Agent skill
adk-agent-handling
Google ADK (Agent Development Kit) multi-agent system architecture for BigQuery data analytics. Covers BigQuery agent vs conversational agent patterns, ADK Single Parent Rule, domain routing with sub-agents, agent selection mechanisms, SQL error recovery with ReflectAndRetryToolPlugin, transfer_to_agent workflows, and frontend-backend agent coordination. Use when working with Google ADK agents, multi-agent systems, BigQuery SQL automation, domain expert routing, agent orchestration, or implementing error recovery strategies in AI agent applications.
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SKILL.md
Google ADK Agent Handling
Purpose
Complete guide for architecting and managing Google ADK multi-agent systems in the ALYac Family data analytics platform. This skill covers the dual-orchestrator pattern (BigQuery vs Conversational agents), ADK framework constraints, domain-based routing, and production-ready error recovery strategies.
When to Use
Automatically activates when you mention:
- Google ADK (Agent Development Kit)
- Multi-agent architecture or agent orchestration
- BigQuery agent or conversational agent patterns
- Domain routing or agent selection logic
- ADK Single Parent Rule or sub-agents
- transfer_to_agent workflows
- ReflectAndRetryToolPlugin
- SQL error recovery or auto-retry mechanisms
- Agent coordination or delegation patterns
Manual activation: Ask about ADK agent architecture, agent selection mechanisms, or error recovery strategies.
System Architecture Overview
Dual-Orchestrator Pattern
This project uses TWO top-level orchestrator agents:
1. bigquery_agent (SQL-based orchestrator)
- File:
adk-backend/src/adk_backend/agents/base/bigquery_agent.py - Role: Domain routing + direct SQL execution
- Tools: BigQuery (list_templates, render_template, dry_run, execute)
- Sub-agents: 4 domain experts (has parent relationship)
- Use case: Explicit SQL control, template-based analysis
2. conversational_analytics_agent (AI-based orchestrator)
- File:
adk-backend/src/adk_backend/agents/base/conversational_analytics_agent.py - Role: Conversational AI analysis + Google Search
- Tools: ask_data_insights, search_catalog, google_search
- Sub-agents: None (tools only, follows ADK Single Parent Rule)
- Use case: Natural language queries, web-enhanced insights
Domain Expert Agents (Shared)
Both orchestrators delegate to these specialists:
- alyac_family_agent - Malware detection, phishing messages
- security_agent - Smishing, FCM security events, threat alerts
- marketing_agent - Campaigns, segmentation, conversion marketing
- conversion_agent - Subscription funnels, retention, SaaS metrics
Critical: Domain experts are sub_agents of bigquery_agent ONLY, following ADK's Single Parent Rule.
ADK Single Parent Rule
The Rule
Every agent can have ONLY ONE parent agent.
Violation example:
# ❌ WRONG - Two parents
bigquery_agent = Agent(sub_agents=[alyac_family_agent, ...])
conversational_agent = Agent(sub_agents=[alyac_family_agent, ...]) # ERROR!
Error: ValidationError: Agent 'alyac_family_analyst' already has a parent agent
Why This Rule Exists
- Context Propagation: Single path for conversation history flow
- Controlled Flow: Prevents circular delegation loops
- Debugging: Clear call hierarchy for tracing
- State Management: Unambiguous session state ownership
Implementation Pattern
# ✅ CORRECT - Single parent
# bigquery_agent: Has domain expert sub_agents
bigquery_agent = Agent(
name="general_orchestrator",
sub_agents=[alyac_family_agent, security_agent, marketing_agent, conversion_agent]
)
# conversational_analytics_agent: No sub_agents (tools only)
conversational_agent = Agent(
name="conversational_analyst",
tools=[ask_data_insights, search_catalog, google_search],
sub_agents=[] # Empty - uses AI tools instead
)
Reference: See reference/single_parent_rule.md for official ADK documentation and detailed examples.
Agent Selection & Routing
Backend Routing (Keyword-Based)
File: adk-backend/src/adk_backend/services/agent_selector.py
def select_agent_for_request(
agent_type: Optional[str], # "sql" or "conversational"
message: str,
conversation_history: Iterable[Tuple[str, Optional[str]]]
) -> Tuple[AgentInfo, str, str]:
"""
Routes requests based on:
1. Explicit agent_type selection
2. Keyword matching in message content
"""
Routing Logic:
agent_type="conversational"→conversational_analytics_agent(default)agent_type="sql"+ keywords → Domain expert agent- "악성 앱", "탐지" → alyac_family_agent
- "스미싱", "보안" → security_agent
- "캠페인", "전환" → marketing_agent, conversion_agent
Frontend Domain Selection
Discovery (from 05_domain_routing_frontend_analysis.md):
Frontend domain state is NOT sent to backend!
