feat(usage): cache the TokenTracker export with single-flight refresh

src/ClaudeDo.Worker/Usage/TokenTracker/TokenTrackerService.cs

@@ -0,0 +1,98 @@
+using ClaudeDo.Worker.Usage.TokenTracker.Interfaces;
+
+namespace ClaudeDo.Worker.Usage.TokenTracker;
+
+/// <summary>
+/// Owns the cached export. One fetch covers <see cref="WindowDays"/> days because
+/// <c>buildSessionAnalytics</c> walks the whole history regardless of <c>--from</c>/<c>--to</c>
+/// (v0.88.4 returns the same rows either way), so narrowing the request would buy nothing while
+/// making every range switch pay the cost again.
+/// </summary>
+public sealed class TokenTrackerService
+{
+    public const int WindowDays = 90;
+
+    private readonly ITokenTrackerClient _client;
+    private readonly Func<DateTime> _utcNow;
+    private readonly SemaphoreSlim _refreshLock = new(1, 1);
+    private TokenTrackerProbe? _probe;
+
+    public TokenTrackerService(ITokenTrackerClient client, TokenTrackerState state, Func<DateTime>? utcNow = null)
+    {
+        _client = client;
+        State = state;
+        _utcNow = utcNow ?? (() => DateTime.UtcNow);
+    }
+
+    public TokenTrackerState State { get; }
+
+    public async Task<TokenTrackerProbe> ProbeAsync(bool force = false, CancellationToken ct = default)
+    {
+        if (!force && _probe is { } cached) return cached;
+
+        var probe = await _client.ProbeAsync(ct);
+        _probe = probe;
+        return probe;
+    }
+
+    /// <summary>Fetches only when the cached export is missing or older than
+    /// <paramref name="maxAge"/>. Safe to call on every modal open.</summary>
+    public Task EnsureFreshAsync(TimeSpan maxAge, CancellationToken ct = default) =>
+        State.IsOlderThan(maxAge, _utcNow()) ? RefreshAsync(ct) : Task.CompletedTask;
+
+    public async Task RefreshAsync(CancellationToken ct = default)
+    {
+        // A refresh already in flight is the refresh this caller wanted — waiting for it and
+        // returning is correct, and it stops a burst of range switches from spawning processes.
+        if (!await _refreshLock.WaitAsync(0, ct))
+        {
+            await _refreshLock.WaitAsync(ct);
+            _refreshLock.Release();
+            return;
+        }
+
+        try
+        {
+            var now = _utcNow();
+            var to = DateOnly.FromDateTime(now.ToLocalTime());
+            var from = to.AddDays(-WindowDays);
+
+            var run = await _client.ExportAsync(from, to, ct);
+            if (!run.Ok)
+            {
+                State.ReportFailure(run.Error ?? "TokenTracker export failed.", now);
+                return;
+            }
+
+            var export = TokenTrackerExportParser.Parse(run.StdOut, now);
+            if (export is null)
+            {
+                State.ReportFailure("TokenTracker returned output we could not parse.", now);
+                return;
+            }
+
+            if (export.FormatVersion != TokenTrackerExportParser.SupportedFormatVersion)
+            {
+                State.ReportFailure(
+                    $"Unexpected TokenTracker export format v{export.FormatVersion} " +
+                    $"(supported: v{TokenTrackerExportParser.SupportedFormatVersion}).",
+                    now);
+                return;
+            }
+
+            State.ReportSuccess(export);
+        }
+        finally
+        {
+            _refreshLock.Release();
+        }
+    }
+
+    public async Task<TokenTrackerRunResult> InstallAsync(
+        IProgress<string>? output = null, CancellationToken ct = default)
+    {
+        var result = await _client.InstallAsync(output, ct);
+        await ProbeAsync(force: true, ct);
+        return result;
+    }
+}