## Summary
- When KB retrieval fails (e.g. ES `AssertionError` on empty
`index_names`), `kbinfos` falls back to a dict without a `total` key
- `_async_update_chunk_info` then iterates over `chunk_info.keys()`
(which includes `total`) and tries `kbinfos['total']`, raising a
`KeyError`
- This error surfaces when using Tavily web retrieval in a chat with no
knowledge base attached
## Changes
- Add `'total': 0` to all default `kbinfos` dicts in
`_retrieve_information`
- Add `setdefault('total', 0)` guard after successful KB retrieval to
handle cases where the retrieval result omits the key
- Accumulate `total` correctly in the merge branch of
`_async_update_chunk_info`
## Test plan
- [ ] Start a chat with Tavily configured and no knowledge base
- [ ] Verify no `KeyError: 'total'` is raised
- [ ] Verify Tavily results are returned correctly
---------
Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
### What problem does this PR solve?
Fixes#14051.
The chat UI already sends an `internet` flag with each request, but the
backend previously triggered Tavily web retrieval whenever
`prompt_config.tavily_api_key` was configured. As a result, web search
could still run even when the internet toggle was off.
This PR makes web search an explicit opt-in at request time:
- `tavily_api_key` only indicates that web search is available
- Tavily retrieval runs only when `internet` is explicitly enabled
- the same behavior now applies to both the normal retrieval path and
the deep-research / reasoning path
This also fixes the no-KB fallback case so chats without KBs fall back
to normal solo chat when `internet` is off.
### Type of change
- [x] Bug Fix (non-breaking change which fixes an issue)
