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/CLAUDE.md

@@ -21,7 +21,7 @@ Worker/
   Report/       — ClaudeHistoryReader, WeekReportPromptBuilder, WeekReportService; interfaces in Report/Interfaces/
   Prime/        — daily-prep ("Prime Claude"): PrimeScheduler (BackgroundService), PrimeRunner (runs the daily prep), DailyPrepPrompt (fixed prompt + CLI args + LogPath() helper), NextDueCalculator, PrimeScheduleSignal; interfaces in Prime/Interfaces/ (IPrimeRunner, IPrimeClock, IPrimeScheduleSignal, IPrimeBroadcaster)
   Online/       — optional Online Inbox sync: OnlineInboxConfig (config record), Dtos (RemoteList/RemoteTask/MirrorTask), IOnlineInboxApi, OnlineInboxApiClient (typed HttpClient, bearer auth, HTTPS guard), OnlineTokenStore (DPAPI refresh-token store, Windows-only), StaticTokenAuthProvider (default/test IOnlineAuthProvider), ZitadelAuthProvider (OIDC discovery + refresh-token flow), OnlineSyncService (BackgroundService: reconcile loop), OnlineBacklog (Idle-backlog filter/query); interface in Online/Interfaces/ (IOnlineAuthProvider)
-  Usage/        — OAuth usage monitor: UsageModels (UsageBucket/UsageLimitRow/UsageSnapshot), ClaudeOAuthUsageClient (reads the access token Claude Code keeps fresh at `~/.claude/.credentials.json`, calls `GET https://api.anthropic.com/api/oauth/usage`; defensive parsing — missing/null buckets → null, missing `limits` → empty list; never logs the token), UsageState (threadsafe singleton; a failed poll never overwrites the last good snapshot, only sets `LastError`), UsageMonitorService (BackgroundService, polls on `usage_poll_interval_seconds`, one poll at startup, logs a failure at most once per distinct error message), TranscriptUsageReader (aggregates Claude Code transcript token usage from `~/.claude/projects/**/*.jsonl` by date/model/scope (ClaudeDo vs Other), deduped by requestId, with a per-file length+mtime cache); interfaces in Usage/Interfaces/ (IUsageClient, ITranscriptUsageReader)
+  Usage/        — OAuth usage monitor: UsageModels (UsageBucket/UsageLimitRow/UsageSnapshot), ClaudeOAuthUsageClient (reads the access token Claude Code keeps fresh at `~/.claude/.credentials.json`, calls `GET https://api.anthropic.com/api/oauth/usage`; defensive parsing — missing/null buckets → null, missing `limits` → empty list; never logs the token), UsageState (threadsafe singleton; a failed poll never overwrites the last good snapshot, only sets `LastError`), UsageMonitorService (BackgroundService, polls on `usage_poll_interval_seconds`, one poll at startup, logs a failure at most once per distinct error message), TranscriptUsageReader (aggregates Claude Code transcript token usage from `~/.claude/projects/**/*.jsonl` by date/model/scope (ClaudeDo vs Other), deduped by requestId, with a per-file length+mtime cache), UsageGate (reads `UsageState` + `AppSettings.UsageGateFiveHourPct`/`UsageGateSevenDayPct`, returns a `UsageGateDecision(IsBlocked, Reason)`; `Utilization` from `UsageBucket` is already a 0–100 percent, compared directly against the threshold with `>=`; threshold `0` = that bucket never gates; fail-open — no snapshot yet, a failed last poll, or a settings-read error all resolve to not-blocked); interfaces in Usage/Interfaces/ (IUsageClient, ITranscriptUsageReader, IUsageGate)
 ```
 
 Interfaces (e.g. `IQueueWaker`, `IPrimeClock`, `ITaskStateService`) live in an `Interfaces/` subfolder within their area; the namespace stays the area namespace.
@@ -30,7 +30,7 @@ Interfaces (e.g. `IQueueWaker`, `IPrimeClock`, `ITaskStateService`) live in an `
 
 - **Program.cs** — loads config, inits schema, registers DI, configures SignalR on `/hub`, binds to `127.0.0.1:47821`
 - **TaskStateService** — only component that writes `Status`, `PlanningPhase`, `BlockedByTaskId`. All transitions return a `TransitionResult` (no exceptions on invalid moves). Wakes the queue and broadcasts `TaskUpdated` automatically; advances the planning chain on child terminal transitions.
-- **IQueueWaker / IQueuePicker / QueueService** — waker is a singleton `SemaphoreSlim`; picker performs the atomic `Queued → Running` claim filtered by `BlockedByTaskId IS NULL`, `is_manual = 0` and schedule; QueueService is a thin `BackgroundService` that loops on the waker and dispatches via `TaskRunner`.
+- **IQueueWaker / IQueuePicker / QueueService** — waker is a singleton `SemaphoreSlim`; picker performs the atomic `Queued → Running` claim filtered by `BlockedByTaskId IS NULL`, `is_manual = 0` and schedule; QueueService is a thin `BackgroundService` that loops on the waker and dispatches via `TaskRunner`. On each loop tick, after computing `maxParallel`, it also asks `IUsageGate.EvaluateAsync` — if blocked, the slot-fill loop is skipped entirely for that tick (already-running slots are untouched; `RunNow`/`ContinueTask`/interactive/planning/daily-prep all bypass the queue and are unaffected). A blocked↔free transition is logged/broadcast (`WorkerLog`, Warn on block / Info on resume) exactly once per change, not on every tick; the 30 s backstop timer re-evaluates the gate on its own even with no wake signal, so the queue self-recovers once usage drops back under the threshold.
 - **OverrideSlotService** — owns `RunNow` / `ContinueTask`; goes through `TaskStateService.StartRunningAsync` (caller-driven, serialized by slot lock).
 - **StaleTaskRecovery** — startup-only service; calls `TaskStateService.RecoverStaleRunningAsync` to flip orphaned `Running` rows to `Failed`.
 - **External/*** — always-on MCP tools for general Claude sessions, scoped to *starting* and *observing* sessions (no worktree/merge, multi-turn, planning, or app-settings writes). Auth via optional `X-ClaudeDo-Key` header. Registered explicitly in `Program.cs`'s external app via `.WithTools<T>()`. Every optional/filter parameter across these tools must carry a C# default value (e.g. `string? status = null`) — the MCP schema only marks a parameter optional when it has one; nullability alone doesn't do it (`ExternalMcpToolSchemaTests` guards this by reflection). `ExternalMcpExceptionFilter.Wrap` is registered as a call-tool filter so `InvalidOperationException`/`ArgumentException` messages survive as `McpException` — otherwise the SDK's own catch-all replaces any non-`McpException` with a generic "An error occurred invoking 'X'." Organized by concern: