[cscheid]

Follows #954 (merged). Braid: bd-lwvumpfk. Plan: claude-notes/plans/2026-10-28-config-path-late-binding.md, Phase 1.

What

Phase 0 (#954) introduced quarto_core::config_paths::resolve_config_path and made filters its first consumer. This PR migrates every remaining filesystem-space consumer that joined a config-authored path string onto the consuming document's directory, so a path declared in _quarto.yml or a _metadata.yml resolves against the file that declared it for every page, and a leading / means the project root.

• Resolver additions (config_paths.rs): PathCtx::for_document, ConfigPath (a carrier that keeps a path unresolved inside a parsed type until the context is known; used by Listing.template and ComponentSource::File), resolve_config_file_with / ConfigPath::resolve_file_with (the existence policy with an explicit probe, for transforms that carry no runtime handle), and brand_path_resolver.
• Migrated consumers: template-partials (HTML and Typst legs) and a missing template; shortcodes; language: <file>.yml; title-block-banner image probe and copy source; listing.template (bd-o1meelim: leading / = project root); epub-cover-image / epub-metadata / epub-embed-font / css flags; Typst template, bibliography, csl; reference-doc / template forwarding; highlight-style / syntax-highlighting theme files (pandoc and Typst legs); font-paths (the per-site leading-/ rule is gone); brand: read from merged metadata at its five call sites; book.chapters / appendices / references leading /.
• Mechanism-3 consumers routed through the resolver with the stored form unchanged (include-*, css, components[].src, reference-doc, epub-*, Typst template and partials), so Phase 1b can flip the stored form in one commit. Still joining a marked value below quarto-core, for 1b to change at the hand-over: quarto-sass ThemeContext::resolve_path (theme) and pampa's citeproc base dir (HTML leg bibliography / csl).
• quarto-sass API: resolve_brand, resolve_brand_variants and ThemeConfig::resolve_variants take a BrandPathResolver closure instead of a base directory; brand_base_dir(dir) is the old join form for callers with no provenance.
• Contract inventory (claude-notes/designs/path-resolution-model.md) updated. Scope-outs, both URL-space emitters needing the resource-resolver exit rather than a filesystem join: revealjs logo (new strand bd-7328beha) and listing image (bd-epk8cmdl).

Behaviour changes

All in the "declared in a parent or other file" case; front-matter declarations are unchanged.

• A project- or directory-level template-partials, shortcodes, highlight theme file, font-paths entry, banner image or listing template now reaches subdirectory pages; /x anchors at the project root.
• brand: in a _metadata.yml or front matter resolves against that file, not the project root. One fixture (unreferenced_brand.rs) relied on the old reading and now spells its path ../_brand.yml. Open question flagged in the plan: Quarto 1's effective rule for most keys is "declaring dir if the file exists there, else the project root"; the resolver only falls back for a leading /. Adding a project-root fallback for existence-driven keys would be more lenient; not done here.
• language: <file> tries one candidate at the declaring file instead of document dir then project root.
• An unmarked (missing) Typst template: is reported at its declaration-resolved path instead of silently using the vendored template.

Tests

• crates/quarto-core/tests/integration/config_path_consumers.rs: nine failing-first tests, one per consumer, in the subdir-page or leading-/ shape (all failed at the branch base for the predicted reason).
• Unit tests updated for the new signatures (format_defaults, typst_highlight, typst_compile, title_banner, listing_render, include_resolve, components, quarto-sass brand tests); resolver unit tests extended (for_document, ConfigPath round trip).

Verification

• cargo xtask verify --skip-hub-build: green, with the WASM artifact rebuilt first (npm run build:wasm) so the hub-client WASM tests ran against this change (17,463+ Rust tests; hub-client unit, integration and WASM suites).
• cargo clippy -p quarto-core -p quarto-sass --all-targets -- -D warnings: clean. cargo check --workspace --tests: clean.
• Windows cross-check of quarto-core is not possible from macOS (C build scripts); no cfg(windows) code was added in this PR.

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