The chat timeline lost per-turn changed file cards when the visible user message ids did not match persisted transcript ids, and sessions without SDK file-history snapshots had no fallback source for turn changes. Match live cards by stable user-message index when needed and derive checkpoint previews from transcript tool calls when snapshots are absent.
Constraint: Right-side workspace changes already derive from transcript tool calls, so chat checkpoint data must remain consistent with that source.
Rejected: Force a history reload after every turn | would hide the id mismatch but add churn and still not cover transcript-only sessions.
Confidence: high
Scope-risk: moderate
Directive: Keep snapshot checkpoints as the preferred source, and use transcript extraction only as the compatibility fallback.
Tested: bun test src/server/__tests__/sessions.test.ts
Tested: bun test src/server/__tests__/workspace-service.test.ts
Tested: cd desktop && bun run test src/components/chat/MessageList.test.tsx
Tested: cd desktop && bun run lint
Tested: cd desktop && bun run test
Tested: git diff --check
Not-tested: Browser E2E against a live model session.
103a6cc42b