[Core] Give the OpenAI Realtime wire codec a reusable home (RFC #6592 P0a) (#7640)

Signed-off-by: psv666 <2693925048@qq.com>

vllm_omni/protocol/realtime/errors.py

@@ -0,0 +1,37 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM-Omni project
+
+"""The OpenAI Realtime error envelope.
+
+A Realtime server reports a rejected client event as one ``error`` event whose
+``error`` object carries ``type`` / ``code`` / ``message`` (plus the client's
+``event_id`` and an optional ``param``). ``type`` is not free-form: it is one
+of OpenAI's four buckets, derived from our internal code by
+:data:`REALTIME_ERROR_TYPES_BY_CODE`.
+
+OpenAI standardises the three ``type`` classes but not the *codes*, so the code
+vocabulary is a consumer's own. vLLM-Omni's lives in
+``vllm_omni.protocol.duplex.errors`` (Tier 3 in
+``docs/serving/realtime_duplex_api.md``); what stays here is the exception type
+every consumer raises, so the envelope is rendered identically whoever built it.
+"""
+
+from __future__ import annotations
+
+__all__ = ["RealtimeProtocolError"]
+
+
+class RealtimeProtocolError(ValueError):
+    """A client payload could not be decoded into a valid Realtime intent.
+
+    ``code`` is the internal error code that :data:`REALTIME_ERROR_TYPES_BY_CODE`
+    maps to an OpenAI ``error.type``; ``event_id`` is the *client* event id the
+    error answers. ``vllm_omni.engine.duplex.commands.DuplexCommandError`` is
+    the duplex specialization, so a consumer catching either sees the same
+    three attributes.
+    """
+
+    def __init__(self, message: str, *, code: str = "bad_event", event_id: str | None = None) -> None:
+        super().__init__(message)
+        self.code = code
+        self.event_id = event_id