[Windows] GPT-6 Astra rejects every prompt with "Invalid prompt"

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

26.911.7940.0 (build 9647)

What subscription do you have?

ChatGPT Pro

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

GPT-6 Astra rejects every prompt as a potential usage-policy violation, including harmless prompts such as "hi" and "你好".

Steps to reproduce

1. Open a new task in the Codex Windows app.
2. Select GPT-6 Astra.
3. Send hi or 你好.
4. The request fails before the model returns a response.

Actual result

The following error is shown:

Invalid prompt: your prompt was flagged as potentially violating our usage policy. Please try again with a different prompt: https://platform.openai.com/docs/guides/reasoning#advice-on-prompting

Expected result

GPT-6 Astra should respond normally to harmless prompts.

Minimal CLI reproduction

The issue is also reproducible outside the desktop conversation with user configuration ignored:

codex exec --ephemeral --ignore-user-config --skip-git-repo-check -s read-only -m gpt-6-astra -c 'model_reasoning_effort="low"' --json "hi"

### What steps can reproduce the bug?

GPT-6 Astra rejects every prompt as a potential usage-policy violation, including harmless prompts such as "hi" and "你好".

## Steps to reproduce

1. Open a new task in the Codex Windows app.
2. Select GPT-6 Astra.
3. Send `hi` or `你好`.
4. The request fails before the model returns a response.

## Actual result

The following error is shown:

> Invalid prompt: your prompt was flagged as potentially violating our usage policy. Please try again with a different prompt: https://platform.openai.com/docs/guides/reasoning#advice-on-prompting

## Expected result

GPT-6 Astra should respond normally to harmless prompts.

## Minimal CLI reproduction

The issue is also reproducible outside the desktop conversation with user configuration ignored:

```powershell
codex exec --ephemeral --ignore-user-config --skip-git-repo-check -s read-only -m gpt-6-astra -c 'model_reasoning_effort="low"' --json "hi"

### What is the expected behavior?

_No response_

### Additional information

_No response_

Start with the minimal PowerShell CLI reproduction using gpt-6-astra, then trace the model-selection and request path used by the Codex CLI and Windows app. Compare the behavior with another model and confirm the issue is resolved when harmless prompts such as "hi" and "你好" succeed in both interfaces.