diff --git a/src/ClaudeDo.Ui/Services/Interfaces/IWorkerClient.cs b/src/ClaudeDo.Ui/Services/Interfaces/IWorkerClient.cs
index bab8d1df..8b0ba673 100644
--- a/src/ClaudeDo.Ui/Services/Interfaces/IWorkerClient.cs
+++ b/src/ClaudeDo.Ui/Services/Interfaces/IWorkerClient.cs
@@ -87,6 +87,9 @@ public interface IWorkerClient : INotifyPropertyChanged
     // Picks up a task's Claude session in a real terminal window (--resume) — distinct
     // from OpenInteractiveTerminalAsync (the in-app streaming session).
     Task ResumeTaskInTerminalAsync(string taskId, CancellationToken ct = default);
+    /// <summary>Launch spec for an embedded ConPTY terminal to open an interactive session
+    /// in a task's worktree (same worktree prep as an autonomous run).</summary>
+    Task<LaunchSpec> GetInteractiveLaunchSpecAsync(string taskId, CancellationToken ct = default);
     Task ResumePlanningSessionAsync(string taskId, CancellationToken ct = default);
     Task<DiscardPlanningOutcome> DiscardPlanningSessionAsync(string taskId, bool dequeueQueuedChildren = false, CancellationToken ct = default);
     Task FinalizePlanningSessionAsync(string taskId, bool queueAgentTasks = true, CancellationToken ct = default);
diff --git a/src/ClaudeDo.Ui/Services/WorkerClient.cs b/src/ClaudeDo.Ui/Services/WorkerClient.cs
index 09677cb3..cd250ce6 100644
--- a/src/ClaudeDo.Ui/Services/WorkerClient.cs
+++ b/src/ClaudeDo.Ui/Services/WorkerClient.cs
@@ -564,6 +564,9 @@ public partial class WorkerClient : ObservableObject, IAsyncDisposable, IWorkerC
     public async Task ResumeTaskInTerminalAsync(string taskId, CancellationToken ct = default)
         => await _hub.InvokeAsync("ResumeTaskInTerminal", taskId, ct);
 
+    public async Task<LaunchSpec> GetInteractiveLaunchSpecAsync(string taskId, CancellationToken ct = default)
+        => await _hub.InvokeAsync<LaunchSpec>("GetInteractiveLaunchSpec", taskId, ct);
+
     public async Task<DiscardPlanningOutcome> DiscardPlanningSessionAsync(string taskId, bool dequeueQueuedChildren = false, CancellationToken ct = default)
         => await _hub.InvokeAsync<DiscardPlanningOutcome>("DiscardPlanningSessionAsync", taskId, dequeueQueuedChildren, ct);
 
@@ -677,6 +680,12 @@ public sealed record WorktreeOverviewDto(
     DateTime CreatedAt,
     bool PathExistsOnDisk);
 
+public sealed record LaunchSpec(
+    string Cwd,
+    string Exe,
+    IReadOnlyList<string> Args,
+    IReadOnlyDictionary<string, string> Env);
+
 public sealed record ForceRemoveResultDto(bool Removed, string? Reason);
 public sealed record PendingQuestionDto(string TaskId, string QuestionId, string Question);
 
diff --git a/src/ClaudeDo.Worker/Hub/WorkerHub.cs b/src/ClaudeDo.Worker/Hub/WorkerHub.cs
index 3d9a5cf7..98a2fad6 100644
--- a/src/ClaudeDo.Worker/Hub/WorkerHub.cs
+++ b/src/ClaudeDo.Worker/Hub/WorkerHub.cs
@@ -130,6 +130,7 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
     private readonly InteractiveSessionService _interactive;
     private readonly LogRingBuffer? _logBuffer;
     private readonly ISessionSkillRegistry _skillRegistry;
+    private readonly IInteractiveLaunchSpecService? _interactiveLaunchSpec;
 
     public WorkerHub(
         QueueService queue,
@@ -157,7 +158,8 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         Runner.PendingQuestionRegistry pendingQuestions,
         InteractiveSessionService interactive,
         ISessionSkillRegistry skillRegistry,
-        LogRingBuffer? logBuffer = null)
+        LogRingBuffer? logBuffer = null,
+        IInteractiveLaunchSpecService? interactiveLaunchSpec = null)
     {
         _queue = queue;
         _waker = waker;
@@ -185,6 +187,7 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         _interactive = interactive;
         _skillRegistry = skillRegistry;
         _logBuffer = logBuffer;
+        _interactiveLaunchSpec = interactiveLaunchSpec;
     }
 
     // Persistence boundary for the session_skills JSON-array columns (task/list/global).
