fix(usage): stop 429s with an activity-dependent poll cadence + manual refresh

The usage monitor polled the undocumented OAuth usage endpoint every 60s and
earned 429s. It now polls every 5 min while any task is Running and every
15 min while idle (usage_poll_interval_active_seconds / _idle_seconds, both
clamped to >= 60; the old single usage_poll_interval_seconds key is gone).

A 429 comes back as UsageRateLimitedException carrying Retry-After and adds
exponential backoff on top, capped at 30 min and never shorter than the normal
cadence; the strike count resets on the first success. The schedule arithmetic
is the pure static UsagePollSchedule.NextDelay.

Since the idle cadence is slow on purpose, WorkerHub.RefreshUsage drives
UsageMonitorService.RefreshNowAsync behind a Refresh now button in the Usage
Monitor modal: an out-of-band poll that pushes the loop's next-due time out so
no double poll follows, with a 10s cooldown so click-spam can't earn a 429.

Staleness now measures against the slower (idle) interval so an idle worker
isn't flagged stale just for not polling.

src/ClaudeDo.Worker/Usage/ClaudeOAuthUsageClient.cs

@@ -1,3 +1,4 @@
+using System.Net;
 using System.Net.Http.Headers;
 using System.Text.Json;
 using System.Text.Json.Nodes;
@@ -36,6 +37,8 @@ public sealed class ClaudeOAuthUsageClient : IUsageClient
         request.Headers.Add("anthropic-beta", "oauth-2025-04-20");
 
         using var response = await _http.SendAsync(request, ct);
+        if (response.StatusCode == HttpStatusCode.TooManyRequests)
+            throw new UsageRateLimitedException(ReadRetryAfter(response));
         if (!response.IsSuccessStatusCode)
             throw new InvalidOperationException($"Usage request failed with status {(int)response.StatusCode}.");
 
@@ -43,6 +46,27 @@ public sealed class ClaudeOAuthUsageClient : IUsageClient
         return Parse(body);
     }
 
+    /// <summary>
+    /// Reads the <c>Retry-After</c> header in either form (delta-seconds or HTTP-date).
+    /// A missing/past value returns null — the caller then uses its own backoff.
+    /// </summary>
+    internal static TimeSpan? ReadRetryAfter(HttpResponseMessage response)
+    {
+        var header = response.Headers.RetryAfter;
+        if (header is null) return null;
+
+        if (header.Delta is { } delta)
+            return delta > TimeSpan.Zero ? delta : null;
+
+        if (header.Date is { } date)
+        {
+            var remaining = date - DateTimeOffset.UtcNow;
+            return remaining > TimeSpan.Zero ? remaining : null;
+        }
+
+        return null;
+    }
+
     private string ReadAccessToken()
     {
         if (!File.Exists(_credentialsPath))
@@ -162,3 +186,20 @@ public sealed class ClaudeOAuthUsageClient : IUsageClient
             ? dto
             : null;
 }
+
+/// <summary>
+/// The usage endpoint answered 429. Carries the server's <c>Retry-After</c> when it sent one so
+/// <see cref="UsageMonitorService"/> can honour it instead of guessing a backoff.
+/// </summary>
+public sealed class UsageRateLimitedException : InvalidOperationException
+{
+    public UsageRateLimitedException(TimeSpan? retryAfter)
+        : base(retryAfter is { } r
+            ? $"Usage request was rate-limited (429); retry after {(int)r.TotalSeconds}s."
+            : "Usage request was rate-limited (429).")
+    {
+        RetryAfter = retryAfter;
+    }
+
+    public TimeSpan? RetryAfter { get; }
+}

src/ClaudeDo.Worker/Usage/Interfaces/IRunningTaskProbe.cs

@@ -0,0 +1,10 @@
+namespace ClaudeDo.Worker.Usage.Interfaces;
+
+/// <summary>
+/// Tells the usage monitor whether ClaudeDo is currently burning tokens, so it can poll
+/// often while work is in flight and back off to a slow heartbeat while idle.
+/// </summary>
+public interface IRunningTaskProbe
+{
+    Task<bool> AnyRunningAsync(CancellationToken ct = default);
+}

