Merge remote-tracking branch 'origin/dev' into agent/dex/CUB-32-usage-logging-service

# Conflicts:
#	backend/Infrastructure/Data/ExtrudexDbContext.cs
#	backend/Infrastructure/Data/Migrations/ExtrudexDbContextModelSnapshot.cs

backend/API/Controllers/PrintJobsController.cs

@@ -413,6 +413,92 @@ public class PrintJobsController : ControllerBase
         return NoContent();
     }
 
+    // ── GET /api/printjobs/{id}/cost-summary ──────────────────────────
+
+    /// <summary>
+    /// Gets the material cost summary for a specific print job.
+    /// Calculates total material cost from filament usage (grams derived)
+    /// and the spool's purchase price. Returns warnings instead of errors
+    /// when cost data is unavailable.
+    /// </summary>
+    /// <param name="id">The unique identifier of the print job.</param>
+    /// <returns>A cost summary with breakdown and any warnings about missing data.</returns>
+    /// <response code="200">Returns the cost summary. Warnings field lists any missing data.</response>
+    /// <response code="404">If the print job with the given ID is not found.</response>
+    [HttpGet("{id:guid}/cost-summary")]
+    [ProducesResponseType(typeof(CostSummaryResponse), StatusCodes.Status200OK)]
+    [ProducesResponseType(StatusCodes.Status404NotFound)]
+    public async Task<ActionResult<CostSummaryResponse>> GetCostSummary(Guid id)
+    {
+        _logger.LogDebug("Getting cost summary for print job {Id}", id);
+
+        var job = await _dbContext.PrintJobs
+            .Include(j => j.Spool)
+                .ThenInclude(s => s!.MaterialBase)
+            .FirstOrDefaultAsync(j => j.Id == id);
+
+        if (job is null)
+        {
+            _logger.LogWarning("Print job {Id} not found for cost summary", id);
+            return NotFound(new { error = $"Print job with ID '{id}' not found." });
+        }
+
+        var warnings = new List<string>();
+        var spool = job.Spool;
+
+        // Build response with what we have
+        var response = new CostSummaryResponse
+        {
+            PrintJobId = job.Id,
+            PrintName = job.PrintName,
+            SpoolId = job.SpoolId,
+            SpoolSerial = spool?.SpoolSerial ?? string.Empty,
+            SpoolBrand = spool?.Brand ?? string.Empty,
+            SpoolColorName = spool?.ColorName ?? string.Empty,
+            MmExtruded = job.MmExtruded,
+            GramsDerived = job.GramsDerived,
+            SpoolPurchasePrice = spool?.PurchasePrice,
+            SpoolWeightTotalGrams = spool?.WeightTotalGrams,
+            StoredCostPerPrint = job.CostPerPrint
+        };
+
+        // Validate spool data availability
+        if (spool is null)
+        {
+            warnings.Add("Spool data is not available for this print job. Cost cannot be calculated.");
+            response.Warnings = warnings;
+            return Ok(response);
+        }
+
+        // Check if we can calculate cost
+        if (!spool.PurchasePrice.HasValue)
+        {
+            warnings.Add("Spool purchase price is not set. Cost per gram and total material cost cannot be calculated.");
+        }
+
+        if (spool.WeightTotalGrams <= 0)
+        {
+            warnings.Add("Spool total weight is zero or invalid. Cost per gram and total material cost cannot be calculated.");
+        }
+
+        // If we have enough data, calculate the cost
+        if (spool.PurchasePrice.HasValue && spool.WeightTotalGrams > 0)
+        {
+            var pricePerGram = spool.PurchasePrice.Value / spool.WeightTotalGrams;
+            response.PricePerGram = Math.Round(pricePerGram, 4);
+            response.TotalMaterialCost = Math.Round(job.GramsDerived * pricePerGram, 4);
+        }
+
+        // Warn if grams derived is zero but mm extruded is non-zero
+        if (job.GramsDerived == 0 && job.MmExtruded > 0)
+        {
+            warnings.Add("GramsDerived is zero despite MmExtruded being non-zero. Cost may be inaccurate. Consider re-deriving grams from filament parameters.");
+        }
+
+        response.Warnings = warnings;
+        return Ok(response);
+    }
+
     // ── Gram Derivation Formula ────────────────────────────────────
 
