Add NewModel/v2/deployment/RTC_INTERFACE_EN.md

NewModel/v2/deployment/RTC_INTERFACE_EN.md

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+# RTC deployment-interface verification
+
+Date: 2026-09-18
+
+## Result
+
+The deployed msgpack/WebSocket interface supports RTC inference correctly for
+both active action representations. Verification used the real policy server,
+the public `PolicyClient`, real DiT-S ttRTC checkpoints on GPU, and localhost
+wire serialization—not only direct Python wrapper calls.
+
+| Representation | Tested policy | Required history | Delay 3 result |
+| --- | --- | --- | --- |
+| raw | FM ttRTC | physical `prev_action_chunk`, `[1,30,7]` | finite `[1,30,7]`; 3 fixed action rows |
+| B-spline | joint-DD ttRTC | normalized `prev_control_rows`, `[1,18,7]` | finite `[1,30,7]`; 2 affected spans and 5 fixed cubic-support rows |
+
+The server advertises the contract in its handshake. `PolicyClient` reads
+`rtc_requires_previous_field` and sends the matching field through
+`infer_realtime`. Delay is measured in raw 30 Hz action steps and is strictly
+limited to 1–10. Base checkpoints reject realtime calls. The server keeps no
+cross-client plan cache; the previous plan is explicit in every request.
+
+## Important B-spline constraint
+
+B-spline RTC must receive the normalized parameter rows returned by the prior
+request. It intentionally rejects decoded 30×7 actions. Re-fitting and cubic
+support expansion map raw delay 3 to two affected spans and five preserved
+control rows, avoiding the incorrect assumption that raw action indices equal
+spline-control indices.
+
+## Hardening performed
+
+The live wire test revealed that msgpack-decoded NumPy arrays can be read-only.
+The deployment boundary now creates an owned float32 copy before converting
+previous actions or control rows to torch tensors. This prevents transport
+buffer aliasing and removes PyTorch's non-writable-array warning. Versioned
+Hugging Face layouts now auto-resolve `vN/sidecars/{raw,bspline}`.
+
+## Evidence
+
+- `outputs/FULL_VISION_512/summary/deployment/rtc_websocket_validation.json`
+- `outputs/FULL_VISION_512/summary/deployment_validation_dit_{s,b}.json`
+- Full project test suite, including read-only transport arrays and versioned
+  release sidecar discovery.
+
+This validates policy-server inference only; it does not constitute a
+closed-loop robot safety or task-success validation.