diff --git a/src/agents/pi-embedded-runner/run/attempt.spawn-workspace.websocket.test.ts b/src/agents/pi-embedded-runner/run/attempt.spawn-workspace.websocket.test.ts
index 906624dff9d..0b73dc6b4b6 100644
--- a/src/agents/pi-embedded-runner/run/attempt.spawn-workspace.websocket.test.ts
+++ b/src/agents/pi-embedded-runner/run/attempt.spawn-workspace.websocket.test.ts
@@ -1,5 +1,8 @@
 import { describe, expect, it } from "vitest";
-import { shouldUseOpenAIWebSocketTransport } from "./attempt.thread-helpers.js";
+import {
+  shouldUseOpenAIWebSocketTransport,
+  shouldUseOpenAIWebSocketTransportForAttempt,
+} from "./attempt.thread-helpers.js";
 
 describe("openai websocket transport selection", () => {
   it("accepts direct OpenAI Responses endpoints", () => {
@@ -76,4 +79,24 @@ describe("openai websocket transport selection", () => {
       }),
     ).toBe(false);
   });
+
+  it("honors prepared SSE transport params before selecting websocket", () => {
+    expect(
+      shouldUseOpenAIWebSocketTransportForAttempt({
+        provider: "openai",
+        modelApi: "openai-responses",
+        modelBaseUrl: "https://api.openai.com/v1",
+        effectiveExtraParams: { transport: "sse" },
+      }),
+    ).toBe(false);
+
+    expect(
+      shouldUseOpenAIWebSocketTransportForAttempt({
+        provider: "openai",
+        modelApi: "openai-responses",
+        modelBaseUrl: "https://api.openai.com/v1",
+        effectiveExtraParams: { transport: "auto" },
+      }),
+    ).toBe(true);
+  });
 });
diff --git a/src/agents/pi-embedded-runner/run/attempt.thread-helpers.ts b/src/agents/pi-embedded-runner/run/attempt.thread-helpers.ts
index c1760c970f6..314e39f6b82 100644
--- a/src/agents/pi-embedded-runner/run/attempt.thread-helpers.ts
+++ b/src/agents/pi-embedded-runner/run/attempt.thread-helpers.ts
@@ -55,6 +55,29 @@ export function shouldUseOpenAIWebSocketTransport(params: {
   return endpointClass === "default" || endpointClass === "openai-public";
 }
 
