docs(tess): add migration evidence set

docs/tess/M5-MIGRATION-RETENTION-DEPRECATION.md

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+# TESS-MIG-001 — Retention and Legacy Deprecation Policy
+
+## Retention
+
+- Hermes is not a Mosaic persistence authority. The adapter maps runtime behavior only; it does not import or persist Hermes legacy session shapes.
+- Mosaic operator memory is scoped by tenant, owner, and session in `packages/memory/src/operator-memory-plugin.ts`; gateway session ownership is derived before that plugin is made available in `apps/gateway/src/agent/agent.service.ts`.
+- Existing Hermes archives remain in their source system under its existing retention policy. This project has no landed automatic transcript, profile, or preference migration.
+- Any future import requires an explicit, scoped design and redaction/provenance evidence; it must not extend `packages/types` with Hermes schema.
+
+## Deprecation
+
+- Session adapter use remains transitional until M5 qualification demonstrates the normalized provider path.
+- Kanban, skills, memory, tools, and cron are not deprecated into a Hermes bridge: they remain explicitly unsupported until their Mosaic-owned contracts are implemented and qualified.
+- A future deprecation change must remove the external binding first, retain rollback evidence, and then remove the adapter in a separately reviewed code change. It must not silently replace or widen a registered provider.