From 2bfe9fabbc248f038a680b0ea8c2dd758da403b9 Mon Sep 17 00:00:00 2001
From: Tranquil-Flow <tranquil_flow@protonmail.com>
Date: Mon, 13 Jul 2026 15:23:05 +0000
Subject: [PATCH] fix(image_gen/codex): remove unsupported tool_choice from
 request payload (#19505)
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The chatgpt.com/backend-api/codex backend 400s on every tool_choice
shape for the hosted image_generation tool — it looks up tool_choice as
a function name and never recognizes hosted-tool entries. Removing the
field from _build_responses_payload() lets the host model decide; the
instructions field nudges it toward the tool.

Salvaged from PR #19979 (originally targeted the old
client.responses.stream call, which no longer exists on upstream/main;
the live request now flows through _build_responses_payload + httpx in
_collect_image_b64).
---
 plugins/image_gen/openai-codex/__init__.py         | 14 +++++++++-----
 .../image_gen/test_openai_codex_provider.py        |  7 ++++---
 2 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/plugins/image_gen/openai-codex/__init__.py b/plugins/image_gen/openai-codex/__init__.py
index d8d5ea80d97..e4e7cd0fc09 100644
--- a/plugins/image_gen/openai-codex/__init__.py
+++ b/plugins/image_gen/openai-codex/__init__.py
@@ -307,11 +307,15 @@ def _build_responses_payload(
             "background": "opaque",
             "partial_images": 1,
         }],
-        "tool_choice": {
-            "type": "allowed_tools",
-            "mode": "required",
-            "tools": [{"type": "image_generation"}],
-        },
+        # No ``tool_choice`` is sent: the chatgpt.com/backend-api/codex backend
+        # rejects every shape we have for forcing the hosted ``image_generation``
+        # tool. ``{"type": "allowed_tools", "mode": "required", "tools": [{"type":
+        # "image_generation"}]}`` (and the simpler ``{"type": "image_generation"}``
+        # form) both 400 with ``Tool choice 'image_generation' not found in 'tools'
+        # parameter`` — the backend looks up tool_choice as a *function* name and
+        # never recognizes hosted-tool entries. Letting the host model decide is
+        # the only shape Codex currently accepts; the ``instructions`` above are
+        # what nudge it toward the tool. See issue #19505.
         "stream": True,
     }
 
diff --git a/tests/plugins/image_gen/test_openai_codex_provider.py b/tests/plugins/image_gen/test_openai_codex_provider.py
index 338ea97418a..e0d1f2a6e6a 100644
--- a/tests/plugins/image_gen/test_openai_codex_provider.py
+++ b/tests/plugins/image_gen/test_openai_codex_provider.py
@@ -149,9 +149,10 @@ class TestGenerate:
         assert captured["input"][0]["type"] == "message"
         assert captured["input"][0]["role"] == "user"
         assert captured["input"][0]["content"][0]["type"] == "input_text"
-        assert captured["tool_choice"]["type"] == "allowed_tools"
-        assert captured["tool_choice"]["mode"] == "required"
-        assert captured["tool_choice"]["tools"] == [{"type": "image_generation"}]
+        # Regression for #19505: the Codex backend 400s on every tool_choice
+        # shape we have for the hosted ``image_generation`` tool, so the
+        # provider must omit tool_choice entirely and rely on instructions.
+        assert "tool_choice" not in captured
 
         tool = captured["tools"][0]
         assert tool["type"] == "image_generation"