fix: detect and warn about opencode-skills conflict

When opencode-skills plugin is registered alongside oh-my-openagent,
all user skills are loaded twice, causing 'Duplicate tool names detected'
warnings and HTTP 400 errors.

This fix:
1. Detects if opencode-skills plugin is loaded in opencode.json
2. Emits a startup warning explaining the conflict
3. Suggests fixes: either remove opencode-skills or disable skills in oh-my-openagent

Fixes #2881

src/shared/external-plugin-detector.ts

@@ -24,6 +24,16 @@ const KNOWN_NOTIFICATION_PLUGINS = [
   "mohak34/opencode-notifier",
 ]
 
+/**
+ * Known skill plugins that conflict with oh-my-opencode's skill loading.
+ * Both plugins scan ~/.config/opencode/skills/ and register tools independently,
+ * causing "Duplicate tool names detected" warnings and HTTP 400 errors.
+ */
+const KNOWN_SKILL_PLUGINS = [
+  "opencode-skills",
+  "@opencode/skills",
+]
+
 function getWindowsAppdataDir(): string | null {
   return process.env.APPDATA || null
 }
@@ -88,12 +98,68 @@ function matchesNotificationPlugin(entry: string): string | null {
   return null
 }
 
+/**
+ * Check if a plugin entry matches a known skill plugin.
+ * Handles various formats: "name", "name@version", "npm:name", "file://path/name"
+ */
+function matchesSkillPlugin(entry: string): string | null {
+  const normalized = entry.toLowerCase()
+  for (const known of KNOWN_SKILL_PLUGINS) {
+    // Exact match
+    if (normalized === known) return known
+    // Version suffix: "opencode-skills@1.2.3"
+    if (normalized.startsWith(`${known}@`)) return known
+    // npm: prefix
+    if (normalized === `npm:${known}` || normalized.startsWith(`npm:${known}@`)) return known
+    // file:// path ending exactly with package name
+    if (normalized.startsWith("file://") && (
+      normalized.endsWith(`/${known}`) || 
+      normalized.endsWith(`\\${known}`)
+    )) return known
+  }
+  return null
+}
+
+/**
+ * Check if a plugin entry matches a known skill plugin.
+ * Handles various formats: "name", "name@version", "npm:name", "file://path/name"
+ */
+function matchesSkillPlugin(entry: string): string | null {
+  const normalized = entry.toLowerCase()
+  for (const known of KNOWN_SKILL_PLUGINS) {
+    // Exact match
+    if (normalized === known) return known
+    // Version suffix: "opencode-skills@1.2.3"
+    if (normalized.startsWith(`${known}@`)) return known
+    // npm: prefix
+    if (normalized === `npm:${known}` || normalized.startsWith(`npm:${known}@`)) return known
+    // file:// path ending exactly with package name
+    if (normalized.startsWith("file://") && (
+      normalized.endsWith(`/${known}`) || 
+      normalized.endsWith(`\\${known}`)
+    )) return known
+  }
+  return null
+}
+
 export interface ExternalNotifierResult {
   detected: boolean
   pluginName: string | null
   allPlugins: string[]
 }
 
+export interface ExternalSkillPluginResult {
+  detected: boolean
+  pluginName: string | null
+  allPlugins: string[]
+}
+
+export interface ExternalSkillPluginResult {
+  detected: boolean
+  pluginName: string | null
+  allPlugins: string[]
+}
+
 /**
  * Detect if any external notification plugin is configured.
  * Returns information about detected plugins for logging/warning.
@@ -120,6 +186,58 @@ export function detectExternalNotificationPlugin(directory: string): ExternalNot
   }
 }
 
+/**
+ * Detect if any external skill plugin is configured.
+ * Returns information about detected plugins for logging/warning.
+ */
+export function detectExternalSkillPlugin(directory: string): ExternalSkillPluginResult {
+  const plugins = loadOpencodePlugins(directory)
+  
+  for (const plugin of plugins) {
+    const match = matchesSkillPlugin(plugin)
+    if (match) {
+      log(`Detected external skill plugin: ${plugin}`)
+      return {
+        detected: true,
+        pluginName: match,
+        allPlugins: plugins,
+      }
+    }
+  }
+
+  return {
+    detected: false,
+    pluginName: null,
+    allPlugins: plugins,
+  }
+}
+
+/**
+ * Detect if any external skill plugin is configured.
+ * Returns information about detected plugins for logging/warning.
+ */
+export function detectExternalSkillPlugin(directory: string): ExternalSkillPluginResult {
+  const plugins = loadOpencodePlugins(directory)
+  
+  for (const plugin of plugins) {
+    const match = matchesSkillPlugin(plugin)
+    if (match) {
+      log(`Detected external skill plugin: ${plugin}`)
+      return {
+        detected: true,
+        pluginName: match,
+        allPlugins: plugins,
+      }
+    }
+  }
+
+  return {
+    detected: false,
+    pluginName: null,
+    allPlugins: plugins,
+  }
+}
+
 /**
  * Generate a warning message for users with conflicting notification plugins.
  */
@@ -135,3 +253,32 @@ Both oh-my-opencode and ${pluginName} listen to session.idle events.
    1. Remove ${pluginName} from your opencode.json plugins
    2. Or set "notification": { "force_enable": true } in oh-my-opencode.json`
 }
+
+/**
+ * Generate a warning message for users with conflicting skill plugins.
+ */
+export function getSkillPluginConflictWarning(pluginName: string): string {
+  return `[oh-my-opencode] External skill plugin detected: ${pluginName}
+
+Both oh-my-opencode and ${pluginName} scan ~/.config/opencode/skills/ and register tools independently.
+   Running both simultaneously causes "Duplicate tool names detected" warnings and HTTP 400 errors.
+
+   Consider either:
+   1. Remove ${pluginName} from your opencode.json plugins to use oh-my-opencode's skill loading
+   2. Or disable oh-my-opencode's skill loading by setting "claude_code.skills": false in oh-my-opencode.json
+   3. Or uninstall oh-my-opencode if you prefer ${pluginName}'s skill management`
+}
+
+/**
+ * Generate a warning message for users with conflicting skill plugins.
+ */
+export function getSkillPluginConflictWarning(pluginName: string): string {
+  return `[oh-my-openagent] WARNING: External skill plugin detected: ${pluginName}
+
+Both oh-my-openagent and ${pluginName} scan ~/.config/opencode/skills/ and register tools.
+Running both simultaneously causes "Duplicate tool names detected" errors.
+
+To fix this issue, either:
+1. Remove ${pluginName} from your opencode.json plugins
+2. Or disable skills in oh-my-openagent by setting "claude_code": { "skills": false } in oh-my-openagent.json`
+}