diff --git a/src/ClaudeDo.Worker/Prime/IPrimeClock.cs b/src/ClaudeDo.Worker/Prime/IPrimeClock.cs
new file mode 100644
index 0000000..ec3204e
--- /dev/null
+++ b/src/ClaudeDo.Worker/Prime/IPrimeClock.cs
@@ -0,0 +1,2 @@
+namespace ClaudeDo.Worker.Prime;
+public interface IPrimeClock { DateTimeOffset Now { get; } }
diff --git a/src/ClaudeDo.Worker/Prime/IPrimeRunner.cs b/src/ClaudeDo.Worker/Prime/IPrimeRunner.cs
new file mode 100644
index 0000000..2efb578
--- /dev/null
+++ b/src/ClaudeDo.Worker/Prime/IPrimeRunner.cs
@@ -0,0 +1,8 @@
+namespace ClaudeDo.Worker.Prime;
+
+public interface IPrimeRunner
+{
+    Task<PrimeRunOutcome> FireAsync(PrimeScheduleDto schedule, CancellationToken ct);
+}
+
+public sealed record PrimeRunOutcome(bool Success, string Message);
diff --git a/src/ClaudeDo.Worker/Prime/IPrimeScheduleSignal.cs b/src/ClaudeDo.Worker/Prime/IPrimeScheduleSignal.cs
new file mode 100644
index 0000000..c633eb9
--- /dev/null
+++ b/src/ClaudeDo.Worker/Prime/IPrimeScheduleSignal.cs
@@ -0,0 +1,6 @@
+namespace ClaudeDo.Worker.Prime;
+public interface IPrimeScheduleSignal
+{
+    void Signal();
+    CancellationToken CurrentToken { get; }
+}
diff --git a/src/ClaudeDo.Worker/Prime/PrimeClock.cs b/src/ClaudeDo.Worker/Prime/PrimeClock.cs
new file mode 100644
index 0000000..9ce107e
--- /dev/null
+++ b/src/ClaudeDo.Worker/Prime/PrimeClock.cs
@@ -0,0 +1,5 @@
+namespace ClaudeDo.Worker.Prime;
+public sealed class PrimeClock : IPrimeClock
+{
+    public DateTimeOffset Now => DateTimeOffset.Now;
+}
diff --git a/src/ClaudeDo.Worker/Prime/PrimeRunner.cs b/src/ClaudeDo.Worker/Prime/PrimeRunner.cs
new file mode 100644
index 0000000..0c88eeb
--- /dev/null
+++ b/src/ClaudeDo.Worker/Prime/PrimeRunner.cs
@@ -0,0 +1,53 @@
+using ClaudeDo.Data;
+using ClaudeDo.Worker.Runner;
+
+namespace ClaudeDo.Worker.Prime;
+
+public sealed class PrimeRunner : IPrimeRunner
+{
+    private static readonly TimeSpan FireTimeout = TimeSpan.FromSeconds(60);
+    private readonly IClaudeProcess _claude;
+    private readonly ILogger<PrimeRunner> _logger;
+
+    public PrimeRunner(IClaudeProcess claude, ILogger<PrimeRunner> logger)
+    {
+        _claude = claude;
+        _logger = logger;
+    }
+
+    public async Task<PrimeRunOutcome> FireAsync(PrimeScheduleDto schedule, CancellationToken ct)
+    {
+        var cwd = Paths.AppDataRoot();
+        Directory.CreateDirectory(cwd);
+
+        using var timeoutCts = CancellationTokenSource.CreateLinkedTokenSource(ct);
+        timeoutCts.CancelAfter(FireTimeout);
+
+        try
+        {
+            var prompt = schedule.PromptOverride ?? "ping";
+            var result = await _claude.RunAsync(
+                arguments: "-p --max-turns 1",
+                prompt: prompt,
+                workingDirectory: cwd,
+                onStdoutLine: _ => Task.CompletedTask,
+                ct: timeoutCts.Token);
+
+            if (IsSuccess(result))
+                return new PrimeRunOutcome(true, "Primed Claude");
+            return new PrimeRunOutcome(false, FailureMessage(result));
+        }
+        catch (OperationCanceledException) when (timeoutCts.IsCancellationRequested && !ct.IsCancellationRequested)
+        {
+            return new PrimeRunOutcome(false, $"timed out after {FireTimeout.TotalSeconds:0}s");
+        }
+        catch (Exception ex)
+        {
+            _logger.LogWarning(ex, "Prime fire failed");
+            return new PrimeRunOutcome(false, ex.Message);
+        }
+    }
+
+    private static bool IsSuccess(RunResult result) => result.IsSuccess;
+    private static string FailureMessage(RunResult result) => $"exit code {result.ExitCode}";
+}
diff --git a/src/ClaudeDo.Worker/Prime/PrimeScheduleSignal.cs b/src/ClaudeDo.Worker/Prime/PrimeScheduleSignal.cs
new file mode 100644
index 0000000..f7ab7e7
--- /dev/null
+++ b/src/ClaudeDo.Worker/Prime/PrimeScheduleSignal.cs
@@ -0,0 +1,29 @@
+namespace ClaudeDo.Worker.Prime;
+
+public sealed class PrimeScheduleSignal : IPrimeScheduleSignal, IDisposable
+{
+    private CancellationTokenSource _cts = new();
+    private readonly object _lock = new();
+
+    public CancellationToken CurrentToken
+    {
+        get { lock (_lock) return _cts.Token; }
+    }
+
+    public void Signal()
+    {
+        CancellationTokenSource old;
+        lock (_lock)
+        {
+            old = _cts;
+            _cts = new CancellationTokenSource();
+        }
+        try { old.Cancel(); } catch { /* already cancelled */ }
+        old.Dispose();
+    }
+
+    public void Dispose()
+    {
+        lock (_lock) _cts.Dispose();
+    }
+}
diff --git a/src/ClaudeDo.Worker/Prime/PrimeSchedulerOptions.cs b/src/ClaudeDo.Worker/Prime/PrimeSchedulerOptions.cs
new file mode 100644
index 0000000..a6d8a1b
--- /dev/null
+++ b/src/ClaudeDo.Worker/Prime/PrimeSchedulerOptions.cs
@@ -0,0 +1,7 @@
+namespace ClaudeDo.Worker.Prime;
+
+public sealed record PrimeSchedulerOptions(TimeSpan CatchUpWindow)
+{
+    public static PrimeSchedulerOptions Default { get; } =
+        new(TimeSpan.FromMinutes(30));
+}