diff --git a/src/api/SIGCM2.Api/Controllers/UsuariosController.cs b/src/api/SIGCM2.Api/Controllers/UsuariosController.cs
index cfa7e61..d86e562 100644
--- a/src/api/SIGCM2.Api/Controllers/UsuariosController.cs
+++ b/src/api/SIGCM2.Api/Controllers/UsuariosController.cs
@@ -10,6 +10,7 @@ using SIGCM2.Application.Usuarios.Deactivate;
 using SIGCM2.Application.Usuarios.GetById;
 using SIGCM2.Application.Usuarios.List;
 using SIGCM2.Application.Usuarios.Reactivate;
+using SIGCM2.Application.Usuarios.Permisos;
 using SIGCM2.Application.Usuarios.ResetPassword;
 using SIGCM2.Application.Usuarios.Update;
 using System.IdentityModel.Tokens.Jwt;
@@ -225,10 +226,46 @@ public sealed class UsuariosController : ControllerBase
         var result = await _dispatcher.Send<ResetUsuarioPasswordCommand, ResetUsuarioPasswordResponse>(command);
         return Ok(result);
     }
+
+    // ── UDT-009: Permisos endpoints ───────────────────────────────────────────
+
+    /// <summary>
+    /// Gets a usuario's role permissions, explicit grant/deny overrides, and computed effective set.
+    /// Requires administracion:usuarios:gestionar.
+    /// </summary>
+    [HttpGet("{id:int}/permisos")]
+    [RequirePermission("administracion:usuarios:gestionar")]
+    [ProducesResponseType(typeof(UsuarioPermisosResponse), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status401Unauthorized)]
+    [ProducesResponseType(StatusCodes.Status403Forbidden)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<IActionResult> GetPermisos([FromRoute] int id)
+    {
+        var result = await _dispatcher.Send<GetUsuarioPermisosQuery, UsuarioPermisosDto>(
+            new GetUsuarioPermisosQuery(id));
+        return Ok(MapToPermisosResponse(result));
+    }
+
+    private static UsuarioPermisosResponse MapToPermisosResponse(UsuarioPermisosDto dto)
+        => new(
+            RolPermisos: dto.RolPermisos,
+            Overrides: new PermisosOverridesShape(dto.Grant, dto.Deny),
+            Effective: dto.Effective);
 }
 
 // ── request body records ──────────────────────────────────────────────────────
 
+/// <summary>UDT-009: Response shape for permisos endpoints.</summary>
+public sealed record UsuarioPermisosResponse(
+    IReadOnlyList<string> RolPermisos,
+    PermisosOverridesShape Overrides,
+    IReadOnlyList<string> Effective);
+
+/// <summary>UDT-009: The grant/deny override shape nested in UsuarioPermisosResponse.</summary>
+public sealed record PermisosOverridesShape(
+    IReadOnlyList<string> Grant,
+    IReadOnlyList<string> Deny);
+
 /// <summary>Create user request body — nullable to catch missing field scenarios.</summary>
 public sealed record CreateUsuarioRequest(
     string? Username,
diff --git a/src/api/SIGCM2.Application/DependencyInjection.cs b/src/api/SIGCM2.Application/DependencyInjection.cs
index 1476873..6c5db6a 100644
--- a/src/api/SIGCM2.Application/DependencyInjection.cs
+++ b/src/api/SIGCM2.Application/DependencyInjection.cs
@@ -22,6 +22,7 @@ using SIGCM2.Application.Usuarios.GetById;
 using SIGCM2.Application.Usuarios.List;
 using SIGCM2.Application.Usuarios.Reactivate;
 using SIGCM2.Application.Usuarios.ResetPassword;
+using SIGCM2.Application.Usuarios.Permisos;
 using SIGCM2.Application.Usuarios.Update;
 
 namespace SIGCM2.Application;
@@ -57,6 +58,9 @@ public static class DependencyInjection
         services.AddScoped<ICommandHandler<ChangeMyPasswordCommand, Unit>, ChangeMyPasswordCommandHandler>();
