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.

cmd/mavweb/handlers_test.go

@@ -67,8 +67,9 @@ type fakeCore struct {
 	traceErr  error
 
 	// for handleChatAPI tests
-	chatText string
-	chatErr  error
+	chatText   string
+	chatSource string
+	chatErr    error
 
 	// for the MCP section of /tools
 	mcpServers []ipc.MCPServerStatus
@@ -79,12 +80,12 @@ func (f *fakeCore) MCPServers(context.Context) ([]ipc.MCPServerStatus, error) {
 	return f.mcpServers, f.mcpErr
 }
 
-func (f *fakeCore) Chat(_ context.Context, _, text string) (string, error) {
+func (f *fakeCore) Chat(_ context.Context, _, text string) (ipc.ChatReply, error) {
 	f.chatText = text
 	if f.chatErr != nil {
-		return "", f.chatErr
+		return ipc.ChatReply{}, f.chatErr
 	}
-	return "поняла", nil
+	return ipc.ChatReply{Reply: "поняла", Source: f.chatSource}, nil
 }
 
 func (f *fakeCore) EnableTool(_ context.Context, name string, cmd []string, destructive bool, scope string, _ time.Time) error {
@@ -1285,3 +1286,37 @@ func TestHandleNotifications_ShowsTheOutbox(t *testing.T) {
 		}
 	}
 }
+
+// --- the query source badge (V-539) ---
+//
+// Which query source claimed a turn was readable in the daemon log and nowhere
+// else, so a QA step could not tell a wrong answer from a wrongly ordered
+// chain. It now rides the redirect and renders beside the reply.
+
+func TestHandleChatAPI_CarriesTheClaimingSource(t *testing.T) {
+	core := &fakeCore{chatSource: "kiwix"}
+	rr := httptest.NewRecorder()
+	handleChatAPI(rr, postChat("почему небо голубое"), core, nil, false)
+	loc := rr.Header().Get("Location")
+	if !strings.Contains(loc, "s=kiwix") {
+		t.Errorf("redirect = %q; want the claiming source in it", loc)
+	}
+}
+
+func TestHandleChatAPI_OmitsTheSourceWhenNothingClaimed(t *testing.T) {
+	core := &fakeCore{}
+	rr := httptest.NewRecorder()
+	handleChatAPI(rr, postChat("запиши что я пил воду"), core, nil, false)
+	if loc := rr.Header().Get("Location"); strings.Contains(loc, "s=") {
+		t.Errorf("redirect = %q; a turn no source claimed carries no badge", loc)
+	}
+}
+
+func TestChatPageRendersTheSourceBadge(t *testing.T) {
+	req := httptest.NewRequest(http.MethodGet, "/chat?q=%D1%82%D0%B5%D1%81%D1%82&r=%D0%BE%D1%82%D0%B2%D0%B5%D1%82&s=search", nil)
+	rr := httptest.NewRecorder()
+	handleChatPage(rr, req, &fakeCore{})
+	if body := rr.Body.String(); !strings.Contains(body, ">search</span>") {
+		t.Errorf("chat page does not render the source badge; body=%s", body)
+	}
+}