VoicePresence.OpenAI: migrate session.update to GA shape (blocks ADR-0026 Stage 5)

[eanzhao]

Background

Tracked in the operational memory reference_openai_realtime_beta_ga_shape_mismatch:

OpenAI Realtime GA token (ek_*) connects fine, gets session.created, then WS close 4000 beta_api_shape_disabled once beta-shape session.update lands. OpenAI .NET SDK 2.9.1 RealtimeConversationSessionOptions is beta-shape; aevatar VoicePresence.OpenAI needs GA migration before ek_ flow works end-to-end.

This blocks the voice convergence stage of #808 (ADR-0026 Stage 5). Stages 1–4 of #808 do not depend on this issue.

Scope

Migrate Aevatar.Foundation.VoicePresence.OpenAI from the beta-shape session.update payload to the GA shape that ek_ ephemeral tokens require. Confirm:

• ek_* ephemeral token mint via NyxID (reference_openai_realtime_ephemeral_via_nyxid) → WS open
• session.update GA payload accepted (no beta_api_shape_disabled 4000 close)
• audio in/out works against wss://api.openai.com/v1/realtime
• session-level tools declaration via GA shape works (this is what ADR-0026 Stage 5 will exercise)

Out of scope

• ADR-0026 Stage 5 itself (VoiceSessionActor, /ws/voice resolver change, tool-set declaration logic) — done in epic: collapse chat route actions to ForwardToModel + tools (ADR-0026) #808 once this is unblocked
• /ws/voice/{actorId} dev bypass behavior

Why it isn't folded into #808

External-dependency surface change with its own validation matrix (audio quality, latency, codec). Keeping it independent avoids coupling its release cycle to the routing refactor.

References

• ADR-0026 §D6 "Voice converges on the same ingress shape" (prerequisite paragraph)
• ADR-0025 (voice v1 — superseded by epic: collapse chat route actions to ForwardToModel + tools (ADR-0026) #808)
• reference_openai_realtime_beta_ga_shape_mismatch (operational memory)
• reference_openai_realtime_ephemeral_via_nyxid (ek_ mint recipe)

[eanzhao]

Blocks ADR-0026 Stage 5 (voice convergence) tracked in #808.