A resumed hook firing is a brand-new claude -p process, and Claude Code
rebuilds that process's environment preamble from scratch — any drift there
(near-certain on a shared checkout) invalidates the finished run's prompt
cache entirely. Sampled real transcripts confirm every firing re-creates the
whole prior conversation as fresh input tokens rather than reading it from
cache, regardless of delay. maxContextK was defaulted to 0 (no cap), so an
unbounded conversation meant an unbounded tidy-up bill. Default it to 60k and
document why, in both the backend docstring and CLAUDE.md.
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