Release Mail Tools 0.1.0

.gitignore

@@ -0,0 +1,9 @@
+node_modules/
+dist/
+release/*.zip
+release/*.zip.sha256
+coverage/
+playwright-report/
+test-results/
+*.tsbuildinfo
+.DS_Store

.npmrc

@@ -0,0 +1 @@
+@add-ideas:registry=https://git.add-ideas.de/api/packages/lotobo/npm/

CHANGELOG.md

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+# Changelog
+
+## 0.1.0 - 2026-09-01
+
+- Initial local-first EML/MIME inspection release.
+- Added bounded header, multipart, transfer-encoding and attachment parsing.
+- Added inert body comparison and opaque sandboxed sanitized HTML preview.
+- Added header diagnostics, canonical EML export and focused redaction report.
+- Added offline PWA packaging, Toolbox integration and reproducible ZIP output.

CONTRIBUTING.md

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+# Contributing
+
+Keep processing local, bounded and deterministic. New MIME features require
+malformed-input, nesting/size-limit and inert-rendering tests. Never add remote
+content loading or message execution. Run `npm run check` and both Playwright
+projects before submitting a change; update the changelog and security docs
+when a boundary changes.

LICENSE

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+  If the Program specifies that a proxy can decide which future
+versions of the GNU General Public License can be used, that proxy's
+public statement of acceptance of a version permanently authorizes you
+to choose that version for the Program.
+
+  Later license versions may give you additional or different
+permissions.  However, no additional obligations are imposed on any
+author or copyright holder as a result of your choosing to follow a
+later version.
+
+  15. Disclaimer of Warranty.
+
+  THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY
+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.

LICENSES/README.md

@@ -0,0 +1,4 @@
+# Licence materials
+
+`../LICENSE` contains GPL-3.0-or-later terms for Mail Tools. Release builds add
+`npm-runtime-licenses.txt`, generated from the exact locked runtime packages.

README.md

@@ -0,0 +1,45 @@
+# Mail Tools
+
+Mail Tools is a local-first browser workbench for inspecting `.eml` and MIME
+messages. Version 0.1.0 unfolds headers, decodes RFC 2047 words, builds a bounded
+multipart tree, decodes common transfer encodings, inventories attachments,
+compares text bodies, and creates canonical or focused redacted exports.
+
+HTML bodies are sanitized and displayed only in an opaque sandbox with an
+embedded `default-src 'none'` policy. Remote images, links, forms, scripts,
+styles, media, frames and active documents are removed. No message, address,
+attachment, URL or telemetry leaves the browser.
+
+## Development and release
+
+Requires Node.js 22+ and npm 11+.
+
+```sh
+npm ci
+npm run check
+npm run test:browser
+npm run release:artifact
+```
+
+The last command creates deterministic `release/mail-tools-0.1.0.zip` and its
+SHA-256 sidecar. The app uses relative assets and is tested beneath
+`/deep/nested/mail/`. It can run standalone or from add·ideas Toolbox.
+
+## v0.1 boundary
+
+- source limit: 8 MiB; at most 2,000 headers, 500 MIME parts, nesting depth 20,
+  and a conservative 16 MiB decoded-data budget;
+- folded headers, duplicate fields and RFC 2047 B/Q words;
+- multipart and nested `message/rfc822`, Base64 and quoted-printable;
+- safe text previews, sanitized HTML, attachment inventory/download;
+- address/date and unverified SPF/DKIM/DMARC/ARC header diagnostics;
+- bounded line comparison and normalized EML plus top-level header redaction
+  with a JSON report.
+
+This is not a mail client, spam detector, forensic verifier or anonymity tool.
+It does not open mailbox containers, contact servers, decrypt S/MIME/OpenPGP,
+validate DKIM signatures, establish sender identity, scan malware, render CID
+resources, or guarantee round-trip byte identity. See
+[`docs/PRIVACY-SECURITY.md`](docs/PRIVACY-SECURITY.md).
+
+Licensed under GPL-3.0-or-later.

SECURITY.md

@@ -0,0 +1,9 @@
+# Security
+
+Report vulnerabilities privately to the repository owner through the Gitea
+security contact. Do not attach sensitive real messages to public issues.
+
+Treat every message and attachment as hostile. The app does not execute or open
+attachments, does not validate sender identity, and does not make authentication
+headers trustworthy. Deploy with the documented same-origin CSP and restrictive
+Permissions Policy. Supported security fixes are made on the current release.

SOURCE.md

@@ -0,0 +1,8 @@
+# Corresponding source
+
+The corresponding source for Mail Tools 0.1.0 is available at:
+
+https://git.add-ideas.de/lotobo/mail-tools/src/tag/v0.1.0
+
+Build with Node.js 22+, npm 11+, and the exact dependencies in
+`package-lock.json`. Run `npm ci && npm run release:artifact`.

THIRD_PARTY_NOTICES.md

@@ -0,0 +1,9 @@
+# Third-party notices
+
+Mail Tools is GPL-3.0-or-later. Runtime components include React and React DOM
+(MIT), DOMPurify (MPL-2.0 OR Apache-2.0), and the add·ideas Toolbox contract,
+shell and helpers (their package metadata and corresponding source apply).
+
+The build generates `LICENSES/npm-runtime-licenses.txt` from the exact lockfile
+and installed packages. No remote font, icon, script, stylesheet or service is
+used at runtime.

docs/ACCESSIBILITY.md

@@ -0,0 +1,7 @@
+# Accessibility
+
+Workspaces use native headings, labels, buttons, tables, lists, status regions
+and keyboard-operable tabs. Focus indicators and system light/dark selection
+come from the shared Toolbox shell. Dense tables and previews scroll rather
+than clipping; narrow layouts collapse to one column; reduced-motion preference
+is respected. Sanitized HTML preview has a descriptive iframe title.

docs/ARCHITECTURE.md

@@ -0,0 +1,11 @@
+# Architecture
+
+The React shell lazy-loads one workbench. `core/mime.ts` turns bounded source
+text into immutable-looking header and MIME-part records; parsing never creates
+DOM. Transfer decoding consumes a global byte budget. Diagnostics, comparison,
+canonicalization and redaction are separate pure modules.
+
+Only the selected HTML text is passed through DOMPurify. It is then embedded in
+an iframe without sandbox capabilities and with an inner policy that denies all
+connections and active content. Attachment downloads are explicit Blob URLs
+with sanitized filenames. The service worker caches only same-origin app files.

docs/PRIVACY-SECURITY.md

@@ -0,0 +1,15 @@
+# Privacy and security
+
+Messages are read through browser file APIs or pasted text and kept only in
+memory. There is no storage, telemetry, analytics, remote-resource request or
+server integration. Closing/reloading the page clears the workbench.
+
+Limits reduce accidental resource exhaustion but do not make Mail Tools a
+forensic parser. HTML loses links, styling and embedded resources by design.
+Downloaded attachments remain untrusted. Authentication results and Received
+headers are self-asserted text; no DNS or cryptographic verification occurs.
+
+Focused redaction removes a fixed set of top-level transport/authentication
+headers. It does not rewrite nested `message/rfc822` content and can leave names,
+addresses, message IDs, MIME metadata, tracking tokens, body content, document
+metadata and attachments. Review outputs independently.

eslint.config.mjs

@@ -0,0 +1,37 @@
+import js from "@eslint/js";
+import globals from "globals";
+import reactHooks from "eslint-plugin-react-hooks";
+import reactRefresh from "eslint-plugin-react-refresh";
+import tseslint from "typescript-eslint";
+
+export default tseslint.config(
+  {
+    ignores: [
+      "dist",
+      "release",
+      "coverage",
+      "test-results",
+      "playwright-report",
+    ],
+  },
+  {
+    extends: [js.configs.recommended, ...tseslint.configs.recommended],
+    files: ["**/*.{ts,tsx}"],
+    languageOptions: {
+      ecmaVersion: 2023,
+      globals: { ...globals.browser, ...globals.worker },
+    },
+    plugins: { "react-hooks": reactHooks, "react-refresh": reactRefresh },
+    rules: {
+      ...reactHooks.configs.recommended.rules,
+      "react-refresh/only-export-components": [
+        "warn",
+        { allowConstantExport: true },
+      ],
+    },
+  },
+  {
+    files: ["scripts/**/*.mjs", "playwright.config.ts"],
+    languageOptions: { globals: globals.node },
+  },
+);

index.html

@@ -0,0 +1,19 @@
+<!doctype html>
+<html lang="en">
+  <head>
+    <meta charset="UTF-8" />
+    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
+    <meta
+      name="description"
+      content="Inspect and redact email messages locally in the browser."
+    />
+    <link rel="icon" type="image/svg+xml" href="./favicon.svg" />
+    <link rel="manifest" href="./manifest.webmanifest" />
+    <meta name="theme-color" content="#29255f" />
+    <title>Mail Tools</title>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="./src/main.tsx"></script>
+  </body>
+</html>

