- Move lifecycle end event after finalizeSubprocessOutput() so
submit_result({status:'aborted'}) is correctly reflected in the
observer instead of showing completed/failed (P1)
- Reset observer registry on session resume and /new command so
stale subagent sessions from prior conversations are cleared (P2)
- Cache parsed JSONL transcript incrementally: track byte offset,
only read and parse new bytes on each refresh instead of reparsing
the entire file, avoiding render loop blocking on large sessions (P2)
