diff --git a/packages/gambit-simulator/simulator-ui/src/utils.test.ts b/packages/gambit-simulator/simulator-ui/src/utils.test.ts
index 372ed5d7..6b3b448f 100644
--- a/packages/gambit-simulator/simulator-ui/src/utils.test.ts
+++ b/packages/gambit-simulator/simulator-ui/src/utils.test.ts
@@ -225,6 +225,62 @@ Deno.test("deriveBuildDisplayMessages dedupes model.result after streamed output
   assertEquals(assistantRows[0]?.content, "hi there");
 });
 
+Deno.test("deriveBuildDisplayMessages preserves whitespace in streamed output text deltas", () => {
+  const traces: Array<TraceEvent> = [
+    {
+      type: "model.stream.event",
+      actionCallId: "action-1",
+      event: {
+        type: "codex.event",
+        payload: {
+          type: "response.output_text.delta",
+          output_index: 0,
+          item_id: "msg_1",
+          delta: "Hello",
+        },
+      },
+    },
+    {
+      type: "model.stream.event",
+      actionCallId: "action-1",
+      event: {
+        type: "codex.event",
+        payload: {
+          type: "response.output_text.delta",
+          output_index: 0,
+          item_id: "msg_1",
+          delta: " ",
+        },
+      },
+    },
+    {
+      type: "model.stream.event",
+      actionCallId: "action-1",
+      event: {
+        type: "codex.event",
+        payload: {
+          type: "response.output_text.delta",
+          output_index: 0,
+          item_id: "msg_1",
+          delta: "world",
+        },
+      },
+    },
+    {
+      type: "model.result",
+      actionCallId: "action-1",
+      message: { role: "assistant", content: "Hello world " },
+    },
+  ];
+
+  const display = deriveBuildDisplayMessages([], traces);
+  const assistantRows = display.filter((row) =>
+    row.kind === "message" && row.role === "assistant"
+  );
+  assertEquals(assistantRows.length, 1);
+  assertEquals(assistantRows[0]?.content, "Hello world ");
+});
+
 Deno.test("deriveBuildDisplayMessages projects namespaced extension items", () => {
   const traces: Array<TraceEvent> = [
     {
diff --git a/packages/gambit-simulator/simulator-ui/src/utils.ts b/packages/gambit-simulator/simulator-ui/src/utils.ts
index 8a8ff198..498bb23b 100644
--- a/packages/gambit-simulator/simulator-ui/src/utils.ts
+++ b/packages/gambit-simulator/simulator-ui/src/utils.ts
@@ -1119,20 +1119,29 @@ export function deriveBuildDisplayMessages(
       return String(value);
     }
   };
+  const hasVisibleText = (value: string): boolean => value.trim().length > 0;
   const pushAssistantMessage = (content: string) => {
+    if (!hasVisibleText(content)) return;
     const normalized = content.trim();
-    if (!normalized) return;
     for (let i = entries.length - 1; i >= 0; i -= 1) {
       const entry = entries[i];
       if (entry?.kind !== "message") continue;
       if (entry.role !== "assistant") continue;
-      if ((entry.content ?? "").trim() === normalized) return;
+      if ((entry.content ?? "").trim() === normalized) {
+        if (entry.content !== content) {
+          entries[i] = {
+            ...entry,
+            content,
+          };
+        }
+        return;
+      }
       break;
     }
     entries.push({
       kind: "message",
       role: "assistant",
-      content: normalized,
+      content,
     });
   };
   const extractReasoningText = (payload: Record<string, unknown>): string => {
@@ -1282,28 +1291,45 @@ export function deriveBuildDisplayMessages(
     };
   };
   const upsertAssistantMessage = (
-    input: { messageId: string; text: string },
+    input: { messageId: string; text: string; mode?: "append" | "replace" },
   ) => {
-    const text = input.text.trim();
-    if (!text) return;
     const messageId = input.messageId || `assistant-${entries.length}`;
+    const existingIndex = assistantIndexById.get(messageId);
+    if (
+      !hasVisibleText(input.text) &&
+      existingIndex === undefined &&
+      input.mode !== "append"
+    ) return;
     for (let i = entries.length - 1; i >= 0; i -= 1) {
       const entry = entries[i];
       if (entry?.kind !== "message") continue;
       if (entry.role !== "assistant") continue;
-      if ((entry.content ?? "").trim() === text) {
+      if (
+        hasVisibleText(input.text) &&
+        (entry.content ?? "").trim() === input.text.trim()
+      ) {
+        if (entry.content !== input.text) {
+          entries[i] = {
+            ...entry,
