the query source that claimed a turn is readable on /chat (V-539)

V-539 said SearXNG claims every world question, including invented terms,
so Kiwix is never reached. Measured today against the configured instance:
seven of eight invented Russian questions now return zero results, and
Response.Empty() already passes those to the ZIM. The premise moved with the
upstream engine set in three days.

The three quality signals the task named were recorded per query and none
separate the sets. Token overlap is zero for the one bad claim and also zero
for "столица Франции", whose answer is Париж. Empty snippets never fire,
because ParseResponse already drops a hit with no text. SearXNG returned no
corrections or suggestions even for the query it silently respelled. So no
threshold is built: it would cost a real answer to save one invented word.

What ships is the second half. The claiming query source crosses the IPC seam
on ipc.ChatReply.Source and renders as a badge beside the reply on /chat. It
rides the context rather than a return value, because handleText answers every
reach through one string and the mic, telegram and the web all share it.
Chat now returns ChatReply instead of a bare string.

Full -race suite green.

CLAUDE.md

@@ -286,6 +286,15 @@ world questions, so she needs to read external sources. What replaces it:
 - **In the world, live search leads and the ZIMs are the fallback** (owner's call,
   2026-08-02). A self-hosted SearXNG (`search` block) answers first; the Kiwix ZIMs on
   homesrv answer when the search is empty, unreachable, or the line is down.
+  `Response.Empty()` is the whole gate and there is no quality threshold in front of it:
+  the three signals one could read were measured on 2026-08-05 and none of them separate a
+  real question from an invented one. Token overlap would cost "столица Франции" its
+  answer, because the answer is Париж and that word is not in the question. See
+  `docs/evals/2026-08-05-search-quality-signals.md` (V-539). **Which query source claimed
+  a turn is readable on `/chat`** as a badge beside the reply, carried on
+  `ipc.ChatReply.Source` and noted by `noteQuerySource` in `cmd/mavend/querysource.go`. It
+  rides the context, so `handleText` keeps the one string signature the mic, telegram and
+  the web share.
 - **External search is allowed and off unless configured**, like the weather and telegram
   capabilities. The code default is still off. `deploy/mavend.json` now ships a `search`
   block (owner's call, 2026-08-02), so it is on for this box and deleting the block turns