Protecting against misuse of debug_output

Failure/Error: @debug_output << '<- ' if @debug_output

NoMethodError:
  undefined method `<<' for an instance of Hash

/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/net-protocol-0.2.2/lib/net/protocol.rb:303:in `writing'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/net-protocol-0.2.2/lib/net/protocol.rb:286:in `write'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/net-http-0.6.0/lib/net/http/generic_request.rb:410:in `write_header'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/net-http-0.6.0/lib/net/http/generic_request.rb:264:in `send_request_with_body'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/net-http-0.6.0/lib/net/http/generic_request.rb:200:in `exec'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/net-http-0.6.0/lib/net/http.rb:2413:in `block in transport_request'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/net-http-0.6.0/lib/net/http.rb:2411:in `catch'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/net-http-0.6.0/lib/net/http.rb:2411:in `transport_request'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/net-http-0.6.0/lib/net/http.rb:2384:in `request'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/fakeweb-1.3.0/lib/fake_web/ext/net_http.rb:50:in `request_with_fakeweb'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/webmock-3.25.1/lib/webmock/http_lib_adapters/net_http.rb:108:in `block in request'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/webmock-3.25.1/lib/webmock/http_lib_adapters/net_http.rb:113:in `request'
./plugins/discourse-ai/lib/completions/endpoints/base.rb:158:in `block in perform_completion!'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/webmock-3.25.1/lib/webmock/http_lib_adapters/net_http.rb:130:in `start_without_connect'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/webmock-3.25.1/lib/webmock/http_lib_adapters/net_http.rb:157:in `start'
/var/www/discourse/vendor/bundle/ruby/3.3.0/gems/net-http-0.6.0/lib/net/http.rb:1070:in `start'
./plugins/discourse-ai/lib/completions/endpoints/base.rb:129:in `perform_completion!'
./plugins/discourse-ai/lib/completions/llm.rb:374:in `generate'

Not 100% sure, but worth opening this. Somehow fakeweb or webmock are initializing a protocol with an invalid object as @debug_output.

Clearly the fault is not here, but I wonder if we should add a simple check to the initializer?

raise ArgumentError, "debug_output must support <<" if @debug_output&.respond_to(:<<)

Start at the net-protocol-0.2.2 Protocol#writing stack frame and trace the request through plugins/discourse-ai/lib/completions/endpoints/base.rb:129 and :158. Determine how @debug_output becomes a Hash and whether the initializer is the right boundary for validation. Done means the failure is prevented with a clear error and the behavior is covered by a regression test.