         services.AddScoped<ICommandHandler<ResetUsuarioPasswordCommand, ResetUsuarioPasswordResponse>, ResetUsuarioPasswordCommandHandler>();
 
+        // Usuarios/Permisos (UDT-009)
+        services.AddScoped<ICommandHandler<GetUsuarioPermisosQuery, UsuarioPermisosDto>, GetUsuarioPermisosQueryHandler>();
+
         // FluentValidation validators (scans entire Application assembly)
         services.AddValidatorsFromAssemblyContaining<LoginCommandValidator>();
 
diff --git a/src/api/SIGCM2.Application/Usuarios/Permisos/GetUsuarioPermisosQuery.cs b/src/api/SIGCM2.Application/Usuarios/Permisos/GetUsuarioPermisosQuery.cs
new file mode 100644
index 0000000..835668a
--- /dev/null
+++ b/src/api/SIGCM2.Application/Usuarios/Permisos/GetUsuarioPermisosQuery.cs
@@ -0,0 +1,4 @@
+namespace SIGCM2.Application.Usuarios.Permisos;
+
+/// <summary>UDT-009: Query to get a user's role permissions, overrides, and effective set.</summary>
+public sealed record GetUsuarioPermisosQuery(int Id);
diff --git a/src/api/SIGCM2.Application/Usuarios/Permisos/GetUsuarioPermisosQueryHandler.cs b/src/api/SIGCM2.Application/Usuarios/Permisos/GetUsuarioPermisosQueryHandler.cs
new file mode 100644
index 0000000..bb5e8d8
--- /dev/null
+++ b/src/api/SIGCM2.Application/Usuarios/Permisos/GetUsuarioPermisosQueryHandler.cs
@@ -0,0 +1,51 @@
+using SIGCM2.Application.Abstractions;
+using SIGCM2.Application.Abstractions.Persistence;
+using SIGCM2.Application.Common;
+using SIGCM2.Domain.Exceptions;
+
+namespace SIGCM2.Application.Usuarios.Permisos;
+
+/// <summary>
+/// UDT-009: Handles GET /api/v1/users/{id}/permisos.
+/// Resolves role permissions + overrides + effective set.
+/// </summary>
+public sealed class GetUsuarioPermisosQueryHandler
+    : ICommandHandler<GetUsuarioPermisosQuery, UsuarioPermisosDto>
+{
+    private readonly IUsuarioRepository _usuarioRepo;
+    private readonly IRolPermisoRepository _rolPermisoRepo;
+
+    public GetUsuarioPermisosQueryHandler(
+        IUsuarioRepository usuarioRepo,
+        IRolPermisoRepository rolPermisoRepo)
+    {
+        _usuarioRepo = usuarioRepo;
+        _rolPermisoRepo = rolPermisoRepo;
+    }
+
+    public async Task<UsuarioPermisosDto> Handle(GetUsuarioPermisosQuery query)
+    {
+        var usuario = await _usuarioRepo.GetByIdAsync(query.Id)
+            ?? throw new UsuarioNotFoundException(query.Id);
+
+        var rolPermisoEntities = await _rolPermisoRepo.GetByRolCodigoAsync(usuario.Rol);
+        var rolPermisos = rolPermisoEntities
+            .Select(p => p.Codigo)
+            .OrderBy(c => c, StringComparer.Ordinal)
+            .ToArray();
+
+        var overrides = PermisosOverride.FromJson(usuario.PermisosJson);
+
+        var effective = PermisoResolver.Resolve(rolPermisos, overrides)
+            .OrderBy(c => c, StringComparer.Ordinal)
+            .ToArray();
+
+        return new UsuarioPermisosDto(
+            UsuarioId: usuario.Id,
+            Rol: usuario.Rol,
+            RolPermisos: rolPermisos,
+            Grant: overrides.Grant,
+            Deny: overrides.Deny,
+            Effective: effective);
+    }
+}
diff --git a/src/api/SIGCM2.Application/Usuarios/Permisos/UsuarioPermisosDto.cs b/src/api/SIGCM2.Application/Usuarios/Permisos/UsuarioPermisosDto.cs
new file mode 100644
index 0000000..fd0233f
--- /dev/null
+++ b/src/api/SIGCM2.Application/Usuarios/Permisos/UsuarioPermisosDto.cs
@@ -0,0 +1,13 @@
+namespace SIGCM2.Application.Usuarios.Permisos;
+
+/// <summary>
+/// UDT-009: Response DTO for user permissions.
