fix(discord): define view classes after lazy discord.py install

When discord.py is not installed at import time, DISCORD_AVAILABLE=False
and the view class definitions at module bottom are skipped.
check_discord_requirements() performs a lazy install and sets
DISCORD_AVAILABLE=True but never re-ran the class definitions, causing
NameError on the first button interaction (exec approval, slash confirm, etc.).

Extract the five ui.View subclasses into _define_discord_view_classes() and
call it both at module load (when discord.py is pre-installed) and inside
check_discord_requirements() after a successful lazy install.

tests/gateway/test_discord_lazy_install_views.py

@@ -0,0 +1,81 @@
+"""Regression: Discord UI view classes must be defined after lazy-install.
+
+When discord.py is NOT installed at module load time, the
+``if DISCORD_AVAILABLE:`` guard at the bottom of gateway/platforms/discord.py
+evaluates to False and is skipped — leaving ExecApprovalView and its four
+siblings undefined in the module globals.
+
+check_discord_requirements() must call _define_discord_view_classes() after
+a successful lazy install so that all view classes are available the moment
+DISCORD_AVAILABLE flips to True.  Without this, the first button interaction
+(exec approval, slash confirm, etc.) raises NameError even though
+DISCORD_AVAILABLE=True.
+
+Fixes: lazy-install path NameError for ExecApprovalView, SlashConfirmView,
+UpdatePromptView, ModelPickerView, ClarifyChoiceView.
+"""
+import importlib
+import sys
+from unittest.mock import patch
+
+import pytest
+
+_VIEW_NAMES = [
+    "ExecApprovalView",
+    "SlashConfirmView",
+    "UpdatePromptView",
+    "ModelPickerView",
+    "ClarifyChoiceView",
+]
+
+
+class TestDefineDiscordViewClasses:
+    """_define_discord_view_classes() registers all UI view classes in module globals."""
+
+    def test_registers_all_five_view_classes(self, monkeypatch):
+        """Calling _define_discord_view_classes() must (re)define all 5 view classes."""
+        dp = importlib.import_module("gateway.platforms.discord")
+
+        # Remove the classes to simulate the state where the module was loaded
+        # with DISCORD_AVAILABLE=False (the lazy-install scenario).
+        for name in _VIEW_NAMES:
+            monkeypatch.delattr(dp, name)
+
+        # Pre-condition: classes are gone
+        for name in _VIEW_NAMES:
+            assert not hasattr(dp, name), f"{name} should be absent before the call"
+
+        dp._define_discord_view_classes()
+
+        for name in _VIEW_NAMES:
+            assert hasattr(dp, name), f"{name} must be defined after _define_discord_view_classes()"
+            assert isinstance(getattr(dp, name), type), f"{name} must be a class"
+
+    def test_check_discord_requirements_calls_define_on_lazy_install(self, monkeypatch):
+        """check_discord_requirements() must call _define_discord_view_classes() on
+        a successful lazy install so view classes exist when DISCORD_AVAILABLE=True."""
+        dp = importlib.import_module("gateway.platforms.discord")
+
+        # Simulate discord not yet available at module load.
+        monkeypatch.setattr(dp, "DISCORD_AVAILABLE", False)
+
+        define_called = [False]
+        orig_define = dp._define_discord_view_classes
+
+        def _spy_define():
+            define_called[0] = True
+            orig_define()
+
+        monkeypatch.setattr(dp, "_define_discord_view_classes", _spy_define)
+
+        # Patch lazy_deps.ensure to be a no-op (pretend install succeeds).
+        # The discord imports inside check_discord_requirements() succeed because
+        # _ensure_discord_mock() in conftest.py already registered the mock.
+        with patch("tools.lazy_deps.ensure"):
+            result = dp.check_discord_requirements()
+
+        assert result is True, "check_discord_requirements() should return True after lazy install"
+        assert define_called[0], (
+            "check_discord_requirements() must call _define_discord_view_classes() "
+            "after a successful lazy install so view classes are not undefined"
+        )