка со ссылкой.</returns>
+    /// <exception cref="NotFoundException">Карточка не найдена.</exception>
     public async Task<CardResultDto> AddLinkAsync(
         string cardId,
         string name,
         string url,
         CancellationToken ct)
     {
-        CardDto? card = await _store.GetCardAsync(cardId, ct);
-        if (card is null)
-        {
-            return new CardResultDto(null, null);
-        }
+        CardDto card = await _store.GetCardAsync(cardId, ct)
+            ?? throw new NotFoundException(CardEntityName, cardId);
 
         string normalizedUrl = (url ?? string.Empty).Trim();
         if (normalizedUrl.Length == 0)
@@ -191,11 +192,11 @@ public sealed partial class CardsService
             normalizedUrl);
         if (!await _store.AddLinkAsync(cardId, link, ct))
         {
-            return new CardResultDto(null, null);
+            throw new NotFoundException(CardEntityName, cardId);
         }
 
         CardDto saved = await _store.GetCardAsync(cardId, ct)
-            ?? throw new InvalidOperationException("Карточка не прочиталась после добавления ссылки: " + cardId);
+            ?? throw new NotFoundException(CardEntityName, cardId);
         return new CardResultDto(null, saved);
     }
 
@@ -204,7 +205,8 @@ public sealed partial class CardsService
     /// </summary>
     /// <param name="cardId">Id карточки (<c>c_...</c>).</param>
     /// <param name="linkId">Id удаляемой ссылки (<c>pl_...</c>).</param>
-    /// <returns>Результат: Card=null без Error (404) | Card — карточка без ссылки.</returns>
+    /// <returns>Карточка без ссылки.</returns>
+    /// <exception cref="NotFoundException">Карточка или ссылка не найдены.</exception>
     public async Task<CardResultDto> RemoveLinkAsync(
         string cardId,
         string linkId,
@@ -212,11 +214,11 @@ public sealed partial class CardsService
     {
         if (!await _store.RemoveLinkAsync(cardId, linkId, ct))
         {
-            return new CardResultDto(null, null);
+            throw new NotFoundException(CardLinkEntityName, linkId);
         }
 
         CardDto saved = await _store.GetCardAsync(cardId, ct)
-            ?? throw new InvalidOperationException("Карточка не прочиталась после удаления ссылки: " + cardId);
+            ?? throw new NotFoundException(CardEntityName, cardId);
         return new CardResultDto(null, saved);
     }
 
@@ -225,7 +227,8 @@ public sealed partial class CardsService
     /// </summary>
     /// <param name="cardId">Id карточки (<c>c_...</c>).</param>
     /// <param name="containerId">Новый контейнер-стадия — id каталога <see cref="CardsDefaultContainers"/>.</param>
-    /// <returns>Результат: Error «Неизвестная стадия» (400) | Card=null без Error (карточки нет, 404) | Card — карточка после переноса.</returns>
+    /// <returns>Результат: Error «Неизвестная стадия» (400) | Card — карточка после переноса.</returns>
+    /// <exception cref="NotFoundException">Карточка не найдена.</exception>
     public async Task<CardResultDto> MoveStageCardAsync(
         string cardId,
         string containerId,
@@ -241,11 +244,11 @@ public sealed partial class CardsService
         bool moved = await _store.MoveCardStageAsync(cardId, containerId, entry, nowMs, ct);
         if (!moved)
         {
-            return new CardResultDto(null, null);
+            throw new NotFoundException(CardEntityName, cardId);
         }
 
         CardDto card = await _store.GetCardAsync(cardId, ct)
-            ?? throw new InvalidOperationException("Карточка не прочиталась после move: " + cardId);
+            ?? throw new NotFoundException(CardEntityName, cardId);
         return new CardResultDto(null, card);
     }
 
diff --git a/src/core/Deal.Modules.Pipeline/Application/Services/MlReviewService.cs b/src/core/Deal.Modules.Pipeline/Application/Services/MlReviewService.cs
index 2fabdbf..14c2426 100644
--- a/src/core/Deal.Modules.Pipeline/Application/Services/MlReviewService.cs
+++ b/src/core/Deal.Modules.Pipeline/Application/Services/MlReviewService.cs
@@ -8,6 +8,7 @@ using Deal.Modules.Kanban.Application.Models;
 using Deal.Modules.Kanban.Application.Services;
 using Deal.Modules.Pipeline.Application.Abstractions;
 using Deal.Modules.Pipeline.Application.Models;
+using Deal.SharedKernel.Errors;
 
 namespace Deal.Modules.Pipeline.Application.Services;
 
