feat(preview): single-file deck transitive include + image closure (bd-9cyza5vy)

[cscheid]

What

Single-file q2 preview deck.qmd (no _quarto.yml) previously synced only the deck, a sibling _brand.yml, and the deck's direct images into the preview VFS. So {{< include part.qmd >}} rendered as a literal ?include placeholder, and any image referenced inside an included file was missing — single-file preview diverged from both q2 render and project-mode preview.

This resolves the deck's full transitive static dependency closure natively — without walking the directory (preserving the bd-tnm3k safety property) — by running the renderer's own ParseDocumentStage + IncludeExpansionStage against the real filesystem and reading back what it consumed:

• includes from DocumentAst::recorded_includes (transitive, cycle-truncated)
• images from collect_referenced_asset_urls over the expanded AST, deck-dir-anchored — matching render's "no path retargeting" design

Reusing the real stages (rather than a parallel walker) keeps preview path resolution in exact lock-step with render, including a latent nested-include retargeting bug (filed separately as bd-udrn0q47), which preview now inherits automatically instead of hard-coding one side of a contested rule.

Changes

• quarto-preview config.rs: resolve_single_file_deps -> SingleFileDeps (supersedes + deletes resolve_single_file_assets); build_hub_config makes one resolver call filling both channels.
• quarto-hub discovery.rs + context.rs: included .qmd ride a new invisible text path — HubConfig.single_file_text_deps → ProjectFiles.text_dep_files + with_text_deps (in text_files()/all_files()/counts, not qmd_files, mirroring resource_files). The single-file preview SPA has no file list, so included files stay VFS-only dependencies.
• quarto-hub watch.rs + server.rs: extend the single-file watch set to the resolved closure (WatchConfig.single_file_deps) so editing an included file or referenced image re-renders, while unrelated siblings still never surface (bd-tnm3k preserved).

Tests

TDD throughout:

• 6 resolver tests: include + image-in-include, transitive, deck-dir anchoring (render parity), cycle termination, under-root guard, deck-own direct image.
• discovery + context: invisible-text-dep invariants (synced as text, absent from qmd_files, in the index).
• watcher: closure dep surfaces while an unrelated sibling is ignored.
• cargo xtask verify --skip-hub-build passes (clippy -D warnings + full-workspace nextest). The fix is native-only; WASM/quarto-core unchanged.

E2E

Browser inspection of q2 preview main.qmd (no _quarto.yml) where main.qmd includes part.qmd which references inc-image.png: the include expands ("Included Section" renders, no literal ?include), and the image inside the include displays via a blob: URL (naturalWidth 1, the 1×1 PNG loaded).

Notes

• Render-side bug bd-udrn0q47 (nested-include path retargeting vs the documented "no retargeting" design) is filed but intentionally not addressed here — it's a separate render change this resolver will inherit.
• Design + research: claude-notes/research/2026-06-16-include-shortcode-path-resolution.md, claude-notes/plans/2026-06-16-single-file-preview-transitive-deps.md.

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