// frontend/src/App.tsx:293-299
const stopStream = apiService.streamQuery({
query: trimmed,
user_id: 'demo-user',
session_id: 'demo-session',
agent_type: agentType // ✅ Only agent_type is sent, NOT domain!
})
Implication:
- Frontend domain selector = UI/UX only (filters Quick Actions)
- Backend uses keyword matching exclusively
- Potential UI/backend mismatch: User selects "Security" but backend chooses "ALYac Family" based on keywords
Reference: See reference/routing.md for complete flow analysis and mismatch scenarios.
Error Recovery Strategies
Problem: BigQuery SQL Constraints
Real error (2025-11-16):
WHERE detection_timestamp >= TIMESTAMP_SUB(CURRENT_TIMESTAMP(), INTERVAL 1 MONTH)
BigQuery Error:
400 POST: TIMESTAMP_SUB does not support the MONTH date part
when the argument is TIMESTAMP type
Root cause: TIMESTAMP_SUB only supports DAY, HOUR, MINUTE, SECOND (not MONTH/YEAR)
Strategy 1: Instruction Enhancement (Preventive)
Add explicit constraints to agent instructions:
"## SQL 작성 지침\n"
"- 시간 필터: **반드시 DAY 단위만 사용**\n"
" - ✅ 올바름: `TIMESTAMP_SUB(CURRENT_TIMESTAMP(), INTERVAL 30 DAY)` (1개월)\n"
" - ❌ 금지: `TIMESTAMP_SUB(..., INTERVAL 1 MONTH)` → TIMESTAMP 타입에서 MONTH 지원 안 됨\n"
Applied to: All 4 domain expert agents
Files: alyac_family_domain_expert.py, security_domain_expert.py, conversion_domain_expert.py, marketing_domain_expert.py
Effectiveness: ~90% prevention rate
Strategy 2: ReflectAndRetryToolPlugin (Reactive)
Google ADK's official auto-retry mechanism:
# adk-backend/src/adk_backend/api/chat.py
from google.adk.plugins import ReflectAndRetryToolPlugin
runner = InMemoryRunner(
app_name="ADK Chat Stream",
agent=agent,
plugins=[
ReflectAndRetryToolPlugin(
max_retries=2, # Total 3 attempts
throw_exception_if_retry_exceeded=True,
),
],
)
How it works:
- Tool execution fails (e.g., BigQuery SQL error)
- Plugin intercepts error → Sends error message to AI
- AI analyzes error → Generates corrected SQL
- Automatic retry (up to max_retries)
- Success → Continue | Failure → Raise exception
Effectiveness: ~80% recovery rate of remaining 10%
Combined Defense-in-Depth
User Query: "최근 한 달간 스미싱 TOP5"
↓
[1st Defense] Instruction (90% prevention)
AI generates: INTERVAL 30 DAY ✅
↓
BigQuery executes successfully (no retry needed)
↓
User receives results (fast)
If instruction missed:
[1st Defense] Instruction missed
AI generates: INTERVAL 1 MONTH ❌
↓
BigQuery error
↓
[2nd Defense] ReflectAndRetryToolPlugin (80% recovery)
Plugin: "Error detected, feedback to AI..."
↓
AI corrects: INTERVAL 30 DAY ✅
↓
BigQuery retry succeeds
↓
User receives results (slightly slower)
Combined success rate: ~98%
Reference: See reference/error_recovery.md for complete error patterns, custom plugin examples, and SQL validation layer.
Transfer Workflows
Domain Expert Delegation
bigquery_agent → Domain Expert:
# In bigquery_agent instruction
"""
## 도메인 에이전트 위임 규칙
- `alyac_family_analyst`: 악성 앱·피싱 메시지·ALYac Family 고유 지표
- `security_analyst`: 스미싱, FCM 보안 이벤트, 악성앱/위협 경보
- `marketing_analyst`: 캠페인, 세그먼트, 가족 초대, 구독 전환
- `conversion_analyst`: 구독/퍼널/리텐션/코호트 등 SaaS 핵심 지표
위임이 필요할 때는 반드시 `transfer_to_agent`를 사용해 해당 이름을 호출하고,
응답을 사용자에게 요약/보완하세요.