@@ -34,6 +35,9 @@ public sealed class MlReviewService(
     // Размер одного чтения из очереди/отсева при объединении кандидатов.
     private const int MaxScan = 500;
 
+    // Имя сущности для текста ошибки «не найдено».
+    private const string MessageEntityName = "Исходное сообщение";
+
     private const int TextPreviewLength = 600;
 
     /// <summary>
@@ -157,8 +161,9 @@ public sealed class MlReviewService(
     /// <param name="dialogId">Оригинал источника (OriginRef) записи.</param>
     /// <param name="msgId">Внешний id записи в источнике.</param>
     /// <param name="action">Действие: <c>skip</c> | <c>spam</c> | <c>board:&lt;id&gt;</c>.</param>
-    /// <returns>Результат решения; null — исходная запись не найдена (404-семантика эндпоинта).</returns>
-    public async Task<MlApplyResult?> ApplyAsync(
+    /// <returns>Результат решения.</returns>
+    /// <exception cref="NotFoundException">Исходная запись не найдена.</exception>
+    public async Task<MlApplyResult> ApplyAsync(
         string dialogId,
         long msgId,
         string? action,
@@ -168,17 +173,14 @@ public sealed class MlReviewService(
         string dialog = (dialogId ?? string.Empty).Trim();
         string externalId = msgId.ToString(CultureInfo.InvariantCulture);
 
-        SourceRef? source = await ResolveSourceAsync(dialog, externalId, ct);
-        if (source is null)
-        {
-            return null; // 404: исходная запись не найдена
-        }
+        SourceRef source = await ResolveSourceAsync(dialog, externalId, ct)
+            ?? throw new NotFoundException(MessageEntityName, externalId);
 
         CardDto? card = await cardStore.GetCardBySourceAsync(source, ct);
         string? text = await FindTextAsync(dialog, externalId, card, ct);
         if (string.IsNullOrWhiteSpace(text))
         {
-            return null; // 404: исходная запись не найдена
+            throw new NotFoundException(MessageEntityName, externalId);
         }
 
         if (normalized == ActionSkip)
diff --git a/src/core/Deal.Modules.Pipeline/Application/Services/PipelineProcessingService.cs b/src/core/Deal.Modules.Pipeline/Application/Services/PipelineProcessingService.cs
index d845dd0..2a79770 100644
--- a/src/core/Deal.Modules.Pipeline/Application/Services/PipelineProcessingService.cs
+++ b/src/core/Deal.Modules.Pipeline/Application/Services/PipelineProcessingService.cs
@@ -4,6 +4,7 @@ using Deal.Modules.Cards.Application.Sources;
 using Deal.Modules.Pipeline.Application.Abstractions;
 using Deal.Modules.Pipeline.Application.Models;
 using Deal.Modules.Pipeline.Application.Parse;
+using Deal.SharedKernel.Errors;
 
 namespace Deal.Modules.Pipeline.Application.Services;
 
@@ -48,6 +49,9 @@ public sealed class PipelineProcessingService(
 
     private const string DuplicateSource = "dup";
 
+    // Имя сущности для текста ошибки «не найдено».
+    private const string RejectedEntityName = "Запись отсева";
+
     private static readonly HashSet<string> SpamStages = new(StringComparer.Ordinal)
     {
         "spam_ml",
@@ -154,17 +158,15 @@ public sealed class PipelineProcessingService(
     /// </summary>
     /// <param name="rejectedId">Id записи отсева (<c>r_...</c>).</param>
     /// <param name="reason">Причина возврата (trim, ≤500; пишется на запись для аудита).</param>
-    /// <returns>null — записи нет (404); иначе результат: Error (400) либо {id, returned:true, returnedAt}.</returns>
-    public async Task<RejectReturnResultDto?> ReturnAsync(
+    /// <returns>Результат: Error (400) либо {id, returned:true, returnedAt}.</returns>
+    /// <exception cref="NotFoundException">Запись отсева не найдена.</exception>
+    public async Task<RejectReturnResultDto> ReturnAsync(
         string rejectedId,
         string reason,
         CancellationToken ct)
     {
-        RejectedItemDto? row = await store.GetAsync(rejectedId, ct);
-        if (row is null)
-        {
-            return null;
-        }
+        RejectedItemDto row = await store.GetAsync(rejectedId, ct)
+            ?? throw new NotFoundException(RejectedEntityName, rejectedId);
 
