fix(coverage): reject package: and dart: URIs outside known roots in Resolver - #2640

Summary

Completes the containment check added in #2534.

#2534 added _isWithinKnownRoots to the file: branch of Resolver.resolve(), on the basis — stated in its own _knownRoots doc comment — that coverage source entries are untrusted and their resolved contents are read into formatter output. The package: and dart: branches were left without the same check, so they can still resolve outside the known roots.

The gap

Plain .. does not traverse, because Uri.parse performs RFC 3986 dot-segment removal before the resolver sees the path. But Uri.pathSegments percent-decodes after that, so an encoded separator survives as a single segment:

package:foo/..%2f..%2foutside.txt  ->  pathSegments = [foo, ../../outside.txt]

packageName stays foo (the package lookup succeeds), and p.join(packagePath, ...) + resolveSymbolicLinks then walk out of the package root. The same applies to dart:. The resolved path's contents are read by format_coverage --pretty-print and filterIgnored, so wherever coverage JSON crosses a trust boundary this reads files outside the roots.

Change

• Apply the existing _isWithinKnownRoots check to the package: and dart: branches, mirroring file:.
• Canonicalize the known roots with resolveSymbolicLinks, since the paths they are compared against are canonicalized the same way. Without this, a root reached through a symlink (a symlinked pub cache, or /var -> /private/var on macOS) would never contain its own files and legitimate resolution would start returning null.

Tests

Three added: a package: encoded-separator escape returns null, a dart: escape returns null, and a package: URI through a symlinked root still resolves. dart analyze, dart format --set-exit-if-changed, and the full coverage suite pass.

Notes

• Scoped to Resolver. BazelResolver returns relative paths (resolved by the caller against the cwd) rather than paths within these roots, so it is a different shape — happy to follow up on it separately if you'd like.
• Severity is modest and already bounded by the trust model the fix(coverage): reject file: URIs outside known roots in Resolver #2534 comment describes; this just extends the same check to the remaining branches it logically covers.