feat(skills): add Claude Code support to generated scripts (#2966)

## Description

Note: We do not yet support binary invocations for claude code. Claude
code skills will be packaged with npx for now.

## PR Checklist

> Thank you for opening a Pull Request! Before submitting your PR, there
are a
> few things you can do to make sure it goes smoothly:

- [ ] Make sure you reviewed

[CONTRIBUTING.md](https://github.com/googleapis/genai-toolbox/blob/main/CONTRIBUTING.md)
- [ ] Make sure to open an issue as a

[bug/issue](https://github.com/googleapis/genai-toolbox/issues/new/choose)
  before writing your code! That way we can discuss the change, evaluate
  designs, and agree on the general idea
- [ ] Ensure the tests and linter pass
- [ ] Code coverage does not decrease (if any source code was changed)
- [ ] Appropriate docs were updated (if necessary)
- [ ] Make sure to add `!` if this involve a breaking change

🛠️ Fixes #<issue_number_goes_here>

---------

Co-authored-by: Haoyu Wang <whaoyu@google.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: 3 people

cmd/internal/skills/generator.go

@@ -135,42 +135,53 @@ const OPTIONAL_VARS_TO_OMIT_IF_EMPTY = [
 {{end}}
 
 function mergeEnvVars(env) {
-	const envPath = path.resolve(__dirname, '../../../.env');
-	if (fs.existsSync(envPath)) {
+	if (process.env.GEMINI_CLI === '1') {
+		const envPath = path.resolve(__dirname, '../../../.env');
+		if (fs.existsSync(envPath)) {
 			const envContent = fs.readFileSync(envPath, 'utf-8');
 			envContent.split('\n').forEach(line => {
-					const trimmed = line.trim();
-					if (trimmed && !trimmed.startsWith('#')) {
-							const splitIdx = trimmed.indexOf('=');
-							if (splitIdx !== -1) {
-									const key = trimmed.slice(0, splitIdx).trim();
-									let value = trimmed.slice(splitIdx + 1).trim();
-									value = value.replace(/(^['"]|['"]$)/g, '');
-									if (env[key] === undefined) {
-											env[key] = value;
-									}
-							}
+				const trimmed = line.trim();
+				if (trimmed && !trimmed.startsWith('#')) {
+					const splitIdx = trimmed.indexOf('=');
+					if (splitIdx !== -1) {
+						const key = trimmed.slice(0, splitIdx).trim();
+						let value = trimmed.slice(splitIdx + 1).trim();
+						value = value.replace(/(^['"]|['"]$)/g, '');
+						if (env[key] === undefined) {
+							env[key] = value;
+						}
 					}
+				}
 			});
+		}
+	} else if (process.env.CLAUDECODE === '1') {
+		const prefix = 'CLAUDE_PLUGIN_OPTION_';
+		for (const key in process.env) {
+			if (key.startsWith(prefix)) {
+				env[key.substring(prefix.length)] = process.env[key];
+			}
+		}
 	}
 }
 
 function prepareEnvironment() {
-    let env = { ...process.env };
-		let userAgent = "skills";
-		if (process.env.GEMINI_CLI === '1') {
-				userAgent = "skills-geminicli";
-				mergeEnvVars(env);
+	let env = { ...process.env };
+	let userAgent = "skills";
+	if (process.env.GEMINI_CLI === '1') {
+		userAgent = "skills-geminicli";
+	} else if (process.env.CLAUDECODE === '1') {
+		userAgent = "skills-claudecode";
+	}
+	mergeEnvVars(env);
+	{{if .OptionalVars}}
+	OPTIONAL_VARS_TO_OMIT_IF_EMPTY.forEach(varName => {
+		if (env[varName] === '') {
+			delete env[varName];
 		}
-		{{if .OptionalVars}}
-		OPTIONAL_VARS_TO_OMIT_IF_EMPTY.forEach(varName => {
-				if (env[varName] === '') {
-						delete env[varName];
-				}
-		});
-    {{end}}
+	});
+	{{end}}
 
-    return { env, userAgent };
+	return { env, userAgent };
 }
 
 function main() {

cmd/internal/skills/generator_test.go

@@ -285,6 +285,18 @@ func TestGenerateScriptContent(t *testing.T) {
 				`const npxArgs = ["--yes", "@toolbox-sdk/server@0.31.0"`,
 			},
 		},
+		{
+			name:       "claude code script",
+			toolName:   "claude-tool",
+			configArgs: `"--prebuilt", "test"`,
+			mode:       "bin",
+			wantContains: []string{
+				`userAgent = "skills-claudecode";`,
+				`const prefix = 'CLAUDE_PLUGIN_OPTION_';`,
+				`if (key.startsWith(prefix)) {`,
+				`env[key.substring(prefix.length)] = process.env[key];`,
+			},
+		},
 	}
 
 	for _, tt := range tests {