diff --git a/src/ClaudeDo.Worker/Planning/PlanningChainCoordinator.cs b/src/ClaudeDo.Worker/Planning/PlanningChainCoordinator.cs
index fe8f102..7e87de8 100644
--- a/src/ClaudeDo.Worker/Planning/PlanningChainCoordinator.cs
+++ b/src/ClaudeDo.Worker/Planning/PlanningChainCoordinator.cs
@@ -87,12 +87,8 @@ public sealed class PlanningChainCoordinator
     public async Task<string?> OnChildFinishedAsync(
         string childTaskId, TaskStatus finalStatus, CancellationToken ct = default)
     {
-        if (finalStatus != TaskStatus.Done) return null;
-
         await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
         // The successor is whichever sibling explicitly blocks on this child.
-        // No status check — UnblockAsync flips legacy Waiting to Queued and is a no-op
-        // for already-Queued rows in the new layout.
         var nextId = await ctx.Tasks
             .AsNoTracking()
             .Where(t => t.BlockedByTaskId == childTaskId)
@@ -101,7 +97,16 @@ public sealed class PlanningChainCoordinator
             .FirstOrDefaultAsync(ct);
         if (nextId is null) return null;
 
-        await _state().UnblockAsync(nextId, ct);
-        return nextId;
+        if (finalStatus == TaskStatus.Done)
+        {
+            await _state().UnblockAsync(nextId, ct);
+            return nextId;
+        }
+
+        // Child failed or was cancelled: cancel the immediate successor so the chain
+        // is not left wedged. CancelAsync triggers OnChildTerminalAsync → OnChildFinishedAsync
+        // for that successor, cascading cancellation through the rest of the chain.
+        await _state().CancelAsync(nextId, DateTime.UtcNow, ct);
+        return null;
     }
 }
diff --git a/src/ClaudeDo.Worker/Prime/DailyPrepPrompt.cs b/src/ClaudeDo.Worker/Prime/DailyPrepPrompt.cs
index 2c99506..89ebd6a 100644
--- a/src/ClaudeDo.Worker/Prime/DailyPrepPrompt.cs
+++ b/src/ClaudeDo.Worker/Prime/DailyPrepPrompt.cs
@@ -8,10 +8,13 @@ public static class DailyPrepPrompt
     public static string LogPath() =>
         System.IO.Path.Combine(ClaudeDo.Data.Paths.AppDataRoot(), "logs", "daily-prep.log");
 
-    public static string BuildArgs(int maxTurns) =>
-        "-p --output-format stream-json --verbose --permission-mode acceptEdits " +
-        $"--max-turns {maxTurns} " +
-        $"--allowedTools {CandidatesTool} {SetMyDayTool}";
+    public static IReadOnlyList<string> BuildArgs(int maxTurns) =>
+    [
+        "-p", "--output-format", "stream-json", "--verbose",
+        "--permission-mode", "acceptEdits",
+        "--max-turns", maxTurns.ToString(),
+        "--allowedTools", CandidatesTool, SetMyDayTool,
+    ];
 
     public static string BuildPrompt(int maxTasks, DateOnly today) =>
         ClaudeDo.Data.PromptFiles.Render(
diff --git a/src/ClaudeDo.Worker/Refine/RefinePrompt.cs b/src/ClaudeDo.Worker/Refine/RefinePrompt.cs
index 6dc5401..bf2bd89 100644
--- a/src/ClaudeDo.Worker/Refine/RefinePrompt.cs
+++ b/src/ClaudeDo.Worker/Refine/RefinePrompt.cs
@@ -12,13 +12,22 @@ public static class RefinePrompt
     public static string LogPath(string taskId) =>
         System.IO.Path.Combine(Paths.AppDataRoot(), "logs", $"refine-{Short(taskId)}.log");
 
-    public static string BuildArgs(int maxTurns, bool canReadRepo)
+    public static IReadOnlyList<string> BuildArgs(int maxTurns, bool canReadRepo)
     {
-        var tools = canReadRepo
-            ? $"{GetTaskTool} {UpdateTaskTool} {AddSubtaskTool} Read Grep Glob"
-            : $"{GetTaskTool} {UpdateTaskTool} {AddSubtaskTool}";
-        return "-p --output-format stream-json --verbose --permission-mode acceptEdits " +
-               $"--max-turns {maxTurns} --allowedTools {tools}";
+        var args = new List<string>
+        {
+            "-p", "--output-format", "stream-json", "--verbose",
+            "--permission-mode", "acceptEdits",
+            "--max-turns", maxTurns.ToString(),
+            "--allowedTools", GetTaskTool, UpdateTaskTool, AddSubtaskTool,
+        };
+        if (canReadRepo)
+        {
+            args.Add("Read");
+            args.Add("Grep");
+            args.Add("Glob");
+        }
+        return args;
     }
 
