fix: resolve sub-agent spawning limitation in /spec-flow Phase 4

Phase 4 now calls /implement directly instead of using implement-phase-agent.
Sub-agents cannot spawn other sub-agents, and /implement needs to spawn
parallel worker agents (backend-dev, frontend-shipper, etc.).

Changes:
- Updated .claude/commands/spec-flow.md to call /implement directly
- Updated architecture documentation in README.md
- Added v1.5.1 entry to CHANGELOG.md
- Bumped version to 1.5.1 in package.json

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

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

Author: marcusgoll

.claude/commands/spec-flow.md

@@ -9,7 +9,8 @@ Orchestrate feature delivery through isolated phase agents for maximum efficienc
 **Architecture**: Orchestrator-Workers with Phase Isolation
 - **Orchestrator** (`/spec-flow`): Lightweight state tracking, phase progression
 - **Phase Agents**: Isolated contexts, call slash commands, return summaries
-- **Worker Agents**: Called by implement-phase-agent (backend-dev, frontend-shipper, etc.)
+- **Implementation**: `/implement` called directly (spawns worker agents: backend-dev, frontend-shipper, etc.)
+  - Note: Phase 4 bypasses phase agent due to sub-agent spawning limits
 
 **Benefits**:
 - 67% token reduction (240k → 80k per feature)
@@ -263,31 +264,64 @@ Refer to your agent brief for full instructions.
 
 ### Phase 4: Implementation (EXECUTION)
 
-**Invoke phase agent:**
-
-```
-Task(
-  subagent_type="implement-phase-agent",
-  description="Phase 4: Execute Implementation",
-  prompt=f"""
-Execute Phase 4: Implementation in isolated context.
-
-Feature Slug: {SLUG}
-Previous Phase Summary: {TASKS_SUMMARY}
-
-Your task:
-1. Call /implement slash command (handles parallel worker agents internally)
-2. Extract implementation statistics
-3. Return structured JSON summary
+**Call /implement directly (cannot use phase agent due to sub-agent spawning limits):**
 
-Refer to your agent brief for full instructions.
-  """
-)
+```bash
+# Update state (start phase 4)
+# Set current_phase = 4, status = "in_progress", record start timestamp
 
-# Check for incomplete tasks (block if found)
-# Validate, store summary, log progress with stats
+# Execute /implement slash command directly
+# This command spawns parallel worker agents internally
+# Cannot use implement-phase-agent because sub-agents can't spawn sub-agents
+echo "⏳ Phase 4: Implementation"
+echo ""
 ```
 
+**Execute in sequence:**
+
+1. **Run /implement command:**
+   - INVOKE: `/implement` (use SlashCommand tool)
+   - WAIT: For completion
+   - NOTE: This command handles parallel worker agents (backend-dev, frontend-shipper, etc.)
+   - VERIFY: All tasks completed
+
+2. **Extract implementation statistics:**
+   ```bash
+   FEATURE_DIR="specs/$SLUG"
+   NOTES_FILE="$FEATURE_DIR/NOTES.md"
+   TASKS_FILE="$FEATURE_DIR/tasks.md"
+   ERROR_LOG="$FEATURE_DIR/error-log.md"
+
+   # Count completed tasks
+   COMPLETED_COUNT=$(grep -c "^✅ T[0-9]\{3\}" "$NOTES_FILE" || echo "0")
+   TOTAL_TASKS=$(grep -c "^T[0-9]\{3\}" "$TASKS_FILE" || echo "0")
+
+   # Get files changed
+   FILES_CHANGED=$(git diff --name-only main | wc -l)
+
+   # Check for errors
+   ERROR_COUNT=$(grep -c "❌\|⚠️" "$ERROR_LOG" 2>/dev/null || echo "0")
+   ```
+
+3. **Create phase summary:**
+   - Build summary: "Implemented {COMPLETED_COUNT}/{TOTAL_TASKS} tasks. Changed {FILES_CHANGED} files."
+   - Extract key decisions from NOTES.md
+   - Store in workflow-state.json phase_summaries
+
+4. **Check for blockers:**
+   - IF COMPLETED_COUNT < TOTAL_TASKS:
+     - LOG: "❌ Implementation incomplete: {COMPLETED_COUNT}/{TOTAL_TASKS} tasks completed"
+     - LOG: "Review: {ERROR_LOG}"
+     - PAUSE: Exit workflow, return control to user
+   - ELSE:
+     - LOG: "✅ Implementation complete ({COMPLETED_COUNT}/{TOTAL_TASKS} tasks)"
+     - CONTINUE to Phase 5 (no user input needed)
+
+5. **Update state (complete phase 4):**
+   - Add 4 to phases_completed
+   - Record end timestamp
+   - Update last_updated
+
 ### Phase 5: Optimization (QUALITY)
 
 **Invoke phase agent:**

CHANGELOG.md

@@ -5,6 +5,17 @@ All notable changes to the Spec-Flow Workflow Kit will be documented here.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [1.5.1] - 2025-10-08
+
+### Fixed
+
+**Phase 4 Implementation Architecture:**
+- Fixed sub-agent spawning limitation in `/spec-flow` workflow
+- Phase 4 now calls `/implement` slash command directly instead of using `implement-phase-agent`
+- Reason: Sub-agents cannot spawn other sub-agents, and `/implement` needs to spawn parallel worker agents (backend-dev, frontend-shipper, etc.)
+- Updated documentation in `spec-flow.md`, `README.md`, and architecture diagrams
+- Note: `implement-phase-agent.md` remains in codebase for reference but is bypassed in the workflow
+
 ## [1.5.0] - 2025-10-08
 
 ### Added - Phase Agent Architecture & Performance Optimizations
@@ -72,6 +83,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - New `spec-flow.md` is now the optimized orchestrator
 - `/flow` remains unchanged as backup
 
+**Phase 4 Implementation Architecture:**
+- Phase 4 now calls `/implement` directly instead of using `implement-phase-agent`
+- Reason: Sub-agents cannot spawn other sub-agents, and `/implement` needs to spawn parallel worker agents
+- Note: `implement-phase-agent.md` remains in codebase but is bypassed in actual workflow
+
 **Parallel Execution:**
 - Enhanced `/implement` to use parallel agent execution via batch processing
 - Tasks grouped by domain (backend/frontend/database/tests)

README.md

@@ -128,8 +128,10 @@ Spec-Flow now features an **optimized orchestrator** (`/spec-flow`) that runs ea
   ├→ spec-phase-agent → /specify → Returns summary
   ├→ plan-phase-agent → /plan → Returns summary
   ├→ tasks-phase-agent → /tasks → Returns summary
-  ├→ implement-phase-agent → /implement → Returns summary
+  ├→ /implement → Spawns worker agents directly (bypasses phase agent*)
   └→ ... (each phase isolated, efficient handoffs)
+
+  * Phase 4 calls /implement directly due to sub-agent spawning limits
 ```
 
 **Choose your workflow:**

package.json

@@ -1,6 +1,6 @@
 {
   "name": "spec-flow",
-  "version": "1.5.0",
+  "version": "1.5.1",
   "description": "Spec-Driven Development workflow toolkit for Claude Code - Build high-quality features faster with repeatable AI workflows",
   "keywords": [
     "claude",