@@ -657,6 +660,17 @@ public sealed class WorkerHub : Microsoft.AspNetCore.SignalR.Hub
         }
     });
 
+    // Builds the launch spec an embedded ConPTY terminal (UI process) needs to open an
+    // interactive Claude session in a task's worktree -- same worktree prep as an
+    // autonomous run (session-skills seeding, run env vars), --resume if the task has a
+    // persisted session or a fresh-start spec otherwise. Guards mirror ResumeTaskInTerminal.
+    public Task<LaunchSpec> GetInteractiveLaunchSpec(string taskId) => HubGuard(() =>
+    {
+        if (_interactiveLaunchSpec is null)
+            throw new InvalidOperationException("Interactive launch spec service is not configured.");
+        return _interactiveLaunchSpec.BuildForTaskAsync(taskId, Context.ConnectionAborted);
+    });
+
     public Task SendInteractiveMessage(string taskId, string text) =>
         _interactive.SendAsync(taskId, text, Context.ConnectionAborted);
 
diff --git a/src/ClaudeDo.Worker/Planning/WindowsTerminalLauncher.cs b/src/ClaudeDo.Worker/Planning/WindowsTerminalLauncher.cs
index 274da92c..f2c08797 100644
--- a/src/ClaudeDo.Worker/Planning/WindowsTerminalLauncher.cs
+++ b/src/ClaudeDo.Worker/Planning/WindowsTerminalLauncher.cs
@@ -106,7 +106,12 @@ public sealed class WindowsTerminalLauncher : ITerminalLauncher
     // Resumes a session by id in default (interactive) permission mode: the user drives
     // tool approvals in the terminal, unlike planning which pins --permission-mode plan.
     internal static string BuildResumeCommand(string claudePath, string claudeSessionId) =>
-        BuildPwshCommand(claudePath, new[] { "--resume", claudeSessionId });
+        BuildPwshCommand(claudePath, BuildResumeArgs(claudeSessionId));
+
+    // The raw claude CLI args for a --resume launch, shared with InteractiveLaunchSpecService
+    // (which needs the bare Exe/Args pair for a ConPTY host, not a wrapped pwsh command line).
+    internal static IReadOnlyList<string> BuildResumeArgs(string claudeSessionId) =>
+        new[] { "--resume", claudeSessionId };
 
     // Builds the PowerShell command that launches an interactive planning session.
     // Arg order matters: variadic flags (--allowedTools, --add-dir) come first; the
@@ -174,7 +179,9 @@ public sealed class WindowsTerminalLauncher : ITerminalLauncher
             ?? throw new TerminalLaunchException("Failed to start Windows Terminal process.");
     }
 
-    private static string? Resolve(string pathOrName)
+    // Not private: reused by InteractiveLaunchSpecService to resolve the claude executable
+    // for a ConPTY-hosted launch spec the same way a wt-launched terminal resolves it.
