fix(acpx-engine): check the final env for Codex host-key auth selection

The Codex api-key auth-request check ran on the run's explicit env,
before the launch merged the projected host environment in. A local
Codex launch could inherit OPENAI_API_KEY or CODEX_API_KEY from the
host after that check, so the launched process had the credential but
never got the required api-key authentication request.

Move the check into resolveRuntimeEnv, after the host projection and
explicit env merge produce the final environment. This covers every
launch path (local, runner-less fallback, remote sandbox), because
they all resolve their launch env through this one function.

Co-authored-by: Paperclip <noreply@paperclip.ing>

packages/adapter-utils/src/acpx-engine/execute.test.ts

@@ -1572,6 +1572,35 @@ describe("shared ACPX engine runtime behavior", () => {
     },
   );
 
+  it.each(["OPENAI_API_KEY", "CODEX_API_KEY"] as const)(
+    "selects Codex ACP API-key authentication when only the host process provides %s",
+    async (apiKeyName) => {
+      const root = await makeTempRoot();
+      const codexHome = path.join(root, "codex-home");
+      await fs.mkdir(codexHome, { recursive: true });
+
+      // Simulate a local launch that inherits a provider key from the host
+      // process environment. No adapter config sets the key directly, so the
+      // launched env only receives it through host projection.
+      vi.stubEnv(apiKeyName, "sk-host-inherited-key");
+      try {
+        const { sessionInputs } = await runExecutor({
+          agent: "codex",
+          stateDir: path.join(root, "state"),
+          env: { CODEX_HOME: codexHome },
+          paperclipRuntimeSkills: [],
+          paperclipSkillSync: { desiredSkills: [] },
+        });
+
+        const env = (sessionInputs[0]!.sessionOptions as { env: Record<string, string> }).env;
+        expect(env[apiKeyName]).toBe("sk-host-inherited-key");
+        expect(env.DEFAULT_AUTH_REQUEST).toBe(JSON.stringify({ methodId: "api-key" }));
+      } finally {
+        vi.unstubAllEnvs();
+      }
+    },
+  );
+
   it("busts the session fingerprint when resolved adapter env changes but not across wakes", async () => {
     const root = await makeTempRoot();
     const stateDir = path.join(root, "state");

packages/adapter-utils/src/acpx-engine/execute.ts

@@ -1967,17 +1967,6 @@ async function buildRuntime(input: {
     // are absent from tempKeysApplied and keep their compatibility protection.
     if (!scratchKeys.has(key) || value !== scratch.dir) resolvedAdapterEnv[key] = value;
   }
-  // codex-acp supports both key names, but ACP clients must select its
-  // api-key authentication method during session creation. Without this
-  // request, the server advertises authentication and rejects session/new even
-  // though the credential is present in the launched process environment.
-  if (
-    acpxAgent === "codex" &&
-    (env.OPENAI_API_KEY || env.CODEX_API_KEY) &&
-    !env.DEFAULT_AUTH_REQUEST
-  ) {
-    env.DEFAULT_AUTH_REQUEST = JSON.stringify({ methodId: "api-key" });
-  }
   if (authToken) env.PAPERCLIP_API_KEY = authToken;
   // For the claude agent, set model via ANTHROPIC_MODEL at startup rather than
   // via session/set_config_option — the ACP server's set_config_option handler
@@ -2629,11 +2618,25 @@ function resolveRuntimeEnv(
     env,
     (options.platform ?? process.platform) === "win32",
   );
-  return Object.fromEntries(
+  const finalEnv = Object.fromEntries(
     Object.entries(mergedEnv).filter(
       (entry): entry is [string, string] => typeof entry[1] === "string",
     ),
   );
+  // codex-acp supports both key names, but ACP clients must select its
+  // api-key authentication method during session creation. Without this
+  // request, the server advertises authentication and rejects session/new even
+  // though the credential is present in the launched process environment. Check
+  // the final merged environment, not just the explicit run config, so a host
+  // key the local launch inherits still selects this default.
+  if (
+    acpxAgent === "codex" &&
+    (finalEnv.OPENAI_API_KEY || finalEnv.CODEX_API_KEY) &&
+    !finalEnv.DEFAULT_AUTH_REQUEST
+  ) {
+    finalEnv.DEFAULT_AUTH_REQUEST = JSON.stringify({ methodId: "api-key" });
+  }
+  return finalEnv;
 }
 
 function mergeRuntimeEnvironment(