game-engines: allegro5/bullet3/box2d/dry CWE-407 scan

bullet3-0001: btGhostObject::addOverlappingObjectInternal O(N²) linear dedup
  per broadphase step — even carries "too slow" self-admission comment (HIGH)
bullet3-0002: btSoftRigidCollisionAlgorithm::processCollision O(C×D) per
  frame on m_collisionDisabledObjects plain array (MEDIUM)
allegro5: CLEAN (vector_contains only on non-hot setup paths)
box2d: CLEAN (v3 rewrite uses b2HashSet throughout)
dry: CLEAN (HashSet/HashMap on all hot dedup paths)

defects/synapse/patch/CLEAN.md

@@ -0,0 +1,17 @@
+# synapse — CWE-407 Scan: CLEAN
+
+Scanned: 2026-03-29
+
+## Scope
+
+- `synapse/push/mailer.py` — `deduped_ordered_list`: `seen = set()` (line 939)
+- `synapse/storage/databases/main/event_push_actions.py` — `seen_thread_ids`: `set()` based
+- Event DAG traversal / state resolution: checked state_resolution_v2.py, event_federation.py
+- Room auth chain computation: uses set-based seen throughout
+
+## Verdict
+
+No CWE-407 (algorithmic complexity / quadratic membership check) defects found.
+All deduplication in push notification, event DAG traversal, and state
+resolution uses `set` or `dict` structures. No list-based visited patterns in
+hot paths.