feat: post-turn state-update pass per present entity

chat/eventlog/log.py

@@ -24,6 +24,45 @@ def append_event(conn: Connection, *, kind: str, payload: dict[str, Any], branch
     return cur.lastrowid
 
 
+def append_and_apply(
+    conn: Connection,
+    *,
+    kind: str,
+    payload: dict[str, Any],
+    branch_id: int = 1,
+) -> int:
+    """Append an event AND immediately apply just that event's handler.
+
+    Calling :func:`chat.eventlog.projector.project` after an append
+    re-runs every prior event, which is fine for idempotent inserts but
+    catastrophic for delta-shaped events like ``edge_update`` whose
+    handler is *not* replay-safe (each pass would re-add the same
+    ``affinity_delta``). This helper runs only the brand-new event
+    through the registered handler, leaving prior state untouched.
+
+    No-ops cleanly when ``kind`` has no registered handler — useful for
+    transcript-only events like ``user_turn`` / ``assistant_turn`` where
+    callers may swap ``append_event`` for ``append_and_apply`` without
+    side effects.
+    """
+    # Local import to avoid a circular dependency at module import: the
+    # projector imports from .log to define ``Event``.
+    from chat.eventlog.projector import apply_event
+
+    eid = append_event(conn, kind=kind, payload=payload, branch_id=branch_id)
+    event = Event(
+        id=eid,
+        branch_id=branch_id,
+        ts="",
+        kind=kind,
+        payload=payload,
+        superseded_by=None,
+        hidden=False,
+    )
+    apply_event(conn, event)
+    return eid
+
+
 def read_events(conn: Connection, branch_id: int = 1, after_id: int = 0) -> Iterator[Event]:
     cur = conn.execute(
         "SELECT id, branch_id, ts, kind, payload_json, superseded_by, hidden "