+            content: input.text,
+          };
+        }
         assistantIndexById.set(messageId, i);
         return;
       }
       break;
     }
-    const existingIndex = assistantIndexById.get(messageId);
     if (existingIndex !== undefined) {
       const existing = entries[existingIndex];
       if (existing?.kind === "message" && existing.role === "assistant") {
+        const previousText = existing.content ?? "";
+        const nextText = input.mode === "append"
+          ? `${previousText}${input.text}`
+          : input.text;
+        if (!hasVisibleText(nextText)) return;
         entries[existingIndex] = {
           ...existing,
-          content: text,
+          content: nextText,
         };
       }
       return;
@@ -1311,7 +1337,7 @@ export function deriveBuildDisplayMessages(
     entries.push({
       kind: "message",
       role: "assistant",
-      content: text,
+      content: input.text,
     });
     assistantIndexById.set(messageId, entries.length - 1);
   };
@@ -1385,6 +1411,32 @@ export function deriveBuildDisplayMessages(
       });
       continue;
     }
+    if (
+      payloadType === "response.output_text.delta" ||
+      payloadType === "response.output_text.done"
+    ) {
+      const outputIndex = typeof payload.output_index === "number"
+        ? String(payload.output_index)
+        : "";
+      const actionScope = asString(record.actionCallId) ||
+        asString(record.runId);
+      const baseMessageId = asString(payload.item_id) ||
+        (outputIndex ? `output-${outputIndex}` : payloadType);
+      const text = payloadType === "response.output_text.delta"
+        ? asString(payload.delta)
+        : asString(payload.text);
+      if (payloadType === "response.output_text.delta" && text.length === 0) {
+        continue;
+      }
+      upsertAssistantMessage({
+        messageId: scopedId(actionScope, baseMessageId),
+        text,
+        mode: payloadType === "response.output_text.delta"
+          ? "append"
+          : "replace",
+      });
+      continue;
+    }
     const item = asRecord(payload.item);
     if (!item) continue;
     const itemType = asString(item.type);
diff --git a/packages/gambit-simulator/src/server/workspace/response_events.ts b/packages/gambit-simulator/src/server/workspace/response_events.ts
index c4127c6c..3481d486 100644
--- a/packages/gambit-simulator/src/server/workspace/response_events.ts
+++ b/packages/gambit-simulator/src/server/workspace/response_events.ts
@@ -162,8 +162,8 @@ export const createOpenResponsesEventPersistence = (deps: {
       ) {
         continue;
       }
-      const content = stringifyMessageContent(message.content).trim();
-      if (!content) continue;
+      const content = stringifyMessageContent(message.content);
+      if (content.trim().length === 0) continue;
       const ref = refs[index];
       const messageRefId =
         typeof ref?.id === "string" && ref.id.trim().length > 0
diff --git a/packages/gambit-simulator/src/server_session_store.ts b/packages/gambit-simulator/src/server_session_store.ts
index dacf6b90..214bd5f9 100644
--- a/packages/gambit-simulator/src/server_session_store.ts
+++ b/packages/gambit-simulator/src/server_session_store.ts
@@ -1046,6 +1046,7 @@ export const createSessionStore = (deps: SessionStoreDeps) => {
     itemKind: "message" | "reasoning" | "tool_call";
     role: string | null;
     content: string | null;
+    contentMode?: "replace" | "append";
     messageRefId: string | null;
     reasoningType: string | null;
     summary: string | null;
@@ -1080,6 +1081,7 @@ export const createSessionStore = (deps: SessionStoreDeps) => {
         itemKind: "message",
         role,
         content: text,
+        contentMode: "replace",
         messageRefId: asString(payload.message_id).trim() ||
           asString(payload.messageRefId).trim() ||
           null,
@@ -1096,6 +1098,49 @@ export const createSessionStore = (deps: SessionStoreDeps) => {
         sequence: event.sequence,
       }];
     }
+    if (
+      payloadType === "response.output_text.delta" ||
+      payloadType === "response.output_text.done"
+    ) {
+      const outputIndex = asFiniteNumber(payload.output_index);
+      const itemId = asString(payload.item_id).trim() ||
+        `message-${outputIndex ?? event.sequence}`;
+      const text = payloadType === "response.output_text.delta"
+        ? asString(payload.delta)
