tasks that fail their quality gates after max retries do not merge. instead they move to .sdd/backlog/dead-letter/, with the full agent transcripts, last-known worktree path, gate output, and a synth-generated failure-class label from the eval taxonomy. you can inspect each entry, fix the prompt or split the task, and re-queue. the dead-letter pile is bernstein's escape hatch: rather than burn budget retrying a broken brief, the orchestrator parks it for a human. the eval harness also pulls from this directory to build regression cases for future runs. source: src/bernstein/core/tasks/dead_letter.py.
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