refactor(ai_client): remove deprecated send() function (Phase 6.1)

Removes the @deprecated send() function (was at src/ai_client.py:2939-3000)
and the from typing_extensions import deprecated import (line 38). The
function is replaced by send_result() which has been the canonical public
API since the data_oriented_error_handling_20260606 track (commit 9f86b2be).

All 3 production call sites (src/conductor_tech_lead.py:68,
src/orchestrator_pm.py:86, src/multi_agent_conductor.py:591) and 18 test
files were migrated in Phases 1-2; 4 pre-existing failures were fixed in
Phases 3-4. No remaining callers of ai_client.send(.

Verification:
- uv run rg 'def send\\(' src/ai_client.py returns 0 hits
- import src.ai_client; hasattr(ai, 'send') is False
- 73/73 migrated tests pass

src/ai_client.py

@@ -35,7 +35,6 @@ from collections import deque
 from pathlib     import Path as _P
 from pathlib     import Path
 from typing      import Optional, Callable, Any, List, Union, cast, Iterable
-from typing_extensions import deprecated
 
 from src import project_manager
 from src import file_cache
@@ -2936,69 +2935,6 @@ def get_token_stats(md_content: str) -> dict[str, Any]:
  }
  return _add_bleed_derived(stats, sys_tok=total_tokens)
 
-@deprecated("Use ai_client.send_result() instead. The deprecated send() will be removed in the public_api_migration_20260606 track.")
-def send(
- md_content: str,
- user_message: str,
- base_dir: str = ".",
- file_items: list[dict[str, Any]] | None = None,
- discussion_history: str = "",
- stream: bool = False,
- pre_tool_callback: Optional[Callable[[str, str, Optional[Callable[[str], str]]], Optional[str]]] = None,
- qa_callback: Optional[Callable[[str], str]] = None,
- enable_tools: bool = True,
- stream_callback: Optional[Callable[[str], None]] = None,
- patch_callback: Optional[Callable[[str, str], Optional[str]]] = None,
- rag_engine: Optional[Any] = None,
-) -> str:
- """
-  [DEPRECATED] Sends a request to the configured AI provider and returns the raw response text.
-
-  Functional Purpose:
-   Acts as the legacy wrapper around send_result(). It extracts the string payload ('data')
-   from the returned Result container, logging warnings for any internal execution errors
-   to the communication logs, but suppressing the actual error objects from the caller.
-
-  Parameters & Inputs:
-   md_content (str): Base/system prompt template or markdown content.
-   user_message (str): The primary user instruction.
-   base_dir (str): Base workspace directory path (defaults to ".").
-   file_items (list[dict[str, Any]] | None): Optional list of active context files.
-   discussion_history (str): Contextual discussion history lines.
-   stream (bool): Whether to stream the response chunks.
-   pre_tool_callback (Optional[Callable]): Hook called before a tool call is executed.
-   qa_callback (Optional[Callable]): Hook for Tier 4 quality/validation checks.
-   enable_tools (bool): Controls whether LLM tool usage is enabled.
-   stream_callback (Optional[Callable]): Hook to stream response chunks to.
-   patch_callback (Optional[Callable]): Custom callback for interactive patch validation.
-   rag_engine (Optional[Any]): The RAG engine instance for retrieving vector context.
-
-  Returns:
-   str: The raw text response from the active AI provider.
-
-  Immediate-Mode DAG / Thread Context:
-   Called by: Various legacy scripts, tests, PM/Tech Lead orchestrators, and GUI event loops.
-              See list below.
-   Calls: send_result()
-
-  SSDL:
-   `[I:send_result] -> [T:text]`
-
-  Thread Boundaries:
-   Executes on whichever thread calls it (typically the GUI main thread, API hook handlers,
-   or a background async worker pool thread).
-
-  [C: simulation/user_agent.py:UserSimAgent.generate_response, src/api_hooks.py:WebSocketServer._handler, src/api_hooks.py:WebSocketServer.broadcast, src/app_controller.py:AppController._handle_request_event, src/app_controller.py:_api_generate, src/conductor_tech_lead.py:generate_tickets, src/multi_agent_conductor.py:run_worker_lifecycle, src/orchestrator_pm.py:generate_tracks, tests/test_ai_cache_tracking.py:test_gemini_cache_tracking, tests/test_ai_client_cli.py:test_ai_client_send_gemini_cli, tests/test_api_events.py:test_send_emits_events_proper, tests/test_api_events.py:test_send_emits_tool_events, tests/test_deepseek_provider.py:test_deepseek_completion_logic, tests/test_deepseek_provider.py:test_deepseek_payload_verification, tests/test_deepseek_provider.py:test_deepseek_reasoner_payload_verification, tests/test_deepseek_provider.py:test_deepseek_reasoning_logic, tests/test_deepseek_provider.py:test_deepseek_streaming, tests/test_deepseek_provider.py:test_deepseek_tool_calling, tests/test_gemini_cli_adapter.py:TestGeminiCliAdapter.test_full_flow_integration, tests/test_gemini_cli_adapter.py:TestGeminiCliAdapter.test_send_captures_usage_metadata, tests/test_gemini_cli_adapter.py:TestGeminiCliAdapter.test_send_handles_tool_use_events, tests/test_gemini_cli_adapter.py:TestGeminiCliAdapter.test_send_parses_jsonl_output, tests/test_gemini_cli_adapter.py:TestGeminiCliAdapter.test_send_starts_subprocess_with_correct_args, tests/test_gemini_cli_adapter_parity.py:TestGeminiCliAdapterParity.test_send_parses_tool_calls_from_streaming_json, tests/test_gemini_cli_adapter_parity.py:TestGeminiCliAdapterParity.test_send_starts_subprocess_with_model, tests/test_gemini_cli_edge_cases.py:test_gemini_cli_context_bleed_prevention, tests/test_gemini_cli_edge_cases.py:test_gemini_cli_loop_termination, tests/test_gemini_cli_integration.py:test_gemini_cli_full_integration, tests/test_gemini_cli_integration.py:test_gemini_cli_rejection_and_history, tests/test_gemini_cli_parity_regression.py:test_send_invokes_adapter_send, tests/test_gui2_mcp.py:test_mcp_tool_call_is_dispatched, tests/test_tier4_interceptor.py:test_ai_client_passes_qa_callback, tests/test_token_usage.py:test_token_usage_tracking, tests/test_websocket_server.py:test_websocket_subscription_and_broadcast]
- """
- result = send_result(
-  md_content, user_message, base_dir, file_items, discussion_history,
-  stream, pre_tool_callback, qa_callback, enable_tools, stream_callback, patch_callback, rag_engine,
- )
- if not result.ok:
-  for err in result.errors:
-   _append_comms("WARN", "deprecated_send_with_errors", {"error": err.ui_message()})
- return result.data
-
 def send_result(
  md_content: str,
  user_message: str,