Polish/audit: fix bugs found by 3 subsystem audits

Correctness/data:
- Fix demo cost double-count: reference importer no longer imports the Kosten Strom/Wasser
  columns for categories that are metered (only Heizung), so Wasser rollup is 70€ not 140€.
- Spurious-decrease guard: only a reset/swap in the window (prevReading, thisReading] explains
  a decrease — an old historical reset no longer permanently disables the guard.
- Gate swap auto-detection on MappingProfile.DetectCumulativeSwaps (flag was ignored).
- Prorate basePrice by bucket length (day/month/year); guard virtual expressions against NaN/Inf.

Concurrency/infra:
- Blazor: register a DbContextFactory; CostService/DashboardService and the read pages now use
  short-lived per-operation contexts (no shared circuit DbContext); guard Trends re-entrancy.
- /events: wrap event insert + consumption recompute in one transaction (atomic); 404 (not 500)
  on unknown meter.
- MQTT worker: subscribe to newly-added topics on each tick; move client cleanup into finally.
- Migrations: CREATE MATERIALIZED VIEW IF NOT EXISTS + if_not_exists on CAgg/compression/
  hypertable calls (re-run-safe after a mid-migration crash).
- HA worker: prune stale poll-schedule entries; export: null dangling ImportBatchIds on restore.

API/security:
- API fail-closed by default: with no keys and AllowAnonymousApi off, /api/v1 returns 401
  (protects /export and /import). New MeterVault:AllowAnonymousApi opt-in.
- Cap /readings batch at 5000; report ignored (unknown-meter) count; enums as strings in JSON.

+4 regression tests (guard window, API closed, /events 404, no demo double-count). 98 tests
green; Docker deploy re-verified healthy with the API fail-closed.

Claude-Session: https://claude.ai/code/session_01WujdMtMJPbxDpDnMeK22rr

src/App/Api/ApiEndpoints.cs

@@ -17,18 +17,25 @@ public sealed record EventPush(int MeterId, DateTimeOffset Time, MeterEventType
 public sealed record TariffPush(TariffScope ScopeType, int? ScopeId, TariffComponent Component,
     double Value, string Unit, DateOnly ValidFrom, DateOnly? ValidTo);
 
-public sealed record IngestResult(int Written, int Updated, int Rejected);
+public sealed record IngestResult(int Written, int Updated, int Rejected, int Ignored);
 
 /// <summary>Maps the versioned REST API. All endpoints require a valid API key (SDD §9).</summary>
 public static class ApiEndpoints
 {
+    private const int MaxReadingsPerRequest = 5000;
+
     public static IEndpointRouteBuilder MapMeterVaultApi(this IEndpointRouteBuilder app)
     {
         var api = app.MapGroup("/api/v1").AddEndpointFilter<ApiKeyFilter>().WithTags("MeterVault");
 
         api.MapPost("/readings", async (ReadingPush[] readings, IngestionService ingestion, CancellationToken ct) =>
         {
-            int written = 0, updated = 0, rejected = 0;
+            if (readings.Length > MaxReadingsPerRequest)
+            {
+                return Results.BadRequest(new { error = $"At most {MaxReadingsPerRequest} readings per request." });
+            }
+
+            int written = 0, updated = 0, rejected = 0, ignored = 0;
             foreach (var r in readings)
             {
                 switch (await ingestion.IngestByMeterAsync(r.MeterId, r.Time, r.Value, ct))
@@ -36,11 +43,11 @@ public static class ApiEndpoints
                     case IngestionOutcome.Written: written++; break;
                     case IngestionOutcome.Updated: updated++; break;
                     case IngestionOutcome.RejectedDecrease: rejected++; break;
-                    default: break;
+                    default: ignored++; break; // unknown meter
                 }
             }
 
-            return Results.Ok(new IngestResult(written, updated, rejected));
+            return Results.Ok(new IngestResult(written, updated, rejected, ignored));
         }).WithSummary("Ingest one or more readings (idempotent). Lets Home Assistant push.");
 
         api.MapGet("/meters", async (MeterVaultDbContext db, CancellationToken ct) =>
@@ -70,6 +77,14 @@ public static class ApiEndpoints
         api.MapPost("/events", async (EventPush push, MeterVaultDbContext db,
             NormalizationService normalization, CancellationToken ct) =>
         {
+            if (!await db.Meters.AnyAsync(m => m.Id == push.MeterId, ct))
+            {
+                return Results.NotFound(new { error = $"Meter {push.MeterId} does not exist." });
+            }
+
+            // One transaction so the event insert + consumption recompute (which deletes then
+            // re-inserts) are atomic — a failure must not leave the meter with no consumption.
+            await using var tx = await db.Database.BeginTransactionAsync(ct);
             db.MeterEvents.Add(new MeterEvent
             {
                 MeterId = push.MeterId,
@@ -84,6 +99,7 @@ public static class ApiEndpoints
             await db.SaveChangesAsync(ct);
             await normalization.RecomputeMeterAsync(push.MeterId, null, ct);
             await db.SaveChangesAsync(ct);
+            await tx.CommitAsync(ct);
             return Results.Ok();
         }).WithSummary("Record a delivery / swap / tank level / correction and recompute the meter.");
 