+function hasExplicitSseTransport(sources: Array<Record<string, unknown> | undefined>): boolean {
+  return sources.some((source) => {
+    const transport = typeof source?.transport === "string" ? source.transport : "";
+    return transport.trim().toLowerCase() === "sse";
+  });
+}
+
+export function shouldUseOpenAIWebSocketTransportForAttempt(params: {
+  provider: string;
+  modelApi?: string | null;
+  modelBaseUrl?: string | null;
+  streamParams?: Record<string, unknown>;
+  effectiveExtraParams?: Record<string, unknown>;
+  modelParams?: Record<string, unknown>;
+}): boolean {
+  if (
+    hasExplicitSseTransport([params.streamParams, params.effectiveExtraParams, params.modelParams])
+  ) {
+    return false;
+  }
+  return shouldUseOpenAIWebSocketTransport(params);
+}
+
 function shouldAppendAttemptCacheTtl(params: {
   timedOutDuringCompaction: boolean;
   compactionOccurredThisAttempt: boolean;
diff --git a/src/agents/pi-embedded-runner/run/attempt.ts b/src/agents/pi-embedded-runner/run/attempt.ts
index 7f56c0b12c9..f116dffa970 100644
--- a/src/agents/pi-embedded-runner/run/attempt.ts
+++ b/src/agents/pi-embedded-runner/run/attempt.ts
@@ -172,6 +172,8 @@ import {
   applyExtraParamsToAgent,
   resolveAgentTransportOverride,
   resolveExplicitSettingsTransport,
+  resolveExtraParams,
+  resolvePreparedExtraParams,
 } from "../extra-params.js";
 import { prepareGooglePromptCacheStreamFn } from "../google-prompt-cache.js";
 import { getDmHistoryLimitFromSessionKey, limitHistoryTurns } from "../history.js";
@@ -292,7 +294,7 @@ import {
   composeSystemPromptWithHookContext,
   resolveAttemptSpawnWorkspaceDir,
   shouldPersistCompletedBootstrapTurn,
-  shouldUseOpenAIWebSocketTransport,
+  shouldUseOpenAIWebSocketTransportForAttempt,
 } from "./attempt.thread-helpers.js";
 import {
   shouldRepairMalformedToolCallArguments,
@@ -1769,25 +1771,57 @@ export async function runEmbeddedAttempt(
       const defaultSessionStreamFn = resolveEmbeddedAgentBaseStreamFn({
         session: activeSession,
       });
+      const resolvedTransport = resolveExplicitSettingsTransport({
+        settingsManager,
+        sessionTransport: activeSession.agent.transport,
+      });
+      const streamExtraParamsOverride = {
+        ...params.streamParams,
+        fastMode: params.fastMode,
+      };
+      const preparedRuntimeExtraParams = params.runtimePlan?.transport.resolveExtraParams({
+        extraParamsOverride: streamExtraParamsOverride,
+        thinkingLevel: params.thinkLevel,
+        agentId: sessionAgentId,
+        workspaceDir: effectiveWorkspace,
+        model: params.model,
+        resolvedTransport,
+      });
+      const resolvedExtraParams = resolveExtraParams({
+        cfg: params.config,
+        provider: params.provider,
+        modelId: params.modelId,
+        agentId: sessionAgentId,
+      });
+      const effectiveExtraParams =
+        preparedRuntimeExtraParams ??
+        resolvePreparedExtraParams({
+          cfg: params.config,
+          provider: params.provider,
+          modelId: params.modelId,
+          extraParamsOverride: streamExtraParamsOverride,
+          thinkingLevel: params.thinkLevel,
+          agentId: sessionAgentId,
+          agentDir,
+          workspaceDir: effectiveWorkspace,
+          resolvedExtraParams,
+          model: params.model,
+          resolvedTransport,
+        });
       const providerStreamFn = registerProviderStreamForModel({
         model: params.model,
         cfg: params.config,
         agentDir,
         workspaceDir: effectiveWorkspace,
       });
-      const hasExplicitSseTransport = [
-        (params.streamParams as { transport?: unknown } | undefined)?.transport,
-        (params.model as { params?: { transport?: unknown } }).params?.transport,
-      ]
-        .map((value) => (typeof value === "string" ? value.trim().toLowerCase() : ""))
-        .includes("sse");
-      const shouldUseWebSocketTransport =
-        !hasExplicitSseTransport &&
-        shouldUseOpenAIWebSocketTransport({
-          provider: params.provider,
-          modelApi: params.model.api,
-          modelBaseUrl: params.model.baseUrl,
-        });
+      const shouldUseWebSocketTransport = shouldUseOpenAIWebSocketTransportForAttempt({
+        provider: params.provider,
+        modelApi: params.model.api,
+        modelBaseUrl: params.model.baseUrl,
+        streamParams: params.streamParams,
+        effectiveExtraParams,
+        modelParams: (params.model as { params?: Record<string, unknown> }).params,
+      });
       const wsApiKey = shouldUseWebSocketTransport
         ? await resolveEmbeddedAgentApiKey({
             provider: params.provider,
@@ -1832,23 +1866,7 @@ export async function runEmbeddedAttempt(
         });
       }
 
-      const resolvedTransport = resolveExplicitSettingsTransport({
-        settingsManager,
-        sessionTransport: activeSession.agent.transport,
-      });
-      const streamExtraParamsOverride = {
-        ...params.streamParams,
-        fastMode: params.fastMode,
-      };
-      const preparedRuntimeExtraParams = params.runtimePlan?.transport.resolveExtraParams({
-        extraParamsOverride: streamExtraParamsOverride,
-        thinkingLevel: params.thinkLevel,
-        agentId: sessionAgentId,
-        workspaceDir: effectiveWorkspace,
-        model: params.model,
-        resolvedTransport,
-      });
-      const { effectiveExtraParams } = applyExtraParamsToAgent(
+      applyExtraParamsToAgent(
         activeSession.agent,
         params.config,
         params.provider,
@@ -1860,9 +1878,7 @@ export async function runEmbeddedAttempt(
         params.model,
         agentDir,
         resolvedTransport,
-        preparedRuntimeExtraParams
-          ? { preparedExtraParams: preparedRuntimeExtraParams }
-          : undefined,
+        { preparedExtraParams: effectiveExtraParams },
       );
       const effectivePromptCacheRetention = resolveCacheRetention(
         effectiveExtraParams,