# 093 — Log-line JSON viewer should default to collapsed, not expanded

## Summary

When a log line's text parses as a JSON object, the frontend renders it
via a collapsible tree view — but every node starts expanded, so a
line with a large JSON payload dumps its entire structure into the
timeline by default instead of showing a collapsed summary the user
opts into expanding.

## Where

- `webapp/src/components/LogPreview.tsx:97-107` — `JsonValueView`
  recursively renders JSON values, delegating objects/arrays to
  `JsonNode`.
- `webapp/src/components/LogPreview.tsx:109-156` — `JsonNode` renders
  a collapsible subtree with a ▾/▸ disclosure toggle. Default state is
  set at line 116: `useState(true)`, i.e. expanded. Each nested
  object/array has its own independent `expanded` state.
- `webapp/src/components/LogPreview.tsx:160-164` — `LogMessage` is the
  per-row entry point: parses the line via `tryParseJsonObject`
  (`:82-94`) and renders through `JsonValueView` when it succeeds.
- Empty objects/arrays already short-circuit to plain `{}`/`[]` with
  no toggle (`:118-125`) — unaffected by this change.

## Scope

- Flip the default in `JsonNode` (`LogPreview.tsx:116`) from
  `useState(true)` to `useState(false)` so JSON subtrees render
  collapsed until the user clicks to expand.
- Since expand state is per-node (not shared across the tree), this
  changes every node in a JSON log line's tree independently — confirm
  that's the intended look (top-level object collapsed with `{...}`
  rather than only nested children collapsing) rather than needing a
  "expand root, collapse children" split default.