feat(claude-do): Worker: UsageGate — Queue ab Schwelle pausieren

> **Stand 2026-08-05 (List-Handler):** Der Roadblock aus dem letzten Lauf ist erledigt. Beide Voraussetzungen sind jetzt auf `main` gemerged: die `app_settings`-Schwellen `UsageGateFiveHourPct`/`UsageGateSevenDayPct` (Merge-Commit `b1efcdc`) und `UsageState`/`IUsageClient`/`UsageMonitorService` unter `src/ClaudeDo.Worker/Usage/` (Merge-Commit `b126a21`). Dein Worktree ist frisch von diesem `main`

ClaudeDo-Task: 06a7cc32-6ab7-4758-98f4-bee77149b2bf

src/ClaudeDo.Worker/Usage/UsageGate.cs

@@ -0,0 +1,58 @@
+using ClaudeDo.Data;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Usage.Interfaces;
+using Microsoft.EntityFrameworkCore;
+
+namespace ClaudeDo.Worker.Usage;
+
+public sealed record UsageGateDecision(bool IsBlocked, string? Reason);
+
+/// <summary>
+/// Gates autonomous queue refill on the 5h/7d Claude usage window. Fail-open: no snapshot yet,
+/// a failed last poll, or a settings read error all resolve to "not blocked" — an undocumented
+/// or unreachable usage API must never stall automation. Only queue refill is gated; runs already
+/// in flight (RunNow, ContinueTask, interactive sessions, planning, daily prep) are untouched.
+/// </summary>
+public sealed class UsageGate : IUsageGate
+{
+    private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
+    private readonly UsageState _state;
+    private readonly ILogger<UsageGate> _logger;
+
+    public UsageGate(IDbContextFactory<ClaudeDoDbContext> dbFactory, UsageState state, ILogger<UsageGate> logger)
+    {
+        _dbFactory = dbFactory;
+        _state = state;
+        _logger = logger;
+    }
+
+    public async Task<UsageGateDecision> EvaluateAsync(CancellationToken ct = default)
+    {
+        var snapshot = _state.Snapshot;
+        if (snapshot is null || _state.LastError is not null)
+            return new UsageGateDecision(false, null);
+
+        int fiveHourPct;
+        int sevenDayPct;
+        try
+        {
+            using var context = _dbFactory.CreateDbContext();
+            var settings = await new AppSettingsRepository(context).GetAsync(ct);
+            fiveHourPct = settings.UsageGateFiveHourPct;
+            sevenDayPct = settings.UsageGateSevenDayPct;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "UsageGate: failed to read gate thresholds; not blocking");
+            return new UsageGateDecision(false, null);
+        }
+
+        if (fiveHourPct > 0 && snapshot.FiveHour is not null && snapshot.FiveHour.Utilization >= fiveHourPct)
+            return new UsageGateDecision(true, $"5h-Limit {snapshot.FiveHour.Utilization:0}% >= {fiveHourPct}%");
+
+        if (sevenDayPct > 0 && snapshot.SevenDay is not null && snapshot.SevenDay.Utilization >= sevenDayPct)
+            return new UsageGateDecision(true, $"7d-Limit {snapshot.SevenDay.Utilization:0}% >= {sevenDayPct}%");
+
+        return new UsageGateDecision(false, null);
+    }
+}