[Copilot]

Concurrent CCW queries can observe readiness before vtable and descriptor initialization is published. Competing layout and lazy-IID flag updates can also lose bits, allowing a live vtable to be rebuilt.

• Publication: Acquire-read shared flags and use pointer-width CAS updates that preserve existing bits. Publish class readiness after descriptor assignment and allocation ownership commit; enforce flags-offset alignment at compile time.
• Lazy IID: Generate privately outside the existing Crst, then recheck and commit one immutable IID under the lock. Successful readers remain lock-free; CMT representation and contract-visible bits remain unchanged.
• Coverage: Add fresh-type concurrent class-layout/IID-lookup and explicit-interface layout stress cases, followed by native calls.

• Fixes Concurrent CCW queries can observe incomplete or reinitialized vtables #134232

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[AaronRobinsonMSFT]

/ba-g HTTP failure