Normalize Codex Responses input shape

Ensure the Codex OAuth Responses proxy forwards list-shaped input for empty continuation turns while preserving string prompts as user input items. Add regression coverage for the gpt-5.5 continuation case and document the proxy contract.

plugins/_oauth/AGENTS.md

@@ -40,7 +40,7 @@
 - Stored upstream base URLs and OAuth token endpoints must be validated against provider-owned allowlists before sending bearer or refresh tokens.
 - Browser callback providers must support manual callback paste when the browser cannot reach the local callback route.
 - Local proxy routes must remain loopback or token protected and must not add broad CORS access.
-- Codex Responses proxy requests must include Codex client metadata and compatibility headers such as `client_metadata`, `x-codex-installation-id`, `originator`, `session-id`, and `thread-id`.
+- Codex Responses proxy requests must include Codex client metadata and compatibility headers such as `client_metadata`, `x-codex-installation-id`, `originator`, `session-id`, and `thread-id`, and must forward `input` as a list for upstream Codex compatibility.
 
 ## Work Guidance
 

plugins/_oauth/helpers/codex.py

@@ -666,6 +666,13 @@ def fetch_models() -> list[str]:
 
 def prepare_responses_body(body: dict[str, Any], *, force_stream: bool) -> dict[str, Any]:
     normalized = dict(body)
+    input_value = normalized.get("input")
+    if isinstance(input_value, str):
+        normalized["input"] = (
+            [{"role": "user", "content": input_value}] if input_value else []
+        )
+    elif not isinstance(input_value, list):
+        normalized["input"] = []
     normalized.setdefault("instructions", "")
     normalized.setdefault("store", False)
     normalized["client_metadata"] = merge_client_metadata(normalized.get("client_metadata"))

tests/test_oauth_codex.py

@@ -202,10 +202,27 @@ def test_prepare_responses_body_adds_codex_client_metadata(monkeypatch):
         "thread_id": "thread-1",
         "x-codex-window-id": "agent-zero",
     }
+    assert body["input"] == [{"role": "user", "content": "hello"}]
     assert body["stream"] is True
     assert body["include"] == ["output_text", "reasoning.encrypted_content"]
 
 
+def test_prepare_responses_body_sends_empty_continuation_input_as_list(monkeypatch):
+    monkeypatch.setattr(codex, "build_client_metadata", lambda: {})
+
+    body = codex.prepare_responses_body(
+        {
+            "model": "gpt-5.5",
+            "input": "",
+            "previous_response_id": "resp_1",
+        },
+        force_stream=True,
+    )
+
+    assert body["input"] == []
+    assert body["previous_response_id"] == "resp_1"
+
+
 def test_request_codex_sends_current_codex_headers_from_body(monkeypatch):
     calls = []
     body = json.dumps(