FrameCompressor should expose write errors

`FrameCompressor` currently unwraps any errors from the writer during compression. These errors should be bubbled up to the caller instead, so that they can decide how to handle them.

Start by locating FrameCompressor and trace how writer errors are handled during compression. Verify that those errors reach the caller rather than being unwrapped, and add or update coverage for the error path if the surrounding code provides tests.

Written by the indexing model from the issue text.