* feat(agents): add active-turn steering
Let users choose whether an immediate prompt interrupts or joins the active turn. The daemon owns exact-turn admission, provider delivery, safe fallback, and canonical timeline identity while queueing remains client-side.
* fix(agents): stabilize steering history and replay QA
* fix(agents): preserve steering timeline order
* fix(agents): reconcile resumed provider history
* fix(agents): serialize steering with cancellation
* test(agents): prove Claude multi-tool steering
* test(agents): force explicit history hydration
* fix(agents): flush output before steer admission