+    internal static string? Resolve(string pathOrName)
     {
         if (File.Exists(pathOrName))
             return pathOrName;
diff --git a/src/ClaudeDo.Worker/Program.cs b/src/ClaudeDo.Worker/Program.cs
index c2678b47..59de7900 100644
--- a/src/ClaudeDo.Worker/Program.cs
+++ b/src/ClaudeDo.Worker/Program.cs
@@ -77,6 +77,7 @@ builder.Services.AddSingleton<PendingQuestionRegistry>();
 builder.Services.AddSingleton<IRepoCloner, GitRepoCloner>();
 builder.Services.AddSingleton<ISessionSkillRegistry, SessionSkillRegistry>();
 builder.Services.AddSingleton<ISessionSkillSeeder, SessionSkillSeeder>();
+builder.Services.AddSingleton<IInteractiveLaunchSpecService, InteractiveLaunchSpecService>();
 builder.Services.AddSingleton<TaskRunner>();
 builder.Services.AddSingleton<WorktreeMaintenanceService>();
 builder.Services.AddSingleton<TaskResetService>();
diff --git a/src/ClaudeDo.Worker/Runner/InteractiveLaunchSpecService.cs b/src/ClaudeDo.Worker/Runner/InteractiveLaunchSpecService.cs
new file mode 100644
index 00000000..91b50b59
--- /dev/null
+++ b/src/ClaudeDo.Worker/Runner/InteractiveLaunchSpecService.cs
@@ -0,0 +1,95 @@
+using ClaudeDo.Data;
+using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Config;
+using ClaudeDo.Worker.Planning;
+using ClaudeDo.Worker.Skills;
+using Microsoft.EntityFrameworkCore;
+using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
+
+namespace ClaudeDo.Worker.Runner;
+
+// Builds the launch spec an embedded ConPTY terminal needs to open an interactive Claude
+// session in an existing task's worktree -- the SAME worktree prep as an autonomous run:
+// session-skills seeded onto disk (reuses ISessionSkillSeeder + TaskRunner.UnionSkillNames,
+// exactly like TaskRunner.RunAsync/ContinueAsync) and the same run environment variables
+// (reuses ClaudeProcess's MCP_TOOL_TIMEOUT). Exe/Args reuse WindowsTerminalLauncher's
+// --resume argument construction. Guards mirror WorkerHub.ResumeTaskInTerminal, except a
+// never-run task (no persisted SessionId) is not an error here -- it's a fresh-start spec.
+//
+// The run-scoped "claudedo_run" MCP server (AskUser/SuggestImprovement) that TaskRunner
+// wires per headless run is intentionally NOT reused: it exists so an unattended run can
+// ask the user a question, which is moot when the user is already driving the session by
+// hand. The always-on `mcp__claudedo__*` tools remain available via the globally-registered
+// MCP server (installer's RegisterMcpStep), exactly as they already are for a plain
+// `--resume` pickup in a Windows Terminal window.
+public sealed class InteractiveLaunchSpecService : IInteractiveLaunchSpecService
+{
+    private readonly IDbContextFactory<ClaudeDoDbContext> _dbFactory;
+    private readonly ISessionSkillSeeder _skillSeeder;
+    private readonly ISessionSkillRegistry _skillRegistry;
+    private readonly string _claudePath;
+
+    public InteractiveLaunchSpecService(
+        IDbContextFactory<ClaudeDoDbContext> dbFactory,
+        ISessionSkillSeeder skillSeeder,
+        ISessionSkillRegistry skillRegistry,
+        WorkerConfig cfg)
+    {
+        _dbFactory = dbFactory;
+        _skillSeeder = skillSeeder;
+        _skillRegistry = skillRegistry;
+        _claudePath = cfg.ClaudeBin;
+    }
+
+    public async Task<LaunchSpec> BuildForTaskAsync(string taskId, CancellationToken ct)
+    {
+        await using var ctx = await _dbFactory.CreateDbContextAsync(ct);
+
+        var task = await new TaskRepository(ctx).GetByIdAsync(taskId, ct)
+            ?? throw new KeyNotFoundException();
+        if (task.Status is TaskStatus.Running or TaskStatus.Queued)
