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SessionStart hooks now get cache age, context size and estimated re-caching cost on resume.
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SessionStartseconds_since_last_responsecontext_tokensprompt_cache_likely_expiredestimated_cache_write_usd
What
When a session starts by resuming or forking, the SessionStart hook payload now includes seconds_since_last_response, context_tokens, prompt_cache_likely_expired, and estimated_cache_write_usd. A hook can use these to judge whether the prompt cache has lapsed and what re-caching the context will cost before doing anything expensive.
Details
- Present for SessionStart events whose source is resume or fork.
- The elapsed-time field is measured from the resumed transcript's last assistant response.
Evidence
resume/fork: seconds since the resumed transcript's last assistant response
Strings lifted out of the shipped bundle, so the claim above can be checked against them.