The fail-fast admission path (bounded compress pool, F6) only logged a
WARNING; in the compression-attempt telemetry stream a wedged pool
looked like compression simply stopped being attempted. Emit the
existing attempt telemetry with failure_class='pool_saturated'
(commit_status=aborted, split_status=aborted) on refusal, following
_emit_compression_attempt_telemetry's existing call shape. Regression
extends the F6 saturation test (sabotage-verified).
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