     /// <summary>

backend/API/Controllers/UsageLogsController.cs

@@ -0,0 +1,117 @@
+using Extrudex.API.DTOs.UsageLogs;
+using Extrudex.Domain.Enums;
+using Extrudex.Domain.Interfaces;
+using Microsoft.AspNetCore.Mvc;
+
+namespace Extrudex.API.Controllers;
+
+/// <summary>
+/// API controller for recording and querying filament usage logs.
+/// Usage logs provide a fine-grained audit trail of filament consumption
+/// from printer integrations or manual input.
+/// </summary>
+[ApiController]
+[Route("api/[controller]")]
+[Produces("application/json")]
+public class UsageLogsController : ControllerBase
+{
+    private readonly IUsageLogService _usageLogService;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="UsageLogsController"/> class.
+    /// </summary>
+    /// <param name="usageLogService">The usage log service for recording and querying usage.</param>
+    public UsageLogsController(IUsageLogService usageLogService)
+    {
+        _usageLogService = usageLogService;
+    }
+
+    /// <summary>
+    /// Records a new filament usage entry.
+    /// </summary>
+    /// <param name="request">The usage entry details.</param>
+    /// <returns>The created usage log entry.</returns>
+    [HttpPost]
+    [ProducesResponseType(typeof(UsageLogResponse), StatusCodes.Status201Created)]
+    [ProducesResponseType(StatusCodes.Status400BadRequest)]
+    public async Task<ActionResult<UsageLogResponse>> Create([FromBody] CreateUsageLogRequest request)
+    {
+        if (!Enum.TryParse<DataSource>(request.DataSource, ignoreCase: true, out var dataSource))
+        {
+            return BadRequest($"Invalid data source: '{request.DataSource}'. Valid values: Mqtt, Moonraker, Manual.");
+        }
+
+        var entry = await _usageLogService.RecordUsageAsync(
+            spoolId: request.SpoolId,
+            gramsUsed: request.GramsUsed,
+            dataSource: dataSource,
+            printerId: request.PrinterId,
+            printJobId: request.PrintJobId,
+            mmExtruded: request.MmExtruded,
+            usageTimestamp: request.UsageTimestamp,
+            notes: request.Notes
+        );
+
+        return CreatedAtAction(
+            nameof(GetBySpool),
+            new { spoolId = entry.SpoolId },
+            MapToResponse(entry));
+    }
+
+    /// <summary>
+    /// Gets usage logs for a specific spool, ordered by most recent first.
+    /// </summary>
+    /// <param name="spoolId">The spool ID to filter by.</param>
+    /// <returns>A collection of usage log entries for the spool.</returns>
+    [HttpGet("spool/{spoolId:guid}")]
+    [ProducesResponseType(typeof(IEnumerable<UsageLogResponse>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<IEnumerable<UsageLogResponse>>> GetBySpool(Guid spoolId)
+    {
+        var logs = await _usageLogService.GetBySpoolAsync(spoolId);
+        return Ok(logs.Select(MapToResponse));
+    }
+
+    /// <summary>
+    /// Gets usage logs for a specific printer, ordered by most recent first.
+    /// </summary>
+    /// <param name="printerId">The printer ID to filter by.</param>
+    /// <returns>A collection of usage log entries for the printer.</returns>
+    [HttpGet("printer/{printerId:guid}")]
+    [ProducesResponseType(typeof(IEnumerable<UsageLogResponse>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<IEnumerable<UsageLogResponse>>> GetByPrinter(Guid printerId)
+    {
+        var logs = await _usageLogService.GetByPrinterAsync(printerId);
+        return Ok(logs.Select(MapToResponse));
+    }
+
+    /// <summary>
+    /// Gets usage logs for a specific print job, ordered by most recent first.
+    /// </summary>
+    /// <param name="printJobId">The print job ID to filter by.</param>
+    /// <returns>A collection of usage log entries for the print job.</returns>
+    [HttpGet("print-job/{printJobId:guid}")]
+    [ProducesResponseType(typeof(IEnumerable<UsageLogResponse>), StatusCodes.Status200OK)]
+    public async Task<ActionResult<IEnumerable<UsageLogResponse>>> GetByPrintJob(Guid printJobId)
+    {
+        var logs = await _usageLogService.GetByPrintJobAsync(printJobId);
+        return Ok(logs.Select(MapToResponse));
+    }
+
+    /// <summary>
+    /// Maps a UsageLog domain entity to a UsageLogResponse DTO.
+    /// </summary>
+    private static UsageLogResponse MapToResponse(Domain.Entities.UsageLog log) => new()
+    {
+        Id = log.Id,
+        SpoolId = log.SpoolId,
+        PrinterId = log.PrinterId,
+        PrintJobId = log.PrintJobId,
+        GramsUsed = log.GramsUsed,
+        MmExtruded = log.MmExtruded,
+        UsageTimestamp = log.UsageTimestamp,
+        DataSource = log.DataSource.ToString(),
+        Notes = log.Notes,
+        CreatedAt = log.CreatedAt,
+        UpdatedAt = log.UpdatedAt
+    };
+}