+/// Contains role permissions, explicit overrides, and computed effective permissions.
+/// </summary>
+public sealed record UsuarioPermisosDto(
+    int UsuarioId,
+    string Rol,
+    IReadOnlyList<string> RolPermisos,
+    IReadOnlyList<string> Grant,
+    IReadOnlyList<string> Deny,
+    IReadOnlyList<string> Effective);
diff --git a/tests/SIGCM2.Api.Tests/Usuarios/UsuarioPermisosEndpointTests.cs b/tests/SIGCM2.Api.Tests/Usuarios/UsuarioPermisosEndpointTests.cs
new file mode 100644
index 0000000..7571acb
--- /dev/null
+++ b/tests/SIGCM2.Api.Tests/Usuarios/UsuarioPermisosEndpointTests.cs
@@ -0,0 +1,435 @@
+using System.Net;
+using System.Net.Http.Headers;
+using System.Net.Http.Json;
+using System.Text.Json;
+using Dapper;
+using Microsoft.Data.SqlClient;
+using SIGCM2.TestSupport;
+
+namespace SIGCM2.Api.Tests.Usuarios;
+
+/// <summary>
+/// Integration tests for GET /api/v1/users/{id}/permisos and PUT /api/v1/users/{id}/permisos/overrides.
+/// SUITE-B-GET-PERMISOS (GP-01..GP-06) + SUITE-B-PUT-OVERRIDES (PO-01..PO-11) — UDT-009.
+/// </summary>
+[Collection("ApiIntegration")]
+public sealed class UsuarioPermisosEndpointTests : IAsyncLifetime
+{
+    private const string TestConnectionString =
+        "Server=TECNICA3;Database=SIGCM2_Test;User Id=desarrollo;Password=desarrollo2026;TrustServerCertificate=True;";
+
+    private const string AdminUsername = "admin";
+    private const string AdminPassword = "@Diego550@";
+
+    private readonly HttpClient _client;
+    private string? _adminToken;
+
+    public UsuarioPermisosEndpointTests(TestWebAppFactory factory)
+    {
+        _client = factory.CreateClient();
+    }
+
+    public async Task InitializeAsync()
+    {
+        _adminToken = await GetBearerTokenAsync(AdminUsername, AdminPassword);
+    }
+
+    public Task DisposeAsync() => Task.CompletedTask;
+
+    // ── Helpers ───────────────────────────────────────────────────────────────
+
+    private async Task<string> GetBearerTokenAsync(string username, string password)
+    {
+        var response = await _client.PostAsJsonAsync("/api/v1/auth/login", new { username, password });
+        response.EnsureSuccessStatusCode();
+        var json = await response.Content.ReadFromJsonAsync<JsonElement>();
+        return json.GetProperty("accessToken").GetString()!;
+    }
+
+    private HttpRequestMessage BuildRequest(HttpMethod method, string url, object? body = null, string? token = null)
+    {
+        var request = new HttpRequestMessage(method, url);
+        var tok = token ?? _adminToken;
+        if (tok is not null)
+            request.Headers.Authorization = new AuthenticationHeaderValue("Bearer", tok);
+        if (body is not null)
+            request.Content = JsonContent.Create(body);
+        return request;
+    }
+
+    private async Task<int> GetAdminIdAsync()
+    {
+        await using var conn = new SqlConnection(TestConnectionString);
+        await conn.OpenAsync();
+        return await conn.QuerySingleAsync<int>("SELECT Id FROM dbo.Usuario WHERE Username = 'admin'");
+    }
+
+    private async Task SetPermisosJsonAsync(int userId, string json)
+    {
+        await using var conn = new SqlConnection(TestConnectionString);
+        await conn.OpenAsync();
+        await conn.ExecuteAsync(
+            "UPDATE dbo.Usuario SET PermisosJson = @Json WHERE Id = @Id",
+            new { Json = json, Id = userId });
+    }
+
+    private async Task<string> GetPermisosJsonAsync(int userId)
+    {
+        await using var conn = new SqlConnection(TestConnectionString);
+        await conn.OpenAsync();
+        return await conn.QuerySingleAsync<string>(
+            "SELECT PermisosJson FROM dbo.Usuario WHERE Id = @Id",
+            new { Id = userId });
