Paper 1 · Question 1

A: Write and compaction are unrelated. PostToolUse on Write would fire on every file write whether or not /compact is about to run, producing noise rather than a transcript at the right moment. The dedicated PreCompact event is the correct hook.

B: PreCompact is a first-class hook event in Claude Code that fires immediately before /compact (or auto- compaction) runs. The hook receives the full pre-compaction transcript path and can copy or process it before summarisation discards detail. This is the documented mechanism for exactly this use case.

C: There is no 'Compact' tool exposed to PreToolUse. Compaction is a Claude Code lifecycle operation, not a model-invoked tool, so it has its own dedicated PreCompact event rather than being hooked via PreToolUse.

D: Logging every tool result creates enormous log files and does not capture conversation context (reasoning, planning, user messages). The targeted PreCompact event captures the full transcript at the critical moment without per-tool noise.