lint: fix B904 raise-from in share session-resolve + drop unused importlib

CI ruff gate flagged 3 new violations: two api/routes.py KeyError re-raises in an
except-KeyError block (add 'from None') + an unused importlib import in the share
security test. All trivial.

api/routes.py

@@ -5125,10 +5125,10 @@ def _resolve_share_session_pair(sid: str, handler):
         cli_meta = _lookup_cli_session_metadata(sid) or {}
         effective_profile = cli_meta.get("profile") or None
         if not _session_visible_to_active_profile(effective_profile, handler):
-            raise KeyError(sid)
+            raise KeyError(sid) from None
         synth, reason = _claim_or_synthesize_cli_session(sid, cli_meta=cli_meta)
         if reason == "was_webui" or synth is None:
-            raise KeyError(sid)
+            raise KeyError(sid) from None
         return synth, None, cli_meta
 
 

tests/test_session_public_share_static.py

@@ -87,7 +87,7 @@ def test_share_action_buttons_are_not_duplicated():
 def test_share_snapshot_redaction_is_always_on_regardless_of_setting():
     # The public-share boundary must redact credentials + local paths and drop
     # non-text/tool/system content EVEN IF the operator disabled api_redact_enabled.
-    import os, tempfile, importlib
+    import os, tempfile
     os.environ.setdefault("HERMES_WEBUI_STATE_DIR", tempfile.mkdtemp())
     import api.config as config
     import api.shares as shares