src/api/SIGCM2.Domain/Entities/ProductPrice.cs

@@ -0,0 +1,25 @@
+namespace SIGCM2.Domain.Entities;
+
+/// <summary>
+/// PRD-003 — Immutable record representing a price snapshot for a Product.
+/// Business dates are Cat2 (civil Argentina dates, DateOnly). Forward-only — no mutations.
+/// PriceValidTo = null means the row is the currently active price.
+/// </summary>
+public sealed record ProductPrice(
+    long Id,
+    int ProductId,
+    decimal Price,
+    DateOnly PriceValidFrom,
+    DateOnly? PriceValidTo,
+    DateTime FechaCreacion)
+{
+    /// <summary>True if this row is the currently active price (PriceValidTo is null).</summary>
+    public bool IsActive => PriceValidTo is null;
+
+    /// <summary>
+    /// True if this price's window covers the given civil date (inclusive on both ends).
+    /// An active row (PriceValidTo = null) covers any date on or after PriceValidFrom.
+    /// </summary>
+    public bool CoversDate(DateOnly date)
+        => PriceValidFrom <= date && (PriceValidTo is null || PriceValidTo >= date);
+}

src/api/SIGCM2.Domain/Exceptions/ProductPriceForwardOnlyException.cs

@@ -0,0 +1,23 @@
+namespace SIGCM2.Domain.Exceptions;
+
+/// <summary>
+/// Thrown when attempting to add a ProductPrice with a PriceValidFrom that is not strictly
+/// greater than the currently active price's PriceValidFrom. → HTTP 409
+/// </summary>
+public sealed class ProductPriceForwardOnlyException : DomainException
+{
+    public int ProductId { get; }
+    public DateOnly NewPriceValidFrom { get; }
+    public DateOnly ActivePriceValidFrom { get; }
+
+    public ProductPriceForwardOnlyException(
+        int productId,
+        DateOnly newPriceValidFrom,
+        DateOnly activePriceValidFrom)
+        : base($"El nuevo PriceValidFrom ({newPriceValidFrom:yyyy-MM-dd}) debe ser estrictamente mayor al PriceValidFrom del precio activo ({activePriceValidFrom:yyyy-MM-dd}).")
+    {
+        ProductId = productId;
+        NewPriceValidFrom = newPriceValidFrom;
+        ActivePriceValidFrom = activePriceValidFrom;
+    }
+}

src/api/SIGCM2.Domain/Exceptions/ProductPriceInvalidException.cs

@@ -0,0 +1,19 @@
+namespace SIGCM2.Domain.Exceptions;
+
+/// <summary>
+/// Thrown when a ProductPrice value fails domain business validation
+/// (e.g., Price &lt;= 0, PriceValidFrom in the past). → HTTP 400
+/// Used as defense-in-depth alongside FluentValidation in the Application layer.
+/// </summary>
+public sealed class ProductPriceInvalidException : DomainException
+{
+    public string Field { get; }
+    public string Reason { get; }
+
+    public ProductPriceInvalidException(string field, string reason)
+        : base($"Valor inválido para {field}: {reason}")
+    {
+        Field = field;
+        Reason = reason;
+    }
+}

src/api/SIGCM2.Domain/Exceptions/ProductSinPrecioActivoException.cs

@@ -0,0 +1,18 @@
+namespace SIGCM2.Domain.Exceptions;
+
+/// <summary>
+/// Thrown when no ProductPrice row covers the requested date for the given product. → HTTP 404
+/// Consumers of IProductPricingService may throw this when GetPriceAtAsync returns null.
+/// </summary>
+public sealed class ProductSinPrecioActivoException : DomainException
+{
+    public int ProductId { get; }
+    public DateOnly Date { get; }
+
+    public ProductSinPrecioActivoException(int productId, DateOnly date)
+        : base($"No existe precio registrado para el producto {productId} aplicable a la fecha {date:yyyy-MM-dd}.")
+    {
+        ProductId = productId;
+        Date = date;
+    }
+}

