- Remove pool stats/fetch-age from lifecycle sensor to avoid stale data under state-change filtering; add `next_api_poll` for transparency.
- Clean lifecycle calculator by dropping unused helpers/constants and delete the obsolete cache age test.
- Clarify lifecycle state is diagnostics-only in coordinator comments, keep state-change filtering in timer test, and retain quarter-hour precision notes in constants.
- Keep sensor core aligned with lifecycle state filtering.
Impact: Lifecycle sensor now exposes only state-relevant fields without recorder noise, next API poll is visible, and dead code/tests tied to removed attributes are gone.
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