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The Phase-2 gate: more, smaller wire units must not regress FEC recovery. Adds a GF16 streamed column (three chunk pushes + finish per AU — sentinel blocks then real totals). Measured: identical to whole-AU at every loss rate (50/50 through 1/6, the same 25%-budget cliff). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>