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Flips the migration plan's R7b milestone to done: eleven languages across four same-day batches (rust #1371; csharp/ruby/php #1378-#1380; swift/ kotlin #1381-#1382; r/lua+luau/scala/dart #1383-#1386), batch 4 going 4-for-4 first-run parity (12-of-13 arc-wide). Also records the batch-4 upfront grammar-probe method and the dart wasm byte-copy vendor. Validation note: the full suite (2,688 tests) also ran green on linux-arm64 in a fresh rust:1-bookworm + node 22 container with the kernel built from scratch and CODEGRAPH_KERNEL_EXPECT=1 — the Linux leg for all 11 post-R7a walkers. Co-authored-by: Claude Fable 5 <noreply@anthropic.com>