Use transcript activity timestamps for session list ordering instead of JSONL mtime, and skip duplicate runtime metadata appends.
Tested: bun test src/server/__tests__/sessions.test.ts --test-name-pattern "metadata-only writes|duplicate runtime metadata"
Tested: bun test src/server/__tests__/sessions.test.ts
Tested: bun run check:server
Confidence: high
Scope-risk: moderate