         if (row.Returned)
         {
diff --git a/src/core/Deal.Modules.Tenants/Application/Services/TenantAdminService.cs b/src/core/Deal.Modules.Tenants/Application/Services/TenantAdminService.cs
index 7a4a553..70ec5f5 100644
--- a/src/core/Deal.Modules.Tenants/Application/Services/TenantAdminService.cs
+++ b/src/core/Deal.Modules.Tenants/Application/Services/TenantAdminService.cs
@@ -1,6 +1,7 @@
 using Deal.Modules.Tenants.Application.Abstractions;
 using Deal.Modules.Tenants.Application.Models;
 using Deal.SharedKernel;
+using Deal.SharedKernel.Errors;
 using Deal.SharedKernel.Utilities;
 
 namespace Deal.Modules.Tenants.Application.Services;
@@ -17,6 +18,9 @@ public sealed class TenantAdminService(
     // Случайные байты одноразового пароля владельца: 12 → ровно 16 символов Base64Url (как InviteCodeGenerator).
     private const int InitialPasswordRandomByteCount = 12;
 
+    // Имя сущности для текста ошибки «не найдено» (пользователь = тенант с его окружением).
+    private const string TenantEntityName = "Пользователь";
+
     /// <summary>
     /// Создаёт тенанта оператором
     /// </summary>
@@ -103,14 +107,12 @@ public sealed class TenantAdminService(
     /// Детали тенанта с пользователями
     /// </summary>
     /// <param name="id">Идентификатор тенанта.</param>
-    /// <returns>Детали и пользователи тенанта (по CreatedAt) или null, если тенанта нет.</returns>
-    public async Task<TenantDetailDto?> GetAsync(Guid id, CancellationToken ct)
+    /// <returns>Детали и пользователи тенанта (по CreatedAt).</returns>
+    /// <exception cref="NotFoundException">Тенант не найден.</exception>
+    public async Task<TenantDetailDto> GetAsync(Guid id, CancellationToken ct)
     {
-        var tenant = await tenantRepository.FindByIdAsync(id, ct);
-        if (tenant is null)
-        {
-            return null;
-        }
+        var tenant = await tenantRepository.FindByIdAsync(id, ct)
+            ?? throw new NotFoundException(TenantEntityName, id.ToString("N"));
 
         IReadOnlyList<UserIdentityDto> users = await authStore.ListUsersByTenantIdAsync(id, ct);
         return new TenantDetailDto(tenant.Id, tenant.Name, tenant.Status, tenant.CreatedAt, users);
diff --git a/src/core/tests/Deal.Tests.Unit/Contracts/CardsServiceTests.cs b/src/core/tests/Deal.Tests.Unit/Contracts/CardsServiceTests.cs
index d6ec709..f008aa6 100644
--- a/src/core/tests/Deal.Tests.Unit/Contracts/CardsServiceTests.cs
+++ b/src/core/tests/Deal.Tests.Unit/Contracts/CardsServiceTests.cs
@@ -53,13 +53,12 @@ public sealed class CardsServiceTests
     }
 
     [Fact]
-    public async Task GetCard_Missing_ReturnsNull()
+    public async Task GetCard_Missing_ThrowsNotFound()
     {
         (CardsService service, _, _, _) = Create();
 
-        CardDto? card = await service.GetCardAsync("l_missing", CancellationToken.None);
-
-        Assert.Null(card);
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.GetCardAsync("l_missing", CancellationToken.None));
     }
 
 
@@ -146,15 +145,14 @@ public sealed class CardsServiceTests
     }
 
     [Fact]
-    public async Task Move_CardMissing_ReturnsNullLead()
+    public async Task Move_CardMissing_ThrowsNotFound()
     {
         (CardsService service, TestKanjStore store, _, TestMlClient ml) = Create();
         store.SeedBoard(Board("b_py"));
 
