# 058 — Newly auto-declared params don't appear in the UI until a manual refresh

## Summary

`auto_declare_params` / `auto_declare_log_stream_params` (`src/engine.rs:383`,
`:451`) can add new param declarations on any ingested line, but the
frontend only ever fetches the param list once, on mount
(`webapp/src/App.tsx:278-284`, `fetchParamDeclarations().then(setParams)`).
The main poll loop (`App.tsx:300-350`, interval from
`webapp/src/lib/polling.ts`) refetches timeline entries and logs every
tick but never re-fetches param declarations — the only other place
`setParams` is called is the `onDeclared` callback fired by a user's own
manual edit in `Params.tsx`. So a param that gets auto-declared mid-run
from freshly ingested lines is invisible in the Params panel until the
page is reloaded.

There is no push infrastructure (SSE/websocket) anywhere in the
codebase; all live-refresh today is plain polling.

## Scope

- Add a periodic (or piggybacked on the existing poll loop) refetch of
  param declarations in `App.tsx`, e.g. call `fetchParamDeclarations()`
  alongside the existing timeline/log poll in the loop at
  `App.tsx:300-350`, or on its own lighter-weight interval if refetching
  every tick is wasteful.
- Only update state when the declaration list actually changed, to avoid
  needlessly re-rendering `Params.tsx` on every poll tick.
- Out of scope: introducing SSE/websocket push infrastructure — polling
  is consistent with how the rest of the app already refreshes.

## Acceptance criteria

- Ingesting new lines that trigger auto-declaration of a previously
  unseen param causes that param to appear in the Params UI within one
  poll interval, without a page reload.
- Existing manual param declaration/edit flows (`Params.tsx`'s
  `onDeclared`) are unaffected.

## Depends on

None.