+            throw new InvalidOperationException("Can't open an interactive session for a running or queued task -- interrupt it first.");
+
+        var worktree = await new WorktreeRepository(ctx).GetByTaskIdAsync(taskId, ct);
+        if (worktree is null || worktree.State is not (WorktreeState.Active or WorktreeState.Kept))
+            throw new InvalidOperationException("This task has no active worktree to open a session in.");
+        if (!Directory.Exists(worktree.Path))
+            throw new InvalidOperationException("The task's worktree directory no longer exists.");
+
+        var listConfig = await new ListRepository(ctx).GetConfigAsync(task.ListId, ct);
+        var globalSettings = await new AppSettingsRepository(ctx).GetAsync(ct);
+        var run = await new TaskRunRepository(ctx).GetLatestByTaskIdAsync(taskId, ct);
+
+        var requestedSkills = TaskRunner.UnionSkillNames(task.SessionSkills, listConfig?.SessionSkills, globalSettings.SessionSkills);
+        var skillNames = await FilterToInstalledSkillsAsync(requestedSkills, ct);
+        await _skillSeeder.SeedAsync(worktree.Path, skillNames, isWorktree: true, ct);
+
+        var resolvedClaude = WindowsTerminalLauncher.Resolve(_claudePath)
+            ?? throw new InvalidOperationException($"claude executable not found: {_claudePath}");
+
+        var args = run?.SessionId is { Length: > 0 } sessionId
+            ? WindowsTerminalLauncher.BuildResumeArgs(sessionId)
+            : Array.Empty<string>();
+
+        // Same run environment variable ClaudeProcess sets for every headless run: the
+        // AskUser MCP tool call caps at 60s unless raised, and lifting it is harmless for
+        // every other tool.
+        var env = new Dictionary<string, string>
+        {
+            ["MCP_TOOL_TIMEOUT"] = "200000",
+        };
+
+        return new LaunchSpec(worktree.Path, resolvedClaude, args, env);
+    }
+
+    private async Task<IReadOnlyList<string>> FilterToInstalledSkillsAsync(IReadOnlyList<string> requested, CancellationToken ct)
+    {
+        if (requested.Count == 0) return requested;
+
+        var installed = (await _skillRegistry.ListAsync(ct))
+            .Select(s => s.Name)
+            .ToHashSet(StringComparer.Ordinal);
+        return requested.Where(installed.Contains).ToList();
+    }
+}
diff --git a/src/ClaudeDo.Worker/Runner/Interfaces/IInteractiveLaunchSpecService.cs b/src/ClaudeDo.Worker/Runner/Interfaces/IInteractiveLaunchSpecService.cs
new file mode 100644
index 00000000..b0fdc230
--- /dev/null
+++ b/src/ClaudeDo.Worker/Runner/Interfaces/IInteractiveLaunchSpecService.cs
@@ -0,0 +1,10 @@
+namespace ClaudeDo.Worker.Runner;
+
+public interface IInteractiveLaunchSpecService
+{
+    /// <summary>Builds a LaunchSpec for opening an interactive session in an existing task's
+    /// worktree. Throws KeyNotFoundException if the task doesn't exist, InvalidOperationException
+    /// if it's Running/Queued or has no usable worktree. A task that has never run (no persisted
+    /// SessionId) is not an error -- the spec omits --resume for a fresh start.</summary>
+    Task<LaunchSpec> BuildForTaskAsync(string taskId, CancellationToken ct);
+}
diff --git a/src/ClaudeDo.Worker/Runner/LaunchSpec.cs b/src/ClaudeDo.Worker/Runner/LaunchSpec.cs
new file mode 100644
index 00000000..171dd387
--- /dev/null
+++ b/src/ClaudeDo.Worker/Runner/LaunchSpec.cs
@@ -0,0 +1,10 @@
+namespace ClaudeDo.Worker.Runner;
+
+// What an embedded ConPTY terminal (UI process) needs to start a real `claude` process for
+// a task's worktree, with the same setup as an autonomous run (session-skills seeded onto
+// disk, the same run environment variables) plus the --resume-vs-fresh-start choice.