-        CardResultDto result = await service.MoveDashboardCardAsync("l_ghost", "b_py", CancellationToken.None);
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.MoveDashboardCardAsync("l_ghost", "b_py", CancellationToken.None));
 
-        Assert.Null(result.Error);
-        Assert.Null(result.Card); // эндпоинт отвечает 404 «Карточка не найдена»
         Assert.Empty(store.Moves);
         Assert.Empty(ml.Pushed);
     }
diff --git a/src/core/tests/Deal.Tests.Unit/Infrastructure/CardMoverTests.cs b/src/core/tests/Deal.Tests.Unit/Infrastructure/CardMoverTests.cs
index 8bcd7bd..b33382b 100644
--- a/src/core/tests/Deal.Tests.Unit/Infrastructure/CardMoverTests.cs
+++ b/src/core/tests/Deal.Tests.Unit/Infrastructure/CardMoverTests.cs
@@ -3,10 +3,11 @@ using Deal.Modules.Cards.Application.Dtos;
 using Deal.Modules.Cards.Application.Models;
 using Deal.Modules.Cards.Application.Sources;
 using Deal.Modules.Kanban.Application.Models;
-using Deal.Tests.Unit.Support;
 using Deal.Modules.Kanban.Application.Services;
+using Deal.SharedKernel.Errors;
 using Deal.Tests.Unit.Contracts;
 using Deal.Tests.Unit.Modules.Settings;
+using Deal.Tests.Unit.Support;
 
 namespace Deal.Tests.Unit.Infrastructure;
 
@@ -32,7 +33,6 @@ public sealed class CardMoverTests
         CardMoveResultDto result = await mover.MoveAsync("c_1", CardsDefaultContainers.Planned, UserMove, CancellationToken.None);
 
         Assert.Null(result.Error);
-        Assert.True(result.Exists);
         CardDto card = Assert.Single(store.CardDtos);
         Assert.Equal(CardsDefaultContainers.Planned, card.Col);
         Assert.Null(card.Reminder); // move по стадии сбрасывает напоминание
@@ -50,7 +50,6 @@ public sealed class CardMoverTests
         CardMoveResultDto result = await mover.MoveAsync("c_1", "b_py", UserMove, CancellationToken.None);
 
         Assert.Null(result.Error);
-        Assert.True(result.Exists);
         Assert.Equal("b_py", Assert.Single(store.CardDtos).Col);
         Assert.Single(store.Moves); // журнал CardMoves дашборд-переноса
     }
@@ -64,18 +63,15 @@ public sealed class CardMoverTests
         CardMoveResultDto result = await mover.MoveAsync("c_1", "b_ghost", UserMove, CancellationToken.None);
 
         Assert.Equal(CardsService.MoveTargetInvalidDetail, result.Error);
-        Assert.True(result.Exists); // ошибка важнее признака наличия
     }
 
     [Fact]
-    public async Task Move_ToStage_CardMissing_ReportsNotFound()
+    public async Task Move_ToStage_CardMissing_ThrowsNotFound()
     {
         (CardMover mover, _) = Create();
 
-        CardMoveResultDto result = await mover.MoveAsync("c_ghost", CardsDefaultContainers.Planned, UserMove, CancellationToken.None);
-
-        Assert.Null(result.Error);
-        Assert.False(result.Exists);
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => mover.MoveAsync("c_ghost", CardsDefaultContainers.Planned, UserMove, CancellationToken.None));
     }
 
     private static (CardMover Mover, TestKanjStore Store) Create()
diff --git a/src/core/tests/Deal.Tests.Unit/Modules/Discovery/DiscoveryCandidatesServiceTests.cs b/src/core/tests/Deal.Tests.Unit/Modules/Discovery/DiscoveryCandidatesServiceTests.cs
index 3f68ee5..61f3931 100644
--- a/src/core/tests/Deal.Tests.Unit/Modules/Discovery/DiscoveryCandidatesServiceTests.cs
+++ b/src/core/tests/Deal.Tests.Unit/Modules/Discovery/DiscoveryCandidatesServiceTests.cs
@@ -1,7 +1,8 @@
 using Deal.Modules.Discovery.Application.Exceptions;
 using Deal.Modules.Discovery.Application.Models;
-using Deal.Tests.Unit.Support;
 using Deal.Modules.Discovery.Application.Services;
+using Deal.SharedKernel.Errors;
+using Deal.Tests.Unit.Support;
 
 namespace Deal.Tests.Unit.Modules.Discovery;
 