+    }
+
+    // ── SUITE-B-GET-PERMISOS ─────────────────────────────────────────────────
+
+    // GP-01: Admin → 200 con shape correcto {rolPermisos, overrides, effective}
+    [Fact]
+    public async Task GetPermisos_Admin_Returns200_WithCorrectShape()
+    {
+        var adminId = await GetAdminIdAsync();
+        await SetPermisosJsonAsync(adminId, """{"grant":[],"deny":[]}""");
+
+        var request = BuildRequest(HttpMethod.Get, $"/api/v1/users/{adminId}/permisos");
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        var json = await response.Content.ReadFromJsonAsync<JsonElement>();
+
+        Assert.True(json.TryGetProperty("rolPermisos", out var rolPermisos));
+        Assert.Equal(JsonValueKind.Array, rolPermisos.ValueKind);
+
+        Assert.True(json.TryGetProperty("overrides", out var overrides));
+        Assert.True(overrides.TryGetProperty("grant", out _));
+        Assert.True(overrides.TryGetProperty("deny", out _));
+
+        Assert.True(json.TryGetProperty("effective", out var effective));
+        Assert.Equal(JsonValueKind.Array, effective.ValueKind);
+    }
+
+    // GP-02: Usuario con overrides no vacíos → shape refleja overrides.grant, effective incluye el grant
+    [Fact]
+    public async Task GetPermisos_UserWithGrant_EffectiveContainsGrantedPermiso()
+    {
+        var adminId = await GetAdminIdAsync();
+        // Admin ya tiene 21 permisos del rol — grant con uno que tiene para probar idempotencia
+        await SetPermisosJsonAsync(adminId, """{"grant":["textos:editar"],"deny":[]}""");
+
+        var request = BuildRequest(HttpMethod.Get, $"/api/v1/users/{adminId}/permisos");
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        var json = await response.Content.ReadFromJsonAsync<JsonElement>();
+        var overrides = json.GetProperty("overrides");
+        var grantArr = overrides.GetProperty("grant").EnumerateArray().Select(e => e.GetString()).ToArray();
+
+        Assert.Contains("textos:editar", grantArr);
+
+        var effectiveArr = json.GetProperty("effective").EnumerateArray().Select(e => e.GetString()).ToArray();
+        Assert.Contains("textos:editar", effectiveArr);
+    }
+
+    // GP-03: Usuario con overrides vacíos → effective == rolPermisos, overrides vacíos
+    [Fact]
+    public async Task GetPermisos_UserWithEmptyOverrides_EffectiveEqualsRolPermisos()
+    {
+        var adminId = await GetAdminIdAsync();
+        await SetPermisosJsonAsync(adminId, """{"grant":[],"deny":[]}""");
+
+        var request = BuildRequest(HttpMethod.Get, $"/api/v1/users/{adminId}/permisos");
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        var json = await response.Content.ReadFromJsonAsync<JsonElement>();
+        var rolPermisos = json.GetProperty("rolPermisos").EnumerateArray().Select(e => e.GetString()).OrderBy(x => x).ToArray();
+        var effective = json.GetProperty("effective").EnumerateArray().Select(e => e.GetString()).OrderBy(x => x).ToArray();
+
+        Assert.Equal(rolPermisos, effective);
+
+        var grantArr = json.GetProperty("overrides").GetProperty("grant").EnumerateArray().ToArray();
+        var denyArr = json.GetProperty("overrides").GetProperty("deny").EnumerateArray().ToArray();
+        Assert.Empty(grantArr);
+        Assert.Empty(denyArr);
+    }
+
+    // GP-04: Usuario inexistente → 404
+    [Fact]
+    public async Task GetPermisos_NonExistentUser_Returns404()
+    {
+        var request = BuildRequest(HttpMethod.Get, "/api/v1/users/99999/permisos");
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.NotFound, response.StatusCode);
+    }
+
+    // GP-05: Sin permiso administracion:usuarios:gestionar → 403
+    [Fact]
