feat(environment): system_launch, preference whitelist and operator prompts on COM; declared refusals headlessly

user_pick_point / user_select answer {cancelled: true} on ESC (DISP_E_EXCEPTION)
and {timed_out: true} past COM_CALL_TIMEOUT; preferences_set refuses read-only,
unknown and out-of-range keys before any ActiveX call.

The read-only key is Files.PrinterStyleSheetPath, not the spec's
PrintStyleSheetPath: IAcadPreferencesFiles has no member of that name
(measured live on AutoCAD 2026 / R25.1), and a misspelt key would make
preferences_get() raise on every live call.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FKFStjEFzpGyLq5bMpWxTd

engineering/environment/__init__.py

@@ -1,5 +1,6 @@
 """Environment helpers (v1.6 track E): portable layer states, view and UCS
-argument resolution. Pure data and validation — no ezdxf, no COM."""
+argument resolution, the preference whitelist. Pure data and validation — no
+ezdxf, no COM."""
 
 from .layer_states import (  # noqa: F401
     DICT_NAME,
@@ -12,5 +13,11 @@ from .layer_states import (  # noqa: F401
     validate_state_name,
 )
 from .names import validate_name  # noqa: F401
+from .preferences import (  # noqa: F401
+    PREFERENCE_KEYS,
+    READ_ONLY_KEYS,
+    describe_preferences,
+    validate_preference,
+)
 from .ucs import WORLD, resolve_ucs_axes  # noqa: F401
 from .views import resolve_view_args  # noqa: F401