fix(planning): recover the planning session id from the on-disk transcript

The interactive planning TUI never reports its claude session id back, so
planning_session_id stayed NULL and UpdatePlanningSessionIdAsync had no caller
at all -- ResumeAsync always threw "No Claude session ID captured yet".

Resume now looks the id up in the transcript Claude Code writes to
~/.claude/projects/<encoded cwd>/<sessionId>.jsonl for the planning worktree
(newest file wins; a worktree hosts exactly one session) and persists it, so
the next resume is a plain DB read. No transcript -> a clear "cannot resume"
instead of resuming the wrong session.

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] : '-';
+        });
+    }
 }