[cscheid]

Follows #955 (merged). Braid: bd-okqrjh8v. Plan: claude-notes/plans/2026-10-28-config-path-late-binding.md, §4.6 and Phase 1b.

What

Every marked config path (ConfigValueKind::Path) is now stored in pivot form (config_paths::pivot_form): the path relative to the project root with forward slashes, or absolute for a file outside the project. Before, the merge rebased each value to the consuming document's directory, so one declaration had a different spelling on every page: the SCSS cache-key misses of bd-79c4do6g, the .. chains of bd-s0jupmmv, a different q2 get-config answer per document, and a Lua-visible value that varied by page.

• mark_format_path_values and adjust_paths_to_project_root (renamed from adjust_paths_to_document_dir) write the pivot, normalized lexically on every platform. The inherited platform fork ("keep .. off Windows for symlinks, collapse on Windows for MAX_PATH") is gone: the resolver normalizes at use anyway, pivot form has no long chains, and the fork gave the pivot a per-OS spelling. The symlink caveat is one documented sentence on pivot_form.
• !path /x anchors at the project root, and adjust_paths_recursive classifies URLs with is_external_url instead of an http/https prefix list (two mechanism-2 defects from the sweep).
• A front-matter !path is rewritten at the merge like every other layer, so no marked value is document-relative any more; resolve_config_path joins a relative marked value onto the project root.
• The two consumers below quarto-core follow: ThemeContext is built on the project root (HTML and reveal), and pampa's citeproc base is the project root (the book single-file merge included).
• FormatCssTransform: when a render is served from the source tree (no resource resolver, or VFS-root mode in the browser preview) the template emits the css entry verbatim as <link href>, which only worked while the stored form was document-relative. It now relativizes each marked entry to the page (the WASM smoke-all run of metadata/dir-metadata-paths caught this).
• Docs: docs/guides/authoring/lua-filters.qmd notes that path-shaped keys reach filters project-root-relative, unlike Quarto 1's input-relative form, and points at quarto.project.directory.

Spelling decision (differs from the plan text)

The plan's §4.6 described the pivot with a leading /. The stored form here has no leading slash: a marked /x would be ambiguous on Unix with the OS-absolute form used for files outside the project (a built-in extension extracted to a temp dir), and the resolver cannot tell those apart without probing the filesystem. The value's kind already says "resolved", so consumers gain nothing from the slash; for Lua the rule is documented instead. The leading-/ spelling still applies to the unmarked, extension-rebased website.* strings (bd-0x1znhgb), where the string itself has to be self-describing.

Behaviour changes

• Lua filters (accepted behaviour change, documented): a marked key such as include-in-header, css, bibliography or theme reads as assets/hdr.html on every page, not ../assets/hdr.html on a subdirectory page. New test lua_sees_marked_paths_in_project_root_form pins this.
• An unmarked bibliography/csl (file missing at merge time) declared in a subdirectory document's front matter is now reported relative to the project root rather than the document; the file is missing either way.
• No change to rendered output: css hrefs, copies and includes are derived from the resolved file, which is the same file as before (the smoke-all dir-metadata-paths golden still asserts ../../shared/styles.css in the page's link).

Tests

• Unit expectations in format_paths, project::tests (adjust paths, directory metadata), config_paths, filter_resolve moved from document-relative to pivot strings; pivot_form unit test; metadata_merge test helper simplified.
• tests/integration/config_path_consumers.rs::lua_sees_marked_paths_in_project_root_form.

Verification

• cargo xtask verify --skip-hub-build: green, with the WASM artifact rebuilt first so the hub-client WASM suite (462 tests, smoke-all and pandoc-request goldens included) ran against this change; 17,476 Rust tests; hub-client unit 1,741 and integration 229.
• cargo clippy -p quarto-core -p quarto-sass -p pampa --all-targets -- -D warnings: clean.
• Windows cross-check of quarto-core is not possible from macOS (C build scripts). No platform-conditional code remains in the pivot path.

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