src/ClaudeDo.Worker/Usage/RunningTaskProbe.cs

@@ -0,0 +1,36 @@
+using ClaudeDo.Data;
+using ClaudeDo.Worker.Usage.Interfaces;
+using Microsoft.EntityFrameworkCore;
+using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
+
+namespace ClaudeDo.Worker.Usage;
+
+/// <summary>
+/// Answers "is anything running?" from the task table rather than the in-memory queue slots,
+/// so override-slot runs, continued runs, and runs still marked Running after a worker restart
+/// all count. A read failure reports idle — the usage monitor must never poll harder because
+/// its activity probe broke.
+/// </summary>
+public sealed class RunningTaskProbe : IRunningTaskProbe
+{
+    private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
+
+    public RunningTaskProbe(IDbContextFactory<ClaudeDoDbContext> dbFactory) => _dbFactory = dbFactory;
+
+    public async Task<bool> AnyRunningAsync(CancellationToken ct = default)
+    {
+        try
+        {
+            await using var context = await _dbFactory.CreateDbContextAsync(ct);
+            return await context.Tasks.AnyAsync(t => t.Status == TaskStatus.Running, ct);
+        }
+        catch (OperationCanceledException) when (ct.IsCancellationRequested)
+        {
+            throw;
+        }
+        catch
+        {
+            return false;
+        }
+    }
+}

src/ClaudeDo.Worker/Usage/UsageMonitorService.cs

@@ -5,25 +5,43 @@ using ClaudeDo.Worker.Usage.Interfaces;
 namespace ClaudeDo.Worker.Usage;
 
 /// <summary>
-/// Polls <see cref="IUsageClient"/> on <see cref="WorkerConfig.UsagePollIntervalSeconds"/> and keeps
-/// <see cref="UsageState"/> current. Polls once immediately at startup. A failure is logged as a
-/// warning at most once per distinct error message, to avoid log spam on a persistent outage.
-/// Broadcasts <see cref="HubBroadcaster.UsageUpdated"/> after every poll cycle, success or failure,
-/// so the UI can reflect a stale/blocked state as soon as it happens.
+/// Polls <see cref="IUsageClient"/> and keeps <see cref="UsageState"/> current. Polls once
+/// immediately at startup, then on an **activity-dependent** interval: while any task is
+/// Running it uses <see cref="WorkerConfig.UsagePollIntervalActiveSeconds"/>, otherwise the
+/// slower <see cref="WorkerConfig.UsagePollIntervalIdleSeconds"/>. A 429 adds exponential
+/// backoff on top (honouring <c>Retry-After</c> when the server sends one) — the endpoint is
+/// undocumented and rate-limits aggressively. <see cref="RefreshNowAsync"/> gives the UI a
+/// manual refresh that also resets the schedule, so the slow idle interval never leaves the
+/// user staring at a stale number.
+///
+/// A failure is logged as a warning at most once per distinct error message, to avoid log spam
+/// on a persistent outage. Broadcasts <see cref="HubBroadcaster.UsageUpdated"/> after every
+/// poll cycle, success or failure, so the UI can reflect a stale/blocked state as soon as it
+/// happens.
 /// </summary>
 public sealed class UsageMonitorService : BackgroundService
 {
+    /// <summary>A manual refresh inside this window of the last poll reuses the last result.</summary>
+    internal static readonly TimeSpan ManualRefreshCooldown = TimeSpan.FromSeconds(10);
+
     private readonly IUsageClient _client;
     private readonly UsageState _state;
     private readonly WorkerConfig _config;
     private readonly ILogger<UsageMonitorService> _logger;
     private readonly UsageSnapshotBuilder _snapshotBuilder;
     private readonly HubBroadcaster _broadcaster;
+    private readonly IRunningTaskProbe _runningProbe;
+
+    // Serializes the background loop against a manual refresh so two polls never overlap.
+    private readonly SemaphoreSlim _pollLock = new(1, 1);
     private string? _lastLoggedError;
+    private int _rateLimitStrikes;
+    private DateTime _lastPollUtc = DateTime.MinValue;
+    private DateTime _nextPollDueUtc = DateTime.MinValue;
 
