Resolve leading-/ include paths against the project root (bd-w9koo1i2)

[cscheid]

Summary

{{< include /admin/_includes/license-file.qmd >}} failed with Q-17-2: the leading-/ path was handed to the filesystem as an OS-absolute path. Per the Quarto path convention (Q1's resolvePath in core/handlers/base.ts, q2's own glob decision D2), a leading / is project-root-relative. Found porting the posit-connect docs to Quarto 2.

The defect: base_dir.join(&include_path) — Path::join discards its base when the right-hand side is absolute.

Changes

• include_expansion.rs: new resolve_include_target() anchors leading-/ (or Windows-authored \) paths at ctx.project.dir; everything else resolves against the including file's directory, unchanged. ProjectContext.dir already matches Q1's anchor in both modes (project root, or the input file's directory for single-file renders), so no mode branch is needed. The root anchor stays fixed at every include-nesting level. Also fixes the same class of failure in the WASM/hub-client build, where a leading-/ path escaped the /project/ VFS root.
• quarto-preview/deps.rs: extract_include_deps mirrors the same anchors — previously a leading-/ include never matched the SPA's project-relative dep strings, so editing the included file didn't re-render the includer in q2 preview.
• docs/errors/include/Q-17-2.qmd: documented the old behavior ("not the project root"); now describes both anchors.

Tests (TDD)

• 5 integration tests (include_project_absolute.rs) driving the real HTML pipeline through ProjectContext::discover on temp-dir layouts: project mode, cross-tree target, single-file parity, nested leading-/, relative regression guard. The four leading-/ tests failed with Q-17-2 before the fix.
• 4 unit tests for resolve_include_target; 1 preview deps unit test (failed pre-fix returning the raw absolute path).
• Full workspace: 11060 tests pass; full cargo xtask verify (including WASM + hub-client legs) green.

End-to-end verification

• Minimal repro project: q2 render now emits no warnings and the rendered sub/doc.html contains the included marker (inspected).
• posit-connect docs port: Q-17-2 warnings went from many to 0; the license-file callout content appears 5× in rendered admin/licensing/index.html, one per former warning site.

Plan: claude-notes/plans/2026-08-07-include-project-absolute-paths.md
Strand: bd-w9koo1i2 (docs follow-up filed as bd-ehp5ardt)

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