* refactor(sdk): collapse plan updates to typed steps
Per owner decision, remove the shipped steps: string[] SDK field and its unreleased planSteps replacement early. Collapse onPlanUpdate to one typed steps field. Retain wire-level string normalization for external Codex plugin version skew.
* chore(sdk): tighten rebased surface budget
* feat(channels): render live plan checklists from typed update_plan snapshots
Codex, Copilot, CLI, and embedded update_plan events now carry typed
{step, status} snapshots end to end instead of flattened strings. Slack,
Discord, Telegram, Matrix, and MS Teams render a live checklist in
progress drafts; Slack native task cards show the real plan with
position-keyed rows and id reconciliation. The embedded update_plan tool
is default-on for every model (tools.experimental.planTool: false opts
out). The shipped onPlanUpdate steps: string[] SDK field stays populated
during a deprecation window alongside the canonical planSteps.
* fix(auto-reply): align plan bridge types with SDK callback contract
* fix(auto-reply): split agent event bridge module and fix plan type boundaries
* fix(channels): satisfy oxlint on plan checklist helpers
