fix(web_search): send only the agent's query to Exa search

Exa /search is a neural search endpoint, not a chat model, so prepending
the Perplexity system prompt made Exa match the prompt's own vocabulary
(Kali, OWASP, apt, NIST) instead of the query. The system prompt stays
on the Perplexity path where it is a chat system message; the Exa
summary instruction is unchanged.

strix/tools/web_search/tool.py

@@ -121,7 +121,7 @@ def _exa_content(api_key: str, query: str, search_type: str, num_results: int) -
         api_key,
         "https://api.exa.ai/search",
         {
-            "query": f"{_SYSTEM_PROMPT}\n\n{query}",
+            "query": query,
             "type": search_type,
             "numResults": num_results,
             "contents": {"summary": {"query": _EXA_SUMMARY_PROMPT}},

tests/test_web_search.py

@@ -110,7 +110,7 @@ def test_exa_content_requests_summaries_and_renders_results(
 
     assert captured["url"] == "https://api.exa.ai/search"
     assert captured["headers"]["x-api-key"] == "ek"
-    assert "OpenSSH 7.4 RCE?" in captured["json"]["query"]
+    assert captured["json"]["query"] == "OpenSSH 7.4 RCE?"
     assert captured["json"]["type"] == "auto"
     assert captured["json"]["numResults"] == 5
     assert captured["json"]["contents"] == {"summary": {"query": tool._EXA_SUMMARY_PROMPT}}