@@ -114,14 +115,13 @@ public sealed class DiscoveryCandidatesServiceTests
     }
 
     [Fact]
-    public async Task Add_MissingTask_ReturnsNullWithoutLog()
+    public async Task Add_MissingTask_ThrowsNotFoundWithoutLog()
     {
         (DiscoveryCandidatesService service, TestDiscoveryStore store) = Create();
 
-        DiscoveryCandidateDto? candidate = await service.AddAsync(
-            "dt_missing", "-1001", "Канал", "", DiscoveryCandidateKinds.Channel, "", CancellationToken.None);
+        await Assert.ThrowsAsync<NotFoundException>(() => service.AddAsync(
+            "dt_missing", "-1001", "Канал", "", DiscoveryCandidateKinds.Channel, "", CancellationToken.None));
 
-        Assert.Null(candidate);
         Assert.Empty(store.Candidates);
         Assert.Empty(store.Log);
     }
@@ -175,13 +175,12 @@ public sealed class DiscoveryCandidatesServiceTests
     }
 
     [Fact]
-    public async Task MarkJoined_MissingCandidate_ReturnsNull()
+    public async Task MarkJoined_MissingCandidate_ThrowsNotFound()
     {
         (DiscoveryCandidatesService service, _) = Create();
 
-        DiscoveryCandidateDto? candidate = await service.MarkJoinedAsync("-1001", auto: true, CancellationToken.None);
-
-        Assert.Null(candidate);
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.MarkJoinedAsync("-1001", auto: true, CancellationToken.None));
     }
 
     [Fact]
@@ -238,14 +237,12 @@ public sealed class DiscoveryCandidatesServiceTests
     }
 
     [Fact]
-    public async Task MarkRejected_MissingCandidate_ReturnsNull()
+    public async Task MarkRejected_MissingCandidate_ThrowsNotFound()
     {
         (DiscoveryCandidatesService service, _) = Create();
 
-        DiscoveryCandidateDto? candidate = await service.MarkRejectedAsync(
-            "-1001", "причина", CancellationToken.None);
-
-        Assert.Null(candidate);
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.MarkRejectedAsync("-1001", "причина", CancellationToken.None));
     }
 
     [Fact]
@@ -315,17 +312,15 @@ public sealed class DiscoveryCandidatesServiceTests
     }
 
     [Fact]
-    public async Task Set_WrongTask_ReturnsNull()
+    public async Task Set_WrongTask_ThrowsNotFound()
     {
         (DiscoveryCandidatesService service, TestDiscoveryStore store) = Create();
         store.SeedTask(Task("dt_1"));
         store.SeedTask(Task("dt_2"));
         store.SeedCandidate(Candidate("-1001", "dt_1"));
 
-        DiscoveryCandidateDto? candidate = await service.SetAsync(
-            "dt_2", "-1001", new DiscoveryCandidatePatch { Participants = 10 }, CancellationToken.None);
-
-        Assert.Null(candidate); // кандидат другой задачи (python L465–466)
+        await Assert.ThrowsAsync<NotFoundException>(() => service.SetAsync(
+            "dt_2", "-1001", new DiscoveryCandidatePatch { Participants = 10 }, CancellationToken.None));
     }
 
     [Fact]
diff --git a/src/core/tests/Deal.Tests.Unit/Modules/Kanban/CardsServiceRemindersTests.cs b/src/core/tests/Deal.Tests.Unit/Modules/Kanban/CardsServiceRemindersTests.cs
index ea7bd08..b6974a8 100644
--- a/src/core/tests/Deal.Tests.Unit/Modules/Kanban/CardsServiceRemindersTests.cs
+++ b/src/core/tests/Deal.Tests.Unit/Modules/Kanban/CardsServiceRemindersTests.cs
@@ -1,9 +1,10 @@
 using Deal.Modules.Kanban.Application.Models;
-using Deal.Tests.Unit.Support;
 using Deal.Modules.Kanban.Application.Services;
 using Deal.Modules.Settings.Application.Models;
+using Deal.SharedKernel.Errors;
 using Deal.Tests.Unit.Contracts;
 using Deal.Tests.Unit.Modules.Settings;
+using Deal.Tests.Unit.Support;
 
 namespace Deal.Tests.Unit.Modules.Kanban;
 
