fix(opencode): inherit user-selected models

tests/opencode-config.test.js

@@ -28,6 +28,19 @@ const config = JSON.parse(fs.readFileSync(configPath, 'utf8'));
 let passed = 0;
 let failed = 0;
 
+if (
+  test('model selection inherits the user configured OpenCode provider', () => {
+    assert.ok(!Object.hasOwn(config, 'model'), 'Root config must not pin a provider-specific model');
+    assert.ok(!Object.hasOwn(config, 'small_model'), 'Root config must not pin a provider-specific small model');
+
+    for (const [agentId, agent] of Object.entries(config.agent || {})) {
+      assert.ok(!Object.hasOwn(agent, 'model'), `Agent "${agentId}" must inherit the selected OpenCode model`);
+    }
+  })
+)
+  passed++;
+else failed++;
+
 if (
   test('plugin paths do not duplicate the .opencode directory', () => {
     const plugins = config.plugin || [];