v0.2.1

Added

• background: true support for SDK backend. The Pi task tool now accepts background: true when running inside the SDK (non-tmux backend). The subagent's AgentSession lives in the host's process; its subscriptions and extension context stay valid as long as the parent session is alive, which is what OpenPi's sidecar guarantees.
• stale-ctx filtering. extension_error events that come from a Promise rejection whose message mentions "this extension ctx is stale" are now swallowed before the UI sees them. The host's session-replacement path was triggering a benign race during reload.
• Task-session-history helpers. New .pi/task-session-history.json is the source of truth for runtime task status. The renderer no longer reads TASKS.md for status or navigation.
• Cancelled foreground navigation is normalized. A click on a pending task row no longer aborts the running child; the row stays unclickable until the task settles.

Fixed

• reload_session no longer leaks extension timers. The sidecar now does a full session replacement (dispose + startSession) on reload, which atomically destroys the old runner and its timers.
• Background tmux panes self-destruct on exit. Pane remain-on-exit and setPaneSelfDestruct are set so dead tasks don't accumulate.
• Restore reconciles registry with JSONL. On startup, restoreActiveBackgroundTasks walks the registry and the per-task JSONL, marking tasks done/failed and killing stale panes.

32 commits since v0.2.0. See CHANGELOG.md for the full release notes.