     public static string BuildPrompt(TaskEntity task, IEnumerable<SubtaskEntity> subtasks)
diff --git a/src/ClaudeDo.Worker/Report/WeekReportService.cs b/src/ClaudeDo.Worker/Report/WeekReportService.cs
index 4e8f3e2..da05195 100644
--- a/src/ClaudeDo.Worker/Report/WeekReportService.cs
+++ b/src/ClaudeDo.Worker/Report/WeekReportService.cs
@@ -69,7 +69,12 @@ public sealed class WeekReportService : IWeekReportService
             // alphanumerics, dashes and dots only.
             var safeModel = new string(model.Where(c => char.IsLetterOrDigit(c) || c is '-' or '.').ToArray());
             if (safeModel.Length == 0) safeModel = "sonnet";
-            var args = $"-p --output-format stream-json --verbose --permission-mode auto --model {safeModel}";
+            IReadOnlyList<string> args =
+            [
+                "-p", "--output-format", "stream-json", "--verbose",
+                "--permission-mode", "auto",
+                "--model", safeModel,
+            ];
             var result = await _claude.RunAsync(args, prompt, Path.GetTempPath(), _ => Task.CompletedTask, ct);
             if (!result.IsSuccess)
                 throw new InvalidOperationException(result.ErrorMarkdown ?? "Claude could not generate the report.");
diff --git a/src/ClaudeDo.Worker/Runner/ClaudeArgsBuilder.cs b/src/ClaudeDo.Worker/Runner/ClaudeArgsBuilder.cs
index f9f33fc..162891a 100644
--- a/src/ClaudeDo.Worker/Runner/ClaudeArgsBuilder.cs
+++ b/src/ClaudeDo.Worker/Runner/ClaudeArgsBuilder.cs
@@ -27,12 +27,12 @@ public sealed class ClaudeArgsBuilder
         required = new[] { "summary" },
     });
 
-    public string Build(ClaudeRunConfig config)
+    public IReadOnlyList<string> Build(ClaudeRunConfig config)
     {
         var args = new List<string>
         {
             "-p",
-            "--output-format stream-json",
+            "--output-format", "stream-json",
             "--verbose",
         };
 
@@ -40,50 +40,55 @@ public sealed class ClaudeArgsBuilder
             || config.PermissionMode.Equals("bypassPermissions", StringComparison.OrdinalIgnoreCase)
             ? "auto"
             : config.PermissionMode;
-        args.Add($"--permission-mode {permissionMode}");
+        args.Add("--permission-mode");
+        args.Add(permissionMode);
 
         if (config.Model is not null)
-            args.Add($"--model {config.Model}");
+        {
+            args.Add("--model");
+            args.Add(config.Model);
+        }
 
         if (config.MaxTurns is int turns && turns > 0)
-            args.Add($"--max-turns {turns}");
+        {
+            args.Add("--max-turns");
+            args.Add(turns.ToString());
+        }
 
         if (config.SystemPrompt is not null)
-            args.Add($"--append-system-prompt {Escape(config.SystemPrompt)}");
+        {
+            args.Add("--append-system-prompt");
+            args.Add(config.SystemPrompt);
+        }
 
         if (config.AgentPath is not null)
         {
             var agentJson = JsonSerializer.Serialize(new[] { new { file = config.AgentPath } });
-            args.Add($"--agents {Escape(agentJson)}");
+            args.Add("--agents");
+            args.Add(agentJson);
         }
 
-        args.Add($"--json-schema {Escape(ResultSchema)}");
+        args.Add("--json-schema");
+        args.Add(ResultSchema);
 
         if (config.McpConfigPath is not null)
-            args.Add($"--mcp-config {Escape(config.McpConfigPath)}");
+        {
+            args.Add("--mcp-config");
+            args.Add(config.McpConfigPath);
+        }
 
         if (config.AllowedTools is not null)
-            args.Add($"--allowedTools {config.AllowedTools}");
+        {
+            args.Add("--allowedTools");
+            args.Add(config.AllowedTools);
+        }
 
         if (config.ResumeSessionId is not null)
-            args.Add($"--resume {config.ResumeSessionId}");
-
-        return string.Join(" ", args);
-    }
-
-    private static string Escape(string value)
-    {
-        if (value.Contains(' ') || value.Contains('"') || value.Contains('\'')
-            || value.Contains('\t') || value.Contains('\n') || value.Contains('\r'))
         {
-            var escaped = value
-                .Replace("\\", "\\\\")
-                .Replace("\"", "\\\"")
-                .Replace("\n", "\\n")
-                .Replace("\r", "\\r")
-                .Replace("\t", "\\t");
-            return $"\"{escaped}\"";
+            args.Add("--resume");
+            args.Add(config.ResumeSessionId);
         }
-        return value;
+
+        return args;
     }
 }
diff --git a/src/ClaudeDo.Worker/Runner/ClaudeProcess.cs b/src/ClaudeDo.Worker/Runner/ClaudeProcess.cs
index fb94b96..6d383f5 100644
--- a/src/ClaudeDo.Worker/Runner/ClaudeProcess.cs
+++ b/src/ClaudeDo.Worker/Runner/ClaudeProcess.cs
@@ -18,7 +18,7 @@ public sealed class ClaudeProcess : IClaudeProcess
     }
 
