The old auto path checked `HEAD..origin/branch` right after kicking off a
background fetch, so it read a stale origin ref and only fired on the SECOND
invocation (and never if the agent sat in one long-running `work`).
Now: when AGENTHUB_AUTO_UPDATE is set, a throttled tick (≤1h) spawns
`agenthub update` directly in the background. update does its OWN fresh fetch
+ reset + build and no-ops when current — so it self-heals on the FIRST
invocation, no stale-ref lag. Notify-only path (no flag) unchanged.
Removed the now-unused cooldown const. 122/122 green. Bump 0.6.0 -> 0.6.1.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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