diff --git a/src/ClaudeDo.Worker/Planning/PlanningSessionManager.cs b/src/ClaudeDo.Worker/Planning/PlanningSessionManager.cs
index 6dc58649..9e8358b6 100644
--- a/src/ClaudeDo.Worker/Planning/PlanningSessionManager.cs
+++ b/src/ClaudeDo.Worker/Planning/PlanningSessionManager.cs
@@ -22,6 +22,7 @@ public sealed class PlanningSessionManager
     private readonly GitService _git;
     private readonly WorkerConfig _cfg;
     private readonly string _rootDirectory;
+    private readonly string _projectsRoot;
     private readonly ITaskStateService? _state;
     private readonly PlanningChainCoordinator? _chain;
 
@@ -32,7 +33,8 @@ public sealed class PlanningSessionManager
         WorkerConfig cfg,
         ITaskStateService state,
         PlanningChainCoordinator chain,
-        string rootDirectory)
+        string rootDirectory,
+        string? projectsRoot = null)
     {
         _factory = factory;
         _git = git;
@@ -40,6 +42,7 @@ public sealed class PlanningSessionManager
         _state = state;
         _chain = chain;
         _rootDirectory = rootDirectory;
+        _projectsRoot = projectsRoot ?? Paths.Expand("~/.claude/projects");
     }
 
     // Test constructor.
@@ -51,7 +54,8 @@ public sealed class PlanningSessionManager
         WorkerConfig cfg,
         string rootDirectory,
         ITaskStateService? state = null,
-        PlanningChainCoordinator? chain = null)
+        PlanningChainCoordinator? chain = null,
+        string? projectsRoot = null)
     {
         _tasksOverride = tasks;
         _listsOverride = lists;
@@ -61,6 +65,7 @@ public sealed class PlanningSessionManager
         _state = state;
         _chain = chain;
         _rootDirectory = rootDirectory;
+        _projectsRoot = projectsRoot ?? Paths.Expand("~/.claude/projects");
     }
 
     private (TaskRepository tasks, ListRepository lists, AppSettingsRepository settings, ClaudeDoDbContext? ctx) CreateRepos()
@@ -235,8 +240,6 @@ public sealed class PlanningSessionManager
         if (task.PlanningPhase != PlanningPhase.Active)
             throw new InvalidOperationException(
                 $"Task planning phase is {task.PlanningPhase}; resume requires Active planning.");
-        if (string.IsNullOrEmpty(task.PlanningSessionId))
-            throw new InvalidOperationException("No Claude session ID captured yet; cannot resume.");
 
         var sessionDir = Path.Combine(_rootDirectory, taskId);
         if (!Directory.Exists(sessionDir))
@@ -252,12 +255,26 @@ public sealed class PlanningSessionManager
         if (!Directory.Exists(worktreePath))
             throw new InvalidOperationException($"Planning worktree missing — cannot resume: {worktreePath}");
 
+        // The planning session runs in an interactive TUI, which never reports its session id
+        // back to us — so nothing ever wrote planning_session_id. Recover it from the transcript
+        // Claude Code leaves on disk for the planning worktree, and persist it so the next
+        // resume is a plain DB read.
+        var sessionId = task.PlanningSessionId;
+        if (string.IsNullOrEmpty(sessionId))
+        {
+            sessionId = PlanningTranscriptLocator.FindSessionId(worktreePath, _projectsRoot)
+                ?? throw new InvalidOperationException(
+                    "No Claude session transcript found for this planning worktree; cannot resume. " +
+                    "Finalize or discard the planning session instead.");
+            await tasks.UpdatePlanningSessionIdAsync(taskId, sessionId, ct);
+        }
+
         var token = await ReadTokenFileAsync(TokenFilePathFor(sessionDir), ct);
 