     public async Task<RunResult> RunAsync(
-        string arguments,
+        IReadOnlyList<string> arguments,
         string prompt,
         string workingDirectory,
         Func<string, Task> onStdoutLine,
@@ -27,7 +27,6 @@ public sealed class ClaudeProcess : IClaudeProcess
         var psi = new ProcessStartInfo
         {
             FileName = _cfg.ClaudeBin,
-            Arguments = arguments,
             WorkingDirectory = workingDirectory,
             RedirectStandardInput = true,
             RedirectStandardOutput = true,
@@ -37,6 +36,8 @@ public sealed class ClaudeProcess : IClaudeProcess
             StandardOutputEncoding = Encoding.UTF8,
             StandardErrorEncoding = Encoding.UTF8,
         };
+        foreach (var arg in arguments)
+            psi.ArgumentList.Add(arg);
 
         using var process = new Process { StartInfo = psi };
         process.Start();
diff --git a/src/ClaudeDo.Worker/Runner/Interfaces/IClaudeProcess.cs b/src/ClaudeDo.Worker/Runner/Interfaces/IClaudeProcess.cs
index ebd18b8..7a800f1 100644
--- a/src/ClaudeDo.Worker/Runner/Interfaces/IClaudeProcess.cs
+++ b/src/ClaudeDo.Worker/Runner/Interfaces/IClaudeProcess.cs
@@ -3,7 +3,7 @@ namespace ClaudeDo.Worker.Runner;
 public interface IClaudeProcess
 {
     Task<RunResult> RunAsync(
-        string arguments,
+        IReadOnlyList<string> arguments,
         string prompt,
         string workingDirectory,
         Func<string, Task> onStdoutLine,
diff --git a/src/ClaudeDo.Worker/Runner/TaskRunner.cs b/src/ClaudeDo.Worker/Runner/TaskRunner.cs
index 816d8b4..b481d86 100644
--- a/src/ClaudeDo.Worker/Runner/TaskRunner.cs
+++ b/src/ClaudeDo.Worker/Runner/TaskRunner.cs
@@ -211,19 +211,32 @@ public sealed class TaskRunner
         await _state.StartRunningAsync(taskId, now, ct);
         await _broadcaster.TaskStarted(slot, taskId, now);
 
-        var nextRunNumber = lastRun.RunNumber + 1;
-        var result = await RunOnceAsync(taskId, task.Title, slot, runDir, resolvedConfig, nextRunNumber, false, followUpPrompt, ct);
-
-        if (result.IsSuccess)
+        try
         {
-            await HandleSuccess(task, list, slot, wtCtx, result, ct);
-        }
-        else
-        {
-            await MarkFailed(taskId, task.Title, slot, result.ErrorMarkdown, result.TurnCount);
-        }
+            var nextRunNumber = lastRun.RunNumber + 1;
+            var result = await RunOnceAsync(taskId, task.Title, slot, runDir, resolvedConfig, nextRunNumber, false, followUpPrompt, ct);
 
-        await _broadcaster.TaskUpdated(taskId);
+            if (result.IsSuccess)
+            {
+                await HandleSuccess(task, list, slot, wtCtx, result, ct);
+            }
+            else
+            {
+                await MarkFailed(taskId, task.Title, slot, result.ErrorMarkdown, result.TurnCount);
+            }
+
+            await _broadcaster.TaskUpdated(taskId);
+        }
+        catch (OperationCanceledException)
+        {
+            _logger.LogInformation("Task {TaskId} was cancelled during continue", taskId);
+            await MarkFailed(taskId, task.Title, slot, "Task cancelled.");
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Unhandled exception continuing task {TaskId}", taskId);
+            await MarkFailed(taskId, task.Title, slot, $"Unhandled error: {ex.Message}");
+        }
     }
 
     private readonly record struct RunDirResult(string? RunDir, WorktreeContext? WtCtx, string? FailureReason);
diff --git a/src/ClaudeDo.Worker/State/TaskStateService.cs b/src/ClaudeDo.Worker/State/TaskStateService.cs
index 17dbe8d..d756f20 100644
--- a/src/ClaudeDo.Worker/State/TaskStateService.cs
+++ b/src/ClaudeDo.Worker/State/TaskStateService.cs
@@ -196,14 +196,15 @@ public sealed class TaskStateService : ITaskStateService
         await using (var ctx = await _dbFactory.CreateDbContextAsync(ct))
         {
             var affected = await ctx.Tasks
-                .Where(t => t.Id == taskId && t.Status != TaskStatus.Done)
+                .Where(t => t.Id == taskId &&
+                    (t.Status == TaskStatus.Running || t.Status == TaskStatus.Queued))
                 .ExecuteUpdateAsync(s => s
                     .SetProperty(t => t.Status, TaskStatus.Failed)
                     .SetProperty(t => t.FinishedAt, finishedAt)
                     .SetProperty(t => t.Result, error), ct);
 
             if (affected == 0)
-                return new TransitionResult(false, "Task already done; cannot fail.");
+                return new TransitionResult(false, "Task not in a failable state (must be Running or Queued).");
         }
 
         await OnChildTerminalAsync(taskId, TaskStatus.Failed);
diff --git a/tests/ClaudeDo.Worker.Tests/Planning/PlanningChainCoordinatorTests.cs b/tests/ClaudeDo.Worker.Tests/Planning/PlanningChainCoordinatorTests.cs
index 1e7b9d5..d2b7239 100644
--- a/tests/ClaudeDo.Worker.Tests/Planning/PlanningChainCoordinatorTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Planning/PlanningChainCoordinatorTests.cs
@@ -125,7 +125,7 @@ public sealed class PlanningChainCoordinatorTests : IDisposable
     }
 
