fix(coding-agent): preserved btw codex websocket routing

- Preserved the session websocket preference for ephemeral /btw side-channel turns so Codex websocket-only models do not fall back to SSE.
- Prioritized active /btw and /omfg panels in Esc handling before loop, maintenance, and main-turn interrupts.
- Added regression coverage for side-channel websocket options and /btw Escape priority.

Fixes #5213

packages/coding-agent/src/session/agent-session.ts

@@ -14706,7 +14706,7 @@ export class AgentSession {
 				// stable, but give provider routing a unique request lineage.
 				sessionId: `${cacheSessionId}:side:${Snowflake.next()}`,
 				promptCacheKey: cacheSessionId,
-				preferWebsockets: false,
+				preferWebsockets: this.#preferWebsockets,
 				reasoning: toReasoningEffort(this.thinkingLevel),
 				disableReasoning: shouldDisableReasoning(this.thinkingLevel),
 				hideThinkingSummary: this.agent.hideThinkingSummary,