diff --git a/src/features/opencode-skill-loader/async-loader.ts b/src/features/opencode-skill-loader/async-loader.ts
index 74f1a8e..bfb1e7f 100644
--- a/src/features/opencode-skill-loader/async-loader.ts
+++ b/src/features/opencode-skill-loader/async-loader.ts
@@ -78,7 +78,9 @@ export async function loadSkillFromPathAsync(
 ): Promise<LoadedSkill | null> {
   try {
     const content = await readFile(skillPath, "utf-8")
-    const { data, body } = parseFrontmatter<SkillMetadata>(content)
+    const { data, body, parseError } = parseFrontmatter<SkillMetadata>(content)
+    if (parseError) return null
+    
     const frontmatterMcp = parseSkillMcpConfigFromFrontmatter(content)
     const mcpJsonMcp = await loadMcpJsonFromDirAsync(resolvedPath)
     const mcpConfig = mcpJsonMcp || frontmatterMcp
diff --git a/src/plugin-handlers/config-handler.ts b/src/plugin-handlers/config-handler.ts
index 32b071a..ddc33f1 100644
--- a/src/plugin-handlers/config-handler.ts
+++ b/src/plugin-handlers/config-handler.ts
@@ -152,10 +152,13 @@ export function createConfigHandler(deps: ConfigHandlerDeps) {
       if (builderEnabled) {
         const { name: _buildName, ...buildConfigWithoutName } =
           configAgent?.build ?? {};
+        const migratedBuildConfig = migrateAgentConfig(
+          buildConfigWithoutName as Record<string, unknown>
+        );
         const openCodeBuilderOverride =
           pluginConfig.agents?.["OpenCode-Builder"];
         const openCodeBuilderBase = {
-          ...buildConfigWithoutName,
+          ...migratedBuildConfig,
           description: `${configAgent?.build?.description ?? "Build agent"} (OpenCode default)`,
         };
 
@@ -167,10 +170,14 @@ export function createConfigHandler(deps: ConfigHandlerDeps) {
       if (plannerEnabled) {
         const { name: _planName, ...planConfigWithoutName } =
           configAgent?.plan ?? {};
+        const migratedPlanConfig = migrateAgentConfig(
+          planConfigWithoutName as Record<string, unknown>
+        );
         const plannerSisyphusOverride =
           pluginConfig.agents?.["Planner-Sisyphus"];
         const plannerSisyphusBase = {
-          ...planConfigWithoutName,
+          ...migratedPlanConfig,
+          mode: "primary",
           prompt: PLAN_SYSTEM_PROMPT,
           permission: PLAN_PERMISSION,
           description: `${configAgent?.plan?.description ?? "Plan agent"} (OhMyOpenCode version)`,
@@ -197,6 +204,14 @@ export function createConfigHandler(deps: ConfigHandlerDeps) {
         )
       : {};
 
+      const migratedBuild = configAgent?.build
+        ? migrateAgentConfig(configAgent.build as Record<string, unknown>)
+        : {};
+
+      const planDemoteConfig = replacePlan
+        ? { disable: true }
+        : undefined;
+
       config.agent = {
         ...agentConfig,
         ...Object.fromEntries(
@@ -206,10 +221,8 @@ export function createConfigHandler(deps: ConfigHandlerDeps) {
         ...projectAgents,
         ...pluginAgents,
         ...filteredConfigAgents,
-        build: { ...configAgent?.build, mode: "subagent" },
-        ...(replacePlan
-          ? { plan: { ...configAgent?.plan, mode: "subagent" } }
-          : {}),
+        build: { ...migratedBuild, mode: "subagent", hidden: true },
+        ...(planDemoteConfig ? { plan: planDemoteConfig } : {}),
       };
     } else {
       config.agent = {
diff --git a/src/shared/frontmatter.ts b/src/shared/frontmatter.ts
index 674b03d..db16420 100644
--- a/src/shared/frontmatter.ts
+++ b/src/shared/frontmatter.ts
@@ -3,6 +3,8 @@ import yaml from "js-yaml"
 export interface FrontmatterResult<T = Record<string, unknown>> {
   data: T
   body: string
+  hadFrontmatter: boolean
+  parseError: boolean
 }
 
 export function parseFrontmatter<T = Record<string, unknown>>(
@@ -12,7 +14,7 @@ export function parseFrontmatter<T = Record<string, unknown>>(
   const match = content.match(frontmatterRegex)
 
   if (!match) {
-    return { data: {} as T, body: content }
+    return { data: {} as T, body: content, hadFrontmatter: false, parseError: false }
   }
 
   const yamlContent = match[1]
@@ -22,8 +24,8 @@ export function parseFrontmatter<T = Record<string, unknown>>(
     // Use JSON_SCHEMA for security - prevents code execution via YAML tags
     const parsed = yaml.load(yamlContent, { schema: yaml.JSON_SCHEMA })
     const data = (parsed ?? {}) as T
-    return { data, body }
+    return { data, body, hadFrontmatter: true, parseError: false }
   } catch {
-    return { data: {} as T, body }
+    return { data: {} as T, body, hadFrontmatter: true, parseError: true }
   }
 }