diff --git a/zenith/src/zenith_harness/acp_runner.py b/zenith/src/zenith_harness/acp_runner.py
index 26bfc8d..dadaf70 100644
--- a/zenith/src/zenith_harness/acp_runner.py
+++ b/zenith/src/zenith_harness/acp_runner.py
@@ -119,6 +119,9 @@ def _acp_subprocess_env(provider) -> dict[str, str]:
         # Env-var hints — harmless if codex ignores them.
         env["CODEX_SANDBOX"] = "danger-full-access"
         env["CODEX_DISABLE_SANDBOX"] = "1"
+    else:
+        env.pop("CODEX_SANDBOX", None)
+        env.pop("CODEX_DISABLE_SANDBOX", None)
     return env
 
 
@@ -566,13 +569,6 @@ async def run_node(
         handoff_path = store.attempt_path(project_id, mission_id, spawn_ts, task.id)
         handoff_path.parent.mkdir(parents=True, exist_ok=True)
 
-        # 0) For claude-agent-acp: drop a project-level settings.json that
-        #    overrides the user's global ~/.claude/settings.json. Adapter
-        #    rejects session/new with `Invalid permissions.defaultMode: auto`
-        #    if the user's global setting carries the SDK-unsupported "auto"
-        #    default.
-        _ensure_claude_settings(Path(workspace_dir), role_config.worker_provider)
-
         # 1) Start the worker MCP server subprocess.
         mcp_port = self._find_free_port()
         mcp_process = await self._start_worker_mcp_server(
@@ -646,6 +642,7 @@ async def run_node(
                     "clientInfo": {"name": "zenith", "version": "0.1.0"},
                 },
             )
+            await self._maybe_refresh_auth(client, role_config.worker_provider)
             session_params: dict[str, Any] = {
                 "cwd": workspace_dir,
                 "mcpServers": [worker_mcp_cfg],
@@ -732,9 +729,6 @@ async def run_terminal_review(
         report_path = store.terminal_review_path(project_id, mission_id, spawn_ts)
         report_path.parent.mkdir(parents=True, exist_ok=True)
 
-        # Same claude-agent-acp settings workaround as run_node.
-        _ensure_claude_settings(Path(workspace_dir), role_config.worker_provider)
-
         mcp_port = self._find_free_port()
         mcp_process = await self._start_terminal_reviewer_mcp(
             project_id=project_id,
@@ -792,6 +786,7 @@ async def run_terminal_review(
                     "clientInfo": {"name": "zenith", "version": "0.1.0"},
                 },
             )
+            await self._maybe_refresh_auth(client, role_config.worker_provider)
             session_params: dict[str, Any] = {
                 "cwd": workspace_dir,
                 "mcpServers": [worker_mcp_cfg],
@@ -947,6 +942,17 @@ async def _maybe_set_mode(
                 f"Failed to set ACP runtime mode {mode!r} for {provider.name}: {exc}"
             ) from exc
 
+    async def _maybe_refresh_auth(self, client: ACPClient, provider) -> None:
+        if getattr(provider, "name", None) != "codex":
+            return
+        try:
+            status = await client.send_request("authentication/status", {})
+        except Exception:  # noqa: BLE001
+            return
+        if not isinstance(status, dict) or status.get("type") != "chat-gpt":
+            return
+        await client.send_request("authenticate", {"methodId": "chat-gpt"})
+
     # ------------------------------------------------------------------
     # Prompt rendering
     # ------------------------------------------------------------------
@@ -1190,45 +1196,6 @@ def review(
         )
 