backend/API/DTOs/PrintJobs/CostSummaryResponse.cs

@@ -0,0 +1,55 @@
+namespace Extrudex.API.DTOs.PrintJobs;
+
+/// <summary>
+/// Response DTO for the cost summary of a print job.
+/// Provides a breakdown of material cost based on filament usage
+/// and spool pricing data. If cost data is incomplete, warnings
+/// are returned instead of throwing an error.
+/// </summary>
+public class CostSummaryResponse
+{
+    /// <summary>Unique identifier of the print job.</summary>
+    public Guid PrintJobId { get; set; }
+
+    /// <summary>Human-readable name of the print job.</summary>
+    public string PrintName { get; set; } = string.Empty;
+
+    /// <summary>Foreign key to the spool used for this print job.</summary>
+    public Guid SpoolId { get; set; }
+
+    /// <summary>Serial number of the spool.</summary>
+    public string SpoolSerial { get; set; } = string.Empty;
+
+    /// <summary>Brand of the spool.</summary>
+    public string SpoolBrand { get; set; } = string.Empty;
+
+    /// <summary>Color name of the spool.</summary>
+    public string SpoolColorName { get; set; } = string.Empty;
+
+    /// <summary>Total millimeters of filament extruded during this print.</summary>
+    public decimal MmExtruded { get; set; }
+
+    /// <summary>Derived grams consumed for this print job.</summary>
+    public decimal GramsDerived { get; set; }
+
+    /// <summary>Purchase price of the full spool, if available.</summary>
+    public decimal? SpoolPurchasePrice { get; set; }
+
+    /// <summary>Total weight of the spool in grams when full.</summary>
+    public decimal? SpoolWeightTotalGrams { get; set; }
+
+    /// <summary>Calculated price per gram (purchase price / total weight), if available.</summary>
+    public decimal? PricePerGram { get; set; }
+
+    /// <summary>Calculated total material cost for this print job, if available.</summary>
+    public decimal? TotalMaterialCost { get; set; }
+
+    /// <summary>The CostPerPrint stored on the print job entity, if set.</summary>
+    public decimal? StoredCostPerPrint { get; set; }
+
+    /// <summary>
+    /// Warnings about missing data that prevent cost calculation.
+    /// Empty if all data is available and cost was calculated successfully.
+    /// </summary>
+    public List<string> Warnings { get; set; } = new();
+}

backend/API/DTOs/UsageLogs/UsageLogDtos.cs

@@ -0,0 +1,115 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace Extrudex.API.DTOs.UsageLogs;
+
+/// <summary>
+/// Request DTO for recording a filament usage entry.
+/// </summary>
+public class CreateUsageLogRequest
+{
+    /// <summary>
+    /// The ID of the spool that provided the filament.
+    /// </summary>
+    [Required]
+    public Guid SpoolId { get; set; }
+
+    /// <summary>
+    /// The number of grams of filament consumed.
+    /// </summary>
+    [Required]
+    [Range(0.01, double.MaxValue, ErrorMessage = "GramsUsed must be a positive value.")]
+    public decimal GramsUsed { get; set; }
+
+    /// <summary>
+    /// The source of the usage data (Mqtt, Moonraker, Manual).
+    /// </summary>
+    [Required]
+    public string DataSource { get; set; } = string.Empty;
+
+    /// <summary>
+    /// The ID of the printer that consumed the filament. Optional.
+    /// </summary>
+    public Guid? PrinterId { get; set; }
+
+    /// <summary>
+    /// The ID of the print job associated with this usage. Optional.
+    /// </summary>
+    public Guid? PrintJobId { get; set; }
+
+    /// <summary>
+    /// The number of millimeters of filament extruded. Optional.
+    /// </summary>
+    public decimal? MmExtruded { get; set; }
+
+    /// <summary>
+    /// When the usage occurred (UTC). Defaults to now if not specified.
+    /// </summary>
+    public DateTime? UsageTimestamp { get; set; }
+
+    /// <summary>
+    /// Optional notes about this usage entry.
+    /// </summary>
+    [MaxLength(2000)]
+    public string? Notes { get; set; }
+}
+
+/// <summary>
+/// Response DTO for a usage log entry.
+/// </summary>
+public class UsageLogResponse
+{
+    /// <summary>
+    /// Unique identifier for the usage log entry.
+    /// </summary>
+    public Guid Id { get; set; }
+
+    /// <summary>
+    /// The spool that provided the filament.
+    /// </summary>
+    public Guid SpoolId { get; set; }
+
+    /// <summary>
+    /// The printer that consumed the filament, if applicable.
+    /// </summary>
+    public Guid? PrinterId { get; set; }
+
+    /// <summary>
+    /// The print job associated with this usage, if applicable.
+    /// </summary>
+    public Guid? PrintJobId { get; set; }
+
+    /// <summary>
+    /// Grams of filament consumed.
+    /// </summary>
+    public decimal GramsUsed { get; set; }
+
+    /// <summary>
+    /// Millimeters of filament extruded, if available.
+    /// </summary>
+    public decimal? MmExtruded { get; set; }
+
+    /// <summary>
+    /// When the usage occurred (UTC).
+    /// </summary>
+    public DateTime UsageTimestamp { get; set; }
+
+    /// <summary>
+    /// Source of the usage data (Mqtt, Moonraker, Manual).
+    /// </summary>
+    public string DataSource { get; set; } = string.Empty;
+
+    /// <summary>
+    /// Optional notes about this usage entry.
+    /// </summary>
+    public string? Notes { get; set; }
+
+    /// <summary>
+    /// When the record was created (UTC).
+    /// </summary>
+    public DateTime CreatedAt { get; set; }
+
+    /// <summary>
+    /// When the record was last updated (UTC).
+    /// </summary>
+    public DateTime UpdatedAt { get; set; }
+}