     [Fact]
-    public async Task OnChildFailed_DoesNotAdvanceChain()
+    public async Task OnChildFailed_CancelsPendingSuccessors_ChainIsNotWedged()
     {
         await SeedPlanningFamilyAsync("P", 3);
         await _sut.SetupChainAsync("P", default);
@@ -139,12 +139,43 @@ public sealed class PlanningChainCoordinatorTests : IDisposable
 
         var advanced = await _sut.OnChildFinishedAsync("P-c0", TaskStatus.Failed, default);
 
+        // No "advancement" — the chain does not continue on failure.
         Assert.Null(advanced);
         var kids = await GetChildrenAsync("P");
         Assert.Equal(TaskStatus.Failed, kids[0].Status);
-        // Successors remain blocked on the failed predecessor.
-        Assert.Equal(kids[0].Id, kids[1].BlockedByTaskId);
-        Assert.Equal(kids[1].Id, kids[2].BlockedByTaskId);
+        // Successors must be Cancelled, not left stuck as Queued.
+        Assert.Equal(TaskStatus.Cancelled, kids[1].Status);
+        Assert.Equal(TaskStatus.Cancelled, kids[2].Status);
+    }
+
+    [Fact]
+    public async Task OnChildFailed_MidChain_CancelsAllDownstreamSuccessors()
+    {
+        // Chain: c0 → c1 → c2 → c3. c1 fails mid-chain; c2 and c3 must be cancelled.
+        await SeedPlanningFamilyAsync("P", 4);
+        await _sut.SetupChainAsync("P", default);
+
+        // Mark c0 Done so c1 was unblocked; c1 ran and failed.
+        await using (var ctx = _factory.CreateDbContext())
+        {
+            var c0 = await ctx.Tasks.FirstAsync(t => t.Id == "P-c0");
+            c0.Status = TaskStatus.Done;
+            c0.BlockedByTaskId = null;
+            var c1 = await ctx.Tasks.FirstAsync(t => t.Id == "P-c1");
+            c1.Status = TaskStatus.Failed;
+            c1.BlockedByTaskId = null;
+            await ctx.SaveChangesAsync();
+        }
+
+        // Announce that c1 finished as Failed — the coordinator must cascade to c2/c3.
+        var advanced = await _sut.OnChildFinishedAsync("P-c1", TaskStatus.Failed, default);
+
+        Assert.Null(advanced);
+        var kids = await GetChildrenAsync("P");
+        Assert.Equal(TaskStatus.Done, kids[0].Status);
+        Assert.Equal(TaskStatus.Failed, kids[1].Status);
+        Assert.Equal(TaskStatus.Cancelled, kids[2].Status);
+        Assert.Equal(TaskStatus.Cancelled, kids[3].Status);
     }
 
     [Fact]
diff --git a/tests/ClaudeDo.Worker.Tests/Prime/DailyPrepPromptTests.cs b/tests/ClaudeDo.Worker.Tests/Prime/DailyPrepPromptTests.cs
index 25f0ff3..febda78 100644
--- a/tests/ClaudeDo.Worker.Tests/Prime/DailyPrepPromptTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Prime/DailyPrepPromptTests.cs
@@ -19,8 +19,10 @@ public class DailyPrepPromptTests
     public void Build_args_allows_only_the_two_tools()
     {
         var args = DailyPrepPrompt.BuildArgs(maxTurns: 30);
-        Assert.Contains("--output-format stream-json", args);
-        Assert.Contains("--max-turns 30", args);
+        Assert.Contains("--output-format", args);
+        Assert.Contains("stream-json", args);
+        Assert.Contains("--max-turns", args);
+        Assert.Contains("30", args);
         Assert.Contains("--allowedTools", args);
         Assert.Contains("mcp__claudedo__get_daily_prep_candidates", args);
         Assert.Contains("mcp__claudedo__set_my_day", args);
diff --git a/tests/ClaudeDo.Worker.Tests/Prime/PrimeRunnerTests.cs b/tests/ClaudeDo.Worker.Tests/Prime/PrimeRunnerTests.cs
index be486df..e7acdc3 100644
--- a/tests/ClaudeDo.Worker.Tests/Prime/PrimeRunnerTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Prime/PrimeRunnerTests.cs
@@ -31,7 +31,7 @@ public class PrimeRunnerTests : IDisposable
         }
 
         public async Task<RunResult> RunAsync(
-            string arguments,
+            IReadOnlyList<string> arguments,
             string prompt,
             string workingDirectory,
             Func<string, Task> onStdoutLine,
diff --git a/tests/ClaudeDo.Worker.Tests/Refine/RefinePromptTests.cs b/tests/ClaudeDo.Worker.Tests/Refine/RefinePromptTests.cs
index 57e7027..0d508cb 100644
--- a/tests/ClaudeDo.Worker.Tests/Refine/RefinePromptTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Refine/RefinePromptTests.cs
@@ -11,9 +11,12 @@ public sealed class RefinePromptTests
     {
         var args = RefinePrompt.BuildArgs(20, canReadRepo: true);
 
