bug(meta): corrupted meta files on abrupt shutdown cause JSONDecodeError on startup

[akremenetsky]

Description

When a node is powered off abruptly (power loss, crash), the meta driver files used by JsonFileStorageSingleton can become empty or contain truncated JSON. On the next boot, load() calls json.load(f) on the corrupted file and fails with:

json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

This prevents all meta-based drivers (render, etc.) from starting, leaving the universal agent in a crash loop.

Root cause

JsonFileStorageSingleton.persist() (storage/common.py:47) uses an atomic write pattern (tmp file + os.replace) which is safe against crashes during the replace step. However, the file can still be corrupted if:

1. The crash occurs during the initial write to the .tmp file, and the tmp file is later cleaned up without restoring the original.
2. The meta file was created empty by a previous failed operation.
3. A power loss happens during a write that predates the atomic pattern or bypasses it.

load() (common.py:35) has no defense against this — it opens the file and calls json.load() unconditionally.