@@ -47,14 +48,12 @@ public sealed class CardsServiceRemindersTests
     }
 
     [Fact]
-    public async Task Set_MissingCard_Returns404EvenWhenDisabled()
+    public async Task Set_MissingCard_ThrowsNotFoundEvenWhenDisabled()
     {
         (CardsService service, _, _) = Create(remindersEnabled: false);
 
-        CardResultDto result = await service.SetReminderAsync("c_missing", NowMs(), CancellationToken.None);
-
-        Assert.Null(result.Error);
-        Assert.Null(result.Card); // эндпоинт отвечает 404 «Карточка не найдена»
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.SetReminderAsync("c_missing", NowMs(), CancellationToken.None));
     }
 
     [Fact]
@@ -73,25 +72,23 @@ public sealed class CardsServiceRemindersTests
 
 
     [Fact]
-    public async Task Clear_WithReminder_ClearsItAndReturnsTrue()
+    public async Task Clear_WithReminder_ClearsIt()
     {
         (CardsService service, TestKanjStore store, _) = Create();
         store.SeedCard(Card("c_1", stage: "hold") with { Reminder = new CardReminderDto(NowMs() - 1) });
 
-        bool cleared = await service.ClearReminderAsync("c_1", CancellationToken.None);
+        await service.ClearReminderAsync("c_1", CancellationToken.None);
 
-        Assert.True(cleared);
         Assert.Null(Assert.Single(store.CardDtos).Reminder); // reminder_at=NULL, fired сброшен
     }
 
     [Fact]
-    public async Task Clear_MissingCard_ReturnsFalse()
+    public async Task Clear_MissingCard_ThrowsNotFound()
     {
         (CardsService service, _, _) = Create();
 
-        bool cleared = await service.ClearReminderAsync("c_missing", CancellationToken.None);
-
-        Assert.False(cleared); // эндпоинт отвечает 404 «Карточка не найдена»
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.ClearReminderAsync("c_missing", CancellationToken.None));
     }
 
     [Fact]
@@ -100,9 +97,8 @@ public sealed class CardsServiceRemindersTests
         (CardsService service, TestKanjStore store, _) = Create(remindersEnabled: false);
         store.SeedCard(Card("c_1", stage: "hold") with { Reminder = new CardReminderDto(NowMs() + DayMs) });
 
-        bool cleared = await service.ClearReminderAsync("c_1", CancellationToken.None);
+        await service.ClearReminderAsync("c_1", CancellationToken.None);
 
-        Assert.True(cleared);
         Assert.Null(Assert.Single(store.CardDtos).Reminder);
     }
 
@@ -114,22 +110,20 @@ public sealed class CardsServiceRemindersTests
         store.SeedCard(Card("c_1", stage: "hold") with { Reminder = new CardReminderDto(NowMs() - 1) });
         long beforeMs = NowMs();
 
-        bool snoozed = await service.SnoozeReminderAsync("c_1", CancellationToken.None);
+        await service.SnoozeReminderAsync("c_1", CancellationToken.None);
 
-        Assert.True(snoozed);
         long afterMs = NowMs();
         CardReminderDto reminder = Assert.Single(store.CardDtos).Reminder!;
         Assert.InRange(reminder.At, beforeMs + DayMs, afterMs + DayMs); // now + 24 ч
     }
 
     [Fact]
-    public async Task Snooze_MissingCard_ReturnsFalse()
+    public async Task Snooze_MissingCard_ThrowsNotFound()
     {
         (CardsService service, _, _) = Create();
 
-        bool snoozed = await service.SnoozeReminderAsync("c_missing", CancellationToken.None);
-
-        Assert.False(snoozed); // эндпоинт отвечает 404 «Карточка не найдена»
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.SnoozeReminderAsync("c_missing", CancellationToken.None));
     }
 
