Revert "merge: tier2/phase2_4_5_call_site_completion_20260621 (parent + follow-up + Phase 6e analysis)"

This reverts commit f914b2bcd4, reversing
changes made to 7fef95cc87.

tests/test_ai_client_tool_loop_send_func.py

@@ -11,10 +11,10 @@ from src.ai_client import run_with_tool_loop
 from src.vendor_capabilities import VendorCapabilities
 
 def _make_normalized_response(text: str = "ok", tool_calls: list[dict[str, Any]] | None = None) -> NormalizedResponse:
- from src.openai_schemas import UsageStats
  return NormalizedResponse(
-  text=text, tool_calls=tool_calls or (),
-  usage=UsageStats(input_tokens=10, output_tokens=5),
+  text=text, tool_calls=tool_calls or [],
+  usage_input_tokens=10, usage_output_tokens=5,
+  usage_cache_read_tokens=0, usage_cache_creation_tokens=0,
   raw_response=None,
  )