# 045 — Timeline/log ordering by params other than `ottyl_ts`, with drop/fallback toggle

## Summary

Log lines are currently rendered in whatever order the backend returns
them, which is ingest order (`sequence`, monotonically increasing per
`src/ingest.rs`) surfaced via `webapp/src/components/LogPreview.tsx:258-261`
(`log.sequence`/`log.timestamp_ms`). `webapp/src/components/LogTimeline.tsx`
only draws pre-bucketed histogram bars from `fetchTimeline`
(`webapp/src/lib/api.ts:257` → `GET /api/timeline`, `src/api.rs:249
get_timeline`) and has no per-line sort control at all. There is no way to
order by a declared param, and no defined behavior for lines missing
whatever param is chosen for ordering.

## Scope

- Default ordering stays by `ottyl_ts` (see ticket 044 for the rename).
- Add the ability to choose a different declared param as the sort key for
  the timeline/log list (backend: extend the timeline/log query path in
  `src/api.rs`/`src/engine.rs` to accept a sort-by param; frontend: expose
  the choice near the timeline/log controls, likely in
  `LogTimeline.tsx`/`LogPreview.tsx` or their shared settings).
- Add an explicit toggle controlling how lines lacking the chosen sort
  param are handled: (a) fall back to ordering those lines by `ottyl_seq`,
  or (b) drop them from view entirely. Persist this toggle alongside other
  view settings.
- Ensure the toggle and sort-by selection are scoped sensibly (e.g. per
  timeline/session) rather than silently global if that would surprise
  users switching between dashboards.

## Acceptance criteria

- User can pick any declared param as the ordering key for the
  timeline/log view, in addition to the `ottyl_ts` default.
- With the fallback toggle on, lines missing the sort param appear
  ordered by `ottyl_seq` relative to each other; with it off, those lines
  are excluded from the view — both verified with a seeded fixture mixing
  lines with and without the param.
- Existing default (`ottyl_ts`-ordered) behavior is unchanged when no
  alternate sort param is selected.

## Depends on

044 (reserved param naming — this ticket's default sort key and fallback
key should use the renamed `ottyl_ts`/`ottyl_seq`).