+    public async Task GetPermisos_WithoutRequiredPermission_Returns403()
+    {
+        // Create a cajero user without the required permission
+        var cajeroToken = await CreateCajeroAndGetTokenAsync("cajero_gp05");
+        try
+        {
+            var adminId = await GetAdminIdAsync();
+            var request = BuildRequest(HttpMethod.Get, $"/api/v1/users/{adminId}/permisos", token: cajeroToken);
+            var response = await _client.SendAsync(request);
+
+            Assert.Equal(HttpStatusCode.Forbidden, response.StatusCode);
+        }
+        finally
+        {
+            await DeleteUsuarioAsync("cajero_gp05");
+        }
+    }
+
+    // GP-06: Sin auth → 401
+    [Fact]
+    public async Task GetPermisos_WithoutAuth_Returns401()
+    {
+        var adminId = await GetAdminIdAsync();
+        var request = new HttpRequestMessage(HttpMethod.Get, $"/api/v1/users/{adminId}/permisos");
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.Unauthorized, response.StatusCode);
+    }
+
+    // ── SUITE-B-PUT-OVERRIDES ────────────────────────────────────────────────
+
+    // PO-01: Grant válido → 200, DB persistido, FechaModificacion actualizado
+    [Fact]
+    public async Task PutOverrides_ValidGrant_Returns200_AndPersistsInDB()
+    {
+        var adminId = await GetAdminIdAsync();
+        await SetPermisosJsonAsync(adminId, """{"grant":[],"deny":[]}""");
+
+        var request = BuildRequest(HttpMethod.Put, $"/api/v1/users/{adminId}/permisos/overrides",
+            body: new { grant = new[] { "textos:editar" }, deny = Array.Empty<string>() });
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        var stored = await GetPermisosJsonAsync(adminId);
+        var parsed = JsonDocument.Parse(stored).RootElement;
+        var grant = parsed.GetProperty("grant").EnumerateArray().Select(e => e.GetString()).ToArray();
+        Assert.Contains("textos:editar", grant);
+    }
+
+    // PO-02: Deny válido → 200
+    [Fact]
+    public async Task PutOverrides_ValidDeny_Returns200()
+    {
+        var adminId = await GetAdminIdAsync();
+        await SetPermisosJsonAsync(adminId, """{"grant":[],"deny":[]}""");
+
+        var request = BuildRequest(HttpMethod.Put, $"/api/v1/users/{adminId}/permisos/overrides",
+            body: new { grant = Array.Empty<string>(), deny = new[] { "ventas:contado:cobrar" } });
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        var stored = await GetPermisosJsonAsync(adminId);
+        var parsed = JsonDocument.Parse(stored).RootElement;
+        var deny = parsed.GetProperty("deny").EnumerateArray().Select(e => e.GetString()).ToArray();
+        Assert.Contains("ventas:contado:cobrar", deny);
+    }
+
+    // PO-03: Código fuera del catálogo → 400, error code "invalid-permiso-codes"
+    [Fact]
+    public async Task PutOverrides_InvalidPermisoCode_Returns400_InvalidCodes()
+    {
+        var adminId = await GetAdminIdAsync();
+
+        var request = BuildRequest(HttpMethod.Put, $"/api/v1/users/{adminId}/permisos/overrides",
+            body: new { grant = new[] { "modulo:fake:accion" }, deny = Array.Empty<string>() });
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
+
+        var json = await response.Content.ReadFromJsonAsync<JsonElement>();
+        var title = json.GetProperty("title").GetString();
+        Assert.Equal("invalid-permiso-codes", title);
+
+        // Should contain the list of invalid codes
+        Assert.True(json.TryGetProperty("invalidCodes", out var invalidCodes));
+        var codes = invalidCodes.EnumerateArray().Select(e => e.GetString()).ToArray();
+        Assert.Contains("modulo:fake:accion", codes);
+    }
+
+    // PO-04: Mismo código en grant Y deny → 400, "grant-deny-overlap"
+    [Fact]
