Summary

On agent startup, messages loaded from SQLite that were stored with the old Summary MessagePart schema fail to deserialize with:

WARN zeph_memory::sqlite::messages: failed to deserialize message parts, falling back to empty
  role=assistant parts_json=[{"Summary":{"text":"..."}}]
  error=missing field 'kind' at line 1 column NNN

Root Cause

A kind field was added to MessagePart::Summary (or a related variant) without a #[serde(default)] attribute, breaking deserialization of messages stored before the change.

Impact

• Affected messages fall back to empty (role=assistant, no content) — effective context loss for older sessions
• No crash — graceful fallback exists
• Observed: 6 messages affected in the CI-223 test DB (stored during CI-219/220 sessions)
• May affect production users upgrading across the schema change

Expected Behavior

Old Summary messages should deserialize correctly (add #[serde(default)] to new fields, or add a DB migration to backfill the kind field).

Reproduction

1. Run agent sessions before the schema change (any session storing deferred summaries)
2. Upgrade and start a new session on the same DB
3. Observe WARN lines at startup during restored N message(s)

Config

.local/config/testing.toml, SQLite backend, history_limit=50