The /tree selector and HTML session export rendered chain rows (flattened
user/assistant turns) with bare spaces when their nearest branched ancestor
was the last sibling, breaking the visual connection back to the branch
parent.
Cause: tree-selector.ts and export/html/template.js propagated
`show: !isLast` to descendant gutters, so any chain row under a `└─`
ancestor rendered the gutter as space instead of `│`. Branched
grandchildren correctly need that space to keep standard tree drawing, but
chain-flattened conversation rows lost their anchor.
Fix: at render time, when the row has no connector of its own (chain row),
force the gutter to `│` regardless of the ancestor's `show` flag. Rows
with their own connector still respect the `show` flag so a `│` never
floats below an unrelated `└─` for branched descendants.
Applied identically in tree-selector.ts (TUI) and export/html/template.js
(HTML export, regenerated into template.generated.ts).
Fixes#2298
roboomp
dca4da87f1