package.json

@@ -0,0 +1,72 @@
+{
+  "name": "mail-tools",
+  "version": "0.1.0",
+  "description": "Inspect, compare, redact and export email messages locally in the browser.",
+  "license": "GPL-3.0-or-later",
+  "author": "Albrecht Degering",
+  "repository": {
+    "type": "git",
+    "url": "git+https://git.add-ideas.de/lotobo/mail-tools.git"
+  },
+  "homepage": "https://git.add-ideas.de/lotobo/mail-tools",
+  "bugs": {
+    "url": "https://git.add-ideas.de/lotobo/mail-tools/issues"
+  },
+  "private": true,
+  "type": "module",
+  "engines": {
+    "node": ">=22"
+  },
+  "scripts": {
+    "predev": "npm run manifest:generate",
+    "dev": "vite",
+    "prebuild": "npm run release:prepare && npm run manifest:generate",
+    "build": "tsc -b && vite build",
+    "preview": "vite preview",
+    "typecheck": "tsc -b --pretty false",
+    "lint": "eslint . --max-warnings=0",
+    "format": "prettier --write .",
+    "format:check": "prettier --check .",
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "test:browser": "playwright test",
+    "manifest:generate": "node scripts/generate-toolbox-manifest.mjs",
+    "manifest:check": "node scripts/generate-toolbox-manifest.mjs --check",
+    "release:prepare": "node scripts/prepare-release-files.mjs",
+    "toolbox:check": "toolbox-check dist",
+    "package:release": "node scripts/package-release.mjs",
+    "check": "npm run manifest:check && npm run typecheck && npm run lint && npm run format:check && npm run test && npm run build && npm run toolbox:check",
+    "release:artifact": "npm run check && npm run test:browser && npm run package:release -- --force"
+  },
+  "dependencies": {
+    "@add-ideas/toolbox-contract": "0.2.3",
+    "@add-ideas/toolbox-helpers": "0.1.0",
+    "@add-ideas/toolbox-shell-react": "0.2.3",
+    "dompurify": "3.4.14",
+    "react": "19.2.8",
+    "react-dom": "19.2.8"
+  },
+  "devDependencies": {
+    "@add-ideas/toolbox-testkit": "0.2.3",
+    "@eslint/js": "10.0.1",
+    "@playwright/test": "1.62.1",
+    "@testing-library/jest-dom": "6.9.1",
+    "@testing-library/react": "16.3.2",
+    "@testing-library/user-event": "14.6.1",
+    "@types/node": "25.9.5",
+    "@types/react": "19.2.17",
+    "@types/react-dom": "19.2.5",
+    "@vitejs/plugin-react": "6.0.3",
+    "eslint": "10.7.0",
+    "eslint-plugin-react-hooks": "7.1.1",
+    "eslint-plugin-react-refresh": "0.5.2",
+    "globals": "17.7.0",
+    "jsdom": "29.1.1",
+    "prettier": "3.9.5",
+    "typescript": "6.0.3",
+    "typescript-eslint": "8.64.0",
+    "vite": "8.2.2",
+    "vitest": "4.1.11"
+  },
+  "packageManager": "npm@11.17.0"
+}

playwright.config.ts

@@ -0,0 +1,21 @@
+import { defineConfig, devices } from "@playwright/test";
+
+export default defineConfig({
+  testDir: "./tests/browser",
+  fullyParallel: false,
+  workers: 1,
+  timeout: 120_000,
+  expect: { timeout: 10_000 },
+  reporter: [["list"]],
+  use: { baseURL: "http://127.0.0.1:4195", trace: "retain-on-failure" },
+  webServer: {
+    command: "npm run build && node scripts/serve-test.mjs",
+    url: "http://127.0.0.1:4195",
+    reuseExistingServer: !process.env.CI,
+    timeout: 180_000,
+  },
+  projects: [
+    { name: "chromium", use: { ...devices["Desktop Chrome"] } },
+    { name: "firefox", use: { ...devices["Desktop Firefox"] } },
+  ],
+});

public/CHANGELOG.md

@@ -0,0 +1,9 @@
+# Changelog
+
+## 0.1.0 - 2026-09-01
+
+- Initial local-first EML/MIME inspection release.
+- Added bounded header, multipart, transfer-encoding and attachment parsing.
+- Added inert body comparison and opaque sandboxed sanitized HTML preview.
+- Added header diagnostics, canonical EML export and focused redaction report.
+- Added offline PWA packaging, Toolbox integration and reproducible ZIP output.

public/CONTRIBUTING.md

@@ -0,0 +1,7 @@
+# Contributing
+
+Keep processing local, bounded and deterministic. New MIME features require
+malformed-input, nesting/size-limit and inert-rendering tests. Never add remote
+content loading or message execution. Run `npm run check` and both Playwright
+projects before submitting a change; update the changelog and security docs
+when a boundary changes.

public/LICENSE

@@ -0,0 +1,674 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+                            Preamble
+
+  The GNU General Public License is a free, copyleft license for
+software and other kinds of works.
+
+  The licenses for most software and other practical works are designed
+to take away your freedom to share and change the works.  By contrast,
+the GNU General Public License is intended to guarantee your freedom to
+share and change all versions of a program--to make sure it remains free
+software for all its users.  We, the Free Software Foundation, use the
+GNU General Public License for most of our software; it applies also to
+any other work released this way by its authors.  You can apply it to
+your programs, too.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+them if you wish), that you receive source code or can get it if you
+want it, that you can change the software or use pieces of it in new
+free programs, and that you know you can do these things.
+
+  To protect your rights, we need to prevent others from denying you
+these rights or asking you to surrender the rights.  Therefore, you have
+certain responsibilities if you distribute copies of the software, or if
+you modify it: responsibilities to respect the freedom of others.
+
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+  Developers that use the GNU GPL protect your rights with two steps:
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+  "This License" refers to version 3 of the GNU General Public License.
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+
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+
+                     END OF TERMS AND CONDITIONS
+
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+    (at your option) any later version.
+
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+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
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+
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+<https://www.gnu.org/licenses/why-not-lgpl.html>.

public/LICENSES/README.md

@@ -0,0 +1,4 @@
+# Licence materials
+
+`../LICENSE` contains GPL-3.0-or-later terms for Mail Tools. Release builds add
+`npm-runtime-licenses.txt`, generated from the exact locked runtime packages.

public/README.md

@@ -0,0 +1,45 @@
+# Mail Tools
+
+Mail Tools is a local-first browser workbench for inspecting `.eml` and MIME
+messages. Version 0.1.0 unfolds headers, decodes RFC 2047 words, builds a bounded
+multipart tree, decodes common transfer encodings, inventories attachments,
+compares text bodies, and creates canonical or focused redacted exports.
+
+HTML bodies are sanitized and displayed only in an opaque sandbox with an
+embedded `default-src 'none'` policy. Remote images, links, forms, scripts,
+styles, media, frames and active documents are removed. No message, address,
+attachment, URL or telemetry leaves the browser.
+
+## Development and release
+
+Requires Node.js 22+ and npm 11+.
+
+```sh
+npm ci
+npm run check
+npm run test:browser
+npm run release:artifact
+```
+
+The last command creates deterministic `release/mail-tools-0.1.0.zip` and its
+SHA-256 sidecar. The app uses relative assets and is tested beneath
+`/deep/nested/mail/`. It can run standalone or from add·ideas Toolbox.
+
+## v0.1 boundary
+
+- source limit: 8 MiB; at most 2,000 headers, 500 MIME parts, nesting depth 20,
+  and a conservative 16 MiB decoded-data budget;
+- folded headers, duplicate fields and RFC 2047 B/Q words;
+- multipart and nested `message/rfc822`, Base64 and quoted-printable;
+- safe text previews, sanitized HTML, attachment inventory/download;
+- address/date and unverified SPF/DKIM/DMARC/ARC header diagnostics;
+- bounded line comparison and normalized EML plus top-level header redaction
+  with a JSON report.
+
+This is not a mail client, spam detector, forensic verifier or anonymity tool.
+It does not open mailbox containers, contact servers, decrypt S/MIME/OpenPGP,
+validate DKIM signatures, establish sender identity, scan malware, render CID
+resources, or guarantee round-trip byte identity. See
+[`docs/PRIVACY-SECURITY.md`](docs/PRIVACY-SECURITY.md).
+
+Licensed under GPL-3.0-or-later.

public/SECURITY.md

@@ -0,0 +1,9 @@
+# Security
+
+Report vulnerabilities privately to the repository owner through the Gitea
+security contact. Do not attach sensitive real messages to public issues.
+
+Treat every message and attachment as hostile. The app does not execute or open
+attachments, does not validate sender identity, and does not make authentication
+headers trustworthy. Deploy with the documented same-origin CSP and restrictive
+Permissions Policy. Supported security fixes are made on the current release.

public/SOURCE.md

@@ -0,0 +1,8 @@
+# Corresponding source
+
+The corresponding source for Mail Tools 0.1.0 is available at:
+
+https://git.add-ideas.de/lotobo/mail-tools/src/tag/v0.1.0
+
+Build with Node.js 22+, npm 11+, and the exact dependencies in
+`package-lock.json`. Run `npm ci && npm run release:artifact`.

public/THIRD_PARTY_NOTICES.md

@@ -0,0 +1,9 @@
+# Third-party notices
+
+Mail Tools is GPL-3.0-or-later. Runtime components include React and React DOM
+(MIT), DOMPurify (MPL-2.0 OR Apache-2.0), and the add·ideas Toolbox contract,
+shell and helpers (their package metadata and corresponding source apply).
+
+The build generates `LICENSES/npm-runtime-licenses.txt` from the exact lockfile
+and installed packages. No remote font, icon, script, stylesheet or service is
+used at runtime.

public/docs/ACCESSIBILITY.md

@@ -0,0 +1,7 @@
+# Accessibility
+
+Workspaces use native headings, labels, buttons, tables, lists, status regions
+and keyboard-operable tabs. Focus indicators and system light/dark selection
+come from the shared Toolbox shell. Dense tables and previews scroll rather
+than clipping; narrow layouts collapse to one column; reduced-motion preference
+is respected. Sanitized HTML preview has a descriptive iframe title.

public/docs/ARCHITECTURE.md

@@ -0,0 +1,11 @@
+# Architecture
+
+The React shell lazy-loads one workbench. `core/mime.ts` turns bounded source
+text into immutable-looking header and MIME-part records; parsing never creates
+DOM. Transfer decoding consumes a global byte budget. Diagnostics, comparison,
+canonicalization and redaction are separate pure modules.
+
+Only the selected HTML text is passed through DOMPurify. It is then embedded in
+an iframe without sandbox capabilities and with an inner policy that denies all
+connections and active content. Attachment downloads are explicit Blob URLs
+with sanitized filenames. The service worker caches only same-origin app files.

public/docs/PRIVACY-SECURITY.md

@@ -0,0 +1,15 @@
+# Privacy and security
+
+Messages are read through browser file APIs or pasted text and kept only in
+memory. There is no storage, telemetry, analytics, remote-resource request or
+server integration. Closing/reloading the page clears the workbench.
+
+Limits reduce accidental resource exhaustion but do not make Mail Tools a
+forensic parser. HTML loses links, styling and embedded resources by design.
+Downloaded attachments remain untrusted. Authentication results and Received
+headers are self-asserted text; no DNS or cryptographic verification occurs.
+
+Focused redaction removes a fixed set of top-level transport/authentication
+headers. It does not rewrite nested `message/rfc822` content and can leave names,
+addresses, message IDs, MIME metadata, tracking tokens, body content, document
+metadata and attachments. Review outputs independently.

