feat: append-only event log with projector skeleton

chat/eventlog/log.py

@@ -0,0 +1,38 @@
+from __future__ import annotations
+import json
+from dataclasses import dataclass
+from typing import Any, Iterator
+from sqlite3 import Connection
+
+
+@dataclass
+class Event:
+    id: int
+    branch_id: int
+    ts: str
+    kind: str
+    payload: dict[str, Any]
+    superseded_by: int | None
+    hidden: bool
+
+
+def append_event(conn: Connection, *, kind: str, payload: dict[str, Any], branch_id: int = 1) -> int:
+    cur = conn.execute(
+        "INSERT INTO event_log (branch_id, kind, payload_json) VALUES (?, ?, ?)",
+        (branch_id, kind, json.dumps(payload)),
+    )
+    return cur.lastrowid
+
+
+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 "
+        "FROM event_log WHERE branch_id = ? AND id > ? AND hidden = 0 "
+        "AND superseded_by IS NULL ORDER BY id",
+        (branch_id, after_id),
+    )
+    for row in cur:
+        yield Event(
+            id=row[0], branch_id=row[1], ts=row[2], kind=row[3],
+            payload=json.loads(row[4]), superseded_by=row[5], hidden=bool(row[6]),
+        )