Gate finding 2ab (BN05 final): when the deduped in-flight original was the
first non-system row (cron / first-compression shape), removing it left the
window opening system -> assistant(tool_calls) -> tool -> carrier. The
carrier-flip guard judges template-visible roles, which skip tool_calls
rows, so it saw nothing wrong; native Gemini maps that leading row to a
model functionCall turn, which its API rejects as the first turn.
After the dedup, if the first non-system row is not a user row, move the
carrier there (the existing flip then makes it role=user). The kept test now
asserts the raw role of compressed[1], since the template-visible check
cannot see a leading tool-call row.
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