simplify(compat): gateway — drop 30 re-exports/aliases + 2 shim modules, re-remove 3 shim-only names, repoint 24 callers + 34 test files

Per COMPAT_REMOVAL.md (internal import paths are not a stable API):

Re-exports removed
- gateway/run.py: atomic_json_write, load_dotenv, resolve_delivery_transport,
  TurnRunner, merge_pending_message_event, _arm_loop_floor_timer,
  start_loop_liveness_watchdog, DEFAULT_GATEWAY_POST_INTERRUPT_GRACE_TIMEOUT,
  _UNSET (9) — run_* mixins and tests now import from the defining module
  (gateway.delivery / gateway.run_turn_runner / gateway.platforms.base /
  gateway.shutdown_watchdog / gateway.restart / utils).
- gateway/session.py: SessionResetPolicy, normalize_whatsapp_identifier,
  TranscriptReadError, auto_continue_freshness_window (+ "_now & co." noqa
  facade) — gateway/__init__ takes SessionResetPolicy from .config; callers
  take TranscriptReadError from gateway.session_transcript.
- gateway/kanban_watchers.py: _wake_scope_id + "tests import via origin" noqa
  facade; tests import from kanban_watchers_common / _notifier.
- gateway/slash_commands.py: _model_switch_skew_guard, HISTORY_UNREADABLE.
- gateway/stream_consumer.py: escape_code_fences_for_display.
- gateway/platforms/api_server.py: "re-exported" RunIdempotencyStore comment;
  tui_gateway + tests import gateway.platforms.api_server_run_idempotency.
- gateway/platforms/__init__.py: PEP 562 __getattr__/__dir__ lazy QQAdapter /
  YuanbaoAdapter facade (no in-tree importer).
- gateway/startup_watchdog.py: whole re-export shim module deleted; the three
  in-tree callers import hermes_startup_watchdog directly.

Aliases removed
- gateway/platforms/signal.py: SignalAdapter._markdown_to_signal.
- gateway/shutdown_forensics.py: _parse_systemd_duration_to_us.
- gateway/platforms/yuanbao.py: OutboundManager.start_slow_notifier /
  cancel_slow_notifier / get_chat_lock / _chat_locks / CHAT_DICT_MAX_SIZE
  delegates; module-level get_active_adapter / send_yuanbao_direct;
  MarkdownProcessor has_unclosed_fence / ends_with_table_row /
  split_at_paragraph_boundary static pass-throughs (chunk_markdown_text stays —
  it carries yuanbao's chunking policy). tools/send_message_senders +
  tools/yuanbao_tools call YuanbaoAdapter.get_active() / sender.send_direct().

Shim-only names re-removed (earlier review-fix round 96c104c903)
- CapabilityDescriptor.from_platform_entry (+ tests/gateway/relay/test_descriptor_from_entry.py)
- SessionTurnLeaseRegistry.__len__ (+ its test)
- is_relay_media_url KEPT: download() uses it, real internal helper.

Tests that pinned a shim (startup_watchdog re-export identity, api_server
RunIdempotencyStore identity, signal wrapper parity) are dropped; tests that
pinned live behavior are repointed at the implementation.

Note: the gateway/run.py hunk of this change was swept into 00a3cfe5c9 by a
concurrent commit on the shared worktree; this commit carries the rest.

Verified in an isolated worktree (HEAD + this change only): ruff clean,
import-smoke of all 33 touched modules under a fresh HERMES_HOME,
605 passed / 1 skipped across the 39 covering test files.

gateway/run_agent_cache.py

@@ -17,7 +17,8 @@ from gateway.session import SessionSource, build_session_context_prompt
 from hermes_cli.config import cfg_get
 
 if TYPE_CHECKING:  # string annotations only; never imported at runtime (cycle)
-    from gateway.run import GatewayRunner, TurnRunner  # noqa: F401
+    from gateway.run import GatewayRunner  # noqa: F401
+    from gateway.run_turn_runner import TurnRunner  # noqa: F401
 
 # Log-record parity with the origin module.
 logger = logging.getLogger("gateway.run")