refactor(manager): extract focused collaborators from Manager God Class

Extract VM lifecycle, SSH execution, WireGuard setup, model switching,
end-to-end inference tests, and provisioning orchestration into separate
collaborator classes. Manager becomes a thin facade (~80 lines).

Also fixes CLI edge-cases: status/model-list when no VMs are active,
and threads --vllm/--ollama flags through the provisioning pipeline.

1 files changed, 72 insertions, 0 deletions

diff --git a/lib/hyperstack/model_switcher.rb b/lib/hyperstack/model_switcher.rb
new file mode 100644
index 0000000..07f6cdb
--- /dev/null
+++ b/lib/hyperstack/model_switcher.rb
@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+module HyperstackVM
+  # Hot-switches the running vLLM model on a provisioned VM.
+  class ModelSwitcher
+    def initialize(config:, provisioner:, state_store:, out:)
+      @config = config
+      @provisioner = provisioner
+      @state_store = state_store
+      @out = out
+    end
+
+    def switch(preset_name:, dry_run: false)
+      preset = @config.vllm_preset(preset_name)
+      state  = @state_store.load
+
+      old_container = state&.dig('vllm_container_name') || @config.vllm_container_name
+      new_container = preset['container_name']
+      current_model = state&.dig('vllm_model')
+
+      if dry_run
+        print_dry_run(preset_name, preset, current_model, old_container, new_container)
+        return
+      end
+
+      raise Error, "No tracked VM. Run 'create' first." unless state&.dig('vm_id')
+      host = state['public_ip']
+      raise Error, 'No public IP in state file.' if host.nil? || host.empty?
+
+      @provisioner.decommission_litellm(host)
+      @provisioner.stop_vllm_container(host, old_container) if old_container != new_container
+
+      info "Starting vLLM with preset '#{preset_name}' (#{preset['model']})..."
+      @provisioner.install_vllm(host, preset_config: preset, pull_image: false)
+
+      state['vllm_model']          = preset['model']
+      state['vllm_container_name'] = new_container
+      state['vllm_preset']         = preset_name
+      state['vllm_setup_at']       = Time.now.utc.iso8601
+      state['services'] ||= {}
+      state['services']['vllm_enabled'] = true
+      state['services']['ollama_enabled'] = state_ollama_enabled?(state)
+      @state_store.save(state)
+
+      info "Model switched to '#{preset_name}' (#{preset['model']})."
+      info "Run 'ruby hyperstack.rb test' to verify."
+    end
+
+    private
+
+    def print_dry_run(preset_name, preset, current_model, old_container, new_container)
+      info "DRY RUN: model switch to preset '#{preset_name}'"
+      info "  #{current_model || 'none'} → #{preset['model']}"
+      info "  container: #{old_container} → #{new_container}"
+      trust_note  = preset['trust_remote_code'] ? ', trust_remote_code: true' : ''
+      parser_note = preset['tool_call_parser'].to_s.empty? ? 'none' : preset['tool_call_parser']
+      extra_note  = preset['extra_vllm_args']&.any? ? ", extra_args: #{preset['extra_vllm_args'].join(' ')}" : ''
+      info "  max_model_len: #{preset['max_model_len']}, tool_call_parser: #{parser_note}#{trust_note}#{extra_note}"
+    end
+
+    def state_ollama_enabled?(state)
+      recorded = state&.dig('services', 'ollama_enabled')
+      return recorded unless recorded.nil?
+      return true if state&.key?('ollama_installed_at') || state&.key?('ollama_setup_at')
+      @config.ollama_install_enabled?
+    end
+
+    def info(msg)
+      @out.puts(msg)
+    end
+  end
+end