Desktop rewind previously used the visible user-message index as the primary selector. That can drift from the persisted active chain when hidden or non-rendered user messages exist, so the API now prefers a stable user message id and checks the selected prompt text before mutating transcript or files.
Constraint: Desktop UI can hide transcript entries that still exist in the persisted session chain
Rejected: Keep index-only rewind | can target an earlier user message after UI/server chain drift
Confidence: high
Scope-risk: moderate
Directive: Do not remove targetUserMessageId or expectedContent guards without reproducing shifted visible-index sessions
Tested: bun test src/server/__tests__/sessions.test.ts --timeout 20000
Tested: cd desktop && bun run test MessageList.test.tsx chatStore.test.ts -- --run
Tested: desktop/scripts/e2e-rewind-agent-browser.sh
Tested: desktop/scripts/e2e-rewind-complex-agent-browser.sh
Not-tested: Full desktop Vitest suite still has unrelated locale-sensitive failures
