generate_with inheritance: parent provider options leak into child when switching providers

[TheRealNeil]

Summary

When a child agent overrides generate_with with a different provider, options from the parent provider (e.g., host, api_key, model) leak through and override the child's provider config from YAML.

Steps to Reproduce

# Parent agent
class ApplicationAgent < ActiveAgent::Base
  generate_with :ollama, model: 'gpt-oss:20b'
end

# Child agent — switches to Azure
class BusinessProcedureAgent < ApplicationAgent
  generate_with :azure, model: 'gpt-4.1', stream: true
end

# config/active_agent.yml
development:
  ollama:
    service: "Ollama"
    host: "http://localhost:11434/v1"
  azure:
    service: "AzureOpenAI"
    host: "https://mycompany.cognitiveservices.azure.com/openai/deployments/gpt-4.1"
    api_key: "secret"
    api_version: "2025-01-01-preview"

Expected: BusinessProcedureAgent uses host: "https://mycompany.cognitiveservices.azure.com/..." from the Azure YAML config.

Actual: The Ollama host: "http://localhost:11434/v1" from the parent leaks through and overrides the Azure host, causing requests to go to the wrong endpoint.

Root Cause

In ActiveAgent::Base.generate_with (base.rb, lines 103-115):

def self.generate_with(provider_reference, **agent_options)
  self.prompt_provider = provider_reference

  global_options    = provider_config_load(provider_reference)
  inherited_options = (self.prompt_options || {}).except(:instructions)

  if global_options[:service] != inherited_options[:service]
    inherited_options.extract!(:service, :api_version)
  end

  self.prompt_options = global_options.merge(inherited_options).merge(agent_options)
end

When the service changes, only :service and :api_version are removed from inherited_options. All other parent options (:host, :api_key, :model, :base_url, etc.) remain. Since the merge order is global_options.merge(inherited_options), the inherited (parent) values override the global (YAML) values.

Suggested Fix

When switching to a different service/provider, inherited options from the parent are meaningless and should be discarded entirely:

if global_options[:service] != inherited_options[:service]
  inherited_options = {}
end

This ensures a clean slate when changing providers, while still allowing same-provider inheritance (e.g., a child that tweaks temperature on the same provider).