diff --git a/src/ClaudeDo.Worker/Hub/WorkerHub.cs b/src/ClaudeDo.Worker/Hub/WorkerHub.cs
index 90f6770c..7fda04dc 100644
--- a/src/ClaudeDo.Worker/Hub/WorkerHub.cs
+++ b/src/ClaudeDo.Worker/Hub/WorkerHub.cs
@@ -1033,11 +1033,14 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         using var ctx = _dbFactory.CreateDbContext();
         var rows = await new PrimeScheduleRepository(ctx).ListAsync();
         return rows.Select(e => new PrimeScheduleDto(
-            e.Id, (int)e.Days, e.TimeOfDay, e.Enabled, e.LastRunAt, e.PromptOverride)).ToList();
+            e.Id, (int)e.Days, e.TimeOfDay, e.Enabled, e.LastRunAt, e.PromptOverride, e.Kind)).ToList();
     }
 
     public async Task<PrimeScheduleDto> UpsertPrimeSchedule(PrimeScheduleDto dto)
     {
+        var error = PrimeScheduleValidation.Validate(dto);
+        if (error is not null) throw new HubException(error);
+
         using var ctx = _dbFactory.CreateDbContext();
         var repo = new PrimeScheduleRepository(ctx);
         var existing = await repo.GetAsync(dto.Id);
@@ -1048,13 +1051,14 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
             TimeOfDay = dto.TimeOfDay,
             Enabled = dto.Enabled,
             PromptOverride = dto.PromptOverride,
+            Kind = dto.Kind,
             CreatedAt = existing?.CreatedAt ?? DateTimeOffset.UtcNow,
             LastRunAt = existing?.LastRunAt,
         };
         await repo.UpsertAsync(entity);
         _primeSignal.Signal();
         return new PrimeScheduleDto(entity.Id, (int)entity.Days, entity.TimeOfDay,
-            entity.Enabled, entity.LastRunAt, entity.PromptOverride);
+            entity.Enabled, entity.LastRunAt, entity.PromptOverride, entity.Kind);
     }
 
     public async Task DeletePrimeSchedule(Guid id)
@@ -1072,7 +1076,9 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
 
     public async Task<bool> RunDailyPrepNow()
     {
-        var schedule = new PrimeScheduleDto(Guid.Empty, 0, TimeSpan.Zero, true, null, null);
+        var schedule = new PrimeScheduleDto(
+            Guid.Empty, 0, TimeSpan.Zero, true, null, null,
+            ClaudeDo.Data.Models.PrimeActionKind.FillMyDay);
         var firedAt = DateTimeOffset.Now;
         var outcome = await _primeRunner.FireAsync(schedule, Context.ConnectionAborted);
         await _broadcaster.PrimeFired(Guid.Empty, outcome.Success, outcome.Message, firedAt);
diff --git a/src/ClaudeDo.Worker/Prime/PrimeScheduleValidation.cs b/src/ClaudeDo.Worker/Prime/PrimeScheduleValidation.cs
new file mode 100644
index 00000000..8160780d
--- /dev/null
+++ b/src/ClaudeDo.Worker/Prime/PrimeScheduleValidation.cs
@@ -0,0 +1,14 @@
+using ClaudeDo.Data.Models;
+
+namespace ClaudeDo.Worker.Prime;
+
+public static class PrimeScheduleValidation
+{
+    /// <summary>Returns an error message, or null when the schedule is safe to persist.</summary>
+    public static string? Validate(PrimeScheduleDto dto)
+    {
+        if (dto.Kind == PrimeActionKind.Custom && string.IsNullOrWhiteSpace(dto.PromptOverride))
+            return "A custom Prime schedule needs a prompt.";
+        return null;
+    }
+}
diff --git a/tests/ClaudeDo.Worker.Tests/Prime/NextDueCalculatorTests.cs b/tests/ClaudeDo.Worker.Tests/Prime/NextDueCalculatorTests.cs
index 0a06415a..c9147e50 100644
--- a/tests/ClaudeDo.Worker.Tests/Prime/NextDueCalculatorTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Prime/NextDueCalculatorTests.cs
@@ -8,7 +8,7 @@ public class NextDueCalculatorTests
     private static PrimeScheduleDto Schedule(
         PrimeDays days, TimeSpan time,
         bool enabled = true, DateTimeOffset? lastRun = null) =>
-        new(Guid.NewGuid(), (int)days, time, enabled, lastRun, null);
+        new(Guid.NewGuid(), (int)days, time, enabled, lastRun, null, PrimeActionKind.FillMyDay);
 
     [Fact]
     public void Disabled_Schedule_Returns_Null()
diff --git a/tests/ClaudeDo.Worker.Tests/Prime/PrimeScheduleValidationTests.cs b/tests/ClaudeDo.Worker.Tests/Prime/PrimeScheduleValidationTests.cs
new file mode 100644
index 00000000..ff48d66c
--- /dev/null
+++ b/tests/ClaudeDo.Worker.Tests/Prime/PrimeScheduleValidationTests.cs
@@ -0,0 +1,38 @@
+using ClaudeDo.Data.Models;
+using ClaudeDo.Worker.Prime;
+
+namespace ClaudeDo.Worker.Tests.Prime;
+
+public class PrimeScheduleValidationTests
+{
+    private static PrimeScheduleDto Dto(PrimeActionKind kind, string? prompt) =>
+        new(Guid.NewGuid(), 31, new TimeSpan(7, 0, 0), true, null, prompt, kind);
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData("   ")]
+    public void Custom_without_a_prompt_is_rejected(string? prompt)
+    {
+        var error = PrimeScheduleValidation.Validate(Dto(PrimeActionKind.Custom, prompt));
+        Assert.NotNull(error);
+    }
+
+    [Fact]
+    public void Custom_with_a_prompt_is_accepted()
+    {
+        Assert.Null(PrimeScheduleValidation.Validate(Dto(PrimeActionKind.Custom, "do the thing")));
+    }
+
+    [Fact]
+    public void Ping_without_a_prompt_is_accepted()
+    {
+        Assert.Null(PrimeScheduleValidation.Validate(Dto(PrimeActionKind.Ping, null)));
+    }
+
+    [Fact]
+    public void FillMyDay_without_a_prompt_is_accepted()
+    {
+        Assert.Null(PrimeScheduleValidation.Validate(Dto(PrimeActionKind.FillMyDay, null)));
+    }
+}