tests/SIGCM2.Application.Tests/Domain/ProductPriceExceptionTests.cs

@@ -0,0 +1,128 @@
+using FluentAssertions;
+using SIGCM2.Domain.Exceptions;
+
+namespace SIGCM2.Application.Tests.Domain;
+
+/// <summary>
+/// PRD-003 — Domain unit tests for ProductPrice-related exceptions.
+/// Verifies constructor props, message content, and DomainException inheritance.
+/// </summary>
+public class ProductPriceExceptionTests
+{
+    // ── ProductPriceForwardOnlyException ─────────────────────────────────────
+
+    [Fact]
+    public void ProductPriceForwardOnlyException_SetsProperties()
+    {
+        var newPvf    = new DateOnly(2026, 3, 1);
+        var activePvf = new DateOnly(2026, 4, 1);
+
+        var ex = new ProductPriceForwardOnlyException(productId: 42, newPvf, activePvf);
+
+        ex.ProductId.Should().Be(42);
+        ex.NewPriceValidFrom.Should().Be(newPvf);
+        ex.ActivePriceValidFrom.Should().Be(activePvf);
+    }
+
+    [Fact]
+    public void ProductPriceForwardOnlyException_MessageContainsKeyDates()
+    {
+        var newPvf    = new DateOnly(2026, 3, 1);
+        var activePvf = new DateOnly(2026, 4, 1);
+
+        var ex = new ProductPriceForwardOnlyException(productId: 5, newPvf, activePvf);
+
+        ex.Message.Should().Contain("2026-03-01");
+        ex.Message.Should().Contain("2026-04-01");
+    }
+
+    [Fact]
+    public void ProductPriceForwardOnlyException_InheritsFromDomainException()
+    {
+        var ex = new ProductPriceForwardOnlyException(
+            productId: 1,
+            newPriceValidFrom: new DateOnly(2026, 1, 1),
+            activePriceValidFrom: new DateOnly(2026, 2, 1));
+
+        ex.Should().BeAssignableTo<DomainException>();
+    }
+
+    // ── ProductPriceInvalidException ─────────────────────────────────────────
+
+    [Fact]
+    public void ProductPriceInvalidException_SetsProperties()
+    {
+        var ex = new ProductPriceInvalidException(field: "Price", reason: "must be > 0");
+
+        ex.Field.Should().Be("Price");
+        ex.Reason.Should().Be("must be > 0");
+    }
+
+    [Fact]
+    public void ProductPriceInvalidException_MessageContainsFieldAndReason()
+    {
+        var ex = new ProductPriceInvalidException(field: "Price", reason: "must be > 0");
+
+        ex.Message.Should().Contain("Price");
+        ex.Message.Should().Contain("must be > 0");
+    }
+
+    [Fact]
+    public void ProductPriceInvalidException_InheritsFromDomainException()
+    {
+        var ex = new ProductPriceInvalidException("Price", "invalid");
+
+        ex.Should().BeAssignableTo<DomainException>();
+    }
+
+    // ── ProductSinPrecioActivoException ──────────────────────────────────────
+
+    [Fact]
+    public void ProductSinPrecioActivoException_SetsProperties()
+    {
+        var date = new DateOnly(2026, 4, 19);
+
+        var ex = new ProductSinPrecioActivoException(productId: 99, date);
+
+        ex.ProductId.Should().Be(99);
+        ex.Date.Should().Be(date);
+    }
+
+    [Fact]
+    public void ProductSinPrecioActivoException_MessageContainsProductIdAndDate()
+    {
+        var date = new DateOnly(2026, 4, 19);
+
+        var ex = new ProductSinPrecioActivoException(productId: 99, date);
+
+        ex.Message.Should().Contain("99");
+        ex.Message.Should().Contain("2026-04-19");
+    }
+
+    [Fact]
+    public void ProductSinPrecioActivoException_InheritsFromDomainException()
+    {
+        var ex = new ProductSinPrecioActivoException(1, new DateOnly(2026, 4, 1));
+
+        ex.Should().BeAssignableTo<DomainException>();
+    }
+
+    // ── ProductNotFoundException — already exists, verify it works ────────────
+
+    [Fact]
+    public void ProductNotFoundException_SetsProductIdAndMessage()
+    {
+        var ex = new ProductNotFoundException(77);
+
+        ex.ProductId.Should().Be(77);
+        ex.Message.Should().Contain("77");
+    }
+
+    [Fact]
+    public void ProductNotFoundException_InheritsFromDomainException()
+    {
+        var ex = new ProductNotFoundException(1);
+
+        ex.Should().BeAssignableTo<DomainException>();
+    }
+}

