Fixes #4932

Using AsNoTrackingWithIdentityResolution() with JSON-mapped entity collections could silently corrupt data or throw unhelpful exceptions in EF Core 8 and earlier, due to how JSON is streamed and materialized. EF Core 9 adds a validator and explicit prohibitions to surface these problems clearly.

Changes

• Summary table: Added Low-impact entry for the new restriction in ef-core-9.0/breaking-changes.md
• Breaking change section: Documents the full behavior change — old (silent corruption / cryptic StartObject exception), new (explicit exception), why (key values not propagated for JSON collection queryable operators → null keys), and mitigations

Prohibited pattern (now throws)

var blogs = await context.Blogs
    .AsNoTrackingWithIdentityResolution()
    .Select(b => new
    {
        Blog = b,
        TopPosts = b.JsonPosts.OrderBy(p => p.Rating).Take(3).ToList() // ❌ queryable operator on JSON collection
    })
    .ToListAsync();

Mitigations

Switch to AsTracking() (for identity resolution) or AsNoTracking() (no deduplication needed).