feat: Add multi-session support to workflow system

- Enable multiple active workflow sessions to coexist
- Add session detection logic for multiple .active-* markers
- Update execute command to prompt user selection when multiple sessions found
- Update plan command with multi-session awareness
- Maintain session isolation while allowing parallel workflow instances

🤖 Generated with [Claude Code](https://claude.ai/code)

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

.claude/commands/workflow/execute.md

@@ -31,11 +31,13 @@ Coordinates agents for executing workflow tasks through automatic discovery and
 
 ### 1. Discovery Phase
 ```
-├── Locate workflow folder (current session)
-├── Load workflow-session.json and IMPL_PLAN.md
-├── Scan .task/ directory for task JSON files
-├── Analyze task statuses and dependencies
-└── Build execution queue of ready tasks
+├── Check for .active-* markers in .workflow/
+├── If multiple active sessions found → Prompt user to select
+├── Locate selected session's workflow folder
+├── Load selected session's workflow-session.json and IMPL_PLAN.md
+├── Scan selected session's .task/ directory for task JSON files
+├── Analyze task statuses and dependencies for selected session only
+└── Build execution queue of ready tasks from selected session
 ```
 
 ### 2. TodoWrite Coordination

.claude/commands/workflow/plan.md

@@ -89,10 +89,12 @@ examples:
 4. **Quantity prediction**: Estimate main tasks, subtasks, container vs leaf ratio
 
 ### Session Management ⚠️ CRITICAL
-- **⚡ FIRST ACTION**: Always check for `.workflow/.active-*` marker before any planning
+- **⚡ FIRST ACTION**: Check for all `.workflow/.active-*` markers before any planning
+- **Multiple sessions support**: Different Claude instances can have different active sessions
+- **User selection**: If multiple active sessions found, prompt user to select which one to work with
 - **Auto-session creation**: `WFS-[topic-slug]` only if no active session exists
-- **Session continuity**: MUST use existing active session to maintain context
-- **⚠️ Dependency context**: MUST read ALL previous task summary documents before planning
+- **Session continuity**: MUST use selected active session to maintain context
+- **⚠️ Dependency context**: MUST read ALL previous task summary documents from selected session before planning
 - **Session isolation**: Each session maintains independent context and state
 
 ### Project Structure Analysis & Engineering Enhancement

.claude/workflows/workflow-architecture.md

@@ -43,12 +43,23 @@ This document defines the complete workflow system architecture using a **JSON-o
 
 ### Session Operations
 
-#### Detect Active Session
+#### Detect Active Session(s)
 ```bash
-active_session=$(find .workflow -name ".active-*" | head -1)
-if [ -n "$active_session" ]; then
-  session_name=$(basename "$active_session" | sed 's/^\.active-//')
+active_sessions=$(find .workflow -name ".active-*" 2>/dev/null)
+count=$(echo "$active_sessions" | wc -l)
+
+if [ -z "$active_sessions" ]; then
+  echo "No active session"
+elif [ "$count" -eq 1 ]; then
+  session_name=$(basename "$active_sessions" | sed 's/^\.active-//')
   echo "Active session: $session_name"
+else
+  echo "Multiple active sessions found:"
+  echo "$active_sessions" | while read marker; do
+    session=$(basename "$marker" | sed 's/^\.active-//')
+    echo "  - $session"
+  done
+  echo "Please specify which session to work with"
 fi
 ```