fix(core): prevent secondary crash in ModelRouterService finally block

[gundermanc]

Summary

This PR fixes a bug in ModelRouterService where an exception during routing could result in a secondary crash within the finally block, hiding the original error and aborting the chat turn with a misleading TypeError.

Details

The modelRouterService.route() method executes the routing strategy within a try...catch...finally block. When an unexpected exception occurred during the actual model routing, execution jumped to the catch block. The catch block attempted to formulate a "fallback" decision. However, if something in this catch block also threw an exception before decision could be assigned, decision remained undefined. The finally block then attempted to access decision!.model, resulting in a Cannot read properties of undefined (reading 'model') error.

This fix replaces the non-null assertions (!) with optional chaining (?) and provides safe fallbacks in the finally block when constructing the ModelRoutingEvent. This ensures the finally block executes successfully, allowing the original error from the routing layer to bubble up correctly and be handled or logged.

Related Issues

N/A

How to Validate

1. Trigger a scenario where the route method's catch block fails to assign decision (e.g. forcing config.getModel() to throw an error while processing a fallback).
2. Observe that the original error is now properly reported instead of a generic Cannot read properties of undefined (reading 'model').
3. Check the telemetry logs to ensure a ModelRoutingEvent with failed=true and decision_model='unknown' is still emitted.

Pre-Merge Checklist

• Updated relevant documentation and README (if needed)
• Added/updated tests (if needed)
• Noted breaking changes (if any)
• Validated on required platforms/methods:
  • MacOS
    • npm run
    • npx
    • Docker
    • Podman
    • Seatbelt
  • Windows
    • npm run
    • npx
    • Docker
  • Linux
    • npm run
    • npx
    • Docker

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a bug where exceptions during the model routing process could trigger a secondary crash within the finally block. By ensuring that the decision object is handled safely when undefined, the fix allows the original error to propagate correctly, improving system reliability and debugging clarity.

Highlights

• Error Handling Improvement: Updated the ModelRouterService to prevent secondary crashes in the finally block when an initial routing error occurs.
• Safe Property Access: Replaced non-null assertions with optional chaining and provided safe fallback values to ensure telemetry events are correctly constructed even when a decision is undefined.

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[github-actions]

Size Change: +34 B (0%)

Total Size: 34.1 MB

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[gemini-code-assist]

Code Review

This pull request updates the ModelRouterService to handle potential undefined values for the decision variable by updating its type and using optional chaining in the finally block. However, the change to RoutingDecision | undefined introduces a TypeScript compilation error at the function's return statement, which expects a RoutingDecision. You should explicitly handle the undefined case before returning to ensure type safety and satisfy the interface contract.

[gemini-code-assist]

Changing the type of decision to RoutingDecision | undefined will cause a TypeScript compilation error at the return statement (line 133), as the function's return type is Promise<RoutingDecision>. Instead of using a non-null assertion (!), you should handle the undefined case explicitly (e.g., by providing a default with ?? or throwing an error) to satisfy the compiler. This ensures you are coding against the interface contract rather than relying on implementation details that might change. Note that line 133 is outside the current diff hunks, so you will need to apply this fix manually.

References

1. When a property or variable is optional in its type definition, callers must handle the undefined case explicitly (e.g., by providing a default) rather than relying on implementation details to guarantee a value.

[Samee24]

LGTM