public/favicon.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64" role="img" aria-label="Mail Tools"><path fill="#5b4ec4" d="M11 4h30l12 12v44H11z"/><path fill="#fff" opacity=".28" d="M41 4v14h12"/><path fill="none" stroke="#fff" stroke-width="4" stroke-linejoin="round" d="M18 27h28v20H18zm1 1 13 11 13-11"/></svg>

public/manifest.webmanifest

@@ -0,0 +1,18 @@
+{
+  "name": "Mail Tools",
+  "short_name": "Mail",
+  "description": "Inspect and redact email messages locally in the browser.",
+  "start_url": "./",
+  "scope": "./",
+  "display": "standalone",
+  "background_color": "#f6f7fb",
+  "theme_color": "#29255f",
+  "icons": [
+    {
+      "src": "./favicon.svg",
+      "sizes": "any",
+      "type": "image/svg+xml",
+      "purpose": "any maskable"
+    }
+  ]
+}

public/sw.js

@@ -0,0 +1,59 @@
+const CACHE_PREFIX = "mail-tools-shell-";
+const CACHE_NAME = CACHE_PREFIX + "0.1.0";
+const CORE = [
+  "./",
+  "./manifest.webmanifest",
+  "./favicon.svg",
+  "./toolbox-app.json",
+];
+self.addEventListener("install", (event) => {
+  event.waitUntil(
+    caches.open(CACHE_NAME).then(async (cache) => {
+      await cache.addAll(CORE);
+      const html = await (await fetch("./")).text();
+      const assets = [...html.matchAll(/(?:src|href)="(\.\/assets\/[^"]+)"/g)]
+        .map((match) => match[1])
+        .filter(Boolean);
+      await cache.addAll(assets);
+    }),
+  );
+  self.skipWaiting();
+});
+self.addEventListener("activate", (event) => {
+  event.waitUntil(
+    caches
+      .keys()
+      .then((keys) =>
+        Promise.all(
+          keys
+            .filter((key) => key.startsWith(CACHE_PREFIX) && key !== CACHE_NAME)
+            .map((key) => caches.delete(key)),
+        ),
+      )
+      .then(() => self.clients.claim()),
+  );
+});
+self.addEventListener("fetch", (event) => {
+  if (event.request.method !== "GET") return;
+  const url = new URL(event.request.url);
+  if (
+    url.origin !== self.location.origin ||
+    !url.pathname.startsWith(new URL(self.registration.scope).pathname)
+  )
+    return;
+  event.respondWith(
+    caches.match(event.request).then(
+      (cached) =>
+        cached ??
+        fetch(event.request).then((response) => {
+          if (response.ok) {
+            const copy = response.clone();
+            void caches
+              .open(CACHE_NAME)
+              .then((cache) => cache.put(event.request, copy));
+          }
+          return response;
+        }),
+    ),
+  );
+});

public/toolbox-app.json

@@ -0,0 +1,41 @@
+{
+  "$schema": "https://git.add-ideas.de/lotobo/toolbox-sdk/raw/branch/main/schemas/toolbox-app.v1.schema.json",
+  "schemaVersion": 1,
+  "id": "de.add-ideas.mail-tools",
+  "name": "Mail Tools",
+  "version": "0.1.0",
+  "description": "Inspect and redact email messages locally.",
+  "entry": "./",
+  "icon": "./favicon.svg",
+  "categories": ["documents", "developer", "privacy"],
+  "tags": ["email", "eml", "mime", "headers", "attachments"],
+  "integration": {
+    "contextVersion": 1,
+    "launchModes": ["navigate", "new-tab"],
+    "embedding": "unsupported"
+  },
+  "requirements": {
+    "secureContext": false,
+    "workers": false,
+    "indexedDb": false,
+    "crossOriginIsolated": false,
+    "topLevelContext": false
+  },
+  "privacy": {
+    "processing": "local",
+    "fileUploads": true,
+    "telemetry": false,
+    "label": "Messages stay in this browser; remote content is never loaded."
+  },
+  "source": {
+    "repository": "https://git.add-ideas.de/lotobo/mail-tools",
+    "license": "GPL-3.0-or-later"
+  },
+  "actions": [
+    {
+      "id": "source",
+      "label": "Source",
+      "url": "https://git.add-ideas.de/lotobo/mail-tools"
+    }
+  ]
+}

scripts/generate-toolbox-manifest.mjs

@@ -0,0 +1,33 @@
+import { readFile, writeFile } from "node:fs/promises";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import { format } from "prettier";
+const root = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
+const sourcePath = path.join(root, "src/toolbox/manifest.source.json");
+const outputPath = path.join(root, "public/toolbox-app.json");
+const source = JSON.parse(await readFile(sourcePath, "utf8"));
+const pkg = JSON.parse(await readFile(path.join(root, "package.json"), "utf8"));
+const versionSource = await readFile(path.join(root, "src/version.ts"), "utf8");
+const appVersion = /^export const APP_VERSION = "([^"]+)";$/mu.exec(
+  versionSource,
+)?.[1];
+const repository = "https://git.add-ideas.de/lotobo/" + pkg.name;
+if (source.version !== pkg.version || appVersion !== pkg.version)
+  throw new Error("Version identity drift");
+if (
+  source.id !== "de.add-ideas." + pkg.name ||
+  source.source?.repository !== repository ||
+  source.source?.license !== "GPL-3.0-or-later"
+)
+  throw new Error("Manifest source identity is invalid");
+const serialized = await format(JSON.stringify(source), {
+  filepath: outputPath,
+});
+if (process.argv.includes("--check")) {
+  if ((await readFile(outputPath, "utf8").catch(() => "")) !== serialized)
+    throw new Error("public/toolbox-app.json is stale");
+  console.log("Toolbox manifest is synchronized");
+} else {
+  await writeFile(outputPath, serialized);
+  console.log("Generated public/toolbox-app.json");
+}

scripts/package-release.mjs

@@ -0,0 +1,165 @@
+#!/usr/bin/env node
+import { createHash } from "node:crypto";
+import { execFile } from "node:child_process";
+import {
+  access,
+  chmod,
+  copyFile,
+  cp,
+  lstat,
+  mkdir,
+  mkdtemp,
+  readFile,
+  readdir,
+  rename,
+  rm,
+  utimes,
+  writeFile,
+} from "node:fs/promises";
+import os from "node:os";
+import path from "node:path";
+import { promisify } from "node:util";
+import { fileURLToPath } from "node:url";
+const execute = promisify(execFile);
+const root = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
+const pkg = JSON.parse(await readFile(path.join(root, "package.json"), "utf8"));
+const argument = (name, fallback) => {
+  const index = process.argv.indexOf(name);
+  return index >= 0 ? process.argv[index + 1] : fallback;
+};
+const output = path.resolve(
+  root,
+  argument("--output", "release/" + pkg.name + "-" + pkg.version + ".zip"),
+);
+const checksumOutput = output + ".sha256";
+const force = process.argv.includes("--force");
+if (
+  path.extname(output).toLowerCase() !== ".zip" ||
+  output === root ||
+  output === path.parse(output).root
+)
+  throw new Error("Unsafe release target");
+const exists = (file) =>
+  access(file).then(
+    () => true,
+    () => false,
+  );
+if (!force && ((await exists(output)) || (await exists(checksumOutput))))
+  throw new Error("Release output exists");
+const input = path.join(root, "dist");
+for (const name of [
+  "index.html",
+  "manifest.webmanifest",
+  "sw.js",
+  "toolbox-app.json",
+  "favicon.svg",
+  "README.md",
+  "CHANGELOG.md",
+  "CONTRIBUTING.md",
+  "LICENSE",
+  "SECURITY.md",
+  "SOURCE.md",
+  "THIRD_PARTY_NOTICES.md",
+  "LICENSES/README.md",
+  "LICENSES/npm-runtime-licenses.txt",
+  "docs/ACCESSIBILITY.md",
+  "docs/ARCHITECTURE.md",
+  "docs/PRIVACY-SECURITY.md",
+]) {
+  const details = await lstat(path.join(input, name)).catch(() => null);
+  if (!details?.isFile() || details.isSymbolicLink())
+    throw new Error("Missing release file: " + name);
+}
+const manifest = JSON.parse(
+  await readFile(path.join(input, "toolbox-app.json"), "utf8"),
+);
+const repository = "https://git.add-ideas.de/lotobo/" + pkg.name;
+if (
+  manifest.id !== "de.add-ideas." + pkg.name ||
+  manifest.version !== pkg.version ||
+  manifest.entry !== "./" ||
+  manifest.icon !== "./favicon.svg" ||
+  manifest.source?.repository !== repository
+)
+  throw new Error("Packaged manifest identity is invalid");
+if (
+  /\b(?:src|href)=["']\//iu.test(
+    await readFile(path.join(input, "index.html"), "utf8"),
+  )
+)
+  throw new Error("Root-absolute asset reference");
+async function collect(directory, prefix = "") {
+  const files = [];
+  for (const entry of (await readdir(directory, { withFileTypes: true })).sort(
+    (a, b) => (a.name === b.name ? 0 : a.name < b.name ? -1 : 1),
+  )) {
+    const absolute = path.join(directory, entry.name);
+    const relative = prefix ? prefix + "/" + entry.name : entry.name;
+    if (entry.isSymbolicLink())
+      throw new Error("Symlink in release: " + relative);
+    if (entry.isDirectory()) files.push(...(await collect(absolute, relative)));
+    else if (entry.isFile()) files.push({ absolute, relative });
+    else throw new Error("Unsupported release entry: " + relative);
+  }
+  return files;
+}
+const sourceFiles = await collect(input);
+for (const file of sourceFiles)
+  if (
+    file.relative.endsWith(".map") ||
+    /(?:^|\/)(?:\.env(?:\.|$)|id_rsa|id_ed25519|.*\.pem$|.*\.key$)/iu.test(
+      file.relative,
+    ) ||
+    file.relative.split("/").includes("..")
+  )
+    throw new Error("Forbidden release entry: " + file.relative);
+await mkdir(path.dirname(output), { recursive: true });
+const stagingRoot = await mkdtemp(
+  path.join(os.tmpdir(), pkg.name + "-release-"),
+);
+const publicationRoot = await mkdtemp(
+  path.join(path.dirname(output), "." + pkg.name + "-publish-"),
+);
+const stagedTree = path.join(stagingRoot, "tree");
+const stagedArchive = path.join(stagingRoot, path.basename(output));
+try {
+  await cp(input, stagedTree, { recursive: true });
+  const timestamp = new Date("1980-01-01T00:00:00.000Z");
+  for (const file of await collect(stagedTree)) {
+    await chmod(file.absolute, 0o644);
+    await utimes(file.absolute, timestamp, timestamp);
+  }
+  await execute(
+    "zip",
+    [
+      "-X",
+      "-q",
+      "-9",
+      stagedArchive,
+      ...sourceFiles.map((file) => file.relative),
+    ],
+    {
+      cwd: stagedTree,
+      env: { ...process.env, TZ: "UTC" },
+      maxBuffer: 1024 * 1024,
+    },
+  );
+  const archive = await readFile(stagedArchive);
+  const digest = createHash("sha256").update(archive).digest("hex");
+  const stagedChecksum = stagedArchive + ".sha256";
+  await writeFile(stagedChecksum, digest + "  " + path.basename(output) + "\n");
+  const publicationArchive = path.join(publicationRoot, path.basename(output));
+  const publicationChecksum = publicationArchive + ".sha256";
+  await copyFile(stagedArchive, publicationArchive);
+  await copyFile(stagedChecksum, publicationChecksum);
+  if (force) {
+    await rm(output, { force: true });
+    await rm(checksumOutput, { force: true });
+  }
+  await rename(publicationArchive, output);
+  await rename(publicationChecksum, checksumOutput);
+  console.log("Created " + path.relative(root, output) + "\nSHA-256 " + digest);
+} finally {
+  await rm(stagingRoot, { recursive: true, force: true });
+  await rm(publicationRoot, { recursive: true, force: true });
+}