     public UsageMonitorService(
         IUsageClient client, UsageState state, WorkerConfig config, ILogger<UsageMonitorService> logger,
-        UsageSnapshotBuilder snapshotBuilder, HubBroadcaster broadcaster)
+        UsageSnapshotBuilder snapshotBuilder, HubBroadcaster broadcaster, IRunningTaskProbe runningProbe)
     {
         _client = client;
         _state = state;
@@ -31,49 +49,135 @@ public sealed class UsageMonitorService : BackgroundService
         _logger = logger;
         _snapshotBuilder = snapshotBuilder;
         _broadcaster = broadcaster;
+        _runningProbe = runningProbe;
     }
 
     protected override async Task ExecuteAsync(CancellationToken stoppingToken)
     {
         while (!stoppingToken.IsCancellationRequested)
         {
-            await TickAsync(stoppingToken);
+            // Re-read the due time every iteration: a manual refresh pushes it out, which is
+            // how the loop avoids polling again right after the user hit refresh.
+            var wait = _nextPollDueUtc - DateTime.UtcNow;
+            if (wait > TimeSpan.Zero)
+            {
+                try
+                {
+                    await Task.Delay(wait, stoppingToken);
+                }
+                catch (OperationCanceledException)
+                {
+                    return;
+                }
+                continue;
+            }
 
-            try
-            {
-                await Task.Delay(TimeSpan.FromSeconds(_config.UsagePollIntervalSeconds), stoppingToken);
-            }
-            catch (OperationCanceledException)
-            {
-                return;
-            }
+            await TickAsync(stoppingToken);
         }
     }
 
-    internal async Task TickAsync(CancellationToken ct)
+    /// <summary>
+    /// Forces a poll now and returns the resulting snapshot DTO. Within
+    /// <see cref="ManualRefreshCooldown"/> of the last poll the API call is skipped and the
+    /// current state is returned instead, so click-spamming the refresh button can't earn a 429.
+    /// </summary>
+    public async Task<UsageSnapshotDto> RefreshNowAsync(CancellationToken ct = default)
     {
+        await PollAsync(ct, ManualRefreshCooldown);
+        return await _snapshotBuilder.BuildAsync(ct);
+    }
+
+    internal Task TickAsync(CancellationToken ct) => PollAsync(ct, null);
+
+    private async Task PollAsync(CancellationToken ct, TimeSpan? skipIfPolledWithin)
+    {
+        await _pollLock.WaitAsync(ct);
+        TimeSpan? retryAfter = null;
         try
         {
-            var snapshot = await _client.GetUsageAsync(ct);
-            _state.ReportSuccess(snapshot);
-            _lastLoggedError = null;
-        }
-        catch (OperationCanceledException) when (ct.IsCancellationRequested)
-        {
-            throw;
-        }
-        catch (Exception ex)
-        {
-            _state.ReportFailure(ex.Message, DateTime.UtcNow);
+            // Checked under the lock so a manual refresh that queued behind a background poll
+            // sees that poll's timestamp and reuses its result instead of firing a second call.
+            if (skipIfPolledWithin is { } window && DateTime.UtcNow - _lastPollUtc < window)
+                return;
 