backend/Domain/Entities/UsageLog.cs

@@ -0,0 +1,72 @@
+using Extrudex.Domain.Base;
+using Extrudex.Domain.Enums;
+
+namespace Extrudex.Domain.Entities;
+
+/// <summary>
+/// Represents a single filament usage log entry. Records how much filament
+/// was consumed, by which printer, at what time, and optionally linked to
+/// a print job. This provides a fine-grained audit trail of filament consumption
+/// independent of print job lifecycle.
+/// </summary>
+public class UsageLog : AuditableEntity
+{
+    /// <summary>
+    /// Foreign key to the spool that provided the filament.
+    /// </summary>
+    public Guid SpoolId { get; set; }
+
+    /// <summary>
+    /// Navigation to the spool that provided the filament.
+    /// </summary>
+    public Spool Spool { get; set; } = null!;
+
+    /// <summary>
+    /// Foreign key to the printer that consumed the filament.
+    /// Nullable to support manual entries without a specific printer.
+    /// </summary>
+    public Guid? PrinterId { get; set; }
+
+    /// <summary>
+    /// Navigation to the printer that consumed the filament.
+    /// </summary>
+    public Printer? Printer { get; set; }
+
+    /// <summary>
+    /// Foreign key to the print job associated with this usage entry.
+    /// Nullable because usage can be logged before or without a print job.
+    /// </summary>
+    public Guid? PrintJobId { get; set; }
+
+    /// <summary>
+    /// Navigation to the print job associated with this usage entry.
+    /// </summary>
+    public PrintJob? PrintJob { get; set; }
+
+    /// <summary>
+    /// The number of grams of filament consumed in this usage event.
+    /// </summary>
+    public decimal GramsUsed { get; set; }
+
+    /// <summary>
+    /// The number of millimeters of filament extruded in this usage event.
+    /// Optional — may not be available for all data sources.
+    /// </summary>
+    public decimal? MmExtruded { get; set; }
+
+    /// <summary>
+    /// Timestamp when the usage occurred (UTC). This is the actual time of
+    /// consumption, which may differ from CreatedAt if the entry was recorded later.
+    /// </summary>
+    public DateTime UsageTimestamp { get; set; } = DateTime.UtcNow;
+
+    /// <summary>
+    /// The source of the usage data (which integration path provided it).
+    /// </summary>
+    public DataSource DataSource { get; set; } = DataSource.Manual;
+
+    /// <summary>
+    /// Optional notes about this usage entry.
+    /// </summary>
+    public string? Notes { get; set; }
+}

backend/Domain/Interfaces/IUsageLogService.cs

@@ -0,0 +1,57 @@
+using Extrudex.Domain.Entities;
+using Extrudex.Domain.Enums;
+
+namespace Extrudex.Domain.Interfaces;
+
+/// <summary>
+/// Service for recording filament usage entries. Writes to the usage_logs table
+/// and provides query capabilities for usage history.
+/// </summary>
+public interface IUsageLogService
+{
+    /// <summary>
+    /// Records a filament usage entry.
+    /// </summary>
+    /// <param name="spoolId">The spool that provided the filament.</param>
+    /// <param name="gramsUsed">Grams of filament consumed.</param>
+    /// <param name="dataSource">Where the data came from.</param>
+    /// <param name="printerId">Optional printer ID.</param>
+    /// <param name="printJobId">Optional print job ID.</param>
+    /// <param name="mmExtruded">Optional mm extruded.</param>
+    /// <param name="usageTimestamp">When the usage occurred (defaults to UTC now).</param>
+    /// <param name="notes">Optional notes.</param>
+    /// <returns>The created UsageLog entity.</returns>
+    Task<UsageLog> RecordUsageAsync(
+        Guid spoolId,
+        decimal gramsUsed,
+        DataSource dataSource,
+        Guid? printerId = null,
+        Guid? printJobId = null,
+        decimal? mmExtruded = null,
+        DateTime? usageTimestamp = null,
+        string? notes = null);
+
+    /// <summary>
+    /// Retrieves usage logs for a specific spool, ordered by usage timestamp descending.
+    /// </summary>
+    /// <param name="spoolId">The spool ID to filter by.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A collection of usage logs for the spool.</returns>
+    Task<IEnumerable<UsageLog>> GetBySpoolAsync(Guid spoolId, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Retrieves usage logs for a specific printer, ordered by usage timestamp descending.
+    /// </summary>
+    /// <param name="printerId">The printer ID to filter by.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A collection of usage logs for the printer.</returns>
+    Task<IEnumerable<UsageLog>> GetByPrinterAsync(Guid printerId, CancellationToken cancellationToken = default);
+
+    /// <summary>
+    /// Retrieves usage logs for a specific print job, ordered by usage timestamp descending.
+    /// </summary>
+    /// <param name="printJobId">The print job ID to filter by.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A collection of usage logs for the print job.</returns>
+    Task<IEnumerable<UsageLog>> GetByPrintJobAsync(Guid printJobId, CancellationToken cancellationToken = default);
+}