scripts/prepare-release-files.mjs

@@ -0,0 +1,70 @@
+import { cp, mkdir, readFile, readdir, rm, writeFile } from "node:fs/promises";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+const root = path.resolve(path.dirname(fileURLToPath(import.meta.url)), "..");
+const destination = path.join(root, "public");
+for (const name of [
+  "LICENSE",
+  "README.md",
+  "CHANGELOG.md",
+  "CONTRIBUTING.md",
+  "SECURITY.md",
+  "SOURCE.md",
+  "THIRD_PARTY_NOTICES.md",
+]) {
+  await readFile(path.join(root, name));
+  await cp(path.join(root, name), path.join(destination, name));
+}
+for (const directory of ["LICENSES", "docs"]) {
+  const output = path.join(destination, directory);
+  await rm(output, { recursive: true, force: true });
+  await cp(path.join(root, directory), output, { recursive: true });
+}
+const lock = JSON.parse(
+  await readFile(path.join(root, "package-lock.json"), "utf8"),
+);
+const sections = [];
+for (const [location, locked] of Object.entries(lock.packages ?? {}).sort(
+  ([a], [b]) => (a === b ? 0 : a < b ? -1 : 1),
+)) {
+  if (!location.includes("node_modules/") || locked.dev === true) continue;
+  const packageDirectory = path.join(root, location);
+  const details = JSON.parse(
+    await readFile(path.join(packageDirectory, "package.json"), "utf8"),
+  );
+  const candidates = (await readdir(packageDirectory))
+    .filter((name) => /^(?:licen[cs]e|copying|notice)(?:\.|$)/iu.test(name))
+    .sort();
+  const texts = [];
+  for (const candidate of candidates) {
+    try {
+      texts.push(
+        "--- " +
+          candidate +
+          " ---\n" +
+          (await readFile(path.join(packageDirectory, candidate), "utf8")),
+      );
+    } catch {
+      /* directory */
+    }
+  }
+  sections.push(
+    "=".repeat(78) +
+      "\n" +
+      details.name +
+      "@" +
+      details.version +
+      "\nDeclared licence: " +
+      (details.license ?? locked.license ?? "See upstream") +
+      "\n" +
+      "=".repeat(78) +
+      "\n" +
+      (texts.join("\n\n") || "See upstream package metadata."),
+  );
+}
+await mkdir(path.join(destination, "LICENSES"), { recursive: true });
+await writeFile(
+  path.join(destination, "LICENSES/npm-runtime-licenses.txt"),
+  sections.join("\n\n").trimEnd() + "\n",
+);
+console.log("Prepared release documentation");

scripts/serve-test.mjs

@@ -0,0 +1,69 @@
+import { createServer } from "node:http";
+import { readFile, stat } from "node:fs/promises";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+const root = path.resolve(
+  path.dirname(fileURLToPath(import.meta.url)),
+  "..",
+  "dist",
+);
+const prefix = "/deep/nested/mail/";
+const types = new Map([
+  [".css", "text/css; charset=utf-8"],
+  [".html", "text/html; charset=utf-8"],
+  [".js", "text/javascript; charset=utf-8"],
+  [".json", "application/json; charset=utf-8"],
+  [".webmanifest", "application/manifest+json; charset=utf-8"],
+  [".svg", "image/svg+xml"],
+  [".md", "text/markdown; charset=utf-8"],
+  [".txt", "text/plain; charset=utf-8"],
+  [".wasm", "application/wasm"],
+  [".png", "image/png"],
+  [".jpg", "image/jpeg"],
+  [".webp", "image/webp"],
+]);
+const headers = {
+  "Content-Security-Policy":
+    "default-src 'self'; base-uri 'self'; object-src 'none'; frame-ancestors 'none'; form-action 'self'; script-src 'self' 'wasm-unsafe-eval'; style-src 'self' 'unsafe-inline'; img-src 'self' data: blob:; media-src 'self' blob:; connect-src 'self'; worker-src 'self' blob:; manifest-src 'self'",
+  "Cross-Origin-Opener-Policy": "same-origin",
+  "Cross-Origin-Resource-Policy": "same-origin",
+  "Permissions-Policy":
+    "camera=(), microphone=(), geolocation=(), usb=(), payment=()",
+  "Referrer-Policy": "no-referrer",
+  "X-Content-Type-Options": "nosniff",
+};
+const server = createServer(async (request, response) => {
+  try {
+    const url = new URL(request.url ?? "/", "http://127.0.0.1");
+    const relative = decodeURIComponent(url.pathname).startsWith(prefix)
+      ? decodeURIComponent(url.pathname).slice(prefix.length)
+      : decodeURIComponent(url.pathname).replace(/^\/+/, "");
+    const normalized = path.posix.normalize(relative || "index.html");
+    if (
+      normalized === ".." ||
+      normalized.startsWith("../") ||
+      path.isAbsolute(normalized)
+    ) {
+      response.writeHead(400).end("Bad request");
+      return;
+    }
+    let file = path.join(root, normalized);
+    if ((await stat(file).catch(() => null))?.isDirectory())
+      file = path.join(file, "index.html");
+    const content = await readFile(file);
+    const cacheControl = normalized.startsWith("assets/")
+      ? "public, max-age=31536000, immutable"
+      : "no-cache";
+    response.writeHead(200, {
+      "Content-Type":
+        types.get(path.extname(file)) ?? "application/octet-stream",
+      "Cache-Control": cacheControl,
+      ...headers,
+    });
+    response.end(content);
+  } catch {
+    response.writeHead(404, { "Content-Type": "text/plain; charset=utf-8" });
+    response.end("Not found");
+  }
+});
+server.listen(4195, "127.0.0.1", () => console.log("Test server ready"));

src/App.tsx

@@ -0,0 +1,29 @@
+import { lazy, Suspense, useState } from "react";
+import { AppShell } from "@add-ideas/toolbox-shell-react";
+import "@add-ideas/toolbox-shell-react/styles.css";
+import "./styles.css";
+import { ErrorBoundary } from "./components/ErrorBoundary";
+import { HelpDialog } from "./components/HelpDialog";
+import { manifest } from "./toolbox/manifest";
+
+const Workbench = lazy(async () => ({
+  default: (await import("./components/Workbench")).Workbench,
+}));
+
+export function App() {
+  const [helpOpen, setHelpOpen] = useState(false);
+  return (
+    <ErrorBoundary>
+      <AppShell
+        app={manifest}
+        manifestUrl="./toolbox-app.json"
+        helpAction={{ onClick: () => setHelpOpen(true) }}
+      >
+        <Suspense fallback={<p className="loading">Preparing Mail Tools…</p>}>
+          <Workbench />
+        </Suspense>
+      </AppShell>
+      <HelpDialog open={helpOpen} onClose={() => setHelpOpen(false)} />
+    </ErrorBoundary>
+  );
+}

src/components/ErrorBoundary.tsx

@@ -0,0 +1,27 @@
+import { Component, type ErrorInfo, type ReactNode } from "react";
+
+export class ErrorBoundary extends Component<
+  { children: ReactNode },
+  { error?: Error }
+> {
+  state: { error?: Error } = {};
+  static getDerivedStateFromError(error: Error) {
+    return { error };
+  }
+  componentDidCatch(error: Error, info: ErrorInfo) {
+    console.error("Application failure", error, info);
+  }
+  render() {
+    if (this.state.error)
+      return (
+        <main className="fatal">
+          <h1>Mail Tools could not continue</h1>
+          <p>{this.state.error.message}</p>
+          <button type="button" onClick={() => location.reload()}>
+            Reload
+          </button>
+        </main>
+      );
+    return this.props.children;
+  }
+}

