fix: pass the real docker config home in the P3 acceptance runner

backend/scripts/p3-acceptance.mjs

@@ -1032,7 +1032,7 @@ async function setupRealContext({ repositoryRoot = defaultRepositoryRoot, env =
   const pathValue = [...new Set([dirname(execs.gitPath), dirname(execs.dockerPath), "/usr/bin", "/bin", "/opt/homebrew/bin", "/usr/local/bin"])].join(":");
   // Docker CLI plugins (buildx) live under the real user's ~/.docker; the wrapper runs with a
   // scrubbed environment, so derive the real home from the passwd entry and expose DOCKER_CONFIG.
-  const realHome = env.P2_REAL_HOME ?? realUserHome();
+  const realHome = env.P3_REAL_HOME ?? realUserHome();
   const execEnv = buildSafeEnvironment({ ambient: env, fixture: {
     PATH: pathValue,
     HOME: run.root,