feat: Shepherd hooks for subagent orchestration

[dean0x]

Summary

Implement Claude Code hooks to monitor and orchestrate subagent completion. The "shepherd" pattern uses SubagentStop hooks to validate subagent work, enforce quality gates, and suggest follow-up actions.

Motivation

DevFlow spawns many subagents (Coder, Explore, Review-*, Synthesize). Currently there's no automatic validation that:

• Coder agents actually made changes
• Review agents provided thorough analysis (not rubber-stamp)
• Explore agents found actionable results
• Synthesize didn't lose critical findings

Hooks provide deterministic enforcement vs skills (AI-judged) or commands (user-invoked).

Technical Approach

SubagentStop Hook Mechanics

• Input: Minimal - session_id, transcript_path, cwd, stop_hook_active
• Output: {"decision": "approve"|"block", "reason": "...", "systemMessage": "..."}
• Subagent identification: Must parse transcript file (JSONL) to identify which agent completed
• Two types: command (fast, deterministic) or prompt (LLM-evaluated, context-aware)

Proposed Shepherd Patterns

Pattern 1: Post-Coder Review Gate

Block Coder completion for security-sensitive or large changes without review:

{
  "type": "prompt",
  "prompt": "If Coder agent completed code changes touching auth/crypto/keys OR >50 lines without tests: block and require SecurityReview"
}

Pattern 2: Review Quality Gate

Prevent shallow "looks good" reviews:

{
  "type": "prompt", 
  "prompt": "If Review agent completed: verify it analyzed actual files, provided file:line references, checked multiple concerns. Block if rubber-stamp."
}

Pattern 3: Explore Completeness

Ensure exploration returned useful results:

{
  "type": "prompt",
  "prompt": "If Explore agent completed: verify it found relevant files/patterns with concrete paths. Block if inconclusive."
}

Pattern 4: Chain Trigger (Non-blocking)

Suggest logical next steps without blocking:

{
  "type": "prompt",
  "prompt": "Analyze completed subagent. Approve but suggest next step in systemMessage: Coder→review, Explore→plan, Review→fix"
}

Implementation Options

Approach	Speed	Intelligence	Maintenance
type: "prompt"	Slow (API)	High	Low
type: "command"	Fast	Rules-based	Higher
Hybrid	Medium	Best of both	Medium

Proposed File Structure

.claude/
├── settings.json              # Hook configuration
└── hooks/
    ├── shepherd.py            # Main shepherd logic
    └── transcript-parser.py   # Utility for reading JSONL transcripts

Or ship hooks via DevFlow install to ~/.devflow/hooks/.

Acceptance Criteria

• Shepherd hook script that parses transcript to identify subagent type
• Configurable rules per subagent type (Coder, Review, Explore, Synthesize)
• Both blocking (quality gate) and non-blocking (suggest next) modes
• stop_hook_active check to prevent infinite loops
• Documentation in CLAUDE.md for hook patterns
• Optional: prompt-based hooks for intelligent evaluation

Open Questions

1. Ship hooks via devflow init or keep as opt-in configuration?
2. Default to command (fast) or prompt (smart) hooks?
3. How aggressive should blocking be? (strict vs suggestive)
4. Should hooks write to .docs/ for audit trail?

References

• Claude Code Hooks Guide
• SubagentStop receives: session_id, transcript_path, cwd, stop_hook_active, hook_event_name
• Transcript format: JSONL with type, role, content, id, timestamp per message

[dean0x]

Useful parts (goal-backward verification, artifact depth) extracted into #124 as Shepherd prompt enhancements. Hooks infrastructure deferred indefinitely — the Shepherd agent already provides LLM-judged validation in-pipeline.