feat(mcp): journal d'usage mcp_usage (détection niveau 1, #114)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/mcp/usage.py

@@ -0,0 +1,68 @@
+import sqlite3
+from contextlib import contextmanager
+from datetime import datetime, timedelta, timezone
+from pathlib import Path
+
+SCHEMA = """
+CREATE TABLE IF NOT EXISTS mcp_usage (
+    id         INTEGER PRIMARY KEY,
+    user_id    INTEGER,
+    token_id   INTEGER,
+    kind       TEXT NOT NULL,
+    created_at TEXT NOT NULL
+);
+CREATE INDEX IF NOT EXISTS idx_mcp_usage_user ON mcp_usage(user_id, created_at);
+"""
+
+
+def _utcnow_iso() -> str:
+    return datetime.now(timezone.utc).isoformat(timespec="seconds")
+
+
+@contextmanager
+def _connect(db_path):
+    conn = sqlite3.connect(str(db_path))
+    conn.row_factory = sqlite3.Row
+    try:
+        yield conn
+    finally:
+        conn.close()
+
+
+def init_schema(db_path) -> None:
+    Path(db_path).parent.mkdir(parents=True, exist_ok=True)
+    with _connect(db_path) as conn:
+        conn.executescript(SCHEMA)
+        conn.commit()
+
+
+def record(db_path, user_id: int, token_id: int, kind: str) -> None:
+    """Journalise une requête /_mcp authentifiée. Best-effort : n'échoue jamais."""
+    try:
+        with _connect(db_path) as conn:
+            conn.execute(
+                "INSERT INTO mcp_usage (user_id, token_id, kind, created_at) "
+                "VALUES (?, ?, ?, ?)",
+                (user_id, token_id, kind, _utcnow_iso()),
+            )
+            conn.commit()
+    except sqlite3.Error:
+        pass
+
+
+def count_since(db_path, user_id: int, iso_ts: str) -> int:
+    with _connect(db_path) as conn:
+        row = conn.execute(
+            "SELECT COUNT(*) FROM mcp_usage WHERE user_id = ? AND created_at >= ?",
+            (user_id, iso_ts),
+        ).fetchone()
+    return row[0]
+
+
+def purge_older_than(db_path, days: int = 90) -> None:
+    cutoff = (datetime.now(timezone.utc) - timedelta(days=days)).isoformat(
+        timespec="seconds"
+    )
+    with _connect(db_path) as conn:
+        conn.execute("DELETE FROM mcp_usage WHERE created_at < ?", (cutoff,))
+        conn.commit()