Documentation only; no behavior change.
`firstLiveSeq`'s JSDoc still stated the boundary sits at that seq
unconditionally. Verified reachable on a plain production path: pick up a log,
do no work, pick it up again — the seed already ends in a boundary, so it is
not re-marked and `events[firstLiveSeq]` is undefined. Both that claim and the
firehose-gap sentence are now conditional, with the locate rule ("scan for the
last boundary") matching what types.ts already said.
`repair.ts`'s header claimed this module supplies the boundary. It does not —
the constructor does; this module supplies the activity read that must skip it.
Reworded, and it now names the closer timestamp leak, which is the one real
coupling that justifies `lastActivityTime` living beside the repair synthesis.
Recorded that `Session`'s constructor is the boundary's only legitimate writer,
since the invariant companion constrains nothing and a plugin-side append would
silently turn live brackets below it into dead history.
Hypatia May
b257ed5e8a