Discard handler return value in exception handling to prevent polluting raw_response

[TheRealNeil]

Discard handler return value in exception handling to prevent polluting raw_response

Fixes #305

Summary

• Add explicit nil return after rescue_with_handler in with_exception_handling to prevent the handler's return value leaking into raw_response

Root cause

When an exception occurs during api_prompt_execute, with_exception_handling returns whatever the rescue handler returns (often a truthy value like a String from broadcast_error). This becomes raw_response in resolve_prompt, which then causes a secondary NoMethodError: undefined method 'usage' for an instance of String — swallowing the real error.

Fix

Return nil explicitly after rescue_with_handler(exception) || raise. This ensures raw_response is always nil when an exception has been handled, preventing the secondary error while still letting the agent's rescue_from chain handle the original exception.

Test plan

• Trigger a provider exception with a rescue_from handler that returns a truthy value and confirm no secondary NoMethodError on usage
• Confirm unhandled exceptions still re-raise as expected
• Confirm rescue_from handlers are still invoked correctly

[Copilot]

Pull request overview

This PR addresses an error-handling edge case in provider execution where a truthy rescue_from handler return value can unintentionally become the provider raw_response, causing follow-on failures (e.g., calling usage on a String) and obscuring the original exception.

Changes:

• Ensure with_exception_handling discards the rescue handler’s return value by explicitly returning nil after rescue_with_handler(exception) || raise.

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[Copilot]

This changes with_exception_handling to always return nil when an exception is handled, which alters the existing contract where the handler’s return value is propagated. There is a current unit test that asserts the handler return value is returned (test/providers/concerns/exception_handler_test.rb:57-66), so this PR will fail CI unless the tests (and any other callers) are updated. If you want to avoid a behavior change in this concern, consider keeping with_exception_handling returning the handler result and instead change the BaseProvider call sites to not assign the method’s return value to raw_response (so raw_response stays nil on exceptions).

Suggested change

	nil # Discard handler return value to prevent polluting raw_response
	end
	end