diff --git a/packages/adapters/codex-local/src/ui/build-config.test.ts b/packages/adapters/codex-local/src/ui/build-config.test.ts
index 82db065ae3..019f635a35 100644
--- a/packages/adapters/codex-local/src/ui/build-config.test.ts
+++ b/packages/adapters/codex-local/src/ui/build-config.test.ts
@@ -118,6 +118,11 @@ describe("buildCodexLocalConfig", () => {
 });
 
 describe("buildPaperclipRunnerConfig", () => {
+  it.each(["", "max"])("preserves or overrides saved native Codex reasoning effort (%s)", thinkingEffort => {
+    const values = makeValues({ thinkingEffort, adapterSchemaValues: { provider: "codex", modelReasoningEffort: "high" } });
+    expect(buildPaperclipRunnerConfig(values).modelReasoningEffort).toBe(thinkingEffort || "high");
+    expect(buildPaperclipRunnerConfig({ ...values, adapterSchemaValues: { provider: "acpx", acpxAgent: "claude", modelReasoningEffort: "high" } })).not.toHaveProperty("modelReasoningEffort");
+  });
   it.each([undefined, false, true])("preserves Dot attachment consent in create/import forms: %s", value => {
     const config = buildPaperclipRunnerConfig(makeValues({ adapterType: "paperclip_runner", adapterSchemaValues: { provider: "openai_dot", dotAttachmentAccess: value } }));
     expect(config.dotAttachmentAccess).toBe(value === true);
@@ -142,6 +147,7 @@ describe("buildPaperclipRunnerConfig", () => {
       codexPermissionMode: "never",
       lifecycleMode: "per_turn",
       model: "gpt-5.4",
+      modelReasoningEffort: "high",
       timeoutSec: 0,
       graceSec: 15,
     });
@@ -149,7 +155,6 @@ describe("buildPaperclipRunnerConfig", () => {
       "engine",
       "agentCommand",
       "stateDir",
-      "modelReasoningEffort",
       "search",
       "fastMode",
       "dangerouslyBypassApprovalsAndSandbox",
diff --git a/packages/adapters/codex-local/src/ui/build-config.ts b/packages/adapters/codex-local/src/ui/build-config.ts
index 3a6853b927..51c6a4bf3d 100644
--- a/packages/adapters/codex-local/src/ui/build-config.ts
+++ b/packages/adapters/codex-local/src/ui/build-config.ts
@@ -76,6 +76,7 @@ export function buildCodexLocalConfig(v: CreateConfigValues): Record<string, unk
 export function buildPaperclipRunnerConfig(v: CreateConfigValues): Record<string, unknown> {
   const config = buildCodexLocalConfig(v);
   const schemaValues = normalizeLegacyRunnerProvider({ ...(v.adapterSchemaValues ?? {}) });
+  const codexReasoningEffort = config.modelReasoningEffort ?? schemaValues.modelReasoningEffort ?? schemaValues.reasoningEffort;
   for (const unsupportedKey of [
     "engine",
     "agentCommand",
@@ -232,7 +233,8 @@ export function buildPaperclipRunnerConfig(v: CreateConfigValues): Record<string
     ...schemaValues,
     provider,
     ...(provider === "codex"
-      ? { model: resolvePaperclipRunnerModel("codex", config.model) }
+      ? { model: resolvePaperclipRunnerModel("codex", config.model),
+          ...(codexReasoningEffort !== undefined ? { modelReasoningEffort: codexReasoningEffort } : {}) }
       : {}),
     codexPermissionMode: "never",
     opencodePermissionMode: resolvePaperclipRunnerPermissionMode(