Fixes #3745

[tom-material]

Summary

• Preserve direct child structuredContentBlock nodes during block SDT
  layout conversion
• Add a regression test for nested block SDT content and metadata

Test plan

• pnpm exec vitest run --config packages/layout-engine/tests/ vitest.config.mjs packages/layout-engine/tests/src/sdt-metadata.test.ts
• pnpm exec prettier --check packages/super-editor/src/editors/v1/core/ layout-adapter/sdt/structured-content-block.ts packages/layout-engine/tests/ src/sdt-metadata.test.ts

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Preserve outer SDT metadata when recursing

When a block SDT directly contains another structuredContentBlock (especially outer SDT -> inner SDT -> paragraph with no direct paragraph/table children on the outer), this recursive call converts the inner subtree with only the inner node's metadata, so no emitted FlowBlock carries the outer structuredContentMetadata. The painter derives block-SDT grouping/chrome from attrs.sdt, so the outer content control effectively disappears from layout/rendering for this valid nested shape; pass the inherited metadata through or record it separately instead of dropping it at the recursion boundary.

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[caio-pizzol]

Thanks for this, Tom. You found the right failing path: a block w:sdt nested directly inside another block w:sdt was skipped during layout conversion, so valid content was dropped.

We checked it against the OOXML schema and a Word-authored fixture. Nested block SDTs are valid, and the full fix needs to preserve the outer and inner controls as a hierarchy, not just recurse into the inner one. That crosses more of the rendering stack than this PR touches, so we're going to take it over rather than ask you to keep expanding it.

We're tracking the full fix in #3752 and will open the first follow-up PR linked there, then close this once that's up. We'll keep coverage for the repro shape and credit your work. Thanks again for the clear repro.