fix/test(chat): guard handle_dharma_room_turn_agentic against tool_pending and empty reply

When agentic_loop suspends for an MCP bridge tool it returns a
{"tool_pending":true,...} envelope with no "reply" key. Without an
explicit check, json_get(loop_result, "reply") returns "" and the
function emitted {"response":"","cgi_id":"..."} — a silent empty
response indistinguishable from a successful LLM turn with no content.

Two guards added after the existing error check:

1. tool_pending passthrough: if the loop suspended, return the pending
   envelope directly so callers (dharma room orchestrators) can
   distinguish suspension from failure and route to the approve flow.

2. Empty-reply guard: if final_text is empty after the pending check,
   return an explicit {"error":"no response",...} envelope instead of
   silently succeeding with an empty response field.

Also adds tests/test_agentic_tools.el:
- agentic_tools_all() includes all literal tool names and web_search
- connector_tools_json() returns valid JSON when bridge is down (graceful degradation)
- tool_pending envelope detection patterns (the is_pending logic)
- json_get(pending_envelope, "reply") returns "" confirming the empty-reply
  guard is load-bearing (pure string/JSON, no LLM or network required)

chat.el

@@ -993,7 +993,21 @@ fn handle_dharma_room_turn_agentic(body: String) -> String {
         return "{\"error\":\"" + result_error + "\",\"response\":\"\",\"cgi_id\":\"" + cgi_id + "\"}"
     }
 
+    // If agentic_loop suspended for an MCP bridge tool, pass the pending envelope
+    // straight through so callers can distinguish suspension from failure.
+    // A silent empty response is indistinguishable from an LLM error to any caller.
+    let is_pending: Bool = str_eq(json_get(loop_result, "tool_pending"), "true")
+        || str_starts_with(loop_result, "{\"tool_pending\":true")
+    if is_pending {
+        return loop_result
+    }
+
     let final_text: String = json_get(loop_result, "reply")
+    // Guard against a silent empty response - produce an explicit error so callers
+    // cannot mistake a failed turn for a successful one with empty content.
+    if str_eq(final_text, "") {
+        return "{\"error\":\"no response\",\"response\":\"\",\"cgi_id\":\"" + cgi_id + "\"}"
+    }
     let tools_arr: String = json_get_raw(loop_result, "tools_used")
     let eff_tools: String = if str_eq(tools_arr, "") { "[]" } else { tools_arr }
     let safe_text: String = json_safe(final_text)