The "screen unchanged" result points the model at its previous capture. After
context compression that capture may be summarized away, so the note would refer
to pixels no longer in context. Mirror read_file's reset_file_dedup: the
compaction boundary (both the summary path and the codex app-server path) now
clears the session's screenshot digest, and the first capture afterwards delivers
the image again even when the screen is byte-identical.
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