+        : asString(payload.text);
+      if (payloadType === "response.output_text.delta" && text.length === 0) {
+        return [];
+      }
+      if (
+        text.trim().length === 0 && payloadType !== "response.output_text.delta"
+      ) {
+        return [];
+      }
+      return [{
+        workspaceId: event.workspace_id,
+        runId: event.run_id,
+        itemKey: `message:assistant:${itemId}`,
+        itemId,
+        itemKind: "message",
+        role: "assistant",
+        content: text,
+        contentMode: payloadType === "response.output_text.delta"
+          ? "append"
+          : "replace",
+        messageRefId: null,
+        reasoningType: null,
+        summary: null,
+        summaryMode: "replace",
+        toolCallId: null,
+        toolName: null,
+        toolStatus: null,
+        argumentsText: null,
+        resultText: null,
+        errorText: null,
+        outputIndex,
+        sequence: event.sequence,
+      }];
+    }
     if (
       payloadType === "response.reasoning.delta" ||
       payloadType === "response.reasoning.done" ||
@@ -1200,9 +1245,10 @@ export const createSessionStore = (deps: SessionStoreDeps) => {
       itemType === "message" || itemType === "agent_message" ||
       itemType === "assistant_message"
     ) {
-      const text = toEventMessageText(item.content).trim() ||
-        toEventMessageText(item.text).trim();
-      if (!text) return [];
+      const contentText = toEventMessageText(item.content);
+      const fallbackText = toEventMessageText(item.text);
+      const text = contentText.trim().length > 0 ? contentText : fallbackText;
+      if (text.trim().length === 0) return [];
       const role = asString(item.role).trim() || "assistant";
       const rawItemId = asString(item.id).trim() || null;
       const canonicalBackfill = event.idempotency_key.includes(":canonical:");
@@ -1225,6 +1271,7 @@ export const createSessionStore = (deps: SessionStoreDeps) => {
         itemKind: "message",
         role,
         content: text,
+        contentMode: "replace",
         messageRefId,
         reasoningType: null,
         summary: null,
@@ -1334,6 +1381,18 @@ export const createSessionStore = (deps: SessionStoreDeps) => {
         | undefined;
       summary = `${existing?.summary ?? ""}${row.summary ?? ""}`;
     }
+    let content = row.content;
+    if (row.itemKind === "message" && row.contentMode === "append") {
+      const existing = db.prepare(`
+        SELECT content
+        FROM ${OPENRESPONSES_OUTPUT_ITEMS_SQLITE_TABLE}
+        WHERE workspace_id = ? AND run_id = ? AND item_key = ?
+        LIMIT 1
+      `).get(row.workspaceId, row.runId, itemKey) as
+        | { content?: string | null }
+        | undefined;
+      content = `${existing?.content ?? ""}${row.content ?? ""}`;
+    }
     db.prepare(`
       INSERT INTO ${OPENRESPONSES_OUTPUT_ITEMS_SQLITE_TABLE} (
         workspace_id,
@@ -1381,7 +1440,7 @@ export const createSessionStore = (deps: SessionStoreDeps) => {
       row.itemId,
       row.itemKind,
       row.role,
-      row.content,
+      content,
       row.messageRefId,
       row.reasoningType,
       summary,
diff --git a/src/providers/codex.ts b/src/providers/codex.ts
index 1ed5e30c..882f03ee 100644
--- a/src/providers/codex.ts
+++ b/src/providers/codex.ts
@@ -28,6 +28,7 @@ const CODEX_REASONING_SUMMARY_ENV = "GAMBIT_CODEX_REASONING_SUMMARY";
 const CODEX_VERBOSITY_ENV = "GAMBIT_CODEX_VERBOSITY";
 const CODEX_BIN_ENV = "GAMBIT_CODEX_BIN";
 const CODEX_SKIP_SANDBOX_CONFIG_ENV = "GAMBIT_CODEX_SKIP_SANDBOX_CONFIG";
+const CODEX_DISABLE_WEBSOCKETS_ENV = "GAMBIT_CODEX_DISABLE_WEBSOCKETS";
 const CODEX_DANGEROUS_BYPASS_ENV =
   "GAMBIT_CODEX_DANGEROUSLY_BYPASS_APPROVALS_AND_SANDBOX";
 const MCP_DENO_BIN_ENV = "GAMBIT_MCP_DENO_BIN";
@@ -265,6 +266,11 @@ function shouldSkipCodexSandboxConfig(
   return Boolean(envRaw && parseTruthy(envRaw));
 }
 
+function shouldDisableCodexWebsockets(): boolean {
+  const envRaw = Deno.env.get(CODEX_DISABLE_WEBSOCKETS_ENV);
+  return Boolean(envRaw && parseTruthy(envRaw));
+}
+
 function tomlString(value: string): string {
   return `"${value.replaceAll("\\", "\\\\").replaceAll('"', '\\"')}"`;
 }
@@ -372,6 +378,9 @@ function codexConfigArgs(input: {
 }): Array<string> {
   const args: Array<string> = [];
   args.push(...codexAdditionalConfigArgs(input.params));
+  if (shouldDisableCodexWebsockets()) {