         return new PlanningSessionResumeContext(
             ParentTaskId: taskId,
             WorkingDir: worktreePath,
-            ClaudeSessionId: task.PlanningSessionId,
+            ClaudeSessionId: sessionId,
             Token: token,
             WorktreePath: worktreePath);
     }
@@ -387,4 +404,40 @@ public sealed class PlanningSessionManager
             throw new InvalidOperationException($"Token file missing: {path}");
         return (await File.ReadAllTextAsync(path, ct)).Trim();
     }
+}
+
+/// <summary>
+/// Recovers the Claude session id of an interactive session from the transcript Claude Code
+/// writes to <c>~/.claude/projects/&lt;encoded cwd&gt;/&lt;sessionId&gt;.jsonl</c>. A planning
+/// worktree is used by exactly one session, so the newest transcript in that folder is it.
+/// </summary>
+/// <remarks>
+/// The folder-name encoding is undocumented CLI behaviour (every non-alphanumeric character in
+/// the absolute path becomes '-'). If it ever changes, <see cref="FindSessionId"/> returns null
+/// and the caller reports "cannot resume" instead of resuming the wrong session.
+/// </remarks>
+public static class PlanningTranscriptLocator
+{
+    public static string? FindSessionId(string worktreePath, string projectsRoot)
+    {
+        var dir = Path.Combine(projectsRoot, EncodeCwd(worktreePath));
+        if (!Directory.Exists(dir)) return null;
+
+        var newest = new DirectoryInfo(dir)
+            .EnumerateFiles("*.jsonl")
+            .OrderByDescending(f => f.LastWriteTimeUtc)
+            .FirstOrDefault();
+
+        return newest is null ? null : Path.GetFileNameWithoutExtension(newest.Name);
+    }
+
+    private static string EncodeCwd(string path)
+    {
+        var full = Path.GetFullPath(path);
+        return string.Create(full.Length, full, static (span, src) =>
+        {
+            for (var i = 0; i < src.Length; i++)
+                span[i] = char.IsAsciiLetterOrDigit(src[i]) ? src[i] : '-';
+        });
+    }
 }
\ No newline at end of file
diff --git a/tests/ClaudeDo.Worker.Tests/Planning/PlanningSessionManagerTests.cs b/tests/ClaudeDo.Worker.Tests/Planning/PlanningSessionManagerTests.cs
index 6fcb7162..1e273113 100644
--- a/tests/ClaudeDo.Worker.Tests/Planning/PlanningSessionManagerTests.cs
+++ b/tests/ClaudeDo.Worker.Tests/Planning/PlanningSessionManagerTests.cs
@@ -21,9 +21,11 @@ public sealed class PlanningSessionManagerTests : IDisposable
     private readonly AppSettingsRepository _settingsRepo;
     private readonly PlanningSessionManager _sut;
     private readonly TaskStateServiceBuilder.Built _built;
+    private readonly string _projectsRoot;
 
     public PlanningSessionManagerTests()
     {
+        _projectsRoot = Path.Combine(Path.GetTempPath(), $"cd_projects_{Guid.NewGuid():N}");
         _ctx = _db.CreateContext();
         _tasks = new TaskRepository(_ctx);
         _lists = new ListRepository(_ctx);
@@ -34,7 +36,8 @@ public sealed class PlanningSessionManagerTests : IDisposable
         _settingsRepo.UpdateAsync(new AppSettingsEntity { WorktreeStrategy = "sibling" }).GetAwaiter().GetResult();
         _built = TaskStateServiceBuilder.Build(_db.CreateFactory());
         _sut = new PlanningSessionManager(
-            _tasks, _lists, _settingsRepo, _git, _cfg, _rootDir, _built.State, _built.Chain);
+            _tasks, _lists, _settingsRepo, _git, _cfg, _rootDir, _built.State, _built.Chain,
+            _projectsRoot);
     }
 