+public sealed record LaunchSpec(
+    string Cwd,
+    string Exe,
+    IReadOnlyList<string> Args,
+    IReadOnlyDictionary<string, string> Env);
diff --git a/tests/ClaudeDo.Ui.Tests/StubWorkerClient.cs b/tests/ClaudeDo.Ui.Tests/StubWorkerClient.cs
index 801cf393..1dea0ecc 100644
--- a/tests/ClaudeDo.Ui.Tests/StubWorkerClient.cs
+++ b/tests/ClaudeDo.Ui.Tests/StubWorkerClient.cs
@@ -105,6 +105,8 @@ public abstract class StubWorkerClient : IWorkerClient
     public virtual Task StartPlanningSessionAsync(string taskId, CancellationToken ct = default) => Task.CompletedTask;
     public virtual Task OpenInteractiveTerminalAsync(string taskId, CancellationToken ct = default) => Task.CompletedTask;
     public virtual Task ResumeTaskInTerminalAsync(string taskId, CancellationToken ct = default) => Task.CompletedTask;
+    public virtual Task<LaunchSpec> GetInteractiveLaunchSpecAsync(string taskId, CancellationToken ct = default)
+        => Task.FromResult(new LaunchSpec(".", "claude", Array.Empty<string>(), new Dictionary<string, string>()));
     public virtual Task ResumePlanningSessionAsync(string taskId, CancellationToken ct = default) => Task.CompletedTask;
     public virtual Task<DiscardPlanningOutcome> DiscardPlanningSessionAsync(string taskId, bool dequeueQueuedChildren = false, CancellationToken ct = default)
         => Task.FromResult(new DiscardPlanningOutcome(DiscardPlanningResult.Discarded, 0, 0));
diff --git a/tests/ClaudeDo.Worker.Tests/Runner/InteractiveLaunchSpecServiceTests.cs b/tests/ClaudeDo.Worker.Tests/Runner/InteractiveLaunchSpecServiceTests.cs
new file mode 100644
index 00000000..3f97a005
--- /dev/null
+++ b/tests/ClaudeDo.Worker.Tests/Runner/InteractiveLaunchSpecServiceTests.cs
@@ -0,0 +1,252 @@
+using ClaudeDo.Data.Models;
+using ClaudeDo.Data.Repositories;
+using ClaudeDo.Worker.Config;
+using ClaudeDo.Worker.Runner;
+using ClaudeDo.Worker.Skills;
+using ClaudeDo.Worker.Tests.Infrastructure;
+using TaskStatus = ClaudeDo.Data.Models.TaskStatus;
+
+namespace ClaudeDo.Worker.Tests.Runner;
+
+/// Verifies InteractiveLaunchSpecService's guards mirror WorkerHub.ResumeTaskInTerminal
+/// (Running/Queued rejected, missing/invalid worktree rejected) and that it reuses the
+/// autonomous-run worktree prep: session-skills seeding via ISessionSkillSeeder, and
+/// produces --resume for a resumable task vs. a fresh-start spec for a never-run task.
+/// Never spawns the real claude CLI: ClaudeBin points at a stub file on disk.
