Gemini CLI fails with `Invalid auth method selected` (exit code 41)

## Gemini CLI fails with `Invalid auth method selected` (exit code 41)

`engine: gemini`

### Error

```text
YOLO mode is enabled. All tool calls will be automatically approved.
Invalid auth method selected.
exitCode=41
```

### Environment

```text
gh-aw: v0.88.2
AWF: v0.28.12
Gemini CLI: 0.55.1
```

### Authentication diagnostics

Runner:

```text
GEMINI_API_KEY=SET
GEMINI_API_KEY length=53
GOOGLE_API_KEY=
GOOGLE_GENAI_USE_VERTEXAI=
GOOGLE_GENAI_USE_GCA=
```

Inside the AWF agent container:

```text
GEMINI_API_KEY=SET
GEMINI_API_KEY_LENGTH=51
GEMINI_API_KEY_PREFIX=gemini-api-key-place

GEMINI_API_BASE_URL=http://172.30.0.30:10003
GOOGLE_GEMINI_BASE_URL=http://172.30.0.30:10003

GOOGLE_API_KEY=
GOOGLE_GENAI_USE_VERTEXAI=
GOOGLE_GENAI_USE_GCA=
```

The API-key value inside the container is the AWF credential-isolation placeholder.

Gemini configuration:

```json
{
"selectedAuthType": "gemini-api-key"
}
```

### AWF status

```text
API proxy enabled: OpenAI=false, Anthropic=false, Copilot=false, Gemini=true, Vertex=false
API proxy sidecar enabled - API keys will be held securely in sidecar container
Containers started successfully
```

### Relevant generated command

```bash
gemini --yolo --skip-trust --output-format stream-json --prompt "$(cat /tmp/gh-aw/aw-prompts/prompt.txt)"
```

The AWF command also excludes the real key from the container:

```text
--exclude-env GEMINI_API_KEY
```

### Additional observations

* The Gemini API key is confirmed present on the GitHub Actions runner.
* Google AI Studio shows successful API requests.
* No `GOOGLE_API_KEY`, Vertex, or GCA authentication variables are set.
* Setting `selectedAuthType` to `gemini-api-key` does not resolve the issue.
* Gemini CLI exits during startup/authentication before producing a model response.
* No `gemini-client-error-*.json` is produced.

### Question

Is this a known compatibility issue between AWF `v0.28.12` / `gh-aw v0.88.2` and Gemini CLI `0.55.1` when using the Gemini API proxy?

Specifically, why does Gemini CLI return `Invalid auth method selected` even though the AWF agent receives the expected API-key placeholder and proxy URLs, and what is the recommended supported configuration/version combination to resolve exit code 41?

Start with the generated Gemini command and the selectedAuthType configuration, then compare the runner and AWF agent-container authentication diagnostics. Reproduce the startup failure with the stated gh-aw, AWF, and Gemini CLI versions and the Gemini API proxy enabled. Done means documenting the compatibility cause and a supported version/configuration combination that avoids exit code 41.

Written by the indexing model from the issue text.