+    args.push("-c", "model_providers.openai.supports_websockets=false");
+  }
   args.push("-c", `approval_policy=${tomlString("never")}`);
   const pathEnv = Deno.env.get("PATH")?.trim();
   if (pathEnv) {
diff --git a/src/providers/codex_app_server.test.ts b/src/providers/codex_app_server.test.ts
index ee3eadcf..46da3290 100644
--- a/src/providers/codex_app_server.test.ts
+++ b/src/providers/codex_app_server.test.ts
@@ -1,6 +1,7 @@
 import { assertEquals } from "@std/assert";
 import {
   appServerRequestResultForTest,
+  codexConfigArgsForTest,
   setCodexHostAuthBridgeForTests,
 } from "./codex.ts";
 
@@ -33,3 +34,23 @@ Deno.test("codex app-server refresh host failures are returned as RPC errors", a
     setCodexHostAuthBridgeForTests(null);
   }
 });
+
+Deno.test("codex config can disable OpenAI websocket responses", () => {
+  const previous = Deno.env.get("GAMBIT_CODEX_DISABLE_WEBSOCKETS");
+  Deno.env.set("GAMBIT_CODEX_DISABLE_WEBSOCKETS", "1");
+
+  try {
+    const args = codexConfigArgsForTest({ cwd: "/workspace" });
+
+    assertEquals(
+      args.includes("model_providers.openai.supports_websockets=false"),
+      true,
+    );
+  } finally {
+    if (previous === undefined) {
+      Deno.env.delete("GAMBIT_CODEX_DISABLE_WEBSOCKETS");
+    } else {
+      Deno.env.set("GAMBIT_CODEX_DISABLE_WEBSOCKETS", previous);
+    }
+  }
+});
diff --git a/src/server_session_store_output_projection.test.ts b/src/server_session_store_output_projection.test.ts
index f402f9f9..2a743f66 100644
--- a/src/server_session_store_output_projection.test.ts
+++ b/src/server_session_store_output_projection.test.ts
@@ -387,3 +387,89 @@ leakTolerantTest(
     }
   },
 );
+
+leakTolerantTest(
+  "openresponses output projection preserves whitespace across streamed deltas and final text",
+  async () => {
+    const dir = await Deno.makeTempDir();
+    const sessionsRoot = path.join(dir, "sessions");
+    const workspaceId = "workspace-output-delta-whitespace";
+    const sessionDir = path.join(sessionsRoot, workspaceId);
+    const statePath = path.join(sessionDir, "state.json");
+    const eventsPath = path.join(sessionDir, "events.jsonl");
+    const sqlitePath = path.join(sessionDir, "workspace.sqlite");
+    const store = createProjectionStore({
+      sessionsRoot,
+      workspaceId,
+      sessionDir,
+      statePath,
+      eventsPath,
+    });
+
+    const initialState = store.persistSessionState({
+      runId: workspaceId,
+      messages: [],
+      meta: { workspaceId, sessionId: workspaceId },
+    });
+    const runId = "run-1";
+    const itemId = "msg-assistant-1";
+
+    for (const [index, delta] of ["Hello", " ", "world"].entries()) {
+      await store.appendOpenResponsesRunEvent(initialState, {
+        workspace_id: workspaceId,
+        run_id: runId,
+        event_type: "response.output_text.delta",
+        payload: {
+          type: "response.output_text.delta",
+          output_index: 0,
+          item_id: itemId,
+          delta,
+        },
+        idempotency_key: `${runId}:delta:${index}`,
+      });
+    }
+    await store.appendOpenResponsesRunEvent(initialState, {
+      workspace_id: workspaceId,
+      run_id: runId,
+      event_type: "response.output_text.done",
+      payload: {
+        type: "response.output_text.done",
+        output_index: 0,
+        item_id: itemId,
+        text: "Hello world ",
+      },
+      idempotency_key: `${runId}:done`,
+    });
+
+    const outputItems = store.listOpenResponsesOutputItems({
+      workspaceId,
+      runId,
+    });
+    const assistantMessages = outputItems.filter((item): item is {
+      __typename: "OutputMessage";
+      id: string;
+      role: string;
+      content: string;
+      messageRefId?: string;
+      feedbackEligible: boolean;
+    } =>
+      item.__typename === "OutputMessage" &&
+      item.role === "assistant"
+    );
+    assertEquals(assistantMessages.length, 1);
+    assertEquals(assistantMessages[0]?.content, "Hello world ");
+
+    const db = new DatabaseSync(sqlitePath);
+    try {
+      const rows = db.prepare(`
+        SELECT content
+        FROM openresponses_output_items_v0
+        WHERE workspace_id = ? AND run_id = ?
+      `).all(workspaceId, runId) as Array<{ content: string | null }>;
+      assertEquals(rows.length, 1);
+      assertEquals(rows[0]?.content, "Hello world ");
+    } finally {
+      db.close();
+    }
+  },
+);