backend/Infrastructure/Data/Configurations/UsageLogConfiguration.cs

@@ -0,0 +1,91 @@
+using Extrudex.Domain.Entities;
+using Extrudex.Domain.Enums;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Metadata.Builders;
+
+namespace Extrudex.Infrastructure.Data.Configurations;
+
+/// <summary>
+/// EF Core configuration for the UsageLog entity.
+/// Maps to the usage_logs table with snake_case columns and appropriate indexes.
+/// </summary>
+public class UsageLogConfiguration : BaseEntityConfiguration<UsageLog>
+{
+    /// <inheritdoc/>
+    public override void Configure(EntityTypeBuilder<UsageLog> builder)
+    {
+        base.Configure(builder);
+
+        builder.Property(e => e.SpoolId)
+            .HasColumnName("spool_id")
+            .IsRequired();
+
+        builder.Property(e => e.PrinterId)
+            .HasColumnName("printer_id");
+
+        builder.Property(e => e.PrintJobId)
+            .HasColumnName("print_job_id");
+
+        builder.Property(e => e.GramsUsed)
+            .HasColumnName("grams_used")
+            .HasPrecision(10, 2)
+            .IsRequired();
+
+        builder.Property(e => e.MmExtruded)
+            .HasColumnName("mm_extruded")
+            .HasPrecision(12, 2);
+
+        builder.Property(e => e.UsageTimestamp)
+            .HasColumnName("usage_timestamp")
+            .IsRequired();
+
+        builder.Property(e => e.DataSource)
+            .HasColumnName("data_source")
+            .HasConversion<string>()
+            .HasMaxLength(50)
+            .IsRequired();
+
+        builder.Property(e => e.Notes)
+            .HasColumnName("notes")
+            .HasMaxLength(2000);
+
+        // Index on spool_id for querying usage by spool
+        builder.HasIndex(e => e.SpoolId)
+            .HasDatabaseName("ix_usage_logs_spool_id");
+
+        // Index on printer_id for querying usage by printer
+        builder.HasIndex(e => e.PrinterId)
+            .HasDatabaseName("ix_usage_logs_printer_id");
+
+        // Index on print_job_id for querying usage by print job
+        builder.HasIndex(e => e.PrintJobId)
+            .HasDatabaseName("ix_usage_logs_print_job_id");
+
+        // Index on usage_timestamp for chronological queries
+        builder.HasIndex(e => e.UsageTimestamp)
+            .HasDatabaseName("ix_usage_logs_usage_timestamp");
+
+        // Index on data_source for filtering by integration path
+        builder.HasIndex(e => e.DataSource)
+            .HasDatabaseName("ix_usage_logs_data_source");
+
+        // Relationships
+        builder.HasOne(e => e.Spool)
+            .WithMany()
+            .HasForeignKey(e => e.SpoolId)
+            .HasConstraintName("fk_usage_logs_spool")
+            .OnDelete(DeleteBehavior.Restrict);
+
+        builder.HasOne(e => e.Printer)
+            .WithMany()
+            .HasForeignKey(e => e.PrinterId)
+            .HasConstraintName("fk_usage_logs_printer")
+            .OnDelete(DeleteBehavior.SetNull);
+
+        builder.HasOne(e => e.PrintJob)
+            .WithMany()
+            .HasForeignKey(e => e.PrintJobId)
+            .HasConstraintName("fk_usage_logs_print_job")
+            .OnDelete(DeleteBehavior.SetNull);
+    }
+}

backend/Infrastructure/Data/ExtrudexDbContext.cs

@@ -1,79 +1 @@
-using Extrudex.Domain.Base;
-using Extrudex.Domain.Entities;
-using Microsoft.EntityFrameworkCore;
 
