feat(extensions): serve local media in Flex viewer canvas + bundled MCP server - #8
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…CP server Ports the .NET FlexPreviewService local-media serving (LINE_FLEX_MCP_ASSET_DIR) to the two Node servers so a Flex message can reference local artwork/video by a relative url in every preview path, not just the .NET MCP tool. - Add shared lib/assets.mjs (resolveAssetPath / assetContentType / isLoopbackHost / resolveMediaRequest), a port of the .NET confinement logic kept in one place so the canvas (extension.mjs) and bundled MCP server (mcp/server.mjs) cannot diverge. - Wire both servers to serve assets under LINE_FLEX_MCP_ASSET_DIR (opt-in, loopback host-guarded, extension allowlist .png/.jpg/.jpeg/.mp4, path traversal/symlink escape refused). renderer.js and web assets unchanged. - Add zero-dependency node:test suite (42 tests): a superset of the .NET FlexPreviewAssetServingTests plus DNS-rebinding and resolveMediaRequest cases. Cleanup uses a single async fs.rm to avoid an rmSync recursive crash on Windows with non-ASCII temp paths. - Add npm test script and a CI job (node --test) so JS-specific regressions are caught; runs on Linux where the symlink-escape test is exercised. - Document local media serving in the extension README (en/ja). 3-role gate: security PASS / code PASS / test-arch PASS (non-blocking CONCERNS), no blocking findings. Record: docs/reviews/2026-09-04-flex-preview-extension-parity-review.md Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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概要
Flex プレビューのローカルメディア配信（
LINE_FLEX_MCP_ASSET_DIR配下の画像/動画を相対urlで参照）を、これまで対応していなかった Copilot キャンバス拡張（extension.mjs）と同梱 Node MCP サーバ（mcp/server.mjs） に移植し、.NET Tools（FlexPreviewService）との機能 parity を取りました。これまで両 Node サーバは静的ファイル whitelist ＋
/api/*のみ配信し、相対urlのメディアは 404 でした（.NET MCP 経由のみ配信可＝非対称）。本 PR でこの非対称を解消します。利用シーン: 用意したメディアをフォルダに配置 → Flex JSON からは相対
url（例"assets/hero.png"）で参照 → 本番移行時は origin だけ HTTPS の CDN に差し替え（相対パスは不変）。プレビュー専用の利便機能。変更点
lib/assets.mjs（新規） — 封じ込めロジックを共有モジュールに集約。resolveAssetPath/assetContentType/isLoopbackHost/resolveMediaRequestは .NET の同名ロジックの移植。セキュリティ上重要な封じ込めを 1 箇所に置き、2 サーバが同一のresolveMediaRequestを通す（二重持ち回避）。extension.mjs/mcp/server.mjs—LINE_FLEX_MCP_ASSET_DIR配下メディア配信を配線（opt-in・ループバック Host ガード・拡張子 allowlist.png/.jpg/.jpeg/.mp4・パストラバーサル/symlink 越え拒否）。renderer.jsほかweb/は無改修。lib/assets.test.mjs（新規・42 tests） — 依存ゼロのnode:test。.NETFlexPreviewAssetServingTestsの上位集合＋ DNS リバインド／resolveMediaRequest直接テスト。ci.yml— 依存ゼロのextension-testジョブ追加（node --test・Linux で symlink 越えテストも実走）。mcp/package.jsonにnpm test。テスト
node --test extensions/line-flex-viewer/lib/assets.test.mjs= 42/42 全緑。mcp/server.mjsを stdio 起動した手動 e2e スモークで実配信確認（画像 200/バイト一致・.gif→404・トラバーサル→404・外部 Host→404）。レビュー
3 役ゲート = security PASS / code PASS / test-arch PASS（非ブロッキング CONCERNS）、BLOCKING なし。封じ込め（トラバーサル・エンコード回避・rooted/UNC・制御文字・DNS リバインド・symlink 越え）は .NET 版と等価と実証。
記録:
docs/reviews/2026-09-04-flex-preview-extension-parity-review.md残（非ブロッキング follow-up・次サイクル）
/api/*・静的配信へのホストガード横展開（既存 follow-up と同一課題）handleRequestを SDK 非依存モジュールへ切り出し）X-Content-Type-Options: nosniffの些細な parity（.NET も未対応）未確認
extension.mjs）の実起動は SDK/ホストが必要で未検証。mcp/server.mjsと同一配線・共有関数のため単体テスト＋実 MCP スモークで実質担保。🤖 Generated with Claude Code