feat(studio): HubService.invokePluginTheme + integration test

Wraps the new InvokePluginTheme RPC and ships an end-to-end
test that loads studio-theme-solarized into a fresh
HubFixture and asserts the light/dark schemes round-trip.

Signed-off-by: flemming-it <sf@flemming.it>
Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/data/hub.dart

@@ -396,6 +396,30 @@ class HubService {
     return (state: state, text: r.text, sourcePath: r.sourcePath);
   }
 
+  /// Invoke a Studio theme plugin's `theme` hook and unwrap
+  /// the result into Flutter-friendly `ColorScheme` slots.
+  ///
+  /// Returns a record:
+  ///   - `brightness`: echo of the input.
+  ///   - `tokens`:     14 32-bit ARGB values in Material 3
+  ///                   order. Caller passes them to
+  ///                   `ColorScheme(...)` after deciding the
+  ///                   `brightness` enum.
+  ///
+  /// Throws on hub-side errors (plugin not installed, plugin
+  /// declined the brightness, etc.) — caller routes the
+  /// exception through `friendlyError` like every other RPC.
+  Future<({String brightness, List<int> tokens})> invokePluginTheme({
+    required String capability,
+    required String brightness,
+  }) async {
+    final r = await _client.invokePluginTheme(
+      capability: capability,
+      brightness: brightness,
+    );
+    return (brightness: r.brightness, tokens: r.tokens.toList());
+  }
+
   /// Snapshot of every configured MCP server.
   Future<List<McpClientInfo>> listMcpClients() async {
     final r = await _client.listMcpClients();

test/integration/plugin_theme_test.dart

@@ -0,0 +1,88 @@
+// End-to-end integration test for the Studio-plugin theme
+// hook: spins a real `fai serve`, installs the in-tree
+// `studio-theme-solarized` plugin via direct module-dir
+// staging (mirror-install would also work but takes longer
+// and pulls a network egress), then calls `invokePluginTheme`
+// and asserts the round-trip.
+//
+// Run manually with:
+//
+//   flutter test test/integration/plugin_theme_test.dart
+//
+// Pre-reqs (handled by HubFixture's skip-when-missing path):
+//   - fai binary on PATH or at ../fai_platform/target/release/fai
+//   - studio-theme-solarized plugin built to module.wasm in its
+//     fai_modules dir.
+
+import 'dart:io';
+
+import 'package:flutter_test/flutter_test.dart';
+
+import 'hub_fixture.dart';
+
+void main() {
+  test(
+    'invokePluginTheme returns Solarized Light + Dark schemes',
+    () async {
+      final fixture = await HubFixture.start();
+      if (fixture == null) return;
+      try {
+        // Stage the plugin into the fixture's modules dir
+        // ourselves. Going through `installModule` would
+        // require the plugin to be on the mirror, which would
+        // add network + bundle-fetch latency that doesn't
+        // belong in an in-process round-trip test.
+        final pluginSrc = Directory(
+          '../fai_modules/studio-theme-solarized',
+        );
+        if (!await pluginSrc.exists()) {
+          markTestSkipped('studio-theme-solarized source not available');
+          return;
+        }
+        final wasm = File('${pluginSrc.path}/module.wasm');
+        if (!await wasm.exists()) {
+          markTestSkipped(
+            'studio-theme-solarized has no built module.wasm — '
+            'run `cargo build --release --target wasm32-wasip2` first',
+          );
+          return;
+        }
+        final dest = Directory(
+          '${fixture.tempDir.path}/modules/studio-theme-solarized',
+        );
+        await dest.create(recursive: true);
+        await File('${pluginSrc.path}/module.yaml')
+            .copy('${dest.path}/module.yaml');
+        await wasm.copy('${dest.path}/module.wasm');
+
+        // Call the hook for both brightnesses.
+        final light = await fixture.client.invokePluginTheme(
+          capability: 'studio.theme.solarized',
+          brightness: 'light',
+        );
+        expect(light.brightness, 'light');
+        expect(light.tokens.length, 14);
+        // Solarized blue is the pinned primary in both schemes.
+        expect(light.tokens[0], 0xFF268BD2);
+
+        final dark = await fixture.client.invokePluginTheme(
+          capability: 'studio.theme.solarized',
+          brightness: 'dark',
+        );
+        expect(dark.brightness, 'dark');
+        expect(dark.tokens.length, 14);
+        expect(dark.tokens[0], 0xFF268BD2);
+
+        // Different surface tokens between Light and Dark —
+        // regression guard against a plugin that returns the
+        // same scheme for both.
+        expect(light.tokens[8], isNot(equals(dark.tokens[8])));
+      } finally {
+        await fixture.dispose();
+      }
+    },
+    // Component-Model instantiation can take a few seconds on
+    // first run as wasmtime caches the compiled artefact.
+    timeout: const Timeout(Duration(minutes: 1)),
+  );
+}