`isInheritedSeq` had no production caller — only its own tests — so it was
a public core export shaped by nothing. A bracket owner reads the boundary
positionally; the helper belongs with the compaction seam, where a real
consumer decides its signature.
Also condense the `session/inherited` and `lastActivityTime` docs.
A plugin owning a standalone open/close bracket cannot tell a dead marker
from a live one: an unmatched `compact/start` reads identically whether the
previous writer died mid-compaction or a compaction is running now.
`Session.firstLiveSeq` already holds that answer exactly, but only in memory.
Append the log-only `session/inherited` event at that seq from the seeded
constructor — the single waist all six seeded-start paths pass through
(resume, configured startup on a persisted id, `sessions.fork()`, a subagent
fork child, `adopt()`'s live prefix, and a bare seeded `create`). Read it
through the new `isInheritedSeq(events, seq)`.
The constructor placement means persistence needs no changes: the marker is
already in `events` when a backend captures the creation seed, so it rides
the ordinary seed path with no load-time write. It also covers fork, where
the inherited bracket's owner may still be running — the case a
persistence-layer boundary could not reach.
Activity ordering excludes the boundary through `lastActivityTime()`, since
lazy resume makes browsing a pickup and the three call sites would otherwise
float every opened session to the top of a picker or list.
The seat's height publisher needs a ResizeObserver stub in every spec that
renders ConversationRoot (jsdom has none), and the two branch-tail StatsLine
assertions move to the grouped detail-row output.
Stats line moves into the InputBar's new footer slot (sharing the card's
width column) and expands to the design's grouped detail row: turns/steps,
LLM and tool wall time, cache hit, and input/output token split, all
derived client-side from the snapshot. The composer stack owns one 8px
rhythm, the seat fades the transcript through a fixed 36px gradient band,
back-to-bottom follows a live --dsh-composer-height, and goal/todo strips
share one 752px tip-fill column.
Yichen Jiang