 
-# ---------------------------------------------------------------------------
-# claude-agent-acp settings workaround
-# ---------------------------------------------------------------------------
-
-
-def _ensure_claude_settings(workspace: Path, provider) -> None:
-    """Write `<workspace>/.claude/settings.json` overriding `permissions.defaultMode`.
-
-    The `@zed-industries/claude-agent-acp` adapter loads settings as
-    user → project → local → enterprise (last write wins). Without this, a
-    user with `"permissions": {"defaultMode": "auto"}` in their global
-    `~/.claude/settings.json` will see session/new fail with
-    `Invalid permissions.defaultMode: auto.` — the Claude Code SDK does not
-    accept "auto".
-
-    We touch this file only when:
-    - The provider declares a non-empty `acp_runtime_mode` (i.e. claude).
-    - The file does not already exist (respect any user-authored override).
-
-    In v5 the workspace is the user's repo, so we conservatively no-op on
-    pre-existing files.
-    """
-    mode = getattr(provider, "acp_runtime_mode", None)
-    if not mode:
-        return
-    claude_dir = workspace / ".claude"
-    claude_dir.mkdir(parents=True, exist_ok=True)
-    settings_path = claude_dir / "settings.json"
-    if settings_path.exists():
-        # Respect user-authored settings; the user can put whatever they want
-        # in there. If their setting is "auto" we can't help — they need to
-        # change it manually.
-        return
-    settings_path.write_text(
-        json.dumps({"permissions": {"defaultMode": mode}}, indent=2) + "\n",
-        encoding="utf-8",
-    )
-
-
 __all__ = [
     "ACPClient",
     "ACPError",
diff --git a/zenith/src/zenith_harness/cli.py b/zenith/src/zenith_harness/cli.py
index 7e20918..56b4da7 100644
--- a/zenith/src/zenith_harness/cli.py
+++ b/zenith/src/zenith_harness/cli.py
@@ -288,7 +288,7 @@ def _resolve_selection(
 ) -> ProviderSelection:
     if agent and orchestrator and agent != orchestrator:
         raise click.UsageError("--agent conflicts with --orchestrator-provider")
-    orch = orchestrator or agent or "claude"
+    orch = orchestrator or agent or "codex"
     wrk = worker or (agent if agent in provider_names_for_role("worker") else None) or default_worker_provider_name(orch)
     return ProviderSelection(
         orchestrator=get_provider(orch),
diff --git a/zenith/src/zenith_harness/config.py b/zenith/src/zenith_harness/config.py
index 0508f74..d76f15f 100644
--- a/zenith/src/zenith_harness/config.py
+++ b/zenith/src/zenith_harness/config.py
@@ -68,7 +68,7 @@ def discover(cls) -> HarnessConfig:
             or harness_home / "projects"
         )
         orchestrator_provider_name = os.environ.get(
-            "ZENITH_ORCHESTRATOR_PROVIDER", "claude"
+            "ZENITH_ORCHESTRATOR_PROVIDER", "codex"
         )
         worker_provider_name = os.environ.get(
             "ZENITH_WORKER_PROVIDER"
diff --git a/zenith/src/zenith_harness/providers.py b/zenith/src/zenith_harness/providers.py
index 4c24d51..e3d75e9 100644
--- a/zenith/src/zenith_harness/providers.py
+++ b/zenith/src/zenith_harness/providers.py
@@ -123,10 +123,8 @@ def _dedupe_paths(paths: tuple[str, ...]) -> tuple[str, ...]:
         skill_dirs=(".claude/skills", ".agents/skills"),
         skill_alias_dirs=(".claude/skills", ".agents/skills"),
         config_format="mcp_json",
-        default_worker_acp_command="claude-agent-acp",
         agent_output_dir=".claude/agents",
         orchestrator_prompt_output_path=".claude/orchestrator_prompt.md",
-        acp_runtime_mode="bypassPermissions",
     ),
     "codex": ProviderDefinition(
         name="codex",
@@ -158,4 +156,4 @@ def provider_names_for_role(role: Literal["orchestrator", "worker"]) -> tuple[st
 def default_worker_provider_name(orchestrator_provider_name: str) -> str:
     if orchestrator_provider_name in PROVIDERS:
         return orchestrator_provider_name
-    return "claude"
+    return "codex"