-namespace Extrudex.Infrastructure.Data;
-
-/// <summary>
-/// Main EF Core database context for the Extrudex system.
-/// Handles entity registration, snake_case naming, and automatic timestamp management.
-/// </summary>
-public class ExtrudexDbContext : DbContext
-{
-    public ExtrudexDbContext(DbContextOptions<ExtrudexDbContext> options) : base(options) { }
-
-    // Lookup tables
-    public DbSet<MaterialBase> MaterialBases => Set<MaterialBase>();
-    public DbSet<MaterialFinish> MaterialFinishes => Set<MaterialFinish>();
-    public DbSet<MaterialModifier> MaterialModifiers => Set<MaterialModifier>();
-
-    // Core entities
-    public DbSet<Spool> Spools => Set<Spool>();
-    public DbSet<Printer> Printers => Set<Printer>();
-    public DbSet<AmsUnit> AmsUnits => Set<AmsUnit>();
-    public DbSet<AmsSlot> AmsSlots => Set<AmsSlot>();
-    public DbSet<PrintJob> PrintJobs => Set<PrintJob>();
-    public DbSet<FilamentUsage> FilamentUsages => Set<FilamentUsage>();
-
-    protected override void OnModelCreating(ModelBuilder modelBuilder)
-    {
-        base.OnModelCreating(modelBuilder);
-
-        // Apply all entity type configurations from the assembly
-        modelBuilder.ApplyConfigurationsFromAssembly(typeof(ExtrudexDbContext).Assembly);
-
-        // Apply seed data
-        modelBuilder.Entity<MaterialBase>().HasData(SeedData.MaterialBases);
-        modelBuilder.Entity<MaterialFinish>().HasData(SeedData.MaterialFinishes);
-        modelBuilder.Entity<MaterialModifier>().HasData(SeedData.MaterialModifiers);
-    }
-
-    /// <summary>
-    /// Automatically set UpdatedAt on auditable entities during SaveChanges.
-    /// </summary>
-    public override int SaveChanges(bool acceptAllChangesOnSuccess)
-    {
-        SetAuditTimestamps();
-        return base.SaveChanges(acceptAllChangesOnSuccess);
-    }
-
-    public override async Task<int> SaveChangesAsync(
-        bool acceptAllChangesOnSuccess,
-        CancellationToken cancellationToken = default)
-    {
-        SetAuditTimestamps();
-        return await base.SaveChangesAsync(acceptAllChangesOnSuccess, cancellationToken);
-    }
-
-    /// <summary>
-    /// Sets UpdatedAt on all auditable entities that have been modified.
-    /// Sets CreatedAt on all auditable entities that are being added.
-    /// </summary>
-    private void SetAuditTimestamps()
-    {
-        var entries = ChangeTracker.Entries<AuditableEntity>();
-
-        foreach (var entry in entries)
-        {
-            if (entry.State == EntityState.Added)
-            {
-                entry.Entity.CreatedAt = DateTime.UtcNow;
-                entry.Entity.UpdatedAt = DateTime.UtcNow;
-            }
-            else if (entry.State == EntityState.Modified)
-            {
-                entry.Entity.UpdatedAt = DateTime.UtcNow;
-            }
-        }
-    }
-}

