[Ian Clanton-Thuon (iclanton)]

Summary

Allow @rushstack/heft-sass-plugin to consume packages that expose stylesheets through package.json exports instead of requiring imports of their physical source paths. Support Sass-aware root exports, subpaths, wildcard patterns, and top-level sass/style entry points.

Details

• Use resolve-pkg-maps to match export maps with the sass, style, and default conditions in manifest order. Apply Sass's extension, partial, and index-file lookup to exported subpaths; require complete stylesheet filenames in export targets.
• Keep Heft's custom importer rather than delegate loading to NodePackageImporter, preserving preprocessing, dependency tracking, incremental recompilation, and source maps.
• Share package resolution across pkg: imports, legacy ~ imports, and opt-in bare package imports. Relative/load-path precedence and the default behavior for bare specifiers remain unchanged.
• Preserve Sass-style filesystem fallbacks when no export matches. Matching invalid or ambiguous exports now produce explicit errors instead of silently falling back.
• Avoid leaving an unreadable exported stylesheet in the dependency cache when loading fails.
• Add one small resolver dependency, update its lockfile/policy entries, document the behavior, and include a patch change file. Manifest reads use the existing per-compilation resolution cache.

How it was tested

• rush build --only @rushstack/heft-sass-plugin - passed.
• rush retest --only @rushstack/heft-sass-plugin - passed on the final commit, including build/lint and all 99 tests.
• rush install --to @rushstack/heft-sass-plugin - passed lockfile and repository-state validation.
• common/autoinstallers/rush-prettier/node_modules/.bin/prettier --check heft-plugins/heft-sass-plugin/src/SassProcessor.ts heft-plugins/heft-sass-plugin/src/test/SassProcessor.test.ts heft-plugins/heft-sass-plugin/package.json - passed.
• git diff --cached --check - passed; the pre-commit formatting hook also passed.

Regression coverage includes scoped packages, root/subpath exports, condition ordering, arrays, wildcard/exact mappings, Sass partials and index files, encoded paths, CSS and indented Sass, legacy/bare imports, entry-point fallbacks, invalid/missing/ambiguous targets, source maps, and dependency-triggered recompilation.

Impacted documentation

Updated the heft-sass-plugin README with package entry-point examples and resolution rules. No website documentation or JSON schemas were changed.