src/components/HelpDialog.tsx

@@ -0,0 +1,48 @@
+import { useEffect, useRef } from "react";
+
+export function HelpDialog({
+  open,
+  onClose,
+}: {
+  open: boolean;
+  onClose: () => void;
+}) {
+  const dialog = useRef<HTMLDialogElement>(null);
+  useEffect(() => {
+    const node = dialog.current;
+    if (!node) return;
+    if (open && !node.open) node.showModal();
+    if (!open && node.open) node.close();
+  }, [open]);
+  return (
+    <dialog
+      ref={dialog}
+      className="help-dialog"
+      onClose={onClose}
+      onCancel={onClose}
+      aria-labelledby="help-title"
+    >
+      <div className="dialog-heading">
+        <div>
+          <p className="eyebrow">Local-first help</p>
+          <h2 id="help-title">About Mail Tools</h2>
+        </div>
+        <button type="button" onClick={onClose} aria-label="Close help">
+          ×
+        </button>
+      </div>
+      <p>
+        Open EML/MIME source, inspect its header and multipart structure,
+        compare body parts, save attachments, and make focused redacted copies.
+      </p>
+      <p>
+        Parsing is bounded and entirely local. HTML is sanitized and shown in an
+        opaque sandbox whose own policy blocks every network request.
+      </p>
+      <p>
+        Authentication headers are unverified claims. Redaction removes selected
+        transport/authentication headers only; it is not an anonymity guarantee.
+      </p>
+    </dialog>
+  );
+}

src/components/Workbench.tsx

@@ -0,0 +1,465 @@
+import { useMemo, useState, type ChangeEvent } from "react";
+import { triggerBlobDownload } from "@add-ideas/toolbox-helpers";
+import { compareBodies } from "../core/compare";
+import { diagnoseMessage } from "../core/diagnostics";
+import { canonicalMessage, redactMessage } from "../core/export";
+import { attachments, parseMessage, walkParts } from "../core/mime";
+import { sanitizeMailHtml } from "../core/sanitize";
+import type { MimePart, ParsedMessage } from "../core/types";
+
+const SAMPLE = `From: =?UTF-8?Q?Ada_Lovelace?= <ada@example.test>
+To: Review Team <review@example.test>
+Date: Tue, 01 Sep 2026 08:15:00 +0200
+Subject: =?UTF-8?Q?Local_MIME_review_=E2=9C=93?=
+Message-ID: <local-example@example.test>
+Authentication-Results: mx.example.test; spf=pass; dkim=pass; dmarc=pass
+MIME-Version: 1.0
+Content-Type: multipart/mixed; boundary="outer"
+
+--outer
+Content-Type: multipart/alternative; boundary="alternative"
+
+--alternative
+Content-Type: text/plain; charset=utf-8
+Content-Transfer-Encoding: quoted-printable
+
+Hello review team,=0Athis message stays local.
+--alternative
+Content-Type: text/html; charset=utf-8
+
+<p>Hello <strong>review team</strong>.</p><img src="https://tracker.invalid/pixel">
+--alternative--
+--outer
+Content-Type: text/plain; name="notes.txt"
+Content-Disposition: attachment; filename="notes.txt"
+Content-Transfer-Encoding: base64
+
+QXR0YWNobWVudCBwcmV2aWV3Lg==
+--outer--`;
+
+type View = "structure" | "bodies" | "attachments" | "diagnostics" | "export";
+
+function PartTree({ part }: { part: MimePart }) {
+  return (
+    <li role="treeitem" aria-expanded={part.children.length ? true : undefined}>
+      <span className="part-label">
+        <strong>{part.id}</strong> {part.mediaType}{" "}
+        <small>{part.bytes.byteLength.toLocaleString()} B</small>
+      </span>
+      {part.filename ? <span className="filename">{part.filename}</span> : null}
+      {part.children.length ? (
+        <ul role="group">
+          {part.children.map((child) => (
+            <PartTree key={child.id} part={child} />
+          ))}
+        </ul>
+      ) : null}
+    </li>
+  );
+}
+
+function downloadText(text: string, filename: string, type: string) {
+  triggerBlobDownload(new Blob([text], { type }), filename);
+}
+
+export function Workbench() {
+  const [source, setSource] = useState(SAMPLE);
+  const [filename, setFilename] = useState("example.eml");
+  const [message, setMessage] = useState<ParsedMessage>(() =>
+    parseMessage(SAMPLE),
+  );
+  const [error, setError] = useState<string>();
+  const [view, setView] = useState<View>("structure");
+  const textParts = useMemo(
+    () => walkParts(message.root).filter((part) => part.text !== undefined),
+    [message],
+  );
+  const files = useMemo(() => attachments(message.root), [message]);
+  const diagnostics = useMemo(() => diagnoseMessage(message), [message]);
+  const [leftId, setLeftId] = useState("1.1");
+  const [rightId, setRightId] = useState("1.2");
+  const left = textParts.find((part) => part.id === leftId) ?? textParts[0];
+  const right =
+    textParts.find((part) => part.id === rightId) ??
+    textParts[1] ??
+    textParts[0];
+  const comparison = useMemo(
+    () => compareBodies(left?.text ?? "", right?.text ?? ""),
+    [left, right],
+  );
+  const htmlPreview = useMemo(
+    () =>
+      left?.mediaType === "text/html"
+        ? sanitizeMailHtml(left.text ?? "")
+        : undefined,
+    [left],
+  );
+  const redacted = useMemo(() => redactMessage(message), [message]);
+
+  const inspect = () => {
+    try {
+      const parsed = parseMessage(source);
+      setMessage(parsed);
+      setError(undefined);
+    } catch (reason) {
+      setError(
+        reason instanceof Error
+          ? reason.message
+          : "The message could not be parsed.",
+      );
+    }
+  };
+  const openFile = async (event: ChangeEvent<HTMLInputElement>) => {
+    const file = event.target.files?.[0];
+    event.target.value = "";
+    if (!file) return;
+    if (file.size > 8 * 1024 * 1024) {
+      setError("File exceeds the 8 MiB source limit.");
+      return;
+    }
+    try {
+      const text = await file.text();
+      const parsed = parseMessage(text);
+      setSource(text);
+      setFilename(file.name);
+      setMessage(parsed);
+      setError(undefined);
+    } catch (reason) {
+      setError(
+        reason instanceof Error
+          ? reason.message
+          : "The file could not be opened.",
+      );
+    }
+  };
+
+  return (
+    <main className="workbench">
+      <section className="hero">
+        <div>
+          <p className="eyebrow">Local email laboratory</p>
+          <h1>Mail Tools</h1>
+          <p>
+            Inspect MIME structure, headers, bodies and attachments without
+            rendering active message content or contacting a mail server.
+          </p>
+        </div>
+        <span className="privacy-pill">No remote content</span>
+      </section>
+
+      <section className="panel input-panel" aria-labelledby="source-title">
+        <div className="panel-heading">
+          <div>
+            <h2 id="source-title">Message source</h2>
+            <p>
+              {filename} · {source.length.toLocaleString()} characters
+            </p>
+          </div>
+          <label className="button file-button">
+            Open .eml
+            <input
+              data-testid="mail-file-input"
+              type="file"
+              accept=".eml,message/rfc822,text/plain"
+              onChange={(event) => void openFile(event)}
+            />
+          </label>
+        </div>
+        <textarea
+          data-testid="source-editor"
+          aria-label="EML source"
+          value={source}
+          onChange={(event) => setSource(event.target.value)}
+          rows={10}
+          spellCheck={false}
+        />
+        <div className="action-row">
+          <button className="primary-button" type="button" onClick={inspect}>
+            Inspect message
+          </button>
+          <span className="muted">8 MiB · 500 parts · depth 20</span>
+        </div>
+        {error ? (
+          <p className="error" role="alert">
+            {error} The last successful inspection remains visible.
+          </p>
+        ) : (
+          <p className="success" role="status">
+            Parsed {walkParts(message.root).length} MIME parts; {files.length}{" "}
+            attachment{files.length === 1 ? "" : "s"}.
+          </p>
+        )}
+      </section>
+
+      <nav className="tabs" aria-label="Mail workspaces">
+        {(
+          [
+            "structure",
+            "bodies",
+            "attachments",
+            "diagnostics",
+            "export",
+          ] as View[]
+        ).map((name) => (
+          <button
+            type="button"
+            key={name}
+            aria-pressed={view === name}
+            onClick={() => setView(name)}
+          >
+            {name[0]!.toUpperCase() + name.slice(1)}
+          </button>
+        ))}
+      </nav>
+
+      {view === "structure" ? (
+        <section className="workspace-grid">
+          <article className="panel">
+            <div className="panel-heading">
+              <h2>Multipart tree</h2>
+              <span className="count-pill">
+                {walkParts(message.root).length} parts
+              </span>
+            </div>
+            <ul className="part-tree" role="tree">
+              <PartTree part={message.root} />
+            </ul>
+          </article>
+          <article className="panel">
+            <h2>Decoded headers</h2>
+            <div className="table-scroll" tabIndex={0}>
+              <table>
+                <thead>
+                  <tr>
+                    <th>Field</th>
+                    <th>Value</th>
+                  </tr>
+                </thead>
+                <tbody>
+                  {message.root.headers.map((header, index) => (
+                    <tr key={`${header.name}-${index}`}>
+                      <th>{header.name}</th>
+                      <td>{header.value}</td>
+                    </tr>
+                  ))}
+                </tbody>
+              </table>
+            </div>
+            {message.warnings.map((warning) => (
+              <p className="warning" key={warning}>
+                {warning}
+              </p>
+            ))}
+          </article>
+        </section>
+      ) : null}
+
+      {view === "bodies" ? (
+        <section className="panel">
+          <div className="panel-heading">
+            <div>
+              <h2>Body-part comparison</h2>
+              <p>
+                Text is inert. HTML links, forms, scripts, styles and remote
+                resources are removed.
+              </p>
+            </div>
+          </div>
+          <div className="selector-grid">
+            <label>
+              Left part
+              <select
+                aria-label="Left body part"
+                value={left?.id ?? ""}
+                onChange={(event) => setLeftId(event.target.value)}
+              >
+                {textParts.map((part) => (
+                  <option key={part.id} value={part.id}>
+                    {part.id} · {part.mediaType}
+                  </option>
+                ))}
+              </select>
+            </label>
+            <label>
+              Right part
+              <select
+                aria-label="Right body part"
+                value={right?.id ?? ""}
+                onChange={(event) => setRightId(event.target.value)}
+              >
+                {textParts.map((part) => (
+                  <option key={part.id} value={part.id}>
+                    {part.id} · {part.mediaType}
+                  </option>
+                ))}
+              </select>
+            </label>
+          </div>
+          <p className="comparison-summary">
+            {comparison.equal
+              ? "Bodies are equal."
+              : `${comparison.removed} removed and ${comparison.added} added lines.`}
+            {comparison.truncated ? " Detailed comparison was bounded." : ""}
+          </p>
+          <div className="body-grid">
+            <div>
+              <h3>Selected body</h3>
+              {htmlPreview ? (
+                <iframe
+                  title="Sanitized HTML message body"
+                  sandbox=""
+                  srcDoc={htmlPreview}
+                />
+              ) : (
+                <pre className="body-preview">{left?.text}</pre>
+              )}
+            </div>
+            <div>
+              <h3>Line comparison</h3>
+              <pre className="diff-preview">
+                {comparison.preview.map((line, index) => (
+                  <span className={`diff-${line.kind}`} key={index}>
+                    {line.kind === "added"
+                      ? "+ "
+                      : line.kind === "removed"
+                        ? "− "
+                        : "  "}
+                    {line.text}
+                    {"\n"}
+                  </span>
+                ))}
+              </pre>
+            </div>
+          </div>
+        </section>
+      ) : null}
+
+      {view === "attachments" ? (
+        <section className="panel">
+          <div className="panel-heading">
+            <div>
+              <h2>Attachment inventory</h2>
+              <p>Downloads use decoded local bytes and sanitized filenames.</p>
+            </div>
+            <span className="count-pill">{files.length}</span>
+          </div>
+          {files.length ? (
+            <ul className="cards">
+              {files.map((file) => (
+                <li key={file.part.id}>
+                  <div>
+                    <strong>{file.filename}</strong>
+                    <p>
+                      {file.part.mediaType} · {file.size.toLocaleString()} bytes
+                      · part {file.part.id}
+                      {file.inline ? " · inline" : ""}
+                    </p>
+                  </div>
+                  <button
+                    type="button"
+                    onClick={() =>
+                      triggerBlobDownload(
+                        new Blob([file.part.bytes as BlobPart], {
+                          type: file.part.mediaType,
+                        }),
+                        file.filename,
+                      )
+                    }
+                  >
+                    Download
+                  </button>
+                </li>
+              ))}
+            </ul>
+          ) : (
+            <p className="empty">
+              No attachment disposition or filename was found.
+            </p>
+          )}
+        </section>
+      ) : null}
+
+      {view === "diagnostics" ? (
+        <section className="panel">
+          <div className="panel-heading">
+            <div>
+              <h2>Header diagnostics</h2>
+              <p>
+                Reported SPF, DKIM, DMARC and ARC results are displayed as
+                claims, never re-verified.
+              </p>
+            </div>
+          </div>
+          <ul className="diagnostic-list">
+            {diagnostics.map((item, index) => (
+              <li className={item.level} key={`${item.code}-${index}`}>
+                <code>{item.code}</code>
+                <strong>{item.summary}</strong>
+                <p>{item.detail}</p>
+              </li>
+            ))}
+          </ul>
+        </section>
+      ) : null}
+
+      {view === "export" ? (
+        <section className="workspace-grid">
+          <article className="panel">
+            <h2>Canonical text export</h2>
+            <p>
+              Unfolds and refolds headers and normalizes line endings to CRLF.
+              MIME payload content is otherwise retained.
+            </p>
+            <button
+              type="button"
+              onClick={() =>
+                downloadText(
+                  canonicalMessage(message),
+                  "canonical.eml",
+                  "message/rfc822",
+                )
+              }
+            >
+              Download canonical EML
+            </button>
+          </article>
+          <article className="panel">
+            <h2>Focused redaction</h2>
+            <p>
+              Removes {redacted.removed.length} top-level
+              transport/authentication header fields. It does not scan nested
+              messages, bodies or attachments for personal data.
+            </p>
+            <div className="action-row">
+              <button
+                type="button"
+                onClick={() =>
+                  downloadText(
+                    redacted.output,
+                    "redacted.eml",
+                    "message/rfc822",
+                  )
+                }
+              >
+                Download redacted EML
+              </button>
+              <button
+                type="button"
+                onClick={() =>
+                  downloadText(
+                    redacted.report,
+                    "redaction-report.json",
+                    "application/json",
+                  )
+                }
+              >
+                Download report
+              </button>
+            </div>
+            <pre className="report-preview">{redacted.report}</pre>
+          </article>
+        </section>
+      ) : null}
+    </main>
+  );
+}