backend/Infrastructure/Data/Migrations/20260426184329_AddUsageLogTable.cs

@@ -0,0 +1,534 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Extrudex.Infrastructure.Data.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddUsageLogTable : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "usage_logs",
+                columns: table => new
+                {
+                    id = table.Column<Guid>(type: "uuid", nullable: false),
+                    spool_id = table.Column<Guid>(type: "uuid", nullable: false),
+                    printer_id = table.Column<Guid>(type: "uuid", nullable: true),
+                    print_job_id = table.Column<Guid>(type: "uuid", nullable: true),
+                    grams_used = table.Column<decimal>(type: "numeric(10,2)", precision: 10, scale: 2, nullable: false),
+                    mm_extruded = table.Column<decimal>(type: "numeric(12,2)", precision: 12, scale: 2, nullable: true),
+                    usage_timestamp = table.Column<DateTime>(type: "timestamp with time zone", nullable: false),
+                    data_source = table.Column<string>(type: "character varying(50)", maxLength: 50, nullable: false),
+                    notes = table.Column<string>(type: "character varying(2000)", maxLength: 2000, nullable: true),
+                    created_at = table.Column<DateTime>(type: "timestamp with time zone", nullable: false, defaultValueSql: "now() at time zone 'utc'"),
+                    updated_at = table.Column<DateTime>(type: "timestamp with time zone", nullable: false, defaultValueSql: "now() at time zone 'utc'")
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_usage_logs", x => x.id);
+                    table.ForeignKey(
+                        name: "fk_usage_logs_print_job",
+                        column: x => x.print_job_id,
+                        principalTable: "print_jobs",
+                        principalColumn: "id",
+                        onDelete: ReferentialAction.SetNull);
+                    table.ForeignKey(
+                        name: "fk_usage_logs_printer",
+                        column: x => x.printer_id,
+                        principalTable: "printers",
+                        principalColumn: "id",
+                        onDelete: ReferentialAction.SetNull);
+                    table.ForeignKey(
+                        name: "fk_usage_logs_spool",
+                        column: x => x.spool_id,
+                        principalTable: "spools",
+                        principalColumn: "id",
+                        onDelete: ReferentialAction.Restrict);
+                });
+
+            migrationBuilder.UpdateData(
+                table: "material_bases",
+                keyColumn: "id",
+                keyValue: new Guid("10000000-0000-0000-0000-000000000001"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(6535), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(6535) });
+
+            migrationBuilder.UpdateData(
+                table: "material_bases",
+                keyColumn: "id",
+                keyValue: new Guid("10000000-0000-0000-0000-000000000002"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7016), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7016) });
+
+            migrationBuilder.UpdateData(
+                table: "material_bases",
+                keyColumn: "id",
+                keyValue: new Guid("10000000-0000-0000-0000-000000000003"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7027), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7028) });
+
+            migrationBuilder.UpdateData(
+                table: "material_bases",
+                keyColumn: "id",
+                keyValue: new Guid("10000000-0000-0000-0000-000000000004"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7034), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7035) });
+
+            migrationBuilder.UpdateData(
+                table: "material_bases",
+                keyColumn: "id",
+                keyValue: new Guid("10000000-0000-0000-0000-000000000005"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7042), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7042) });
+
+            migrationBuilder.UpdateData(
+                table: "material_bases",
+                keyColumn: "id",
+                keyValue: new Guid("10000000-0000-0000-0000-000000000006"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7049), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7049) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000001"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7291), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7292) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000002"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7453), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7453) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000003"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7461), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7461) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000004"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7468), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7468) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000005"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7474), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7474) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000006"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7480), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7481) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000007"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7487), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7487) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000008"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7493), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7493) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000009"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7500), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7500) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000010"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7507), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7507) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000011"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7513), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7513) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000012"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7519), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7520) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000013"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7526), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7526) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000014"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7532), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7532) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000015"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7538), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7539) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000001"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7690), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7690) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000002"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7838), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7838) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000003"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7846), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7846) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000004"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7853), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7853) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000005"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7859), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7859) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000006"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7865), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7866) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000007"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7872), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7872) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000008"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7878), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7879) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000009"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7885), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7885) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000010"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7891), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7891) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000011"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7898), new DateTime(2026, 4, 26, 18, 43, 28, 895, DateTimeKind.Utc).AddTicks(7898) });
+
+            migrationBuilder.CreateIndex(
+                name: "ix_usage_logs_data_source",
+                table: "usage_logs",
+                column: "data_source");
+
+            migrationBuilder.CreateIndex(
+                name: "ix_usage_logs_print_job_id",
+                table: "usage_logs",
+                column: "print_job_id");
+
+            migrationBuilder.CreateIndex(
+                name: "ix_usage_logs_printer_id",
+                table: "usage_logs",
+                column: "printer_id");
+
+            migrationBuilder.CreateIndex(
+                name: "ix_usage_logs_spool_id",
+                table: "usage_logs",
+                column: "spool_id");
+
+            migrationBuilder.CreateIndex(
+                name: "ix_usage_logs_usage_timestamp",
+                table: "usage_logs",
+                column: "usage_timestamp");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "usage_logs");
+
+            migrationBuilder.UpdateData(
+                table: "material_bases",
+                keyColumn: "id",
+                keyValue: new Guid("10000000-0000-0000-0000-000000000001"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1096), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1096) });
+
+            migrationBuilder.UpdateData(
+                table: "material_bases",
+                keyColumn: "id",
+                keyValue: new Guid("10000000-0000-0000-0000-000000000002"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1620), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1620) });
+
+            migrationBuilder.UpdateData(
+                table: "material_bases",
+                keyColumn: "id",
+                keyValue: new Guid("10000000-0000-0000-0000-000000000003"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1630), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1630) });
+
+            migrationBuilder.UpdateData(
+                table: "material_bases",
+                keyColumn: "id",
+                keyValue: new Guid("10000000-0000-0000-0000-000000000004"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1638), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1638) });
+
+            migrationBuilder.UpdateData(
+                table: "material_bases",
+                keyColumn: "id",
+                keyValue: new Guid("10000000-0000-0000-0000-000000000005"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1645), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1645) });
+
+            migrationBuilder.UpdateData(
+                table: "material_bases",
+                keyColumn: "id",
+                keyValue: new Guid("10000000-0000-0000-0000-000000000006"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1651), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1652) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000001"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1850), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(1850) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000002"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2041), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2041) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000003"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2049), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2049) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000004"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2055), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2056) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000005"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2062), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2062) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000006"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2068), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2068) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000007"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2075), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2075) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000008"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2081), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2081) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000009"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2100), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2100) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000010"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2107), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2107) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000011"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2113), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2113) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000012"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2120), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2120) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000013"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2126), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2126) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000014"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2132), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2133) });
+
+            migrationBuilder.UpdateData(
+                table: "material_finishes",
+                keyColumn: "id",
+                keyValue: new Guid("20000000-0000-0000-0000-000000000015"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2139), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2139) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000001"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2304), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2304) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000002"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2463), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2463) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000003"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2471), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2471) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000004"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2477), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2478) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000005"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2484), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2484) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000006"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2490), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2491) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000007"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2497), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2497) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000008"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2503), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2503) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000009"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2510), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2510) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000010"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2516), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2516) });
+
+            migrationBuilder.UpdateData(
+                table: "material_modifiers",
+                keyColumn: "id",
+                keyValue: new Guid("30000000-0000-0000-0000-000000000011"),
+                columns: new[] { "created_at", "updated_at" },
+                values: new object[] { new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2522), new DateTime(2026, 4, 26, 13, 14, 18, 745, DateTimeKind.Utc).AddTicks(2523) });
+        }
+    }
+}