+public sealed class InteractiveLaunchSpecServiceTests : IDisposable
+{
+    private readonly DbFixture _db = new();
+    private readonly string _tempDir;
+    private readonly string _worktreeDir;
+    private readonly string _claudeStubPath;
+    private readonly FakeSessionSkillSeeder _seeder = new();
+    private readonly FakeSessionSkillRegistry _registry = new();
+
+    public InteractiveLaunchSpecServiceTests()
+    {
+        _tempDir = Path.Combine(Path.GetTempPath(), $"cd_ilss_{Guid.NewGuid():N}");
+        Directory.CreateDirectory(_tempDir);
+
+        _worktreeDir = Path.Combine(_tempDir, "worktree");
+        Directory.CreateDirectory(_worktreeDir);
+
+        _claudeStubPath = Path.Combine(_tempDir, "claude.exe");
+        File.WriteAllText(_claudeStubPath, "stub");
+    }
+
+    public void Dispose()
+    {
+        _db.Dispose();
+        try { Directory.Delete(_tempDir, true); } catch { /* best effort */ }
+    }
+
+    private sealed class FakeSessionSkillRegistry : ISessionSkillRegistry
+    {
+        public List<SessionSkillEntity> Installed { get; } = new();
+
+        public Task<IReadOnlyList<string>> InstallAsync(string url, CancellationToken ct) => throw new NotImplementedException();
+        public Task UpdateAsync(string sourceUrl, CancellationToken ct) => throw new NotImplementedException();
+        public Task RemoveAsync(string sourceUrl, CancellationToken ct) => throw new NotImplementedException();
+        public Task<IReadOnlyList<SessionSkillEntity>> ListAsync(CancellationToken ct)
+            => Task.FromResult<IReadOnlyList<SessionSkillEntity>>(Installed);
+    }
+
+    private InteractiveLaunchSpecService BuildService() =>
+        new(_db.CreateFactory(), _seeder, _registry, new WorkerConfig { ClaudeBin = _claudeStubPath });
+
+    private async Task<string> SeedListAsync()
+    {
+        var listId = Guid.NewGuid().ToString();
+        using var ctx = _db.CreateContext();
+        await new ListRepository(ctx).AddAsync(new ListEntity
+        {
+            Id = listId, Name = "L", WorkingDir = _tempDir, CreatedAt = DateTime.UtcNow,
+        });
+        return listId;
+    }
+
+    private async Task SeedTaskAsync(string taskId, string listId, TaskStatus status, string? sessionSkillsJson = null)
+    {
+        using var ctx = _db.CreateContext();
+        await new TaskRepository(ctx).AddAsync(new TaskEntity
+        {
+            Id = taskId, ListId = listId, Title = "T", Status = status,
+            CreatedAt = DateTime.UtcNow, SessionSkills = sessionSkillsJson,
+        });
+    }
+
+    private async Task SeedWorktreeAsync(string taskId, WorktreeState state, string? path = null)
+    {
+        using var ctx = _db.CreateContext();
+        ctx.Worktrees.Add(new WorktreeEntity
+        {
+            TaskId = taskId, Path = path ?? _worktreeDir, BranchName = "claudedo/x",
+            BaseCommit = "abc123", State = state, CreatedAt = DateTime.UtcNow,
+        });
+        await ctx.SaveChangesAsync();
+    }
+
+    private async Task SeedRunAsync(string taskId, string? sessionId)
+    {
+        using var ctx = _db.CreateContext();
+        await new TaskRunRepository(ctx).AddAsync(new TaskRunEntity
+        {
+            Id = Guid.NewGuid().ToString(), TaskId = taskId, RunNumber = 1, IsRetry = false,
+            Prompt = "p", SessionId = sessionId,
+            StartedAt = DateTime.UtcNow.AddMinutes(-5), FinishedAt = DateTime.UtcNow.AddMinutes(-1),
+            ExitCode = 0, ResultMarkdown = "ok",
+        });
+    }
+
+    [Fact]
+    public async Task BuildForTaskAsync_TaskNotFound_ThrowsKeyNotFound()
+    {
+        var svc = BuildService();
+        await Assert.ThrowsAsync<KeyNotFoundException>(
+            () => svc.BuildForTaskAsync(Guid.NewGuid().ToString(), CancellationToken.None));
+    }
+
+    [Theory]