src/core/compare.ts

@@ -0,0 +1,71 @@
+export interface BodyComparison {
+  equal: boolean;
+  leftLines: number;
+  rightLines: number;
+  added: number;
+  removed: number;
+  preview: Array<{ kind: "same" | "added" | "removed"; text: string }>;
+  truncated: boolean;
+}
+
+export function compareBodies(
+  left: string,
+  right: string,
+  maximumCells = 250_000,
+): BodyComparison {
+  const a = left.replace(/\r\n?/gu, "\n").split("\n");
+  const b = right.replace(/\r\n?/gu, "\n").split("\n");
+  if (a.length * b.length > maximumCells) {
+    return {
+      equal: left === right,
+      leftLines: a.length,
+      rightLines: b.length,
+      added: 0,
+      removed: 0,
+      preview: [],
+      truncated: true,
+    };
+  }
+  const table = Array.from(
+    { length: a.length + 1 },
+    () => new Uint32Array(b.length + 1),
+  );
+  for (let i = a.length - 1; i >= 0; i -= 1)
+    for (let j = b.length - 1; j >= 0; j -= 1)
+      table[i]![j] =
+        a[i] === b[j]
+          ? table[i + 1]![j + 1]! + 1
+          : Math.max(table[i + 1]![j]!, table[i]![j + 1]!);
+  const preview: BodyComparison["preview"] = [];
+  let i = 0,
+    j = 0,
+    added = 0,
+    removed = 0;
+  while (i < a.length || j < b.length) {
+    if (i < a.length && j < b.length && a[i] === b[j]) {
+      preview.push({ kind: "same", text: a[i]! });
+      i += 1;
+      j += 1;
+    } else if (
+      j < b.length &&
+      (i === a.length || table[i]![j + 1]! >= table[i + 1]![j]!)
+    ) {
+      preview.push({ kind: "added", text: b[j]! });
+      added += 1;
+      j += 1;
+    } else {
+      preview.push({ kind: "removed", text: a[i]! });
+      removed += 1;
+      i += 1;
+    }
+  }
+  return {
+    equal: added === 0 && removed === 0,
+    leftLines: a.length,
+    rightLines: b.length,
+    added,
+    removed,
+    preview: preview.slice(0, 500),
+    truncated: preview.length > 500,
+  };
+}

src/core/diagnostics.ts

@@ -0,0 +1,109 @@
+import { headerValues, walkParts } from "./mime";
+import type { ParsedMessage } from "./types";
+
+export interface Diagnostic {
+  level: "info" | "warning";
+  code: string;
+  summary: string;
+  detail: string;
+}
+
+function addresses(value: string): string[] {
+  const found = value.match(
+    /[A-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[A-Z0-9.-]+\.[A-Z]{2,63}/giu,
+  );
+  return found ?? [];
+}
+
+export function diagnoseMessage(message: ParsedMessage): Diagnostic[] {
+  const headers = message.root.headers;
+  const result: Diagnostic[] = [];
+  const date = headerValues(headers, "date")[0];
+  if (date) {
+    const parsed = Date.parse(date);
+    result.push(
+      Number.isNaN(parsed)
+        ? {
+            level: "warning",
+            code: "date.invalid",
+            summary: "Date is not parseable",
+            detail: date,
+          }
+        : {
+            level: "info",
+            code: "date.parsed",
+            summary: "Parsed message date",
+            detail: new Date(parsed).toISOString(),
+          },
+    );
+  }
+  for (const name of ["from", "to", "cc", "reply-to"]) {
+    for (const value of headerValues(headers, name)) {
+      const found = addresses(value);
+      result.push({
+        level: found.length ? "info" : "warning",
+        code: `address.${name}`,
+        summary: `${name} contains ${found.length} recognizable address${found.length === 1 ? "" : "es"}`,
+        detail:
+          found.join(", ") ||
+          "Display syntax retained verbatim; no address was inferred.",
+      });
+    }
+  }
+  const received = headerValues(headers, "received");
+  result.push({
+    level: "info",
+    code: "transport.received",
+    summary: `${received.length} Received hop${received.length === 1 ? "" : "s"}`,
+    detail: "Transport headers are unverified text and may be forged.",
+  });
+  const authResults = headerValues(headers, "authentication-results");
+  for (const value of authResults) {
+    const mechanisms = ["spf", "dkim", "dmarc", "arc"].filter((name) =>
+      new RegExp(`\\b${name}=`, "iu").test(value),
+    );
+    result.push({
+      level: "info",
+      code: "auth.claim",
+      summary: `Authentication-Results claims: ${mechanisms.join(", ") || "unclassified"}`,
+      detail: value,
+    });
+  }
+  for (const value of headerValues(headers, "dkim-signature")) {
+    const tags = Object.fromEntries(
+      value
+        .split(";")
+        .map((item) => item.trim().split(/=(.*)/su).slice(0, 2))
+        .filter(([key, val]) => key && val),
+    );
+    result.push({
+      level: "info",
+      code: "dkim.signature",
+      summary: `DKIM signature claim for ${tags.d ?? "unknown domain"}`,
+      detail: `selector=${tags.s ?? "unknown"}; algorithm=${tags.a ?? "unknown"}. Signature not cryptographically verified.`,
+    });
+  }
+  if (!authResults.length && !headerValues(headers, "dkim-signature").length)
+    result.push({
+      level: "warning",
+      code: "auth.absent",
+      summary: "No authentication diagnostics are present",
+      detail: "This says nothing about whether the message is trustworthy.",
+    });
+  const parts = walkParts(message.root);
+  result.push({
+    level: "info",
+    code: "mime.summary",
+    summary: `${parts.length} MIME part${parts.length === 1 ? "" : "s"}`,
+    detail: `${parts.filter((part) => part.mediaType.startsWith("text/")).length} text part(s), ${parts.filter((part) => part.filename).length} named part(s).`,
+  });
+  for (const part of parts)
+    for (const warning of part.warnings)
+      result.push({
+        level: "warning",
+        code: "mime.warning",
+        summary: `Part ${part.id}`,
+        detail: warning,
+      });
+  return result;
+}