backend/Infrastructure/Services/UsageLogService.cs

@@ -0,0 +1,81 @@
+using Extrudex.Domain.Entities;
+using Extrudex.Domain.Enums;
+using Extrudex.Domain.Interfaces;
+using Extrudex.Infrastructure.Data;
+using Microsoft.EntityFrameworkCore;
+
+namespace Extrudex.Infrastructure.Services;
+
+/// <summary>
+/// Implementation of <see cref="IUsageLogService"/> that persists usage entries
+/// to the usage_logs table via EF Core.
+/// </summary>
+public class UsageLogService : IUsageLogService
+{
+    private readonly ExtrudexDbContext _dbContext;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="UsageLogService"/> class.
+    /// </summary>
+    /// <param name="dbContext">The EF Core database context for data persistence.</param>
+    public UsageLogService(ExtrudexDbContext dbContext)
+    {
+        _dbContext = dbContext;
+    }
+
+    /// <inheritdoc/>
+    public async Task<UsageLog> RecordUsageAsync(
+        Guid spoolId,
+        decimal gramsUsed,
+        DataSource dataSource,
+        Guid? printerId = null,
+        Guid? printJobId = null,
+        decimal? mmExtruded = null,
+        DateTime? usageTimestamp = null,
+        string? notes = null)
+    {
+        var entry = new UsageLog
+        {
+            SpoolId = spoolId,
+            GramsUsed = gramsUsed,
+            DataSource = dataSource,
+            PrinterId = printerId,
+            PrintJobId = printJobId,
+            MmExtruded = mmExtruded,
+            UsageTimestamp = usageTimestamp ?? DateTime.UtcNow,
+            Notes = notes
+        };
+
+        _dbContext.UsageLogs.Add(entry);
+        await _dbContext.SaveChangesAsync();
+
+        return entry;
+    }
+
+    /// <inheritdoc/>
+    public async Task<IEnumerable<UsageLog>> GetBySpoolAsync(Guid spoolId, CancellationToken cancellationToken = default)
+    {
+        return await _dbContext.UsageLogs
+            .Where(u => u.SpoolId == spoolId)
+            .OrderByDescending(u => u.UsageTimestamp)
+            .ToListAsync(cancellationToken);
+    }
+
+    /// <inheritdoc/>
+    public async Task<IEnumerable<UsageLog>> GetByPrinterAsync(Guid printerId, CancellationToken cancellationToken = default)
+    {
+        return await _dbContext.UsageLogs
+            .Where(u => u.PrinterId == printerId)
+            .OrderByDescending(u => u.UsageTimestamp)
+            .ToListAsync(cancellationToken);
+    }
+
+    /// <inheritdoc/>
+    public async Task<IEnumerable<UsageLog>> GetByPrintJobAsync(Guid printJobId, CancellationToken cancellationToken = default)
+    {
+        return await _dbContext.UsageLogs
+            .Where(u => u.PrintJobId == printJobId)
+            .OrderByDescending(u => u.UsageTimestamp)
+            .ToListAsync(cancellationToken);
+    }
+}

backend/Program.cs

@@ -50,6 +50,9 @@ builder.Services.AddSwaggerGen(c =>
 // ── QR Code Generation ──────────────────────────────────────
 builder.Services.AddSingleton<IQrCodeService, QrCodeService>();
 
+// ── Usage Logging ───────────────────────────────────────────
+builder.Services.AddScoped<IUsageLogService, UsageLogService>();
+
 // ── FluentValidation ──────────────────────────────────────
 // Registers all validators from the API assembly into DI.
 builder.Services.AddValidatorsFromAssembly(Assembly.GetExecutingAssembly());