Add plugins input to GitHub Action

This commit adds support for installing Claude Code plugins via a new `plugins` input parameter.

Changes:
- Added `plugins` input to action.yml (comma-separated list)
- Created `install-plugins.ts` with plugin installation logic
- Added comprehensive tests in `install-plugins.test.ts`
- Updated base-action index.ts to call plugin installation
- Plugins are installed after settings setup but before Claude execution

Usage example:
```yaml
- uses: anthropic-ai/claude-code-action@main
  with:
    plugins: "feature-dev,test-coverage-reviewer"
```

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

base-action/src/index.ts

@@ -5,6 +5,7 @@ import { preparePrompt } from "./prepare-prompt";
 import { runClaude } from "./run-claude";
 import { setupClaudeCodeSettings } from "./setup-claude-code-settings";
 import { validateEnvironmentVariables } from "./validate-env";
+import { installPlugins } from "./install-plugins";
 
 async function run() {
   try {
@@ -15,6 +16,12 @@ async function run() {
       undefined, // homeDir
     );
 
+    // Install plugins if specified
+    await installPlugins(
+      process.env.INPUT_PLUGINS,
+      process.env.INPUT_PATH_TO_CLAUDE_CODE_EXECUTABLE || "claude",
+    );
+
     const promptConfig = await preparePrompt({
       prompt: process.env.INPUT_PROMPT || "",
       promptFile: process.env.INPUT_PROMPT_FILE || "",

base-action/src/install-plugins.ts

@@ -0,0 +1,80 @@
+#!/usr/bin/env bun
+
+import { spawn } from "child_process";
+
+// Declare console as global for TypeScript
+declare const console: {
+  log: (message: string) => void;
+  error: (message: string) => void;
+};
+
+/**
+ * Parses a comma-separated list of plugin names and returns an array of trimmed plugin names
+ */
+export function parsePlugins(pluginsInput: string | undefined): string[] {
+  if (!pluginsInput || pluginsInput.trim() === "") {
+    return [];
+  }
+
+  return pluginsInput
+    .split(",")
+    .map((plugin) => plugin.trim())
+    .filter((plugin) => plugin.length > 0);
+}
+
+/**
+ * Installs a single Claude Code plugin
+ */
+export async function installPlugin(
+  pluginName: string,
+  claudeExecutable: string = "claude",
+): Promise<void> {
+  return new Promise((resolve, reject) => {
+    const process = spawn(claudeExecutable, ["plugin", "install", pluginName], {
+      stdio: "inherit",
+    });
+
+    process.on("close", (code: number | null) => {
+      if (code === 0) {
+        resolve();
+      } else {
+        reject(
+          new Error(
+            `Failed to install plugin '${pluginName}' (exit code: ${code})`,
+          ),
+        );
+      }
+    });
+
+    process.on("error", (err: Error) => {
+      reject(
+        new Error(`Failed to install plugin '${pluginName}': ${err.message}`),
+      );
+    });
+  });
+}
+
+/**
+ * Installs Claude Code plugins from a comma-separated list
+ */
+export async function installPlugins(
+  pluginsInput: string | undefined,
+  claudeExecutable: string = "claude",
+): Promise<void> {
+  const plugins = parsePlugins(pluginsInput);
+
+  if (plugins.length === 0) {
+    console.log("No plugins to install");
+    return;
+  }
+
+  console.log(`Installing ${plugins.length} plugin(s)...`);
+
+  for (const plugin of plugins) {
+    console.log(`Installing plugin: ${plugin}`);
+    await installPlugin(plugin, claudeExecutable);
+    console.log(`✓ Successfully installed: ${plugin}`);
+  }
+
+  console.log("All plugins installed successfully");
+}

base-action/test/install-plugins.test.ts

@@ -0,0 +1,84 @@
+#!/usr/bin/env bun
+
+import { describe, test, expect } from "bun:test";
+import { parsePlugins } from "../src/install-plugins";
+
+describe("parsePlugins", () => {
+  test("should return empty array for undefined input", () => {
+    expect(parsePlugins(undefined)).toEqual([]);
+  });
+
+  test("should return empty array for empty string", () => {
+    expect(parsePlugins("")).toEqual([]);
+  });
+
+  test("should return empty array for whitespace-only string", () => {
+    expect(parsePlugins("   \n\t  ")).toEqual([]);
+  });
+
+  test("should parse single plugin", () => {
+    expect(parsePlugins("feature-dev")).toEqual(["feature-dev"]);
+  });
+
+  test("should parse multiple plugins", () => {
+    expect(parsePlugins("feature-dev,test-coverage-reviewer")).toEqual([
+      "feature-dev",
+      "test-coverage-reviewer",
+    ]);
+  });
+
+  test("should trim whitespace around plugin names", () => {
+    expect(parsePlugins("  feature-dev  ,  test-coverage-reviewer  ")).toEqual([
+      "feature-dev",
+      "test-coverage-reviewer",
+    ]);
+  });
+
+  test("should handle spaces between commas", () => {
+    expect(
+      parsePlugins(
+        "feature-dev, test-coverage-reviewer, code-quality-reviewer",
+      ),
+    ).toEqual([
+      "feature-dev",
+      "test-coverage-reviewer",
+      "code-quality-reviewer",
+    ]);
+  });
+
+  test("should filter out empty values from consecutive commas", () => {
+    expect(parsePlugins("feature-dev,,test-coverage-reviewer")).toEqual([
+      "feature-dev",
+      "test-coverage-reviewer",
+    ]);
+  });
+
+  test("should handle trailing comma", () => {
+    expect(parsePlugins("feature-dev,test-coverage-reviewer,")).toEqual([
+      "feature-dev",
+      "test-coverage-reviewer",
+    ]);
+  });
+
+  test("should handle leading comma", () => {
+    expect(parsePlugins(",feature-dev,test-coverage-reviewer")).toEqual([
+      "feature-dev",
+      "test-coverage-reviewer",
+    ]);
+  });
+
+  test("should handle plugins with special characters", () => {
+    expect(parsePlugins("@scope/plugin-name,plugin-name-2")).toEqual([
+      "@scope/plugin-name",
+      "plugin-name-2",
+    ]);
+  });
+
+  test("should handle complex whitespace patterns", () => {
+    expect(
+      parsePlugins(
+        "\n  feature-dev  \n,\t  test-coverage-reviewer\t,  code-quality  \n",
+      ),
+    ).toEqual(["feature-dev", "test-coverage-reviewer", "code-quality"]);
+  });
+});