chore: prune unused imports and duplicate import redefinitions

Remove unused imports (F401) and duplicate/shadowed import
redefinitions (F811) across the codebase using ruff's safe
autofixes. No behavioral changes -- imports only.

- ~1400 safe autofixes applied across 644 files (net -1072 lines)
- __init__.py re-exports preserved (excluded from F401 removal so
  public re-export surfaces stay intact)
- Re-exports that are imported or monkeypatched by tests but look
  unused in their defining module are kept with explicit # noqa:
  F401 (gateway/run.py load_dotenv; run_agent re-exports from
  agent.message_sanitization, agent.context_compressor,
  agent.retry_utils, agent.prompt_builder, agent.process_bootstrap,
  agent.codex_responses_adapter)
- Unsafe F841 (unused-variable) fixes deliberately skipped -- those
  can change behavior when the RHS has side effects
- ruff lints remain disabled in pyproject.toml (only PLW1514 is
  selected); this is a one-time cleanup, not a config change

Verification:
- python -m compileall: clean
- pytest --collect-only: all 27161 tests collect (zero import errors)
- core entry points import clean (run_agent, model_tools, cli,
  toolsets, hermes_state, batch_runner, gateway)
- static scan: every name any test imports directly from an edited
  module still resolves

agent/conversation_loop.py

@@ -27,8 +27,6 @@ import time
 import uuid
 from typing import Any, Dict, List, Optional
 
-from agent.anthropic_adapter import _is_oauth_token
-from agent.auxiliary_client import set_runtime_main
 from agent.codex_responses_adapter import _summarize_user_message_for_log
 from agent.display import KawaiiSpinner
 from agent.error_classifier import FailoverReason, classify_api_error
@@ -53,20 +51,13 @@ from agent.model_metadata import (
     parse_available_output_tokens_from_error,
     save_context_length,
 )
-from agent.nous_rate_guard import (
-    clear_nous_rate_limit,
-    is_genuine_nous_rate_limit,
-    nous_rate_limit_remaining,
-    record_nous_rate_limit,
-)
 from agent.process_bootstrap import _install_safe_stdio
 from agent.prompt_caching import apply_anthropic_cache_control
 from agent.retry_utils import jittered_backoff
 from agent.trajectory import has_incomplete_scratchpad
 from agent.usage_pricing import estimate_usage_cost, normalize_usage
-from hermes_constants import display_hermes_home as _dhh_fn, PARTIAL_STREAM_STUB_ID
+from hermes_constants import PARTIAL_STREAM_STUB_ID
 from hermes_logging import set_session_context
-from tools.schema_sanitizer import strip_pattern_and_format
 from tools.skill_provenance import set_current_write_origin
 from utils import base_url_host_matches, env_var_enabled
 
@@ -409,7 +400,6 @@ def run_conversation(
 
     # Tag all log records on this thread with the session ID so
     # ``hermes logs --session <id>`` can filter a single conversation.
-    from hermes_logging import set_session_context
     set_session_context(agent.session_id)
 
     # Bind the skill write-origin ContextVar for this thread so tool
@@ -418,7 +408,6 @@ def run_conversation(
     # a foreground user-directed turn. Set at the top of each call;
     # the review fork runs on its own thread with a fresh context,
     # so the foreground value here does not leak into it.
-    from tools.skill_provenance import set_current_write_origin
     set_current_write_origin(getattr(agent, "_memory_write_origin", "assistant_tool"))
 
     # If the previous turn activated fallback, restore the primary