+    [InlineData(TaskStatus.Running)]
+    [InlineData(TaskStatus.Queued)]
+    public async Task BuildForTaskAsync_TaskRunningOrQueued_ThrowsInvalidOperation(TaskStatus status)
+    {
+        var listId = await SeedListAsync();
+        var taskId = Guid.NewGuid().ToString();
+        await SeedTaskAsync(taskId, listId, status);
+        await SeedWorktreeAsync(taskId, WorktreeState.Active);
+
+        var svc = BuildService();
+        await Assert.ThrowsAsync<InvalidOperationException>(
+            () => svc.BuildForTaskAsync(taskId, CancellationToken.None));
+    }
+
+    [Fact]
+    public async Task BuildForTaskAsync_NoWorktreeRow_ThrowsInvalidOperation()
+    {
+        var listId = await SeedListAsync();
+        var taskId = Guid.NewGuid().ToString();
+        await SeedTaskAsync(taskId, listId, TaskStatus.Idle);
+
+        var svc = BuildService();
+        await Assert.ThrowsAsync<InvalidOperationException>(
+            () => svc.BuildForTaskAsync(taskId, CancellationToken.None));
+    }
+
+    [Theory]
+    [InlineData(WorktreeState.Merged)]
+    [InlineData(WorktreeState.Discarded)]
+    public async Task BuildForTaskAsync_WorktreeNotActiveOrKept_ThrowsInvalidOperation(WorktreeState state)
+    {
+        var listId = await SeedListAsync();
+        var taskId = Guid.NewGuid().ToString();
+        await SeedTaskAsync(taskId, listId, TaskStatus.Idle);
+        await SeedWorktreeAsync(taskId, state);
+
+        var svc = BuildService();
+        await Assert.ThrowsAsync<InvalidOperationException>(
+            () => svc.BuildForTaskAsync(taskId, CancellationToken.None));
+    }
+
+    [Fact]
+    public async Task BuildForTaskAsync_WorktreeDirectoryMissing_ThrowsInvalidOperation()
+    {
+        var listId = await SeedListAsync();
+        var taskId = Guid.NewGuid().ToString();
+        await SeedTaskAsync(taskId, listId, TaskStatus.Idle);
+        await SeedWorktreeAsync(taskId, WorktreeState.Active, path: Path.Combine(_tempDir, "does-not-exist"));
+
+        var svc = BuildService();
+        await Assert.ThrowsAsync<InvalidOperationException>(
+            () => svc.BuildForTaskAsync(taskId, CancellationToken.None));
+    }
+
+    [Fact]
+    public async Task BuildForTaskAsync_ResumableTask_ProducesResumeArgsAndCwd()
+    {
+        var listId = await SeedListAsync();
+        var taskId = Guid.NewGuid().ToString();
+        await SeedTaskAsync(taskId, listId, TaskStatus.Idle);
+        await SeedWorktreeAsync(taskId, WorktreeState.Active);
+        await SeedRunAsync(taskId, "sess-123");
+
+        var svc = BuildService();
+        var spec = await svc.BuildForTaskAsync(taskId, CancellationToken.None);
+
+        Assert.Equal(_worktreeDir, spec.Cwd);
+        Assert.Equal(_claudeStubPath, spec.Exe);
+        Assert.Equal(new[] { "--resume", "sess-123" }, spec.Args);
+        Assert.Equal("200000", spec.Env["MCP_TOOL_TIMEOUT"]);
+    }
+
+    [Fact]
+    public async Task BuildForTaskAsync_KeptWorktree_IsAllowed()
+    {
+        var listId = await SeedListAsync();
+        var taskId = Guid.NewGuid().ToString();
+        await SeedTaskAsync(taskId, listId, TaskStatus.Idle);
+        await SeedWorktreeAsync(taskId, WorktreeState.Kept);
+        await SeedRunAsync(taskId, "sess-kept");
+
+        var svc = BuildService();
+        var spec = await svc.BuildForTaskAsync(taskId, CancellationToken.None);
+
+        Assert.Equal(new[] { "--resume", "sess-kept" }, spec.Args);
+    }
+
+    [Fact]
+    public async Task BuildForTaskAsync_NeverRunTask_ProducesFreshStartSpec_NoResumeArg()
+    {
+        var listId = await SeedListAsync();
+        var taskId = Guid.NewGuid().ToString();
+        await SeedTaskAsync(taskId, listId, TaskStatus.Idle);
+        await SeedWorktreeAsync(taskId, WorktreeState.Active);
+        // No TaskRunEntity at all -- never run.
