fix(hooks): Prevent duplicate agent captures and skip background launch messages

[ajbmachon]

Summary

This PR fixes two bugs in the AgentOutputCapture.hook.ts that were causing issues with research capture:

• Duplicate file prevention: Same agent output was being captured 4-6 times with slightly different timestamps
• Background agent handling: Background agents were only capturing the "launched" message, missing the actual research results

Problem Details

1. Duplicate Captures

When multiple SubagentStop events fired in sequence, each one would find and capture the same Task result from the transcript, creating multiple identical files:

2026-01-25-103947_AGENT-default_RESEARCH_council-response...md  (3013 bytes)
2026-01-25-103957_AGENT-default_RESEARCH_council-response...md  (3013 bytes)
2026-01-25-104132_AGENT-default_RESEARCH_council-response...md  (3013 bytes)
2026-01-25-104133_AGENT-default_RESEARCH_council-response...md  (3013 bytes)

2. Background Agents Not Captured

For background agents (run_in_background: true), the hook was capturing the launch message instead of waiting for actual completion:

Full task output for debugging: Async agent launched successfully.
agentId: a27e24b
output_file: /private/tmp/claude/.../tasks/a27e24b.output

The actual research results in the .output file were never captured.

Solution

Deduplication

• Added contentHash() using MD5 to fingerprint content
• Added isDuplicateContent() to check existing files before writing
• Compares both full file hash and extracted agent output section

Background Agent Detection

• Added parseBackgroundAgentLaunch() to detect async launch messages
• Hook exits early for background launches
• Capture happens when agent actually completes (subsequent SubagentStop event)

Files Changed

• Releases/v2.4/.claude/hooks/AgentOutputCapture.hook.ts
• Packs/pai-hook-system/src/hooks/AgentOutputCapture.hook.ts

Testing

• Verified hook compiles and runs without errors
• Logic tested against observed debug logs showing the failure patterns
• Changes are backward compatible with existing captures

Impact

• Eliminates duplicate files in MEMORY/RESEARCH/
• Background agents captured with actual results
• No behavioral changes for synchronous agents

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Thank you for reviewing! Happy to make any adjustments.

🤖 Generated with Claude Code