     public void Dispose()
@@ -42,6 +45,20 @@ public sealed class PlanningSessionManagerTests : IDisposable
         _ctx.Dispose();
         _db.Dispose();
         try { Directory.Delete(_rootDir, recursive: true); } catch { /* ignore */ }
+        try { Directory.Delete(_projectsRoot, recursive: true); } catch { /* ignore */ }
+    }
+
+    // Mirrors what Claude Code writes: ~/.claude/projects/<cwd, every non-alphanumeric char
+    // replaced by '-'>/<sessionId>.jsonl
+    private void WriteTranscript(string cwd, string sessionId, DateTime lastWriteUtc)
+    {
+        var encoded = string.Concat(Path.GetFullPath(cwd)
+            .Select(c => char.IsAsciiLetterOrDigit(c) ? c : '-'));
+        var dir = Path.Combine(_projectsRoot, encoded);
+        Directory.CreateDirectory(dir);
+        var file = Path.Combine(dir, $"{sessionId}.jsonl");
+        File.WriteAllText(file, "{}\n");
+        File.SetLastWriteTimeUtc(file, lastWriteUtc);
     }
 
     private async Task<(string listId, string workingDir)> SeedListAsync()
@@ -165,17 +182,52 @@ public sealed class PlanningSessionManagerTests : IDisposable
     }
 
     [Fact]
-    public async Task ResumeAsync_NoClaudeSessionId_Throws()
+    public async Task ResumeAsync_NoSessionIdAndNoTranscript_Throws()
     {
         var (listId, _) = await SeedListAsync();
         var parent = await SeedManualTaskAsync(listId);
         await _sut.StartAsync(parent.Id, CancellationToken.None);
-        // UpdatePlanningSessionIdAsync not called
+        // Nothing persisted planning_session_id, and no transcript exists on disk.
 
         await Assert.ThrowsAsync<InvalidOperationException>(() =>
             _sut.ResumeAsync(parent.Id, CancellationToken.None));
     }
 
+    // The interactive TUI never reports its session id, so planning_session_id stays NULL.
+    // Resume has to recover it from the transcript Claude Code left for the planning worktree.
+    [Fact]
+    public async Task ResumeAsync_NoSessionId_RecoversNewestTranscriptAndPersistsIt()
+    {
+        var (listId, _) = await SeedListAsync();
+        var parent = await SeedManualTaskAsync(listId);
+        var startCtx = await _sut.StartAsync(parent.Id, CancellationToken.None);
+
+        WriteTranscript(startCtx.WorktreePath, "older-session", new DateTime(2026, 8, 1, 10, 0, 0, DateTimeKind.Utc));
+        WriteTranscript(startCtx.WorktreePath, "newest-session", new DateTime(2026, 8, 2, 10, 0, 0, DateTimeKind.Utc));
+
+        var resumeCtx = await _sut.ResumeAsync(parent.Id, CancellationToken.None);
+
+        Assert.Equal("newest-session", resumeCtx.ClaudeSessionId);
+        var reloaded = await _tasks.GetByIdAsync(parent.Id);
+        Assert.Equal("newest-session", reloaded!.PlanningSessionId);
+    }
+
+    // A transcript must never override an id we already captured.
+    [Fact]
+    public async Task ResumeAsync_ExistingSessionId_IgnoresTranscript()
+    {
+        var (listId, _) = await SeedListAsync();
+        var parent = await SeedManualTaskAsync(listId);
+        var startCtx = await _sut.StartAsync(parent.Id, CancellationToken.None);
+        await _tasks.UpdatePlanningSessionIdAsync(parent.Id, "persisted-session");
+
+        WriteTranscript(startCtx.WorktreePath, "transcript-session", new DateTime(2026, 8, 2, 10, 0, 0, DateTimeKind.Utc));
+
+        var resumeCtx = await _sut.ResumeAsync(parent.Id, CancellationToken.None);
+
+        Assert.Equal("persisted-session", resumeCtx.ClaudeSessionId);
+    }
+
     [Fact]
     public async Task FinalizeAsync_PromotesDraftsAndMarksPlanningFinalized()
     {