fix: mark the plugin bundle as ESM so it loads on Node 20.0-20.18 and 22.0-22.6

[satsukies]

Summary

The installed plugin fails to start on Node 20.0–20.18 and 22.0–22.6 with SyntaxError: Cannot use import statement outside a module. This PR adds plugin/scripts/package.json with "type": "module" so Node always loads bundle.js as ESM.

plugin/scripts/bundle.js is an ESM bundle with a .js extension. In this repository, the root package.json ("type": "module") tells Node to treat it as ESM. But the Claude Code plugin cache copies only the plugin/ directory (for example ~/.claude/plugins/cache/deploygate-marketplace/deploygate/1.5.1/scripts/bundle.js), so no package.json sits above the bundle there. Node then falls back to CommonJS unless it has module syntax detection, which is on by default only from 20.19.0 and 22.7.0.

• plugin/scripts/package.json (new): { "type": "module" }. It sits next to the bundle, so it travels with any copy of plugin/.
• src/__tests__/plugin.test.ts: assert the file exists and declares "type": "module".

The npm package (@deploygate/mcp) is not affected. It ships the root package.json, and npm pack --dry-run still lists only LICENSE, README.md, package.json and plugin/scripts/bundle.js. No bundle regeneration is needed.

Related Issue

Refs #77 (found while adding the Node 20 compatibility check in #78)

Type of change

• Bug fix
• New feature
• Documentation
• Refactor / internal change
• Build / CI / tooling

Test plan

• npm run build passes
• npm test passes (235 tests)
• Manually verified the change (describe how below)

I reproduced the plugin cache layout (only scripts/bundle.js, with no package.json above it) and launched it with the exact node -e "...import(entry)" command from plugin/.mcp.json:

Node	Without this PR	With scripts/package.json
20.0.0	SyntaxError: Cannot use import statement outside a module	loads, smoke test passes
20.18.3	SyntaxError	passes
20.19.0	loads	passes
22.0.0	SyntaxError	passes
22.6.0	SyntaxError	passes
22.7.0 / 22.12.0 / 24.0.0	loads	passes

"Passes" means scripts/smoke-bundle.mjs from #78 (initialize + tools/list, 58 tools). The bundle built from #73 (@modelcontextprotocol/sdk 1.32.0, zod 4.6.5) also passes on Node 20.0.0 with this file in place.

Users get the fix once a release updates the plugin cache. #78 will pin the compatibility job to Node 20.0.0 and run the copied plugin/ directory, so it depends on this PR being merged first.

Checklist

• I have updated the plugin version in plugin/.codex-plugin/plugin.json and plugin/.claude-plugin/plugin.json if applicable (handled by release-please)
• I have read and agree to the Code of Conduct

🤖 Generated with Claude Code

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[devin-ai-integration]

✅ Devin Review: No Issues Found

Devin Review analyzed this PR and found no bugs or issues to report.

[Copilot]

Copilot review overview

🟢 Approval recommended

The focused configuration fix correctly addresses isolated plugin installations and includes appropriate regression coverage.

Review effort: Balanced
Findings: None

What changed in this PR

Ensures the standalone plugin bundle loads as ESM on older supported Node.js 20 and 22 releases.

Changes:

• Adds a local ESM package boundary beside bundle.js.
• Tests that the bundle directory declares ESM mode.

File	Description
plugin/​scripts/​package.json	Marks bundled scripts as ESM.
src/​__tests__/​plugin.test.ts	Verifies the ESM declaration.

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[enomoto-kazuya]

LGTM!

[satsukies]

thanks!