MCP tool results lose content when structuredContent is present (Codex App 26.803.81509)

What version of the Codex App are you using (From “About Codex” dialog)?

26.803.81509 (build 6415) Also reproduced on 26.803.61601 (build 6396). After downgrading to 26.803.41515 (build 6321), the issue no longer reproduces.

What subscription do you have?

plus

What platform is your computer?

Darwin 24.6.0 arm64 arm

What issue are you seeing?

MCP tool call results lose their visible text (the content array) whenever the
result also contains structuredContent. The transcription layer that converts
MCP tool results into the assistant-visible function call output keeps only
structuredContent and drops content entirely.

Example: the built-in node_repl/js MCP server returns
content: [{"type":"text","text":"REINSTALL_TEST 1786582832541"}]
structuredContent: {"execution_duration_ms":0}
but the conversation only receives {"execution_duration_ms":0}. The text block
is never visible to the assistant. Code still executes and side effects still
happen, so this is purely an output-transcription bug.

Session evidence (rollout logs in ~/.codex/sessions/2026/08/12/, same call_id):

• mcp_tool_call_end (raw JSON-RPC result received from the MCP server):
  {"Ok": {"content": [{"type": "text", "text": "REINSTALL_TEST 1786582832541"}],
  "structuredContent": {"execution_duration_ms": 0}, "isError": false}}
• function_call_output (what is actually sent to the model):
  Output: {"execution_duration_ms":0}
  So content is complete on the server side and lost in the app-side transcription.

What steps can reproduce the bug?

1. In any Codex session, call the built-in node_repl/js MCP tool with:
   nodeRepl.write("x");
2. The tool executes fine, but the conversation only sees
   {"execution_duration_ms":0} instead of "x".
3. In the same session, node_repl/js_reset returns normally (it has no
   structuredContent field), which shows the bug only triggers when
   structuredContent is present.
4. Connecting directly to the node_repl binary over stdio
   (initialize -> notifications/initialized -> tools/call) returns the full
   content, confirming the MCP server itself is healthy.

What is the expected behavior?

content (the primary output per the MCP spec) should be preserved when
transcribing MCP tool results. structuredContent is an optional extra field
and should be merged with, or ignored in favor of, content.

Additional information

• The regression appeared between build 6321 (26.803.41515, Aug 7) and build
  6396 (26.803.61601, Aug 10): the newer node_repl starts attaching
  structuredContent to js responses, which triggers the bug. Downgrading to
  26.803.41515 makes it disappear.
• Affects every tool routed through this MCP server, including the
  computer-use/@oai/sky underlying channel.

Start by tracing the transcription path from mcp_tool_call_end to the function_call_output shown in the rollout logs, then reproduce the issue with the built-in node_repl/js tool using nodeRepl.write("x"). Done means the assistant-visible output preserves the content text when structuredContent is also present; verify that node_repl/js_reset remains unaffected and add or run a regression test if the relevant test location is found.