Address review: validate the component constant, test the props path

render_component now rejects constants that are not
Funicular::Component subclasses with a clear ArgumentError instead
of failing later with a confusing NoMethodError. The props test
misnomer is fixed with a ProbeComponent fixture that reads both
props and state, so each channel is asserted through the public API.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: hasumikin

lib/funicular/ssr.rb

@@ -52,6 +52,10 @@ def self.render_component(component_name, props: {}, state: {}, source_dir: nil)
       raise "Funicular router is not configured; check app/funicular/initializer.rb" unless router
 
       component_class = Object.const_get(component_name.to_s)
+      unless component_class.is_a?(Class) && component_class < Funicular::Component
+        raise ArgumentError, "#{component_name} is not a Funicular::Component subclass"
+      end
+
       instance = component_class.new(symbolize_keys(props))
       instance.runtime = Funicular::Runtime.new(router)
       instance.seed_state(state)

minitest/fixtures/funicular_app/components/probe_component.rb

@@ -0,0 +1,15 @@
+# Reads both props and state so SSR.render_component tests can assert
+# each channel is wired through. Not routed on purpose: rendering it
+# is only possible through the single-component entry point.
+class ProbeComponent < Funicular::Component
+  def initialize_state
+    { note: "default note" }
+  end
+
+  def render
+    div(class: "probe") do
+      h2 { props[:label].to_s }
+      p { state[:note] }
+    end
+  end
+end

minitest/ssr_test.rb

@@ -124,7 +124,7 @@ def test_route_params_become_props
 
   # --- Single-component render (no route lookup) ------------------------
 
-  def test_render_component_renders_by_name_with_props_and_state
+  def test_render_component_renders_by_name_without_a_route
     html = Funicular::SSR.render_component(
       "GreetingComponent",
       state: { title: "Embedded" },
@@ -134,6 +134,17 @@ def test_render_component_renders_by_name_with_props_and_state
     assert_includes html, 'class="greeting"'
   end
 
+  def test_render_component_passes_props_and_state
+    html = Funicular::SSR.render_component(
+      "ProbeComponent",
+      props: { "label" => "From Props" },
+      state: { note: "injected note" },
+      source_dir: APP_DIR
+    )
+    assert_includes html, "<h2>From Props</h2>"
+    assert_includes html, "<p>injected note</p>"
+  end
+
   def test_render_component_uses_initialize_state_without_injection
     html = Funicular::SSR.render_component("GreetingComponent", source_dir: APP_DIR)
     assert_includes html, "<h1>Default Title</h1>"
@@ -145,6 +156,13 @@ def test_render_component_raises_on_unknown_component
     end
   end
 
+  def test_render_component_rejects_a_non_component_constant
+    error = assert_raises(ArgumentError) do
+      Funicular::SSR.render_component("String", source_dir: APP_DIR)
+    end
+    assert_match(/not a Funicular::Component/, error.message)
+  end
+
   def test_symbolize_keys_handles_nil_and_string_keys
     assert_equal({}, Funicular::SSR.symbolize_keys(nil))
     assert_equal({ a: 1, b: 2 }, Funicular::SSR.symbolize_keys("a" => 1, "b" => 2))