[VenRoot]

What

Isolate stub QML module descriptors in both test runners and correct integration sandboxing, localization, fixture paths and mutation-fixture signing.

Why

Mixed versioned/unversioned imports can resolve the installed native module instead of test stubs, causing read-only-property errors and native side effects. A targeted qmldir URL interceptor keeps the intended descriptor; a mixed-import regression checks a stub-only property. Production QML remains unchanged. Temporary Git fixtures disable inherited signing locally.

Test plan

• Complete default preflight passes in isolation — the unchanged renderer font-test blockers remain; no pass marker claimed.
• Fresh compatibility check against upstream 474dc8a: conflict-free merge; none of the six contribution files changed upstream.
• Focused QML, integration and mutation-fixture CTest suites 3/3 passed using existing binaries whose contribution sources exactly match this branch. This is not a fresh current-upstream build.
• Prior independent Clang Debug configure/build and serial CTest 29/29 passed. Previous formatting/syntax checks passed; ShellCheck unavailable.

Notes for reviewer

Only test infrastructure changes: CMake integration, shared QML stubs, both runners, integration QML and the mutation fixture script. No production QML import pin, renderer-pointer update or dependency on unpublished renderer code. No full-preflight rerun was necessary for this compatibility audit because no source was updated. Known external sanitizer findings and unavailable live rendering checks remain separate limitations. Draft for upstream review.