tests/SIGCM2.Application.Tests/Domain/ProductPriceTests.cs

@@ -0,0 +1,158 @@
+using FluentAssertions;
+using SIGCM2.Domain.Entities;
+
+namespace SIGCM2.Application.Tests.Domain;
+
+/// <summary>
+/// PRD-003 — Domain unit tests for ProductPrice record.
+/// Covers: §REQ-4.1 (IsActive), §REQ-4.2 (CoversDate inclusive bounds),
+///          §REQ-4.4 (active row covers any date on or after PriceValidFrom).
+/// </summary>
+public class ProductPriceTests
+{
+    private static ProductPrice MakePrice(
+        long id = 1,
+        int productId = 10,
+        decimal price = 1500.00m,
+        DateOnly? from = null,
+        DateOnly? to = null,
+        DateTime? fechaCreacion = null)
+        => new(
+            Id: id,
+            ProductId: productId,
+            Price: price,
+            PriceValidFrom: from ?? new DateOnly(2026, 4, 1),
+            PriceValidTo: to,
+            FechaCreacion: fechaCreacion ?? new DateTime(2026, 4, 1, 0, 0, 0, DateTimeKind.Utc));
+
+    // ── §REQ-4.1: IsActive ────────────────────────────────────────────────────
+
+    [Fact]
+    public void IsActive_TrueWhenPriceValidToIsNull()
+    {
+        var price = MakePrice(to: null);
+
+        price.IsActive.Should().BeTrue();
+    }
+
+    [Fact]
+    public void IsActive_FalseWhenPriceValidToHasValue()
+    {
+        var price = MakePrice(to: new DateOnly(2026, 4, 30));
+
+        price.IsActive.Should().BeFalse();
+    }
+
+    // ── §REQ-4.2: CoversDate — inclusive lower bound ──────────────────────────
+
+    [Fact]
+    public void CoversDate_InclusiveLowerBound_ReturnsTrue()
+    {
+        // Row: 2026-04-01 → 2026-04-30. Query date = PriceValidFrom.
+        var price = MakePrice(from: new DateOnly(2026, 4, 1), to: new DateOnly(2026, 4, 30));
+
+        price.CoversDate(new DateOnly(2026, 4, 1)).Should().BeTrue();
+    }
+
+    // ── §REQ-4.2: CoversDate — inclusive upper bound ──────────────────────────
+
+    [Fact]
+    public void CoversDate_InclusiveUpperBound_ReturnsTrue()
+    {
+        // Row: 2026-04-01 → 2026-04-30. Query date = PriceValidTo.
+        var price = MakePrice(from: new DateOnly(2026, 4, 1), to: new DateOnly(2026, 4, 30));
+
+        price.CoversDate(new DateOnly(2026, 4, 30)).Should().BeTrue();
+    }
+
+    // ── §REQ-4.2: CoversDate — exclusive outside range ────────────────────────
+
+    [Fact]
+    public void CoversDate_DateBeforePriceValidFrom_ReturnsFalse()
+    {
+        var price = MakePrice(from: new DateOnly(2026, 4, 10), to: new DateOnly(2026, 4, 20));
+
+        price.CoversDate(new DateOnly(2026, 4, 9)).Should().BeFalse();
+    }
+
+    [Fact]
+    public void CoversDate_DateAfterPriceValidTo_ReturnsFalse()
+    {
+        var price = MakePrice(from: new DateOnly(2026, 4, 10), to: new DateOnly(2026, 4, 20));
+
+        price.CoversDate(new DateOnly(2026, 4, 21)).Should().BeFalse();
+    }
+
+    // ── §REQ-4.4: Active row (PriceValidTo = null) covers any date on or after PriceValidFrom ──
+
+    [Fact]
+    public void ActiveRow_CoversAnyDateOnOrAfterPvf()
+    {
+        // Active row: PriceValidFrom = 2026-04-01, PriceValidTo = null
+        var price = MakePrice(from: new DateOnly(2026, 4, 1), to: null);
+
+        // On PriceValidFrom itself
+        price.CoversDate(new DateOnly(2026, 4, 1)).Should().BeTrue();
+        // Well in the future
+        price.CoversDate(new DateOnly(2030, 12, 31)).Should().BeTrue();
+    }
+
+    [Fact]
+    public void ActiveRow_DoesNotCoverDateBeforePvf()
+    {
+        var price = MakePrice(from: new DateOnly(2026, 4, 1), to: null);
+
+        price.CoversDate(new DateOnly(2026, 3, 31)).Should().BeFalse();
+    }
+
+    // ── Record value equality (records compare by value) ─────────────────────
+
+    [Fact]
+    public void Equality_TwoIdenticalRecords_AreEqual()
+    {
+        var a = MakePrice(id: 1, productId: 10, price: 1500m,
+            from: new DateOnly(2026, 4, 1), to: null,
+            fechaCreacion: new DateTime(2026, 4, 1, 0, 0, 0, DateTimeKind.Utc));
+
+        var b = MakePrice(id: 1, productId: 10, price: 1500m,
+            from: new DateOnly(2026, 4, 1), to: null,
+            fechaCreacion: new DateTime(2026, 4, 1, 0, 0, 0, DateTimeKind.Utc));
+
+        a.Should().Be(b);
+        (a == b).Should().BeTrue();
+    }
+
+    [Fact]
+    public void Equality_DifferentId_AreNotEqual()
+    {
+        var a = MakePrice(id: 1);
+        var b = MakePrice(id: 2);
+
+        a.Should().NotBe(b);
+    }
+
+    // ── Immutability: record positional props are init-only (no regular set) ─
+
+    [Fact]
+    public void Record_PropertiesAreInitOnly_NotMutableSet()
+    {
+        // C# records expose init-only accessors, not regular set.
+        // IsExternalInit attribute on the setter's return type distinguishes init from set.
+        var type = typeof(ProductPrice);
+        var mutableSetters = type.GetProperties()
+            .Where(p =>
+            {
+                var setter = p.GetSetMethod(nonPublic: false);
+                if (setter is null) return false;
+                // init-only setters have a modreq on IsExternalInit in their signature;
+                // a simple way to detect them: they are NOT init-only when
+                // ReturnParameter.GetRequiredCustomModifiers() does NOT contain IsExternalInit.
+                var modifiers = setter.ReturnParameter.GetRequiredCustomModifiers();
+                bool isInitOnly = modifiers.Any(m => m.Name == "IsExternalInit");
+                return !isInitOnly; // only flag non-init setters as mutable
+            })
+            .ToList();
+
+        mutableSetters.Should().BeEmpty("ProductPrice must be immutable — all setters should be init-only.");
+    }
+}