src/core/export.ts

@@ -0,0 +1,81 @@
+import { stableStringify } from "@add-ideas/toolbox-helpers";
+import type { MailHeader, ParsedMessage } from "./types";
+
+export const DEFAULT_REDACTED_HEADERS = [
+  "received",
+  "return-path",
+  "authentication-results",
+  "dkim-signature",
+  "arc-authentication-results",
+  "arc-message-signature",
+  "arc-seal",
+  "x-originating-ip",
+  "x-forwarded-for",
+] as const;
+
+function titleHeader(name: string): string {
+  return name
+    .split("-")
+    .map((part) =>
+      part ? part[0]!.toUpperCase() + part.slice(1).toLowerCase() : part,
+    )
+    .join("-");
+}
+
+function foldHeader(name: string, value: string): string {
+  const prefix = `${titleHeader(name)}: `;
+  const words = value
+    .replace(/[\r\n]+[ \t]*/gu, " ")
+    .trim()
+    .split(/\s+/u);
+  const lines: string[] = [];
+  let line = prefix;
+  for (const word of words) {
+    if (line.length + word.length + 1 > 78 && line !== prefix) {
+      lines.push(line);
+      line = `\t${word}`;
+    } else line += `${line === prefix ? "" : " "}${word}`;
+  }
+  lines.push(line);
+  return lines.join("\r\n");
+}
+
+function serialize(headers: readonly MailHeader[], body: string): string {
+  return `${headers.map((header) => foldHeader(header.name, header.rawValue)).join("\r\n")}\r\n\r\n${body.replace(/\r\n?|\n/gu, "\r\n")}`;
+}
+
+export function canonicalMessage(message: ParsedMessage): string {
+  return serialize(message.root.headers, message.bodySource);
+}
+
+export function redactMessage(
+  message: ParsedMessage,
+  names: readonly string[] = DEFAULT_REDACTED_HEADERS,
+) {
+  const wanted = new Set(names.map((name) => name.toLowerCase()));
+  const removed = message.root.headers.filter((header) =>
+    wanted.has(header.lowerName),
+  );
+  const retained = message.root.headers.filter(
+    (header) => !wanted.has(header.lowerName),
+  );
+  const output = serialize(retained, message.bodySource);
+  const report = stableStringify(
+    {
+      schemaVersion: 1,
+      operation: "mail-header-redaction",
+      removed: removed.map((header) => ({
+        name: header.name,
+        valueLength: header.rawValue.length,
+      })),
+      retainedHeaderCount: retained.length,
+      caveats: [
+        "Only selected header fields were removed.",
+        "Addresses, identifiers and personal data may remain in other headers, body parts and attachments.",
+        "MIME payload bytes were retained except for line-ending normalization in this text export.",
+      ],
+    },
+    2,
+  );
+  return { output, report, removed };
+}

