fix: rotate log files instead of growing without bound (#885) (#932)

utils/logging_setup.py

@@ -0,0 +1,39 @@
+"""Shared construction of the rotating log file handler.
+
+Centralizes the rotation invariant so both the tray and the CLI log paths
+behave identically and the file can never grow without bound (issue #885).
+
+A ``RotatingFileHandler`` only rotates when ``backupCount >= 1``: CPython's
+``doRollover`` skips the entire rotation block when ``backupCount == 0``, so
+``maxBytes`` is silently ignored and the active file grows forever. We force
+at least one backup here regardless of caller input.
+"""
+
+from __future__ import annotations
+
+import logging.handlers
+
+
+_MIN_BYTES = 32 * 1024
+_MIN_BACKUPS = 1
+
+
+def build_log_handler(
+    path: str,
+    log_max_mb: float = 5,
+    backups: int = 1,
+) -> logging.handlers.RotatingFileHandler:
+    """Create a RotatingFileHandler that actually rotates.
+
+    ``backups`` is clamped to at least 1 so rotation is always active, and
+    ``maxBytes`` keeps a small floor so a misconfigured tiny size can't cause
+    rotation on every line.
+    """
+    max_bytes = max(_MIN_BYTES, int(log_max_mb * 1024 * 1024))
+    backup_count = max(_MIN_BACKUPS, int(backups))
+    return logging.handlers.RotatingFileHandler(
+        path,
+        maxBytes=max_bytes,
+        backupCount=backup_count,
+        encoding="utf-8",
+    )