refactor(run_agent): review fixes — keyword-forward __init__, drop dead code, tighten guards

Four fixes from PR #27248 review:

1. **__init__ forwarder is now keyword-forwarded** (daimon-nous review).
   Previously the run_agent.AIAgent.__init__ wrapper forwarded all 64
   params positionally to agent.agent_init.init_agent, so adding a
   65th param on main would require three lockstep edits (signature,
   init_agent signature, forwarder call) or silently shift every value.
   Keyword forwarding makes this trivially safe — adding a param now
   only needs the two signatures and one extra keyword line.

2. **Drop dead _ra() in agent/codex_runtime.py** (daimon-nous + Copilot).
   The lazy run_agent reference was defined but never called inside
   this module — the codex paths use agent.* accessors only.

3. **Drop unused imports in agent/codex_runtime.py** (Copilot):
   contextvars, threading, time, uuid, Optional. Carried over from
   run_agent.py during the original extraction.

4. **Tighten three source-introspection test guards** (Copilot):
   - test_memory_nudge_counter_hydration.py — was scanning the
     concatenated source of run_agent.py + agent/conversation_loop.py
     and matching self.X or agent.X form.  Now asserts the
     hydration block lives in agent/conversation_loop.py specifically
     with the agent.X form — the body never moves back, so if it
     ever drifts a future re-introduction fails the guard.
   - test_run_agent.py::TestMemoryNudgeCounterPersistence — anchor on
     agent.iteration_budget = IterationBudget exactly (was just
     iteration_budget = IterationBudget) so an unrelated identifier
     ending in iteration_budget can't match.
   - test_run_agent.py::TestMemoryProviderTurnStart — assert the
     agent._user_turn_count form directly (the extracted body uses
     agent.X, not self.X — accepting either was a transitional fudge).
   - test_jsondecodeerror_retryable.py — scan agent/conversation_loop.py
     only, not the concatenation.

Not addressed in this commit:

* Pre-existing bugs in agent/tool_executor.py (heartbeat index
  mismatch when calls are blocked, _current_tool clobber in result
  loop, blocked-counted-as-completed in spinner summary, dead
  result_preview computation). These were preserved byte-for-byte from
  the original _execute_tool_calls_concurrent — worth a separate
  follow-up PR with proper tests.
* _OpenAIProxy.__instancecheck__ concern — pre-existing, not flagged
  by any of the original test patches (nothing actually does
  isinstance(x, OpenAI) against the proxy instance).
* agent_init.py:949 mem_config potential NameError — pre-existing;
  only triggers if _agent_cfg.get('memory', {}) itself raises, which
  it can't with a stock dict.

tests/run_agent/ + tests/agent/: 4313 passed, 1 pre-existing
test_auxiliary_client failure (unchanged).

run_agent.py: 3821 -> 3937 lines (+116 from the keyword-forwarded
init call's verbosity).  Final: 16083 -> 3937 (-12146, 75% reduction).

run_agent.py

@@ -376,7 +376,73 @@ class AIAgent:
     ):
         """Forwarder — see ``agent.agent_init.init_agent``."""
         from agent.agent_init import init_agent
-        init_agent(self, base_url, api_key, provider, api_mode, acp_command, acp_args, command, args, model, max_iterations, tool_delay, enabled_toolsets, disabled_toolsets, save_trajectories, verbose_logging, quiet_mode, ephemeral_system_prompt, log_prefix_chars, log_prefix, providers_allowed, providers_ignored, providers_order, provider_sort, provider_require_parameters, provider_data_collection, openrouter_min_coding_score, session_id, tool_progress_callback, tool_start_callback, tool_complete_callback, thinking_callback, reasoning_callback, clarify_callback, step_callback, stream_delta_callback, interim_assistant_callback, tool_gen_callback, status_callback, max_tokens, reasoning_config, service_tier, request_overrides, prefill_messages, platform, user_id, user_name, chat_id, chat_name, chat_type, thread_id, gateway_session_key, skip_context_files, load_soul_identity, skip_memory, session_db, parent_session_id, iteration_budget, fallback_model, credential_pool, checkpoints_enabled, checkpoint_max_snapshots, checkpoint_max_total_size_mb, checkpoint_max_file_size_mb, pass_session_id)
+        init_agent(
+            self,
+            base_url=base_url,
+            api_key=api_key,
+            provider=provider,
+            api_mode=api_mode,
+            acp_command=acp_command,
+            acp_args=acp_args,
+            command=command,
+            args=args,
+            model=model,
+            max_iterations=max_iterations,
+            tool_delay=tool_delay,
+            enabled_toolsets=enabled_toolsets,
+            disabled_toolsets=disabled_toolsets,
+            save_trajectories=save_trajectories,
+            verbose_logging=verbose_logging,
+            quiet_mode=quiet_mode,
+            ephemeral_system_prompt=ephemeral_system_prompt,
+            log_prefix_chars=log_prefix_chars,
+            log_prefix=log_prefix,
+            providers_allowed=providers_allowed,
+            providers_ignored=providers_ignored,
+            providers_order=providers_order,
+            provider_sort=provider_sort,
+            provider_require_parameters=provider_require_parameters,
+            provider_data_collection=provider_data_collection,
+            openrouter_min_coding_score=openrouter_min_coding_score,
+            session_id=session_id,
+            tool_progress_callback=tool_progress_callback,
+            tool_start_callback=tool_start_callback,
+            tool_complete_callback=tool_complete_callback,
+            thinking_callback=thinking_callback,
+            reasoning_callback=reasoning_callback,
+            clarify_callback=clarify_callback,
+            step_callback=step_callback,
+            stream_delta_callback=stream_delta_callback,
+            interim_assistant_callback=interim_assistant_callback,
+            tool_gen_callback=tool_gen_callback,
+            status_callback=status_callback,
+            max_tokens=max_tokens,
+            reasoning_config=reasoning_config,
+            service_tier=service_tier,
+            request_overrides=request_overrides,
+            prefill_messages=prefill_messages,
+            platform=platform,
+            user_id=user_id,
+            user_name=user_name,
+            chat_id=chat_id,
+            chat_name=chat_name,
+            chat_type=chat_type,
+            thread_id=thread_id,
+            gateway_session_key=gateway_session_key,
+            skip_context_files=skip_context_files,
+            load_soul_identity=load_soul_identity,
+            skip_memory=skip_memory,
+            session_db=session_db,
+            parent_session_id=parent_session_id,
+            iteration_budget=iteration_budget,
+            fallback_model=fallback_model,
+            credential_pool=credential_pool,
+            checkpoints_enabled=checkpoints_enabled,
+            checkpoint_max_snapshots=checkpoint_max_snapshots,
+            checkpoint_max_total_size_mb=checkpoint_max_total_size_mb,
+            checkpoint_max_file_size_mb=checkpoint_max_file_size_mb,
+            pass_session_id=pass_session_id,
+        )
 
     def _get_session_db_for_recall(self):
         """Return a SessionDB for recall, lazily creating it if an entrypoint forgot.