-        Assert.Contains("--permission-mode acceptEdits", args);
+        Assert.Contains("--permission-mode", args);
+        Assert.Contains("acceptEdits", args);
         Assert.Contains("mcp__claudedo__add_subtask", args);
-        Assert.Contains(" Read Grep Glob", args);
+        Assert.Contains("Read", args);
+        Assert.Contains("Grep", args);
+        Assert.Contains("Glob", args);
     }
 
     [Fact]
diff --git a/tests/ClaudeDo.Worker.Tests/Refine/RefineRunnerTests.cs b/tests/ClaudeDo.Worker.Tests/Refine/RefineRunnerTests.cs
index ed4b534..93b6395 100644
--- a/tests/ClaudeDo.Worker.Tests/Refine/RefineRunnerTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Refine/RefineRunnerTests.cs
@@ -105,7 +105,7 @@ internal sealed class RecordingClaudeProcess : IClaudeProcess
 
     public RecordingClaudeProcess(bool success) => _success = success;
 
-    public Task<RunResult> RunAsync(string arguments, string prompt, string workingDirectory,
+    public Task<RunResult> RunAsync(IReadOnlyList<string> arguments, string prompt, string workingDirectory,
         Func<string, Task> onStdoutLine, CancellationToken ct)
     {
         Interlocked.Increment(ref _callCount);
diff --git a/tests/ClaudeDo.Worker.Tests/Report/WeekReportServiceTests.cs b/tests/ClaudeDo.Worker.Tests/Report/WeekReportServiceTests.cs
index ff8196b..df6370a 100644
--- a/tests/ClaudeDo.Worker.Tests/Report/WeekReportServiceTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Report/WeekReportServiceTests.cs
@@ -27,7 +27,7 @@ public class WeekReportServiceTests : IDisposable
     {
         public int Calls;
         public RunResult Next = new() { ExitCode = 0, ResultMarkdown = "## Bericht" };
-        public Task<RunResult> RunAsync(string args, string prompt, string wd, Func<string, Task> onLine, CancellationToken ct)
+        public Task<RunResult> RunAsync(IReadOnlyList<string> args, string prompt, string wd, Func<string, Task> onLine, CancellationToken ct)
         { Calls++; return Task.FromResult(Next); }
     }
 
diff --git a/tests/ClaudeDo.Worker.Tests/Runner/ClaudeArgsBuilderTests.cs b/tests/ClaudeDo.Worker.Tests/Runner/ClaudeArgsBuilderTests.cs
index c3e894d..30e0ad6 100644
--- a/tests/ClaudeDo.Worker.Tests/Runner/ClaudeArgsBuilderTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Runner/ClaudeArgsBuilderTests.cs
@@ -11,9 +11,11 @@ public sealed class ClaudeArgsBuilderTests
     {
         var args = _builder.Build(new ClaudeRunConfig(null, null, null, null));
         Assert.Contains("-p", args);
-        Assert.Contains("--output-format stream-json", args);
+        Assert.Contains("--output-format", args);
+        Assert.Contains("stream-json", args);
         Assert.Contains("--verbose", args);
-        Assert.Contains("--permission-mode auto", args);
+        Assert.Contains("--permission-mode", args);
+        Assert.Contains("auto", args);
         Assert.DoesNotContain("--dangerously-skip-permissions", args);
         Assert.Contains("--json-schema", args);
         Assert.DoesNotContain("--model", args);
@@ -26,7 +28,8 @@ public sealed class ClaudeArgsBuilderTests
     public void Model_Adds_Model_Flag()
     {
         var args = _builder.Build(new ClaudeRunConfig("sonnet-4-6", null, null, null));
-        Assert.Contains("--model sonnet-4-6", args);
+        Assert.Contains("--model", args);
+        Assert.Contains("sonnet-4-6", args);
     }
 
     [Fact]
@@ -42,63 +45,74 @@ public sealed class ClaudeArgsBuilderTests
     {
         var args = _builder.Build(new ClaudeRunConfig(null, null, "/path/to/agent.md", null));
         Assert.Contains("--agents", args);
-        Assert.Contains("/path/to/agent.md", args);
+        Assert.Contains(args, a => a.Contains("/path/to/agent.md"));
     }
 
     [Fact]
     public void ResumeSessionId_Adds_Resume_Flag()
     {
         var args = _builder.Build(new ClaudeRunConfig(null, null, null, "sess-abc-123"));
-        Assert.Contains("--resume sess-abc-123", args);
+        Assert.Contains("--resume", args);
+        Assert.Contains("sess-abc-123", args);
     }
 
     [Fact]
     public void All_Options_Set_Includes_All_Flags()
     {
         var args = _builder.Build(new ClaudeRunConfig("opus-4-6", "Be thorough.", "/agents/dev.md", "sess-xyz"));
-        Assert.Contains("--model opus-4-6", args);
+        Assert.Contains("--model", args);
+        Assert.Contains("opus-4-6", args);
         Assert.Contains("--append-system-prompt", args);
         Assert.Contains("--agents", args);
-        Assert.Contains("--resume sess-xyz", args);
+        Assert.Contains("--resume", args);
+        Assert.Contains("sess-xyz", args);
         Assert.Contains("--json-schema", args);
     }
 
