Get Agent ID Skill

Purpose: Extract the agent ID from the most recent Task tool invocation in the current session for use with the Task tool's resume parameter.

Note: This skill is a workaround for Claude Code issue #10864. Ideally, the Task tool would return the agent ID directly, eliminating the need for manual extraction from conversation logs.

When to Use:

• After invoking a Task tool that spawns an agent
• When you need to resume an agent for multi-phase work (e.g., validation workflows)
• Before calling Task tool with resume parameter

What It Does:

1. Reads the current session's conversation log
2. Extracts the most recent agentId from toolUseResult entries
3. Stores the agent ID in a specified file
4. Outputs the agent ID for verification

Usage

Input Required:

• Session ID (automatically available from SessionStart hook context)
• Output file path (where to store the extracted agent ID)

Output:

• Agent ID stored in specified file
• Agent ID echoed to stdout for verification

Execution Instructions

After invoking a Task tool, extract the agent ID with this bash command:

# Extract most recent agent ID from conversation log
# Replace SESSION_ID with actual value from context (e.g., "2ccd9677-8b8e-4048-a052-16b52b989c7b")
# Replace OUTPUT_FILE with desired storage path (e.g., "/tmp/my-agent-id.txt")

bash -c 'SESSION_ID="<session-id-from-context>" && OUTPUT_FILE="<output-file-path>" && AGENT_ID=$(jq -r "select(.toolUseResult.agentId) | .toolUseResult.agentId" /home/node/.config/projects/-workspace/${SESSION_ID}.jsonl 2>/dev/null | tail -1) && echo "$AGENT_ID" > "$OUTPUT_FILE" && echo "Stored agent ID: $AGENT_ID"'

Parameter Substitution:

• <session-id-from-context>: Replace with session ID from SessionStart system reminder
• <output-file-path>: Replace with path where agent ID should be stored

Example:

bash -c 'SESSION_ID="2ccd9677-8b8e-4048-a052-16b52b989c7b" && OUTPUT_FILE="/tmp/validator-agent-id.txt" && AGENT_ID=$(jq -r "select(.toolUseResult.agentId) | .toolUseResult.agentId" /home/node/.config/projects/-workspace/${SESSION_ID}.jsonl 2>/dev/null | tail -1) && echo "$AGENT_ID" > "$OUTPUT_FILE" && echo "Stored agent ID: $AGENT_ID"'

Using the Extracted Agent ID

After extraction, read the agent ID from the file for use with Task tool resume:

# Read stored agent ID
AGENT_ID=$(cat /tmp/validator-agent-id.txt)

# Use with Task tool resume parameter
Task tool: general-purpose
Resume: $AGENT_ID
Prompt: "Continue from previous analysis..."

How It Works

Step 1: Locate Conversation Log

Conversation logs are stored at /home/node/.config/projects/-workspace/{session-id}.jsonl where each line is a JSON object representing a conversation event.

Step 2: Filter for Agent ID Entries

The jq command filters for entries where:

• Entry has toolUseResult.agentId field (Task tool invocations)
• Returns the agentId value

Step 3: Get Most Recent

Using tail -1 ensures we get the most recent agent ID (last line after filtering).

Step 4: Store and Verify

• Agent ID is written to specified output file
• Agent ID is echoed for visual confirmation

Error Handling

If extraction fails (empty agent ID):

• Verify session ID is correct (check SessionStart system reminder)
• Ensure Task tool was invoked recently in this session
• Check conversation log exists: ls -la /home/node/.config/projects/-workspace/{session-id}.jsonl

If jq errors occur:

• Ensure jq is installed: which jq
• Check conversation log is valid JSON: tail -1 /home/node/.config/projects/-workspace/{session-id}.jsonl | jq

Multi-Agent Workflows

For workflows with multiple agents (e.g., Phase 1 validator, Phase 2 validator):

# Phase 1: Extract first agent ID
bash -c 'SESSION_ID="..." && OUTPUT_FILE="/tmp/phase1-agent.txt" && AGENT_ID=$(jq -r "select(.toolUseResult.agentId) | .toolUseResult.agentId" /home/node/.config/projects/-workspace/${SESSION_ID}.jsonl 2>/dev/null | tail -1) && echo "$AGENT_ID" > "$OUTPUT_FILE" && echo "Phase 1 agent ID: $AGENT_ID"'

# ... Phase 1 work ...

# Phase 2: Extract second agent ID (after invoking new agent)
bash -c 'SESSION_ID="..." && OUTPUT_FILE="/tmp/phase2-agent.txt" && AGENT_ID=$(jq -r "select(.toolUseResult.agentId) | .toolUseResult.agentId" /home/node/.config/projects/-workspace/${SESSION_ID}.jsonl 2>/dev/null | tail -1) && echo "$AGENT_ID" > "$OUTPUT_FILE" && echo "Phase 2 agent ID: $AGENT_ID"'

Important: Always extract immediately after Task invocation to ensure you capture the correct agent ID.

Related Skills

• get-session-id: Provides session ID needed for this skill
• read-conversation-history: Read full conversation log for debugging

Common Use Cases

Use Case 1: Two-Phase Validation

# Phase 1: Invoke validator agent
Task tool: general-purpose
Prompt: "Analyze document..."

# Extract Phase 1 agent ID
bash -c 'SESSION_ID="abc123..." && OUTPUT_FILE="/tmp/validator-phase1.txt" && AGENT_ID=$(jq -r "select(.toolUseResult.agentId) | .toolUseResult.agentId" /home/node/.config/projects/-workspace/${SESSION_ID}.jsonl 2>/dev/null | tail -1) && echo "$AGENT_ID" > "$OUTPUT_FILE" && echo "Stored agent ID: $AGENT_ID"'

# Phase 2: Resume same validator agent
AGENT_ID=$(cat /tmp/validator-phase1.txt)
Task tool: general-purpose
Resume: $AGENT_ID
Prompt: "Now compare with baseline..."

Use Case 2: Iterative Refinement

# Initial analysis agent
Task tool: general-purpose
Prompt: "Review code for issues..."

# Extract agent ID
bash -c '...'  # extraction command

# Resume for follow-up questions
AGENT_ID=$(cat /tmp/analyzer-agent.txt)
Task tool: general-purpose
Resume: $AGENT_ID
Prompt: "Focus on security issues specifically..."

Technical Details

Conversation Log Format:

Each Task tool invocation creates entries like:

{
  "type": "toolResult",
  "toolUseResult": {
    "agentId": "a16346ea",
    "output": "...",
    ...
  },
  ...
}

jq Filter Explanation:

• select(.toolUseResult.agentId): Only entries with agentId field
• .toolUseResult.agentId: Extract the agentId value
• 2>/dev/null: Suppress jq errors on malformed entries
• tail -1: Get last (most recent) match