Summary

Follow-up to #1213. When auto-discovering a tsconfig.json for an importer, claims_ownership_of treated any file the tsconfig doesn't compile as "owned by the nearest tsconfig" and stopped the upward walk. That blanket shortcut intercepted files that an ancestor project genuinely owns.

The problem

The guard was:

if !self.is_file_extension_allowed_in_tsconfig(path) {
    return true; // claimed by the nearest tsconfig
}

is_file_extension_allowed_in_tsconfig is true only for TS extensions (and JS when allowJs is on), so the negation claimed non-TS files (.vue, .css), extensionless paths, and allowJs-off .js alike. Two concrete failures:

1. Non-TS files don't reach their solution project. A child tsconfig.json including only **/*.ts would claim a sibling App.vue. Auto-discovery stopped at the child, so a solution root that references a config with include: ["src/**/*.vue"] and a @/* alias never owned the file and the alias didn't resolve.
2. allowJs-off .js leaks a referenced project's paths. A referenced project with allowJs off but include: ["src/**/*.js"] would still route a .js importer through itself, applying its @lib/* paths to a file TypeScript excludes from the program.

The fix

• claims_ownership_of — narrow the early return true to path.extension().is_none(). A directory (extensionless importer) isn't a file, so files/include ownership doesn't apply and the nearest enclosing tsconfig governs it (many discovery cases rely on its paths/baseUrl/extends). A genuine file — including an allowJs-off .js this config won't compile — is claimed only when actually owned, otherwise the walk continues up.
• is_file_included_in_tsconfig — reject non-program inputs (an allowJs-off .js, even when a glob names .js; or an extensionless path) before consulting include, so resolve_tsconfig_solution won't route such files to a referenced project.
• Extracted is_extensionless_or_uncompiled_js to share that predicate.

Directory importers are unchanged: they still resolve against their nearest tsconfig (verified by the existing tsconfig_discovery cases).

Tests

• solution_style_nested_non_ts_walks_up (new) — a child config including only **/*.ts no longer intercepts App.vue; the walk reaches the solution project that owns @/*. A .ts the child includes stays on the child; an allowJs-off legacy.js walks up like the .vue.
• referenced_config_drops_js_when_allow_js_off (new) — a .ts importer resolves @lib/*; a .js importer does not (dropped because allowJs is off).
• solution_style_non_ts_extensions (updated) — a .css matched by no include walks past the solution root to the outermost ancestor, and the @/* alias does not leak into it.

New fixtures under fixtures/tsconfig/cases/referenced-allow-js-off/ and fixtures/tsconfig/cases/solution-style-non-ts/src/feature/.