     [Fact]
-    public void SystemPrompt_With_Quotes_Is_Escaped()
+    public void SystemPrompt_With_Quotes_Is_Passed_Verbatim()
     {
-        var args = _builder.Build(new ClaudeRunConfig(null, """Don't say "hello".""", null, null));
+        var prompt = """Don't say "hello".""";
+        var args = _builder.Build(new ClaudeRunConfig(null, prompt, null, null));
         Assert.Contains("--append-system-prompt", args);
+        Assert.Contains(prompt, args);
     }
 
     [Fact]
-    public void Build_quotes_system_prompt_with_newline()
+    public void SystemPrompt_With_Newline_Is_Passed_As_Single_Element()
     {
+        var prompt = "line1\nline2";
         var args = _builder.Build(new ClaudeRunConfig(
             Model: null,
-            SystemPrompt: "line1\nline2",
+            SystemPrompt: prompt,
             AgentPath: null,
             ResumeSessionId: null));
 
-        Assert.Contains("--append-system-prompt \"line1\\nline2\"", args);
+        var list = args.ToList();
+        var idx = list.IndexOf("--append-system-prompt");
+        Assert.True(idx >= 0);
+        Assert.Equal(prompt, list[idx + 1]);
     }
 
     [Fact]
-    public void Build_quotes_system_prompt_with_tab()
+    public void SystemPrompt_With_Tab_Is_Passed_As_Single_Element()
     {
+        var prompt = "col1\tcol2";
         var args = _builder.Build(new ClaudeRunConfig(
             Model: null,
-            SystemPrompt: "col1\tcol2",
+            SystemPrompt: prompt,
             AgentPath: null,
             ResumeSessionId: null));
 
-        Assert.Contains("\"col1", args);
+        Assert.Contains(prompt, args);
     }
 
     [Fact]
     public void MaxTurns_Adds_Flag_When_Positive()
     {
         var args = _builder.Build(new ClaudeRunConfig(null, null, null, null, MaxTurns: 25));
-        Assert.Contains("--max-turns 25", args);
+        Assert.Contains("--max-turns", args);
+        Assert.Contains("25", args);
     }
 
     [Fact]
@@ -114,7 +128,8 @@ public sealed class ClaudeArgsBuilderTests
     public void PermissionMode_bypass_Maps_To_Auto()
     {
         var args = _builder.Build(new ClaudeRunConfig(null, null, null, null, PermissionMode: "bypassPermissions"));
-        Assert.Contains("--permission-mode auto", args);
+        Assert.Contains("--permission-mode", args);
+        Assert.Contains("auto", args);
         Assert.DoesNotContain("--dangerously-skip-permissions", args);
     }
 
@@ -122,7 +137,8 @@ public sealed class ClaudeArgsBuilderTests
     public void PermissionMode_acceptEdits_Emits_PermissionMode_Flag()
     {
         var args = _builder.Build(new ClaudeRunConfig(null, null, null, null, PermissionMode: "acceptEdits"));
-        Assert.Contains("--permission-mode acceptEdits", args);
+        Assert.Contains("--permission-mode", args);
+        Assert.Contains("acceptEdits", args);
         Assert.DoesNotContain("--dangerously-skip-permissions", args);
     }
 
@@ -130,7 +146,8 @@ public sealed class ClaudeArgsBuilderTests
     public void PermissionMode_Null_Defaults_To_Auto()
     {
         var args = _builder.Build(new ClaudeRunConfig(null, null, null, null));
-        Assert.Contains("--permission-mode auto", args);
+        Assert.Contains("--permission-mode", args);
+        Assert.Contains("auto", args);
         Assert.DoesNotContain("--dangerously-skip-permissions", args);
     }
 
@@ -142,8 +159,26 @@ public sealed class ClaudeArgsBuilderTests
             McpConfigPath: "C:\\tmp\\t_mcp.json",
             AllowedTools: "mcp__claudedo_run__SuggestImprovement"));
         Assert.Contains("--mcp-config", args);
-        Assert.Contains("t_mcp.json", args);
-        Assert.Contains("--allowedTools mcp__claudedo_run__SuggestImprovement", args);
+        Assert.Contains(args, a => a.Contains("t_mcp.json"));
+        Assert.Contains("--allowedTools", args);
+        Assert.Contains("mcp__claudedo_run__SuggestImprovement", args);
+    }
+
+    [Fact]
+    public void SystemPrompt_ContainingDangerousFlag_IsPassedAsLiteral_NotAsFlag()
+    {
+        // If the system prompt contains "--dangerously-skip-permissions", it must arrive
+        // as the VALUE of --append-system-prompt, not as a standalone CLI flag.
+        const string dangerousPrompt = "--dangerously-skip-permissions";
+        var args = _builder.Build(new ClaudeRunConfig(null, dangerousPrompt, null, null));
+
+        var list = args.ToList();
+        var flagIdx = list.IndexOf("--append-system-prompt");
+        Assert.True(flagIdx >= 0, "--append-system-prompt flag must be present");
+        // The dangerous string sits immediately after the flag as its value.
+        Assert.Equal(dangerousPrompt, list[flagIdx + 1]);
+        // It does NOT appear as a separate element (i.e., not treated as its own flag).
+        Assert.Equal(1, list.Count(a => a == dangerousPrompt));
     }
 }
 
