The time_spent segment rendered Date.now() - sessionStartTime, so an
idle session displayed hours of "time spent" while the agent did
nothing — the only inputs were wall-clock and the unmoving session
start.
Replace sessionStartTime with activeMs in SegmentContext and accumulate
inside StatusLineComponent across agent_start -> agent_end windows.
markActivityStart/markActivityEnd are idempotent (reentrant agent_start
events and superseded agent_end events never double-count); the segment
ticks live during an open window and freezes when the agent yields.
The session-boundary hook drops the now-meaningless wall-clock argument
and is renamed setSessionStartTime -> resetActiveTime; it zeroes the
accumulator and drops any in-flight window so /clear / fresh-session /
joined-collab paths start the meter at zero.
Fixes#3681
roboomp
68db2ce649