Add canonical event log and renderer skeleton (A10)

Build-order step 4, sequenced before the LLM client (step 3) because
the client interface consumes the canonical log.

- canonical.py: typed events for the full A10 table (user_message
  through compaction); canonical tool-call IDs minted locally,
  provider IDs never a join key; strict payload validation on load
- StateStore: canonical_events table via schema v2 — the first real
  migration, exercised in a test against a hand-built v1 database —
  with append_event/read_events on the same fsync-per-commit path
- render.py: request bodies rendered from the log at call time;
  first adapter targets the OpenAI-compatible shape of LiteLLM's
  normalized route; compaction events replace their id range at
  render time while staying in the durable log
- Crash integration test now also verifies transcript appends
  survive process death

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

nisse-dev/src/nisse_dev/state.py

@@ -18,14 +18,35 @@ from datetime import UTC, datetime
 from pathlib import Path
 from typing import Any, Self
 
+from nisse_dev.canonical import (
+    CanonicalEvent,
+    StoredEvent,
+    event_type,
+    from_payload,
+    to_payload,
+)
 from nisse_dev.oplog import OpLog
 
-CURRENT_SCHEMA_VERSION = 1
+CURRENT_SCHEMA_VERSION = 2
 
 Migration = Callable[[sqlite3.Connection], None]
 
+_CANONICAL_EVENTS_DDL = """
+CREATE TABLE canonical_events (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    ts TEXT NOT NULL,
+    type TEXT NOT NULL,
+    payload TEXT NOT NULL
+)
+"""
+
+
+def _migrate_v1_add_canonical_events(conn: sqlite3.Connection) -> None:
+    conn.execute(_CANONICAL_EVENTS_DDL)
+
+
 # Maps version N to the migration that takes the schema from N to N+1.
-MIGRATIONS: Mapping[int, Migration] = {}
+MIGRATIONS: Mapping[int, Migration] = {1: _migrate_v1_add_canonical_events}
 
 
 class StateSchemaError(RuntimeError):
@@ -71,6 +92,7 @@ _SCHEMA = [
         resolved_at TEXT
     )
     """,
+    _CANONICAL_EVENTS_DDL,
 ]
 
 
@@ -249,6 +271,29 @@ class StateStore:
             for row in rows
         ]
 
+    def append_event(self, event: CanonicalEvent) -> int:
+        """Append to the canonical transcript (A10); committed and fsynced
+        before return, like every other durable write."""
+        cursor = self._conn.execute(
+            "INSERT INTO canonical_events (ts, type, payload) VALUES (?, ?, ?)",
+            (_now(), event_type(event), json.dumps(to_payload(event))),
+        )
+        assert cursor.lastrowid is not None
+        return cursor.lastrowid
+
+    def read_events(self, after: int = 0) -> list[StoredEvent]:
+        rows = self._conn.execute(
+            "SELECT * FROM canonical_events WHERE id > ? ORDER BY id", (after,)
+        ).fetchall()
+        return [
+            StoredEvent(
+                id=row["id"],
+                ts=row["ts"],
+                event=from_payload(row["type"], json.loads(row["payload"])),
+            )
+            for row in rows
+        ]
+
     def close(self) -> None:
         self._conn.close()