diff --git a/tests/ClaudeDo.Worker.Tests/Runner/ContinueAsyncExceptionTests.cs b/tests/ClaudeDo.Worker.Tests/Runner/ContinueAsyncExceptionTests.cs
new file mode 100644
index 0000000..3e1769e
--- /dev/null
+++ b/tests/ClaudeDo.Worker.Tests/Runner/ContinueAsyncExceptionTests.cs
@@ -0,0 +1,106 @@
+using ClaudeDo.Data;
+using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Config;
+using ClaudeDo.Worker.Hub;
+using ClaudeDo.Worker.Runner;
+using ClaudeDo.Worker.Tests.Infrastructure;
+using ClaudeDo.Worker.Tests.Services;
+using Microsoft.Extensions.Logging.Abstractions;
+using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
+
+namespace ClaudeDo.Worker.Tests.Runner;
+
+/// <summary>
+/// Verifies that ContinueAsync wraps RunOnceAsync exceptions so the task
+/// is never left stuck in Running status on an unexpected error.
+/// </summary>
+public sealed class ContinueAsyncExceptionTests : IDisposable
+{
+    private readonly DbFixture _db = new();
+    private readonly string _tempDir;
+    private readonly WorkerConfig _cfg;
+
+    public ContinueAsyncExceptionTests()
+    {
+        _tempDir = Path.Combine(Path.GetTempPath(), $"cd_continue_{Guid.NewGuid():N}");
+        Directory.CreateDirectory(_tempDir);
+        _cfg = new WorkerConfig { SandboxRoot = _tempDir, LogRoot = _tempDir };
+    }
+
+    public void Dispose() { _db.Dispose(); try { Directory.Delete(_tempDir, true); } catch { } }
+
+    private TaskRunner BuildRunner(IClaudeProcess claude, ClaudeDoDbContext ctx)
+    {
+        var dbFactory = _db.CreateFactory();
+        var broadcaster = new HubBroadcaster(new FakeHubContext());
+        var state = TaskStateServiceBuilder.Build(dbFactory).State;
+        var wt = new WorktreeManager(new ClaudeDo.Data.Git.GitService(), dbFactory, _cfg, NullLogger<WorktreeManager>.Instance);
+        return new TaskRunner(claude, dbFactory, broadcaster, wt, new ClaudeArgsBuilder(), _cfg,
+            NullLogger<TaskRunner>.Instance, state, new TaskRunTokenRegistry());
+    }
+
+    [Fact]
+    public async Task ContinueAsync_UnhandledException_MarksTaskFailed_NotStuckRunning()
+    {
+        var dbFactory = _db.CreateFactory();
+        string listId, taskId;
+
+        using (var ctx = _db.CreateContext())
+        {
+            listId = Guid.NewGuid().ToString();
+            ctx.Lists.Add(new ListEntity { Id = listId, Name = "L", WorkingDir = null, CreatedAt = DateTime.UtcNow });
+
+            taskId = Guid.NewGuid().ToString();
+            ctx.Tasks.Add(new TaskEntity
+            {
+                Id = taskId,
+                ListId = listId,
+                Title = "Continue me",
+                Status = TaskStatus.WaitingForReview,
+                CreatedAt = DateTime.UtcNow,
+            });
+            await ctx.SaveChangesAsync();
+
+            // A prior run with a session ID is required for ContinueAsync to proceed.
+            await new TaskRunRepository(ctx).AddAsync(new TaskRunEntity
+            {
+                Id = Guid.NewGuid().ToString(),
+                TaskId = taskId,
+                RunNumber = 1,
+                IsRetry = false,
+                Prompt = "original prompt",
+                SessionId = "sess-continue-test",
+                StartedAt = DateTime.UtcNow.AddMinutes(-5),
+                FinishedAt = DateTime.UtcNow.AddMinutes(-1),
+                ExitCode = 0,
+                ResultMarkdown = "first result",
+            });
+        }
+
+        // This process throws a non-cancellation exception to simulate an unexpected failure.
+        var throwingProcess = new ThrowingClaudeProcess(new InvalidOperationException("disk full"));
+
+        using var ctx2 = _db.CreateContext();
+        var runner = BuildRunner(throwingProcess, ctx2);
+
+        // ContinueAsync must not propagate the exception and must leave the task in Failed.
+        await runner.ContinueAsync(taskId, "please continue", "slot-1", CancellationToken.None);
+
+        using var verify = _db.CreateContext();
+        var task = await new TaskRepository(verify).GetByIdAsync(taskId);
+        Assert.NotNull(task);
+        Assert.Equal(TaskStatus.Failed, task.Status);
+    }
+
+    private sealed class ThrowingClaudeProcess : IClaudeProcess
+    {
+        private readonly Exception _ex;
+        public ThrowingClaudeProcess(Exception ex) => _ex = ex;
+
+        public Task<RunResult> RunAsync(
+            IReadOnlyList<string> arguments, string prompt, string workingDirectory,
+            Func<string, Task> onStdoutLine, CancellationToken ct)
+            => throw _ex;
+    }
+}
diff --git a/tests/ClaudeDo.Worker.Tests/Services/QueueServiceSlotGuardTests.cs b/tests/ClaudeDo.Worker.Tests/Services/QueueServiceSlotGuardTests.cs
index 3a0e796..61dc6b2 100644
--- a/tests/ClaudeDo.Worker.Tests/Services/QueueServiceSlotGuardTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Services/QueueServiceSlotGuardTests.cs
@@ -46,7 +46,7 @@ public sealed class QueueServiceSlotGuardTests : IDisposable
     private QueueWaker _waker = null!;
 
