[Bug]: event.model-fallback tests fail — output.message["model"] is undefined after fallback

[guazi04]

Prerequisites

• I have checked the latest version of the plugin
• I have searched for existing issues with the same problem
• I have read the documentation
• I am writing this issue in English

Bug Description

Two tests in src/plugin/event.model-fallback.test.ts fail on the dev branch. The chatMessageHandler returned by createEventHandler does not write the fallback model to output.message["model"] after applying a model fallback. The abort + re-prompt logic works correctly, but the model override is not reflected in the output object.

Steps to Reproduce

1. Check out the dev branch
2. Run bun test src/plugin/event.model-fallback.test.ts
3. Observe 2 test failures out of 5

Expected Behavior

All 5 tests pass. After applying a model fallback, output.message["model"] should contain the fallback model (e.g., { providerID: "anthropic", modelID: "claude-opus-4-6" }).

Actual Behavior

output.message["model"] is undefined after fallback is applied. The failing tests:

• triggers retry prompt on session.status retry events and applies fallback
• advances main-session fallback chain across repeated session.error retries end-to-end

Error output:
```
expect(output.message["model"]).toEqual({
providerID: "anthropic",
modelID: "claude-opus-4-6",
})

Expected: { providerID: "anthropic", modelID: "claude-opus-4-6" }
Received: undefined
```

Doctor Output

```
oMoMoMoMo Doctor

⚠ 3 issues found:

1. Loaded plugin is outdated
   Loaded 3.8.3, latest 3.10.1.
   Fix: Update: cd ~/.config/opencode && bun update oh-my-opencode
   Affects: plugin features

2. Model override uses unavailable provider
   Provider(s) not found in OpenCode model cache: INTSIG_claude, INTSIG_openai, INTSIG_google
   Affects: model resolution

3. Comment checker unavailable
   Comment checker binary is not installed.
   Fix: Install @code-yeongyu/comment-checker
   Affects: comment-checker hook
   ```

Operating System

macOS

OpenCode Version

1.2.20

Additional Context

These failures are reproducible on a clean checkout of the dev branch with no local configuration. The test file was not recently modified — the failures appear to be a regression from changes to the event handler or model fallback logic.