-            if (_lastLoggedError != ex.Message)
+            try
             {
-                _logger.LogWarning(ex, "UsageMonitorService: failed to fetch usage: {Message}", ex.Message);
-                _lastLoggedError = ex.Message;
+                var snapshot = await _client.GetUsageAsync(ct);
+                _state.ReportSuccess(snapshot);
+                _lastLoggedError = null;
+                _rateLimitStrikes = 0;
             }
+            catch (OperationCanceledException) when (ct.IsCancellationRequested)
+            {
+                throw;
+            }
+            catch (UsageRateLimitedException ex)
+            {
+                _rateLimitStrikes = Math.Min(_rateLimitStrikes + 1, UsagePollSchedule.MaxStrikes);
+                retryAfter = ex.RetryAfter;
+                RecordFailure(ex);
+            }
+            catch (Exception ex)
+            {
+                RecordFailure(ex);
+            }
+
+            _lastPollUtc = DateTime.UtcNow;
+            _nextPollDueUtc = _lastPollUtc + await NextDelayAsync(retryAfter, ct);
+        }
+        finally
+        {
+            _pollLock.Release();
         }
 
         var dto = await _snapshotBuilder.BuildAsync(ct);
         await _broadcaster.UsageUpdated(dto);
     }
+
+    private void RecordFailure(Exception ex)
+    {
+        _state.ReportFailure(ex.Message, DateTime.UtcNow);
+
+        if (_lastLoggedError == ex.Message) return;
+        _logger.LogWarning(ex, "UsageMonitorService: failed to fetch usage: {Message}", ex.Message);
+        _lastLoggedError = ex.Message;
+    }
+
+    private async Task<TimeSpan> NextDelayAsync(TimeSpan? retryAfter, CancellationToken ct)
+    {
+        var anyRunning = await _runningProbe.AnyRunningAsync(ct);
+        return UsagePollSchedule.NextDelay(
+            anyRunning,
+            _config.UsagePollIntervalActiveSeconds,
+            _config.UsagePollIntervalIdleSeconds,
+            _rateLimitStrikes,
+            retryAfter);
+    }
+}
+
+/// <summary>
+/// Pure poll-interval arithmetic for <see cref="UsageMonitorService"/>: active-vs-idle base
+/// interval plus 429 backoff. Kept static and side-effect-free so the schedule is testable
+/// without a running background service.
+/// </summary>
+internal static class UsagePollSchedule
+{
+    /// <summary>Strike count is capped so the exponent can't run away on a long outage.</summary>
+    internal const int MaxStrikes = 4;
+
+    /// <summary>Nothing ever waits longer than this, not even an absurd <c>Retry-After</c>.</summary>
+    internal static readonly TimeSpan MaxDelay = TimeSpan.FromMinutes(30);
+
+    internal static TimeSpan NextDelay(
+        bool anyTaskRunning, int activeSeconds, int idleSeconds, int rateLimitStrikes, TimeSpan? retryAfter)
+    {
+        var baseDelay = TimeSpan.FromSeconds(Math.Max(1, anyTaskRunning ? activeSeconds : idleSeconds));
+        if (rateLimitStrikes <= 0)
+            return baseDelay;
+
+        var backoff = retryAfter ?? baseDelay * Math.Pow(2, Math.Min(rateLimitStrikes, MaxStrikes));
+        // Never poll *sooner* than the normal cadence just because Retry-After was small.
+        if (backoff < baseDelay) backoff = baseDelay;
+        return backoff > MaxDelay ? MaxDelay : backoff;
+    }
 }

src/ClaudeDo.Worker/Usage/UsageSnapshotBuilder.cs

@@ -39,7 +39,10 @@ public sealed class UsageSnapshotBuilder
 
         var decision = await _gate.EvaluateAsync(ct);
 
-        var maxAge = TimeSpan.FromSeconds(_cfg.UsagePollIntervalSeconds * 3);
+        // Measured against the *slowest* cadence — the idle interval — so a genuinely idle
+        // worker on its 15-minute heartbeat isn't reported stale just for not polling.
+        var maxAge = TimeSpan.FromSeconds(
+            Math.Max(_cfg.UsagePollIntervalActiveSeconds, _cfg.UsagePollIntervalIdleSeconds) * 3);
         var isStale = snapshot is null || lastError is not null || (DateTime.UtcNow - snapshot.FetchedAtUtc) > maxAge;
 
         var limits = (snapshot?.Limits ?? Array.Empty<UsageLimitRow>())