feat: drawer surgical delete with cascade preview (T98.4)

tests/test_drawer_phase4.py

@@ -383,3 +383,76 @@ def test_t98_3_hidden_turn_disappears_from_read_recent_dialogue(
         after_ids = [t["event_id"] for t in after]
         assert user_id not in after_ids
         assert bot_id in after_ids  # the unhidden bot turn still surfaces
+
+
+# ---------------------------------------------------------------------------
+# T98.4 — surgical delete with cascade preview.
+# ---------------------------------------------------------------------------
+
+
+def test_t98_4_delete_preview_returns_impact_report_html(client, tmp_path):
+    db = tmp_path / "test.db"
+    _seed_chat(db)
+    user_id, bot_id = _seed_turns(db)
+
+    response = client.get(
+        f"/chats/chat_bot_a/drawer/turn/delete-preview/{user_id}"
+    )
+    assert response.status_code == 200
+    body = response.text
+
+    # Modal markup with the event id and the cascade list.
+    assert "delete-impact-modal" in body
+    assert f"Delete event {user_id}?" in body
+    assert "delete-impact-cascade" in body
+    # Both turns ride along in the cascade — user_turn at user_id, then
+    # the assistant_turn at bot_id (>= user_id).
+    assert "user_turn" in body
+    assert "assistant_turn" in body
+    # Confirm-form posts to the delete route.
+    assert f"/drawer/turn/delete/{user_id}" in body
+
+
+def test_t98_4_delete_invokes_rewind_and_drops_cascade(client, tmp_path):
+    db = tmp_path / "test.db"
+    _seed_chat(db)
+    user_id, bot_id = _seed_turns(db)
+
+    # Append a third turn after the assistant_turn so we can verify the
+    # cascade catches everything from user_id forward.
+    with open_db(db) as conn:
+        extra_id = append_and_apply(
+            conn,
+            kind="user_turn",
+            payload={
+                "chat_id": "chat_bot_a",
+                "prose": "follow-up",
+                "segments": [],
+            },
+        )
+
+    # Sanity: all three turn rows exist.
+    with open_db(db) as conn:
+        turn_count = conn.execute(
+            "SELECT COUNT(*) FROM event_log "
+            "WHERE kind IN ('user_turn', 'assistant_turn')"
+        ).fetchone()[0]
+        assert turn_count == 3
+
+    # Delete from user_id forward.
+    response = client.post(f"/chats/chat_bot_a/drawer/turn/delete/{user_id}")
+    assert response.status_code == 200
+
+    # All three turns are gone — the rewind truncated the log past
+    # user_id - 1, removing user_id, bot_id, and extra_id.
+    with open_db(db) as conn:
+        turn_count = conn.execute(
+            "SELECT COUNT(*) FROM event_log "
+            "WHERE kind IN ('user_turn', 'assistant_turn')"
+        ).fetchone()[0]
+        assert turn_count == 0
+        for ev_id in (user_id, bot_id, extra_id):
+            row = conn.execute(
+                "SELECT 1 FROM event_log WHERE id = ?", (ev_id,)
+            ).fetchone()
+            assert row is None, f"event {ev_id} should have been deleted"