Cover all Store interface methods plus edge cases:
- Basic roundtrip, ordering, empty session, tool calls
- Logical truncation (keep last N, keep zero, keep more than exist)
- SetHistory replacing all + resetting skip offset
- Crash recovery with partial JSON lines
- Persistence across store instances
- Concurrent add+read (10 goroutines x 20 msgs)
- Simulated #704 race (summarizer vs main loop)
- Benchmarks for AddMessage and GetHistory (100/1000 msgs)
Add JSONLStore that persists sessions as .jsonl files (one message per
line) plus .meta.json for summary and truncation offset.
Key design decisions:
- Append-only writes — no full-file rewrites on AddMessage
- Logical truncation via skip offset instead of physical deletion
- Per-session mutex for safe concurrent access
- Crash recovery: malformed trailing lines are silently skipped
- Atomic metadata writes using temp+rename
Zero new dependencies — pure stdlib.
Refs #711
Introduce a backend-agnostic Store interface in pkg/memory/ that maps
one-to-one with the current SessionManager API. Each method is atomic
— no separate Save() call needed.
Refs #711
xiaoen