AI Gateway REST: google/gemini-3.1-flash-lite failing all requests with HTTP 500

All AI Gateway REST `/ai/run` requests for `google/gemini-3.1-flash-lite` have been failing with HTTP 500 for over 7 days (Since July 6th).

Reproduction:
Use the provided example CURL on [Cloudflare's official model page](https://developers.cloudflare.com/ai/models/google/gemini-3.1-flash-lite/#API-Schemas):
```
curl https://api.cloudflare.com/client/v4/accounts/$CLOUDFLARE_ACCOUNT_ID/ai/run \
--header "Authorization: Bearer $CLOUDFLARE_API_TOKEN" \
--header "Content-Type: application/json" \
--data '{
"model": "google/gemini-3.1-flash-lite",
"input": {
"contents": [
{
"parts": [
{
"text": "What are the three laws of thermodynamics?"
}
],
"role": "user"
}
]
}
}'
```

HTTP 500 Response:
```
{
"errors": [
{
"message": "Model execution failed (Error)",
"code": 2002
}
],
"success": false,
"result": {},
"messages": []
}
```

Cloudflare support has failed to raise an outage for this issue, or respond to tickets regarding it.

Start by reproducing the failure through the AI Gateway REST `/ai/run` entry point with the Cloudflare model-page cURL example. Trace the request handling for `google/gemini-3.1-flash-lite` and compare it with a working model; done means these requests return a successful model response instead of HTTP 500 with error code 2002.

Written by the indexing model from the issue text.