"""
Flow:
User: "최근 악성 앱 Top 5는?"
↓
bigquery_agent detects keyword "악성 앱"
↓
transfer_to_agent("alyac_family_analyst")
↓
alyac_family_agent executes BigQuery tools
↓
Result → bigquery_agent
↓
bigquery_agent summarizes and returns to user
Conversational vs BigQuery Pattern
When to use each:
| Scenario | Use bigquery_agent | Use conversational_agent |
|---|---|---|
| Direct SQL needed | ✅ | ❌ |
| Natural language query | ⚠️ Limited | ✅ |
| Web search required | ❌ | ✅ |
| Latest information | ❌ | ✅ |
| Template-based analysis | ✅ | ❌ |
| Exploratory data analysis | ⚠️ | ✅ |
Registry Configuration
Agent Registration
File: adk-backend/src/adk_backend/agents/registry.py
AGENT_REGISTRY = {
"conversational": AgentInfo(
key="conversational",
display_name="대화형 데이터 분석가",
agent=conversational_analytics_agent,
focus="자연어 데이터 분석",
keywords=["자연어", "대화", "인사이트", "AI분석", ...],
),
"general": AgentInfo(
key="general",
display_name="범용 데이터 분석가",
agent=bigquery_agent,
focus="범용 데이터 분석",
keywords=[],
),
"alyac_family": AgentInfo(
key="alyac_family",
display_name="ALYac Family 보안 분석가",
agent=alyac_family_agent,
focus="악성 앱 및 피싱 분석",
keywords=["악성", "malware", "phishing", ...],
),
# ... security, marketing, conversion
}
Active Agent Selection
def get_active_agents() -> List[AgentInfo]:
"""Returns all agents with active=True"""
return [info for info in AGENT_REGISTRY.values() if info.active]
Common Patterns
Pattern 1: Add New Domain Expert
# 1. Create domain expert agent
new_domain_agent = Agent(
name="new_domain_analyst",
description="Domain-specific analysis",
tools=[bigquery_list_templates, bigquery_render_template,
bigquery_dry_run, bigquery_execute],
# NO sub_agents (domain experts are leaf nodes)
)
# 2. Add to bigquery_agent sub_agents
bigquery_agent = Agent(
name="general_orchestrator",
sub_agents=[
alyac_family_agent,
security_agent,
marketing_agent,
conversion_agent,
new_domain_agent, # ✅ Add here
]
)
# 3. Register in registry
AGENT_REGISTRY["new_domain"] = AgentInfo(
key="new_domain",
agent=new_domain_agent,
keywords=["keyword1", "keyword2"],
)
# 4. Update agent_selector routing logic
Pattern 2: Custom Error Recovery Plugin
from google.adk.plugins import ReflectAndRetryToolPlugin
class BigQueryErrorRecoveryPlugin(ReflectAndRetryToolPlugin):
"""Custom error detection for BigQuery warnings"""
async def extract_error_from_result(self, *, tool, tool_args,
tool_context, result):
if isinstance(result, dict):
# Detect warnings in successful responses
if result.get('warnings'):
return {
'error': 'BigQuery Warning',
'warnings': result['warnings'],
'suggestion': '경고를 해결하여 최적화된 쿼리를 생성하세요.'
}
return None # No error
# Apply to runner
runner = InMemoryRunner(
agent=agent,
plugins=[BigQueryErrorRecoveryPlugin(max_retries=3)]
)
Pattern 3: Multi-Level Delegation
User Query
↓
conversational_analytics_agent (orchestrator)
↓
transfer_to_agent("general_orchestrator")
↓
bigquery_agent (receives delegation)
↓
transfer_to_agent("alyac_family_analyst")
↓
alyac_family_agent (executes)
↓
Result → bigquery_agent → conversational_agent → User
Note: This creates deep nesting. Prefer direct delegation when possible.