     [Fact]
@@ -138,9 +132,8 @@ public sealed class CardsServiceRemindersTests
         (CardsService service, TestKanjStore store, _) = Create(remindersEnabled: false);
         store.SeedCard(Card("c_1", stage: "hold") with { Reminder = new CardReminderDto(NowMs() - 1) });
 
-        bool snoozed = await service.SnoozeReminderAsync("c_1", CancellationToken.None);
+        await service.SnoozeReminderAsync("c_1", CancellationToken.None);
 
-        Assert.True(snoozed);
         Assert.NotNull(Assert.Single(store.CardDtos).Reminder);
     }
 
diff --git a/src/core/tests/Deal.Tests.Unit/Modules/Kanban/MlReviewServiceTests.cs b/src/core/tests/Deal.Tests.Unit/Modules/Kanban/MlReviewServiceTests.cs
index 9a2e827..9551349 100644
--- a/src/core/tests/Deal.Tests.Unit/Modules/Kanban/MlReviewServiceTests.cs
+++ b/src/core/tests/Deal.Tests.Unit/Modules/Kanban/MlReviewServiceTests.cs
@@ -4,6 +4,7 @@ using Deal.Modules.Kanban.Application.Models;
 using Deal.Modules.Kanban.Application.Services;
 using Deal.Modules.Pipeline.Application.Models;
 using Deal.Modules.Pipeline.Application.Services;
+using Deal.SharedKernel.Errors;
 using Deal.Tests.Unit.Contracts;
 using Deal.Tests.Unit.Modules.Settings;
 using Deal.Tests.Unit.Support;
@@ -241,12 +242,11 @@ public sealed class MlReviewServiceTests
     }
 
     [Fact]
-    public async Task Apply_MessageNotFound_ReturnsNull()
+    public async Task Apply_MessageNotFound_ThrowsNotFound()
     {
         MlReviewService service = Create(new TestPipelineStore(), new TestKanjStore(), new TestMlClient(), out _);
 
-        MlApplyResult? result = await service.ApplyAsync(Dialog, 999, MlReviewService.ActionSpam, CancellationToken.None);
-
-        Assert.Null(result);
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.ApplyAsync(Dialog, 999, MlReviewService.ActionSpam, CancellationToken.None));
     }
 }
diff --git a/src/core/tests/Deal.Tests.Unit/Modules/Pipeline/PipelineProcessingServiceTests.cs b/src/core/tests/Deal.Tests.Unit/Modules/Pipeline/PipelineProcessingServiceTests.cs
index 6ea34d0..6b31631 100644
--- a/src/core/tests/Deal.Tests.Unit/Modules/Pipeline/PipelineProcessingServiceTests.cs
+++ b/src/core/tests/Deal.Tests.Unit/Modules/Pipeline/PipelineProcessingServiceTests.cs
@@ -2,6 +2,7 @@ using System.Globalization;
 using Deal.Modules.Cards.Application.Sources;
 using Deal.Modules.Pipeline.Application.Models;
 using Deal.Modules.Pipeline.Application.Services;
+using Deal.SharedKernel.Errors;
 using Deal.Tests.Unit.Contracts;
 using Deal.Tests.Unit.Support;
 
@@ -165,13 +166,13 @@ public sealed class PipelineProcessingServiceTests
 
 
     [Fact]
-    public async Task ReturnAsync_RecordNotFound_ReturnsNull()
+    public async Task ReturnAsync_RecordNotFound_ThrowsNotFound()
     {
         (PipelineProcessingService service, TestPipelineStore store, TestMlClient ml) = Create();
 
-        RejectReturnResultDto? result = await service.ReturnAsync("r_missing", string.Empty, CancellationToken.None);
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.ReturnAsync("r_missing", string.Empty, CancellationToken.None));
 
-        Assert.Null(result); // эндпоинт ответит 404 «Запись не найдена» (Ruling 10)
         Assert.Empty(store.Queue);
         Assert.Empty(ml.Pushed);
     }
diff --git a/src/core/tests/Deal.Tests.Unit/Modules/Tenants/TenantAdminServiceTests.cs b/src/core/tests/Deal.Tests.Unit/Modules/Tenants/TenantAdminServiceTests.cs
index e0cb343..111639f 100644
--- a/src/core/tests/Deal.Tests.Unit/Modules/Tenants/TenantAdminServiceTests.cs
+++ b/src/core/tests/Deal.Tests.Unit/Modules/Tenants/TenantAdminServiceTests.cs
@@ -1,7 +1,8 @@
+using Deal.Modules.Tenants.Application.Abstractions;
 using Deal.Modules.Tenants.Application.Models;
 using Deal.Modules.Tenants.Application.Services;
+using Deal.SharedKernel.Errors;
 using Deal.Tests.Unit.Support;
-using Deal.Modules.Tenants.Application.Abstractions;
 
 namespace Deal.Tests.Unit.Modules.Tenants;
 
