feat(config): deduplicate plugins by name with priority-based resolution (#5957)

packages/opencode/src/config/config.ts

@@ -178,6 +178,8 @@ export namespace Config {
       result.compaction = { ...result.compaction, prune: false }
     }
 
+    result.plugin = deduplicatePlugins(result.plugin ?? [])
+
     return {
       config: result,
       directories,
@@ -332,6 +334,58 @@ export namespace Config {
     return plugins
   }
 
+  /**
+   * Extracts a canonical plugin name from a plugin specifier.
+   * - For file:// URLs: extracts filename without extension
+   * - For npm packages: extracts package name without version
+   *
+   * @example
+   * getPluginName("file:///path/to/plugin/foo.js") // "foo"
+   * getPluginName("oh-my-opencode@2.4.3") // "oh-my-opencode"
+   * getPluginName("@scope/pkg@1.0.0") // "@scope/pkg"
+   */
+  export function getPluginName(plugin: string): string {
+    if (plugin.startsWith("file://")) {
+      return path.parse(new URL(plugin).pathname).name
+    }
+    const lastAt = plugin.lastIndexOf("@")
+    if (lastAt > 0) {
+      return plugin.substring(0, lastAt)
+    }
+    return plugin
+  }
+
+  /**
+   * Deduplicates plugins by name, with later entries (higher priority) winning.
+   * Priority order (highest to lowest):
+   * 1. Local plugin/ directory
+   * 2. Local opencode.json
+   * 3. Global plugin/ directory
+   * 4. Global opencode.json
+   *
+   * Since plugins are added in low-to-high priority order,
+   * we reverse, deduplicate (keeping first occurrence), then restore order.
+   */
+  export function deduplicatePlugins(plugins: string[]): string[] {
+    // seenNames: canonical plugin names for duplicate detection
+    // e.g., "oh-my-opencode", "@scope/pkg"
+    const seenNames = new Set<string>()
+
+    // uniqueSpecifiers: full plugin specifiers to return
+    // e.g., "oh-my-opencode@2.4.3", "file:///path/to/plugin.js"
+    const uniqueSpecifiers: string[] = []
+
+    for (const specifier of plugins.toReversed()) {
+      const name = getPluginName(specifier)
+      if (!seenNames.has(name)) {
+        seenNames.add(name)
+        uniqueSpecifiers.push(specifier)
+      }
+    }
+
+    return uniqueSpecifiers.toReversed()
+  }
+
   export const McpLocal = z
     .object({
       type: z.literal("local").describe("Type of MCP server connection"),