A Strange File Named '[object Promise].metadata.json' is Generated After Execution

After execution, an unintended and strange file named [object Promise].metadata.json seems to be generated in the current working directory (cwd).

It appears that an await is missing in the part of the code that calculates the path for the metadata file.

https://github.com/denosaurs/cache/blob/83e4287694b0affe39bcad72f4cb7f99d3679057/file.ts#L145

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minimum reproducible example is here

https://gist.github.com/podhmo/476b79c026d24c69abef532c8dcea292

Inspect file.ts around line 145 and reproduce the behavior using the minimum reproducible example in the linked gist. Trace the metadata path calculation and verify that execution no longer creates a [object Promise].metadata.json file in the current working directory.

Written by the indexing model from the issue text.