Plan: reduce Phase 4 degradation from warning-driven retries and parity churn

[jafreck]

Goal

Track execution hardening work to reduce Phase 4 retry churn under the wave/barrier model.

Context

Issue #70 is now the primary execution model: run code-migrator work in waves, then pause for build/test/fix barriers. No concurrent migration during validation/fix loops.

Primary implementation priority

• Runtime: introduce wave/barrier execution (migrate batch first, then build/test/fix) #70 Runtime: introduce wave/barrier execution (first implementation priority)

Ordered implementation sequence

• 1. Runtime: introduce wave/barrier execution (migrate batch first, then build/test/fix) #70 Wave/barrier execution scheduling and barriers
• 2. Config+Runtime: wave/barrier qualityPolicy and barrier-gated strictness #67 Quality policy + strictness controls reframed for barrier checkpoints/final gates
• 3. Runtime: add repeated failure-signature dedup to prevent redundant retries #66 and Runtime: short-circuit deterministic quality failures in build/test recovery loop #65 Retry/control hardening aligned to wave-level execution
• 4. Runtime: add parity retry guardrails based on improvement signal #69 Parity retry guardrails after barrier validation outcomes
• 5. Runtime: barrier checkpoint validation templates (task-scoped with global fallback) #68 Barrier templates/checkpoints for deterministic validation execution

Acceptance Criteria

• Runtime: introduce wave/barrier execution (migrate batch first, then build/test/fix) #70 lands first and becomes the default strategy target for this workstream.
• Follow-on issues align to wave/barrier lifecycle semantics.
• Reduced redundant retries and clearer blocked-task diagnostics under Phase 4.