docs: migrate project memory governance

.project-docs/60-reflection/reflection-index.md

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+# Reflection Index
+
+Use this index for second-order workflow lessons.
+
+| Date | Reflection | Trigger | Action | Detail |
+|---|---|---|---|---|
+| 2026-08-28 | Shared rolling planning files created repeated size pressure and forced semantic compression. | Root `task_plan.md` repeatedly approached or exceeded its fixed limit. | Replaced the legacy system with task-scoped records plus serialized canonical integration in `.project-docs/`. | [Migration task](../30-worklog/tasks/20260828-migrate-project-docs-6f1a9c2d.md) |
+
+## When To Reflect
+
+Create a reflection only when work reveals a reusable lesson: skipped gates, repeated mistakes, durable debugging patterns, ineffective plans, human corrections, or candidates for new scripts or skills.
+
+Routine task completion belongs in `30-worklog/task-history.md`.