+
+        var svc = BuildService();
+        var spec = await svc.BuildForTaskAsync(taskId, CancellationToken.None);
+
+        Assert.Empty(spec.Args);
+        Assert.Equal(_worktreeDir, spec.Cwd);
+    }
+
+    [Fact]
+    public async Task BuildForTaskAsync_RunWithoutSessionId_ProducesFreshStartSpec()
+    {
+        var listId = await SeedListAsync();
+        var taskId = Guid.NewGuid().ToString();
+        await SeedTaskAsync(taskId, listId, TaskStatus.Idle);
+        await SeedWorktreeAsync(taskId, WorktreeState.Active);
+        await SeedRunAsync(taskId, sessionId: null);
+
+        var svc = BuildService();
+        var spec = await svc.BuildForTaskAsync(taskId, CancellationToken.None);
+
+        Assert.Empty(spec.Args);
+    }
+
+    [Fact]
+    public async Task BuildForTaskAsync_SeedsSessionSkills_FilteredToInstalled()
+    {
+        _registry.Installed.Add(new SessionSkillEntity
+        {
+            Name = "installed-skill", SourceUrl = "https://example.com/x.git",
+            PinnedRef = "abc", Subpath = "skills/installed-skill", Description = "d",
+            AddedAt = DateTimeOffset.UtcNow,
+        });
+
+        var listId = await SeedListAsync();
+        var taskId = Guid.NewGuid().ToString();
+        await SeedTaskAsync(taskId, listId, TaskStatus.Idle,
+            sessionSkillsJson: "[\"installed-skill\",\"missing-skill\"]");
+        await SeedWorktreeAsync(taskId, WorktreeState.Active);
+
+        var svc = BuildService();
+        await svc.BuildForTaskAsync(taskId, CancellationToken.None);
+
+        var call = Assert.Single(_seeder.Calls);
+        Assert.Equal(_worktreeDir, call.WorkingDir);
+        Assert.True(call.IsWorktree);
+        Assert.Equal(new[] { "installed-skill" }, call.SkillNames);
+    }
+}
diff --git a/tests/ClaudeDo.Worker.Tests/UiVm/TasksIslandViewModelPlanningTests.cs b/tests/ClaudeDo.Worker.Tests/UiVm/TasksIslandViewModelPlanningTests.cs
index a15e275f..c839c3b4 100644
--- a/tests/ClaudeDo.Worker.Tests/UiVm/TasksIslandViewModelPlanningTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/UiVm/TasksIslandViewModelPlanningTests.cs
@@ -77,6 +77,8 @@ sealed class FakeWorkerClient : IWorkerClient
     public int PickUpInTerminalCalls { get; private set; }
     public string? LastPickUpTaskId { get; private set; }
     public Task ResumeTaskInTerminalAsync(string taskId, CancellationToken ct = default) { PickUpInTerminalCalls++; LastPickUpTaskId = taskId; return Task.CompletedTask; }
+    public Task<LaunchSpec> GetInteractiveLaunchSpecAsync(string taskId, CancellationToken ct = default)
+        => Task.FromResult(new LaunchSpec(".", "claude", Array.Empty<string>(), new Dictionary<string, string>()));
     public Task QueuePlanningSubtasksAsync(string parentTaskId, CancellationToken ct = default) => Task.CompletedTask;
     public Task ResumePlanningSessionAsync(string taskId, CancellationToken ct = default) { ResumePlanningCalls++; return Task.CompletedTask; }
     public Task<DiscardPlanningOutcome> DiscardPlanningSessionAsync(string taskId, bool dequeueQueuedChildren = false, CancellationToken ct = default)