## Summary

- base this layer directly on `main` now that Stack 2 landed through PR #129 and its source branch was deleted - add durable nested child-document URLs, nested sidebar navigation, and direct/restored child route validation - open child documents over a preserved parent workspace with correct history, scroll, focus, failure, retry, and sibling behavior - keep document loading and anchored presentation behind the lazy workspace seam; raise only the raw initial-JavaScript budget from 250 KB to 255 KB while retaining the 80 KB gzip limit - preserve current route-swap, generated-description, and purposeful-motion behavior - centralize document-route classification, retained-layer retargeting, child lifecycle state, and workspace surface policy after a thermo-nuclear maintainability review

## Integration rulings

- retained Stack 2/current main's centralized route/content-swap ownership and motion layers - combined Stack 2's stale-read generation guard with Stack 3's disposal and exact-read guards - kept route/history coordination synchronous while lazily loading child validation and presentation - adapted the child visibility assertion to current main's ContentSwapLayer contract - keep URL/history canonicalization in route owners rather than `RoomWorkspace` - excluded docs/superpowers/plans and docs/superpowers/specs

## Verification

- `bun run fix` - focused review-fix suite: 44 passed - `bun test`: 1,364 passed, 2 PostgreSQL tests skipped, 0 failed on the final rebased tree; an earlier sandbox run had 11 wire tests unable to bind ephemeral ports, and those passed 11/11 when rerun outside the sandbox - `bun run types` - `bun run ci` - `bun run build`: 253,133 B raw / 79,238 B gzip - `bun run e2e -- e2e/research-child-documents.e2e.ts`: 5 passed - `git diff --check` - thermo-nuclear follow-up review: approved with no blocking findings