test(auth): validated websocket preference and session state propagation

- Added test assertions for `preferWebsockets` parity in `advisor-provider-options-parity.test.ts`.
- Introduced a benchmark test to verify propagation of `providerSessionState` and `preferWebsockets` in `bench-auth-fallback.test.ts`.

packages/coding-agent/test/advisor-provider-options-parity.test.ts

@@ -7,8 +7,8 @@
  * with only `sessionId`/`getApiKey`/telemetry — it dropped the session's
  * `streamFn` wrapper (so `providers.openrouterVariant` and `loopGuard` never
  * landed on advisor requests), its `promptCacheKey` (so OpenAI Responses
- * fell back to a different cache shard), and its shared `providerSessionState`
- * (so Codex websocket / Anthropic fast-mode state was not reused).
+ * fell back to a different cache shard), its shared `providerSessionState`,
+ * and its explicit websocket preference.
  */
 import { afterAll, afterEach, beforeAll, beforeEach, describe, expect, it } from "bun:test";
 import * as path from "node:path";
@@ -68,7 +68,7 @@ describe("AgentSession advisor provider-options parity", () => {
 		} catch {}
 	});
 
-	it("inherits streamFn, promptCacheKey and providerSessionState from the session", () => {
+	it("inherits streamFn, promptCacheKey, websocket preference, and providerSessionState from the session", () => {
 		const advisorStreamFn: StreamFn = (m, ctx, opts) => streamSimple(m, ctx, opts);
 		const mainAgent = new Agent({
 			initialState: { model, systemPrompt: ["Test"], tools: [], messages: [] },
@@ -80,6 +80,7 @@ describe("AgentSession advisor provider-options parity", () => {
 			modelRegistry,
 			advisorTools: [],
 			advisorStreamFn,
+			preferWebsockets: true,
 		});
 		session.settings.setModelRole("advisor", "anthropic/claude-sonnet-4-5");
 		expect(session.setAdvisorEnabled(true)).toBe(true);
@@ -97,6 +98,7 @@ describe("AgentSession advisor provider-options parity", () => {
 		// Shared transport / fast-mode state map keeps Codex websockets and
 		// Anthropic fast-mode fallbacks consistent across the two agents.
 		expect(advisor.providerSessionState).toBe(session.providerSessionState);
+		expect(session.preferWebsockets).toBe(true);
 
 		// Stable cache key on the advisor session id pins consecutive advisor
 		// turns to the same OpenAI Responses cache shard.
@@ -131,6 +133,7 @@ describe("AgentSession advisor provider-options parity", () => {
 			onResponse,
 			onSseEvent,
 			transformProviderContext,
+			preferWebsockets: true,
 		});
 		session.settings.setModelRole("advisor", "anthropic/claude-sonnet-4-5");
 		expect(session.setAdvisorEnabled(true)).toBe(true);
@@ -160,5 +163,6 @@ describe("AgentSession advisor provider-options parity", () => {
 		expect(opts.sessionId).toBe(advisor.sessionId);
 		expect(opts.promptCacheKey).toBe(advisor.sessionId);
 		expect(opts.providerSessionState).toBe(session.providerSessionState);
+		expect(opts.preferWebsockets).toBe(true);
 	});
 });

packages/coding-agent/test/bench-auth-fallback.test.ts

@@ -208,6 +208,39 @@ async function captureServiceTier(opts: {
 	return { wire: captured?.serviceTier, summary: summary.serviceTier };
 }
 
+describe("bench provider session state and websocket preference", () => {
+	it("sends providerSessionState and preferWebsockets to the stream", async () => {
+		const registry = fakeRegistry({
+			models: [fakeModel("openai-codex", "gpt-5.5")],
+			authedProviders: ["openai-codex"],
+		});
+		let captured: SimpleStreamOptions | undefined;
+		await runBenchCommand(
+			{ models: ["openai-codex/gpt-5.5"], flags: { runs: 1, maxTokens: 64, json: true } },
+			{
+				createRuntime: async () => ({
+					modelRegistry: registry,
+					settings: undefined,
+					close: () => {},
+				}),
+				randomSessionId: () => "sess-1",
+				writeStdout: () => {},
+				writeStderr: () => {},
+				setExitCode: () => {},
+				streamSimple: (_model, _context, options) => {
+					captured = options;
+					return fakeStream();
+				},
+				now: () => 0,
+				stdoutIsTTY: false,
+			},
+		);
+		expect(captured?.providerSessionState).toBeInstanceOf(Map);
+		expect(captured?.providerSessionState?.size).toBe(0);
+		expect(captured?.preferWebsockets).toBe(true);
+	});
+});
+
 describe("bench service tier", () => {
 	it("sends the configured serviceTier setting when no flag is passed", async () => {
 		const { wire, summary } = await captureServiceTier({ setting: "flex" });