     private (QueueService service, FakeClaudeProcess fakeProcess) CreateService(
-        Func<string, string, string, Func<string, Task>, CancellationToken, Task<RunResult>>? handler = null)
+        Func<string, string, IReadOnlyList<string>, Func<string, Task>, CancellationToken, Task<RunResult>>? handler = null)
     {
         var fake = new FakeClaudeProcess(handler);
         var broadcaster = new HubBroadcaster(new FakeHubContext());
diff --git a/tests/ClaudeDo.Worker.Tests/Services/QueueServiceTests.cs b/tests/ClaudeDo.Worker.Tests/Services/QueueServiceTests.cs
index a0db50b..b67be6d 100644
--- a/tests/ClaudeDo.Worker.Tests/Services/QueueServiceTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Services/QueueServiceTests.cs
@@ -47,7 +47,7 @@ public sealed class QueueServiceTests : IDisposable
     private QueueWaker _waker = null!;
 
     private (QueueService service, FakeClaudeProcess fakeProcess) CreateService(
-        Func<string, string, string, Func<string, Task>, CancellationToken, Task<RunResult>>? handler = null)
+        Func<string, string, IReadOnlyList<string>, Func<string, Task>, CancellationToken, Task<RunResult>>? handler = null)
     {
         var fake = new FakeClaudeProcess(handler);
         var broadcaster = new HubBroadcaster(new FakeHubContext());
@@ -118,7 +118,7 @@ public sealed class QueueServiceTests : IDisposable
     {
         var (listId, _) = await SeedListWithAgentTag();
 
-        string? capturedArgs = null;
+        IReadOnlyList<string>? capturedArgs = null;
         string? capturedPrompt = null;
         var done = new TaskCompletionSource();
 
@@ -157,7 +157,9 @@ public sealed class QueueServiceTests : IDisposable
         _waker.Wake();
         await done.Task.WaitAsync(TimeSpan.FromSeconds(5));
 
-        Assert.Contains("--resume sess-1", capturedArgs);
+        Assert.NotNull(capturedArgs);
+        Assert.Contains("--resume", capturedArgs);
+        Assert.Contains("sess-1", capturedArgs);
         Assert.Equal("fix the bug", capturedPrompt);
 
         // Feedback is cleared after the run reaches a successful terminal state (post-run),
@@ -346,19 +348,19 @@ public sealed class QueueServiceTests : IDisposable
 
 internal sealed class FakeClaudeProcess : IClaudeProcess
 {
-    private readonly Func<string, string, string, Func<string, Task>, CancellationToken, Task<RunResult>> _handler;
+    private readonly Func<string, string, IReadOnlyList<string>, Func<string, Task>, CancellationToken, Task<RunResult>> _handler;
     private int _callCount;
 
     public int CallCount => _callCount;
 
     public FakeClaudeProcess(
-        Func<string, string, string, Func<string, Task>, CancellationToken, Task<RunResult>>? handler = null)
+        Func<string, string, IReadOnlyList<string>, Func<string, Task>, CancellationToken, Task<RunResult>>? handler = null)
     {
         _handler = handler ?? ((_, _, _, _, _) =>
             Task.FromResult(new RunResult { ExitCode = 0, ResultMarkdown = "ok" }));
     }
 
-    public async Task<RunResult> RunAsync(string arguments, string prompt, string workingDirectory,
+    public async Task<RunResult> RunAsync(IReadOnlyList<string> arguments, string prompt, string workingDirectory,
         Func<string, Task> onStdoutLine, CancellationToken ct)
     {
         Interlocked.Increment(ref _callCount);
diff --git a/tests/ClaudeDo.Worker.Tests/State/TaskStateServiceTests.cs b/tests/ClaudeDo.Worker.Tests/State/TaskStateServiceTests.cs
index 7ec4953..531a6e3 100644
--- a/tests/ClaudeDo.Worker.Tests/State/TaskStateServiceTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/State/TaskStateServiceTests.cs
@@ -243,6 +243,17 @@ public sealed class TaskStateServiceTests : IDisposable
         Assert.Equal(TaskStatus.Done, await GetStatusAsync(id));
     }
 
+    [Fact]
+    public async Task FailAsync_FromWaitingForReview_IsNoOp()
+    {
+        var id = await SeedTaskAsync(TaskStatus.WaitingForReview);
+
+        var result = await _sut.FailAsync(id, DateTime.UtcNow, "oops", default);
+
+        Assert.False(result.Ok);
+        Assert.Equal(TaskStatus.WaitingForReview, await GetStatusAsync(id));
+    }
+
     // ─── CancelAsync ──────────────────────────────────────────────────────
 
     [Fact]