fix(worker): harden CLI injection, stuck-Running, chain wedge, and Fail guard

1. ArgumentList (fix injection): ClaudeArgsBuilder.Build() now returns
   IReadOnlyList<string>; ClaudeProcess populates ProcessStartInfo.ArgumentList
   instead of Arguments, so values like system prompts are never shell-split.
   DailyPrepPrompt, RefinePrompt, and WeekReportService migrated similarly.
   All IClaudeProcess fakes updated.

2. ContinueAsync exception guard: wrap RunOnceAsync in try/catch matching
   the RunAsync pattern so an unexpected exception never leaves the task
   stuck in Running status.

3. Planning chain cascade: OnChildFinishedAsync now calls CancelAsync on
   the immediate blocked successor when a child fails or is cancelled,
   triggering a recursive cascade that clears the entire remaining chain
   instead of leaving it wedged.

4. FailAsync guard: restrict valid source states to Running and Queued;
   WaitingForReview -> Failed is now rejected, preventing an invalid
   transition that could corrupt the review workflow.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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;
     }
 }