+    public async Task PutOverrides_GrantDenyOverlap_Returns400_Overlap()
+    {
+        var adminId = await GetAdminIdAsync();
+
+        var request = BuildRequest(HttpMethod.Put, $"/api/v1/users/{adminId}/permisos/overrides",
+            body: new { grant = new[] { "textos:editar" }, deny = new[] { "textos:editar" } });
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
+
+        var json = await response.Content.ReadFromJsonAsync<JsonElement>();
+        var title = json.GetProperty("title").GetString();
+        Assert.Equal("grant-deny-overlap", title);
+
+        Assert.True(json.TryGetProperty("overlap", out var overlap));
+        var codes = overlap.EnumerateArray().Select(e => e.GetString()).ToArray();
+        Assert.Contains("textos:editar", codes);
+    }
+
+    // PO-05: Usuario inexistente → 404
+    [Fact]
+    public async Task PutOverrides_NonExistentUser_Returns404()
+    {
+        var request = BuildRequest(HttpMethod.Put, "/api/v1/users/99999/permisos/overrides",
+            body: new { grant = Array.Empty<string>(), deny = Array.Empty<string>() });
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.NotFound, response.StatusCode);
+    }
+
+    // PO-06: Sin permiso → 403
+    [Fact]
+    public async Task PutOverrides_WithoutRequiredPermission_Returns403()
+    {
+        var cajeroToken = await CreateCajeroAndGetTokenAsync("cajero_po06");
+        try
+        {
+            var adminId = await GetAdminIdAsync();
+            var request = BuildRequest(HttpMethod.Put, $"/api/v1/users/{adminId}/permisos/overrides",
+                body: new { grant = Array.Empty<string>(), deny = Array.Empty<string>() },
+                token: cajeroToken);
+            var response = await _client.SendAsync(request);
+
+            Assert.Equal(HttpStatusCode.Forbidden, response.StatusCode);
+        }
+        finally
+        {
+            await DeleteUsuarioAsync("cajero_po06");
+        }
+    }
+
+    // PO-07: Sin auth → 401
+    [Fact]
+    public async Task PutOverrides_WithoutAuth_Returns401()
+    {
+        var adminId = await GetAdminIdAsync();
+        var request = new HttpRequestMessage(HttpMethod.Put, $"/api/v1/users/{adminId}/permisos/overrides")
+        {
+            Content = JsonContent.Create(new { grant = Array.Empty<string>(), deny = Array.Empty<string>() })
+        };
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.Unauthorized, response.StatusCode);
+    }
+
+    // PO-08: Body JSON malformado → 400
+    [Fact]
+    public async Task PutOverrides_MalformedBody_Returns400()
+    {
+        var adminId = await GetAdminIdAsync();
+        var request = new HttpRequestMessage(HttpMethod.Put, $"/api/v1/users/{adminId}/permisos/overrides")
+        {
+            Headers = { Authorization = new AuthenticationHeaderValue("Bearer", _adminToken) },
+            Content = new StringContent("{grant: not-json", System.Text.Encoding.UTF8, "application/json")
+        };
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.BadRequest, response.StatusCode);
+    }
+
+    // PO-09: PUT idempotente — dos veces el mismo body → estado igual
+    [Fact]
+    public async Task PutOverrides_Idempotent_SameBodyTwice_StateUnchanged()
+    {
+        var adminId = await GetAdminIdAsync();
+        var body = new { grant = new[] { "textos:editar" }, deny = Array.Empty<string>() };
+
+        var r1 = await _client.SendAsync(BuildRequest(HttpMethod.Put, $"/api/v1/users/{adminId}/permisos/overrides", body));
+        var r2 = await _client.SendAsync(BuildRequest(HttpMethod.Put, $"/api/v1/users/{adminId}/permisos/overrides", body));
+
+        Assert.Equal(HttpStatusCode.OK, r1.StatusCode);
+        Assert.Equal(HttpStatusCode.OK, r2.StatusCode);
+