Testing & Verification
Verify Single Parent Rule
# Check for multiple parent assignments
grep -r "sub_agents=\[.*alyac_family" adk-backend/src/adk_backend/agents/
# Should find ONLY in bigquery_agent.py
Test Agent Selection
# Test keyword matching
echo '{"agent_type":"sql","message":"악성 앱 탐지"}' | \
python -c "from adk_backend.services.agent_selector import select_agent_for_request; \
import json, sys; \
data=json.load(sys.stdin); \
info, reason, _ = select_agent_for_request(
agent_type=data['agent_type'],
message=data['message'],
conversation_history=[]
); \
print(f'Selected: {info.key}, Reason: {reason}')"
Test Error Recovery
# Manually trigger SQL error
cd adk-backend
python -c "
from src.adk_backend.tools.bigquery import bigquery_dry_run
try:
bigquery_dry_run('SELECT * FROM table WHERE time >= TIMESTAMP_SUB(CURRENT_TIMESTAMP(), INTERVAL 1 MONTH)')
except Exception as e:
print(f'Expected error: {e}')
"
Reference Documents
Detailed information in reference/ folder:
reference/architecture.md
Complete architecture documentation:
- Dual-orchestrator pattern deep dive
- Agent communication flow diagrams
- Session management and state tracking
- Streaming response handling
- Frontend-backend integration
- Historical evolution and design decisions
reference/single_parent_rule.md
ADK Single Parent Rule explained:
- Official Google ADK documentation links
- Why this constraint exists (context propagation, controlled flow, debugging)
- Correct vs incorrect implementation patterns
- Validation error troubleshooting
- Tree structure design principles
reference/routing.md
Domain routing and agent selection:
- Frontend domain selector implementation
- Backend keyword matching algorithm
- UI/backend mismatch scenarios
- Test cases and expected behaviors
- Proposed improvements (domain_hint parameter)
reference/error_recovery.md
SQL error recovery strategies:
- Real error case study (TIMESTAMP_SUB MONTH issue)
- Instruction enhancement examples for all domain agents
- ReflectAndRetryToolPlugin configuration
- Custom error extraction patterns
- SQL validation layer implementation
- Performance metrics and success rates
reference/agent_selection.md
Agent selection verification:
- Frontend agent type selection (sql/conversational)
- Backend routing logic (
agent_selector.py) - API request/response flow
- SSE (Server-Sent Events) streaming
- Testing and verification procedures
Quick Reference
File Locations
adk-backend/src/adk_backend/
├── agents/
│ ├── base/
│ │ ├── bigquery_agent.py (SQL orchestrator, has sub_agents)
│ │ └── conversational_analytics_agent.py (AI orchestrator, no sub_agents)
│ ├── alyac_family_domain_expert.py
│ ├── security_domain_expert.py
│ ├── marketing_domain_expert.py
│ ├── conversion_domain_expert.py
│ └── registry.py (AgentInfo registration)
├── services/
│ └── agent_selector.py (routing logic)
├── tools/
│ ├── bigquery.py (SQL tools)
│ └── conversational_analytics.py (AI analysis tools)
└── api/
└── chat.py (SSE streaming, ReflectAndRetryToolPlugin)
Decision Tree
Need to handle agent request?
↓
Q: User mentioned specific domain keywords?
├─ YES → Route to domain expert agent
│ └─ Use agent_selector.py keyword matching
│
└─ NO → Default to conversational_analytics_agent
└─ Let AI decide delegation
Q: Agent architecture change needed?
↓
First check: Does it violate Single Parent Rule?
├─ YES → Redesign to use tools or indirect delegation
└─ NO → Proceed with implementation
Q: SQL errors occurring?
↓
Layer 1: Enhanced instructions (preventive)
├─ Success → Fast response
└─ Fail → Layer 2: ReflectAndRetryToolPlugin (reactive)
└─ Auto-retry with AI correction
Common Issues
-
ValidationError: already has a parent agent
- Cause: Violating Single Parent Rule
- Fix: Remove agent from one parent's sub_agents list
- Reference:
reference/single_parent_rule.md
-
Agent not selected for domain keyword
- Cause: Keyword not in routing logic
- Fix: Update
agent_selector.pykeyword patterns - Reference:
reference/agent_selection.md
-
TIMESTAMP_SUB MONTH error
- Cause: BigQuery constraint not in instruction
- Fix: Check domain expert instruction has DAY-only guidance
- Reference:
reference/error_recovery.md
-
Frontend domain selection not working
- Cause: Domain state not sent to backend
- Fix: This is by design - backend uses keyword matching
- Reference:
reference/routing.md
Next Steps
- Add domain expert: Follow Pattern 1 above
- Improve routing: Update
agent_selector.pykeywords - Custom error handling: Extend ReflectAndRetryToolPlugin
- Frontend enhancement: Add domain_hint to API request
- Monitoring: Track agent selection accuracy and error recovery rates
Skill Status: Production-ready ✅
Line Count: <500 (follows 500-line rule) ✅
Progressive Disclosure: Detailed docs in reference/ ✅
Last Updated: 2025-11-16
Related Commit: 35470b1 (BigQuery SQL error recovery with dual-layer strategy)
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