src/App/Api/ApiKeyFilter.cs

@@ -17,7 +17,11 @@ public sealed class ApiKeyFilter(IOptions<MeterVaultOptions> options) : IEndpoin
     {
         if (_options.ApiKeys.Count == 0)
         {
-            return await next(context).ConfigureAwait(false);
+            // Fail closed: an unconfigured deployment must not expose export/import. Opt in explicitly.
+            return _options.AllowAnonymousApi
+                ? await next(context).ConfigureAwait(false)
+                : Results.Problem(statusCode: StatusCodes.Status401Unauthorized,
+                    title: "API is closed: configure MeterVault:ApiKeys or set AllowAnonymousApi=true.");
         }
 
         var provided = context.HttpContext.Request.Headers[HeaderName].ToString();

src/App/Components/Pages/Admin/EnergyTypes.razor

@@ -1,6 +1,6 @@
 @page "/admin/energy-types"
 @rendermode InteractiveServer
-@inject MeterVault.Infrastructure.Persistence.MeterVaultDbContext Db
+@inject Microsoft.EntityFrameworkCore.IDbContextFactory<MeterVault.Infrastructure.Persistence.MeterVaultDbContext> DbFactory
 @using Microsoft.EntityFrameworkCore
 
 <PageTitle>MeterVault — Energy types</PageTitle>
@@ -32,6 +32,9 @@ else
 @code {
     private List<EnergyType>? _types;
 
-    protected override async Task OnInitializedAsync() =>
-        _types = await Db.EnergyTypes.AsNoTracking().OrderBy(t => t.Id).ToListAsync();
+    protected override async Task OnInitializedAsync()
+    {
+        await using var db = await DbFactory.CreateDbContextAsync();
+        _types = await db.EnergyTypes.AsNoTracking().OrderBy(t => t.Id).ToListAsync();
+    }
 }

src/App/Components/Pages/Admin/Tariffs.razor

@@ -1,6 +1,6 @@
 @page "/admin/tariffs"
 @rendermode InteractiveServer
-@inject MeterVault.Infrastructure.Persistence.MeterVaultDbContext Db
+@inject Microsoft.EntityFrameworkCore.IDbContextFactory<MeterVault.Infrastructure.Persistence.MeterVaultDbContext> DbFactory
 @using Microsoft.EntityFrameworkCore
 
 <PageTitle>MeterVault — Tariffs</PageTitle>
@@ -40,8 +40,11 @@ else
 @code {
     private List<Tariff>? _tariffs;
 
-    protected override async Task OnInitializedAsync() =>
-        _tariffs = await Db.Tariffs.AsNoTracking()
+    protected override async Task OnInitializedAsync()
+    {
+        await using var db = await DbFactory.CreateDbContextAsync();
+        _tariffs = await db.Tariffs.AsNoTracking()
             .OrderBy(t => t.Component).ThenBy(t => t.ValidFrom)
             .ToListAsync();
+    }
 }

src/App/Components/Pages/Meters.razor

@@ -1,6 +1,6 @@
 @page "/meters"
 @rendermode InteractiveServer
-@inject MeterVault.Infrastructure.Persistence.MeterVaultDbContext Db
+@inject Microsoft.EntityFrameworkCore.IDbContextFactory<MeterVault.Infrastructure.Persistence.MeterVaultDbContext> DbFactory
 @using Microsoft.EntityFrameworkCore
 
 <PageTitle>MeterVault — Meters</PageTitle>
@@ -54,7 +54,8 @@ else
 
     protected override async Task OnInitializedAsync()
     {
-        _meters = await Db.Meters
+        await using var db = await DbFactory.CreateDbContextAsync();
+        _meters = await db.Meters
             .AsNoTracking()
             .Include(m => m.EnergyType)
             .Include(m => m.Sources)

src/App/Components/Pages/Trends.razor

@@ -13,7 +13,7 @@
             <MudSelectItem T="int" Value="24">Last 24 months</MudSelectItem>
             <MudSelectItem T="int" Value="48">Last 48 months</MudSelectItem>
         </MudSelect>
-        <MudButton Variant="Variant.Filled" Color="Color.Primary" OnClick="LoadAsync">Apply</MudButton>
+        <MudButton Variant="Variant.Filled" Color="Color.Primary" OnClick="LoadAsync" Disabled="_loading">Apply</MudButton>
     </div>
 
     @if (_loading)
@@ -38,10 +38,21 @@
 
     private async Task LoadAsync()
     {
+        if (_loading)
+        {
+            return; // guard against overlapping loads
+        }
+
         _loading = true;
-        var asOf = DateOnly.FromDateTime(DateTime.UtcNow);
-        var from = asOf.AddMonths(-_months);
-        _points = await Dash.GetMonthlyTrendAsync(new DateOnly(from.Year, from.Month, 1), asOf.AddMonths(1));
-        _loading = false;
+        try
+        {
+            var asOf = DateOnly.FromDateTime(DateTime.UtcNow);
+            var from = asOf.AddMonths(-_months);
+            _points = await Dash.GetMonthlyTrendAsync(new DateOnly(from.Year, from.Month, 1), asOf.AddMonths(1));
+        }
+        finally
+        {
+            _loading = false;
+        }
     }
 }

src/App/Program.cs

@@ -39,6 +39,10 @@ try
     builder.Services.AddRazorComponents()
         .AddInteractiveServerComponents();
 
+    // Serialize/accept enums as strings on the REST API (e.g. event Type "Delivery").
+    builder.Services.ConfigureHttpJsonOptions(o =>
+        o.SerializerOptions.Converters.Add(new System.Text.Json.Serialization.JsonStringEnumConverter()));
+
     builder.Services.AddEndpointsApiExplorer();
     builder.Services.AddSwaggerGen(c =>
         c.SwaggerDoc("v1", new() { Title = "MeterVault API", Version = "v1" }));