Adds a safety net to the writeJSON utility to prevent data loss when updating subtasks via the MCP server.
The MCP process was inadvertently causing the _rawTaggedData property, which holds the complete multi-tag structure, to be lost. When writeJSON received the data for only a single tag, it would overwrite the entire tasks.json file, deleting all other tags.
This fix makes writeJSON more robust. If it receives data that looks like a single, resolved tag without the complete structure, it re-reads the full tasks.json file from disk. It then carefully merges the updated data back into the correct tag within the full structure, preserving all other tags.
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