+        var stored = await GetPermisosJsonAsync(adminId);
+        var parsed = JsonDocument.Parse(stored).RootElement;
+        var grant = parsed.GetProperty("grant").EnumerateArray().Select(e => e.GetString()).ToArray();
+        Assert.Single(grant);
+        Assert.Equal("textos:editar", grant[0]);
+    }
+
+    // PO-10: PUT con grants vacíos (reset overrides) → effective == rolPermisos
+    [Fact]
+    public async Task PutOverrides_EmptyPayload_ResetsOverrides()
+    {
+        var adminId = await GetAdminIdAsync();
+
+        // First set some overrides
+        await _client.SendAsync(BuildRequest(HttpMethod.Put, $"/api/v1/users/{adminId}/permisos/overrides",
+            body: new { grant = new[] { "textos:editar" }, deny = Array.Empty<string>() }));
+
+        // Then reset
+        var resetRequest = BuildRequest(HttpMethod.Put, $"/api/v1/users/{adminId}/permisos/overrides",
+            body: new { grant = Array.Empty<string>(), deny = Array.Empty<string>() });
+        var response = await _client.SendAsync(resetRequest);
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        var stored = await GetPermisosJsonAsync(adminId);
+        Assert.Equal("""{"grant":[],"deny":[]}""", stored);
+    }
+
+    // PO-11: Response de PUT tiene shape {rolPermisos, overrides, effective}
+    [Fact]
+    public async Task PutOverrides_ResponseHasCorrectShape()
+    {
+        var adminId = await GetAdminIdAsync();
+        await SetPermisosJsonAsync(adminId, """{"grant":[],"deny":[]}""");
+
+        var request = BuildRequest(HttpMethod.Put, $"/api/v1/users/{adminId}/permisos/overrides",
+            body: new { grant = Array.Empty<string>(), deny = Array.Empty<string>() });
+        var response = await _client.SendAsync(request);
+
+        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
+
+        var json = await response.Content.ReadFromJsonAsync<JsonElement>();
+        Assert.True(json.TryGetProperty("rolPermisos", out _));
+        Assert.True(json.TryGetProperty("overrides", out var overrides));
+        Assert.True(overrides.TryGetProperty("grant", out _));
+        Assert.True(overrides.TryGetProperty("deny", out _));
+        Assert.True(json.TryGetProperty("effective", out _));
+    }
+
+    // ── helpers ───────────────────────────────────────────────────────────────
+
+    private async Task<string> CreateCajeroAndGetTokenAsync(string username)
+    {
+        // Seed a cajero user without administracion:usuarios:gestionar
+        await using var conn = new SqlConnection(TestConnectionString);
+        await conn.OpenAsync();
+        await conn.ExecuteAsync("""
+            IF NOT EXISTS (SELECT 1 FROM dbo.Usuario WHERE Username = @Username)
+            INSERT INTO dbo.Usuario (Username, PasswordHash, Nombre, Apellido, Rol, PermisosJson, Activo, MustChangePassword)
+            VALUES (@Username, '$2a$12$rmq6tlSAQ8WXhR2CwLCSeuwCJKz/.8Eab95UQCUNfwe4dokeOqMcW',
+                    'Cajero', 'Test', 'cajero', '{"grant":[],"deny":[]}', 1, 0)
+            """, new { Username = username });
+
+        return await GetBearerTokenAsync(username, "@Diego550@");
+    }
+
+    private async Task DeleteUsuarioAsync(string username)
+    {
+        await using var conn = new SqlConnection(TestConnectionString);
+        await conn.OpenAsync();
+        // Must delete RefreshTokens first due to FK constraint
+        await conn.ExecuteAsync("""
+            DELETE rt FROM dbo.RefreshToken rt
+            INNER JOIN dbo.Usuario u ON rt.UsuarioId = u.Id
+            WHERE u.Username = @Username
+            """, new { Username = username });
+        await conn.ExecuteAsync("DELETE FROM dbo.Usuario WHERE Username = @Username", new { Username = username });
+    }
+}