@@ -148,11 +149,12 @@ public sealed class TenantAdminServiceTests
     }
 
     [Fact]
-    public async Task GetAsync_ForUnknownTenant_ReturnsNull()
+    public async Task GetAsync_ForUnknownTenant_ThrowsNotFound()
     {
         var service = NewService(new TestTenantStore(), new TestAuthStore());
 
-        Assert.Null(await service.GetAsync(Guid.NewGuid(), CancellationToken.None));
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.GetAsync(Guid.NewGuid(), CancellationToken.None));
     }
 
     [Fact]
diff --git a/src/core/tests/Deal.Tests.Unit/Support/CardsServiceSelectedTests.cs b/src/core/tests/Deal.Tests.Unit/Support/CardsServiceSelectedTests.cs
index 871d678..21fa9a5 100644
--- a/src/core/tests/Deal.Tests.Unit/Support/CardsServiceSelectedTests.cs
+++ b/src/core/tests/Deal.Tests.Unit/Support/CardsServiceSelectedTests.cs
@@ -40,13 +40,12 @@ public sealed class CardsServiceSelectedTests
     }
 
     [Fact]
-    public async Task Get_Missing_ReturnsNull()
+    public async Task Get_Missing_ThrowsNotFound()
     {
         (CardsService service, _, _, _) = Create();
 
-        CardDto? card = await service.GetCardAsync("c_missing", CancellationToken.None);
-
-        Assert.Null(card);
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.GetCardAsync("c_missing", CancellationToken.None));
     }
 
 
@@ -319,14 +318,12 @@ public sealed class CardsServiceSelectedTests
     }
 
     [Fact]
-    public async Task Move_CardMissing_ReturnsNullCard()
+    public async Task Move_CardMissing_ThrowsNotFound()
     {
         (CardsService service, _, _, _) = Create();
 
-        CardResultDto result = await service.MoveStageCardAsync("c_missing", "work", CancellationToken.None);
-
-        Assert.Null(result.Error);
-        Assert.Null(result.Card); // 404 «Карточка не найдена» — текст у эндпоинта
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.MoveStageCardAsync("c_missing", "work", CancellationToken.None));
     }
 
 
@@ -465,14 +462,13 @@ public sealed class CardsServiceSelectedTests
     }
 
     [Fact]
-    public async Task AddLink_CardMissing_ReturnsNullCardBeforeUrlValidation()
+    public async Task AddLink_CardMissing_ThrowsBeforeUrlValidation()
     {
         (CardsService service, TestKanjStore store, _, _) = Create();
 
-        CardResultDto result = await service.AddLinkAsync("c_missing", string.Empty, "example.com", CancellationToken.None);
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.AddLinkAsync("c_missing", string.Empty, "example.com", CancellationToken.None));
 
-        Assert.Null(result.Error);
-        Assert.Null(result.Card); // 404-семантика: карточки нет раньше валидации url
         Assert.Empty(store.CardDtos);
     }
 
@@ -514,14 +510,13 @@ public sealed class CardsServiceSelectedTests
     }
 
     [Fact]
-    public async Task RemoveLink_CardMissing_ReturnsNullCard()
+    public async Task RemoveLink_CardMissing_ThrowsNotFound()
     {
         (CardsService service, TestKanjStore store, _, _) = Create();
 
-        CardResultDto result = await service.RemoveLinkAsync("c_missing", "pl_1", CancellationToken.None);
+        await Assert.ThrowsAsync<NotFoundException>(
+            () => service.RemoveLinkAsync("c_missing", "pl_1", CancellationToken.None));
 
-        Assert.Null(result.Error);
-        Assert.Null(result.Card); // эндпоинт отвечает 404 «Карточка не найдена»
         Assert.Empty(store.CardDtos);
     }