src/core/mime.ts

@@ -0,0 +1,404 @@
+import {
+  assertBoundedText,
+  base64ToBytes,
+  sanitizeDownloadFilename,
+} from "@add-ideas/toolbox-helpers";
+import type {
+  AttachmentInfo,
+  MailHeader,
+  MailLimits,
+  MimePart,
+  ParsedMessage,
+} from "./types";
+
+export const DEFAULT_MAIL_LIMITS: MailLimits = Object.freeze({
+  maxChars: 8 * 1024 * 1024,
+  maxHeaders: 2_000,
+  maxParts: 500,
+  maxDepth: 20,
+  maxDecodedBytes: 16 * 1024 * 1024,
+});
+
+interface ParseBudget {
+  parts: number;
+  decodedBytes: number;
+}
+
+function splitEntity(source: string): [string, string] {
+  const match = /\r?\n\r?\n/u.exec(source);
+  if (!match || match.index === undefined) return [source, ""];
+  return [
+    source.slice(0, match.index),
+    source.slice(match.index + match[0].length),
+  ];
+}
+
+function decoderFor(charset: string | undefined): TextDecoder {
+  const normalized = (charset ?? "utf-8").trim().toLowerCase();
+  const aliases: Record<string, string> = {
+    ascii: "windows-1252",
+    "us-ascii": "windows-1252",
+    latin1: "windows-1252",
+    "iso-8859-1": "windows-1252",
+    utf8: "utf-8",
+  };
+  try {
+    return new TextDecoder(aliases[normalized] ?? normalized, { fatal: false });
+  } catch {
+    return new TextDecoder("utf-8", { fatal: false });
+  }
+}
+
+function decodeEncodedWord(
+  charset: string,
+  encoding: string,
+  payload: string,
+): string {
+  try {
+    let bytes: Uint8Array<ArrayBuffer>;
+    if (encoding.toLowerCase() === "b") {
+      const compact = payload.replace(/\s/gu, "");
+      const padded = compact + "=".repeat((4 - (compact.length % 4)) % 4);
+      bytes = base64ToBytes(padded, { maxOutputBytes: 256 * 1024 });
+    } else {
+      const value = payload.replace(/_/gu, " ");
+      const output: number[] = [];
+      for (let index = 0; index < value.length; index += 1) {
+        if (
+          value[index] === "=" &&
+          /^[0-9a-f]{2}$/iu.test(value.slice(index + 1, index + 3))
+        ) {
+          output.push(Number.parseInt(value.slice(index + 1, index + 3), 16));
+          index += 2;
+        } else output.push(value.charCodeAt(index) & 0xff);
+      }
+      bytes = new Uint8Array(output);
+    }
+    return decoderFor(charset).decode(bytes);
+  } catch {
+    return `=?${charset}?${encoding}?${payload}?=`;
+  }
+}
+
+export function decodeHeaderValue(input: string): string {
+  return input
+    .replace(/(\?=)[ \t\r\n]+(=\?)/gu, "$1$2")
+    .replace(
+      /=\?([^?\s]+)\?([bq])\?([^?]*)\?=/giu,
+      (_whole, charset: string, encoding: string, payload: string) =>
+        decodeEncodedWord(charset, encoding, payload),
+    );
+}
+
+export function parseHeaders(
+  source: string,
+  limits: MailLimits = DEFAULT_MAIL_LIMITS,
+): MailHeader[] {
+  const physical = source.replace(/\r\n?/gu, "\n").split("\n");
+  const logical: string[] = [];
+  for (const line of physical) {
+    if (/^[ \t]/u.test(line) && logical.length > 0)
+      logical[logical.length - 1] += `\n${line}`;
+    else logical.push(line);
+    if (logical.length > limits.maxHeaders)
+      throw new RangeError(`Header count exceeds ${limits.maxHeaders}`);
+  }
+  return logical.filter(Boolean).map((line) => {
+    const colon = line.indexOf(":");
+    if (colon <= 0)
+      throw new SyntaxError(`Malformed header line: ${line.slice(0, 80)}`);
+    const name = line.slice(0, colon).trim();
+    if (!/^[!-9;-~]+$/u.test(name))
+      throw new SyntaxError(`Invalid header name: ${name}`);
+    const rawValue = line
+      .slice(colon + 1)
+      .replace(/\n[ \t]+/gu, " ")
+      .trim();
+    return {
+      name,
+      lowerName: name.toLowerCase(),
+      rawValue,
+      value: decodeHeaderValue(rawValue),
+    };
+  });
+}
+
+export function headerValues(
+  headers: readonly MailHeader[],
+  name: string,
+): string[] {
+  const wanted = name.toLowerCase();
+  return headers
+    .filter((header) => header.lowerName === wanted)
+    .map((header) => header.value);
+}
+
+function splitParameters(input: string): string[] {
+  const result: string[] = [];
+  let current = "";
+  let quoted = false;
+  let escaped = false;
+  for (const character of input) {
+    if (escaped) {
+      current += character;
+      escaped = false;
+      continue;
+    }
+    if (character === "\\" && quoted) {
+      current += character;
+      escaped = true;
+      continue;
+    }
+    if (character === '"') {
+      quoted = !quoted;
+      current += character;
+      continue;
+    }
+    if (character === ";" && !quoted) {
+      result.push(current.trim());
+      current = "";
+      continue;
+    }
+    current += character;
+  }
+  result.push(current.trim());
+  return result;
+}
+
+function unquote(input: string): string {
+  return input.startsWith('"') && input.endsWith('"')
+    ? input.slice(1, -1).replace(/\\([\\"])/gu, "$1")
+    : input;
+}
+
+export function parseParameterizedHeader(input: string | undefined): {
+  value: string;
+  parameters: Record<string, string>;
+} {
+  const chunks = splitParameters(input ?? "");
+  const value = (chunks.shift() ?? "").trim().toLowerCase();
+  const parameters: Record<string, string> = Object.create(null) as Record<
+    string,
+    string
+  >;
+  for (const chunk of chunks) {
+    const equals = chunk.indexOf("=");
+    if (equals <= 0) continue;
+    const key = chunk.slice(0, equals).trim().toLowerCase();
+    let parameter = unquote(chunk.slice(equals + 1).trim());
+    if (key.endsWith("*")) {
+      const match = /^[^']*'[^']*'(.*)$/u.exec(parameter);
+      try {
+        parameter = decodeURIComponent(match?.[1] ?? parameter);
+      } catch {
+        /* retain literal */
+      }
+    }
+    parameters[key] = decodeHeaderValue(parameter);
+  }
+  return { value, parameters };
+}
+
+function decodeQuotedPrintable(input: string): Uint8Array<ArrayBuffer> {
+  const normalized = input.replace(/=\r?\n/gu, "");
+  const bytes: number[] = [];
+  for (let index = 0; index < normalized.length; index += 1) {
+    if (
+      normalized[index] === "=" &&
+      /^[0-9a-f]{2}$/iu.test(normalized.slice(index + 1, index + 3))
+    ) {
+      bytes.push(Number.parseInt(normalized.slice(index + 1, index + 3), 16));
+      index += 2;
+    } else {
+      const code = normalized.charCodeAt(index);
+      if (code <= 0xff) bytes.push(code);
+      else bytes.push(...new TextEncoder().encode(normalized[index]));
+    }
+  }
+  return new Uint8Array(bytes);
+}
+
+function decodeBody(
+  input: string,
+  encoding: string,
+  maximumBytes: number,
+): Uint8Array<ArrayBuffer> {
+  if (encoding === "base64") {
+    const compact = input.replace(/\s/gu, "");
+    const padded = compact + "=".repeat((4 - (compact.length % 4)) % 4);
+    return base64ToBytes(padded, {
+      maxOutputBytes: maximumBytes,
+    });
+  }
+  if (encoding === "quoted-printable") return decodeQuotedPrintable(input);
+  return new TextEncoder().encode(input);
+}
+
+function multipartSegments(body: string, boundary: string): string[] {
+  if (!boundary || boundary.length > 200 || /[\r\n]/u.test(boundary))
+    throw new SyntaxError("Invalid MIME boundary");
+  const lines = body.replace(/\r\n?/gu, "\n").split("\n");
+  const open = `--${boundary}`;
+  const close = `${open}--`;
+  const segments: string[] = [];
+  let current: string[] | undefined;
+  let closed = false;
+  for (const line of lines) {
+    if (line === open || line === close) {
+      if (current) segments.push(current.join("\r\n"));
+      if (line === close) {
+        current = undefined;
+        closed = true;
+        break;
+      }
+      current = [];
+    } else if (current) current.push(line);
+  }
+  if (!closed && current) segments.push(current.join("\r\n"));
+  if (segments.length === 0)
+    throw new SyntaxError("Multipart boundary was not found in the body");
+  return segments;
+}
+
+function parseEntity(
+  source: string,
+  path: number[],
+  limits: MailLimits,
+  budget: ParseBudget,
+): MimePart {
+  if (path.length > limits.maxDepth)
+    throw new RangeError(`MIME nesting exceeds ${limits.maxDepth}`);
+  budget.parts += 1;
+  if (budget.parts > limits.maxParts)
+    throw new RangeError(`MIME part count exceeds ${limits.maxParts}`);
+  const [headerSource, sourceBody] = splitEntity(source);
+  const headers = parseHeaders(headerSource, limits);
+  const contentType = parseParameterizedHeader(
+    headerValues(headers, "content-type")[0] ?? "text/plain; charset=us-ascii",
+  );
+  const disposition = parseParameterizedHeader(
+    headerValues(headers, "content-disposition")[0],
+  );
+  const transferEncoding = (
+    headerValues(headers, "content-transfer-encoding")[0] ?? "7bit"
+  )
+    .trim()
+    .toLowerCase();
+  const warnings: string[] = [];
+  const knownEncoding = [
+    "7bit",
+    "8bit",
+    "binary",
+    "base64",
+    "quoted-printable",
+  ].includes(transferEncoding);
+  if (!knownEncoding)
+    warnings.push(
+      `Unknown transfer encoding “${transferEncoding}”; body retained as bytes.`,
+    );
+  const part: MimePart = {
+    id: path.length === 0 ? "root" : path.join("."),
+    path,
+    headers,
+    mediaType: contentType.value || "text/plain",
+    charset: contentType.parameters.charset,
+    disposition: disposition.value || undefined,
+    filename:
+      disposition.parameters["filename*"] ??
+      disposition.parameters.filename ??
+      contentType.parameters["name*"] ??
+      contentType.parameters.name,
+    transferEncoding,
+    sourceBody,
+    bytes: new Uint8Array(),
+    children: [],
+    warnings,
+  };
+  if (part.mediaType.startsWith("multipart/")) {
+    const boundary = contentType.parameters.boundary;
+    if (!boundary)
+      throw new SyntaxError(`Multipart part ${part.id} has no boundary`);
+    part.children = multipartSegments(sourceBody, boundary).map(
+      (segment, index) =>
+        parseEntity(segment, [...path, index + 1], limits, budget),
+    );
+    return part;
+  }
+  if (part.mediaType === "message/rfc822" && sourceBody.trim()) {
+    part.bytes = decodeBody(
+      sourceBody,
+      knownEncoding ? transferEncoding : "binary",
+      limits.maxDecodedBytes,
+    );
+    budget.decodedBytes += part.bytes.byteLength;
+    if (budget.decodedBytes > limits.maxDecodedBytes)
+      throw new RangeError(
+        `Decoded MIME content exceeds ${limits.maxDecodedBytes} bytes`,
+      );
+    const nestedSource = decoderFor(part.charset).decode(part.bytes);
+    part.children = [parseEntity(nestedSource, [...path, 1], limits, budget)];
+    return part;
+  }
+  part.bytes = decodeBody(
+    sourceBody,
+    knownEncoding ? transferEncoding : "binary",
+    limits.maxDecodedBytes,
+  );
+  budget.decodedBytes += part.bytes.byteLength;
+  if (budget.decodedBytes > limits.maxDecodedBytes)
+    throw new RangeError(
+      `Decoded MIME content exceeds ${limits.maxDecodedBytes} bytes`,
+    );
+  if (part.mediaType.startsWith("text/")) {
+    part.text = decoderFor(part.charset).decode(part.bytes);
+    if (part.charset) {
+      try {
+        new TextDecoder(part.charset);
+      } catch {
+        warnings.push(`Unknown charset “${part.charset}”; decoded as UTF-8.`);
+      }
+    }
+  }
+  return part;
+}
+
+export function parseMessage(
+  raw: string,
+  limits: MailLimits = DEFAULT_MAIL_LIMITS,
+): ParsedMessage {
+  assertBoundedText(raw, limits.maxChars, "Message source length");
+  if (raw.includes("\0"))
+    throw new SyntaxError("Message source contains NUL bytes");
+  const [headerSource, bodySource] = splitEntity(raw);
+  const budget: ParseBudget = { parts: 0, decodedBytes: 0 };
+  const root = parseEntity(raw, [], limits, budget);
+  const warnings = [...root.warnings];
+  if (!headerValues(root.headers, "from").length)
+    warnings.push("No From header is present.");
+  if (!headerValues(root.headers, "date").length)
+    warnings.push("No Date header is present.");
+  return { raw, headerSource, bodySource, root, warnings };
+}
+
+export function walkParts(root: MimePart): MimePart[] {
+  const result: MimePart[] = [];
+  const visit = (part: MimePart) => {
+    result.push(part);
+    for (const child of part.children) visit(child);
+  };
+  visit(root);
+  return result;
+}
+
+export function attachments(root: MimePart): AttachmentInfo[] {
+  return walkParts(root)
+    .filter((part) => part.filename || part.disposition === "attachment")
+    .map((part, index) => ({
+      part,
+      filename: sanitizeDownloadFilename(
+        part.filename ?? `attachment-${index + 1}.bin`,
+      ),
+      size: part.bytes.byteLength,
+      inline: part.disposition === "inline",
+    }));
+}

src/core/sanitize.ts

@@ -0,0 +1,41 @@
+import DOMPurify from "dompurify";
+
+const FRAME_POLICY =
+  "default-src 'none'; img-src data:; style-src 'unsafe-inline'; font-src 'none'; media-src 'none'; connect-src 'none'; form-action 'none'; base-uri 'none'";
+
+export function sanitizeMailHtml(input: string): string {
+  const clean = DOMPurify.sanitize(input, {
+    WHOLE_DOCUMENT: false,
+    FORBID_TAGS: [
+      "script",
+      "style",
+      "iframe",
+      "object",
+      "embed",
+      "form",
+      "input",
+      "button",
+      "video",
+      "audio",
+      "source",
+      "link",
+      "meta",
+      "base",
+      "svg",
+      "math",
+    ],
+    FORBID_ATTR: [
+      "style",
+      "src",
+      "srcset",
+      "href",
+      "action",
+      "formaction",
+      "poster",
+      "background",
+      "xlink:href",
+    ],
+    ALLOW_DATA_ATTR: false,
+  });
+  return `<!doctype html><html><head><meta charset="utf-8"><meta http-equiv="Content-Security-Policy" content="${FRAME_POLICY}"><style>body{font:16px/1.5 system-ui,sans-serif;color:#202332;background:#fff;padding:1rem;overflow-wrap:anywhere}pre{white-space:pre-wrap}</style></head><body>${clean}</body></html>`;
+}

src/core/types.ts

@@ -0,0 +1,45 @@
+export interface MailHeader {
+  name: string;
+  lowerName: string;
+  rawValue: string;
+  value: string;
+}
+
+export interface MimePart {
+  id: string;
+  path: number[];
+  headers: MailHeader[];
+  mediaType: string;
+  charset?: string;
+  disposition?: string;
+  filename?: string;
+  transferEncoding: string;
+  sourceBody: string;
+  bytes: Uint8Array<ArrayBuffer>;
+  text?: string;
+  children: MimePart[];
+  warnings: string[];
+}
+
+export interface ParsedMessage {
+  raw: string;
+  headerSource: string;
+  bodySource: string;
+  root: MimePart;
+  warnings: string[];
+}
+
+export interface MailLimits {
+  maxChars: number;
+  maxHeaders: number;
+  maxParts: number;
+  maxDepth: number;
+  maxDecodedBytes: number;
+}
+
+export interface AttachmentInfo {
+  part: MimePart;
+  filename: string;
+  size: number;
+  inline: boolean;
+}

src/main.tsx

@@ -0,0 +1,18 @@
+import { StrictMode } from "react";
+import { createRoot } from "react-dom/client";
+import { App } from "./App";
+
+createRoot(document.getElementById("root")!).render(
+  <StrictMode>
+    <App />
+  </StrictMode>,
+);
+
+if ("serviceWorker" in navigator && import.meta.env.PROD) {
+  window.addEventListener("load", () => {
+    const url = new URL("./sw.js", document.baseURI);
+    void navigator.serviceWorker
+      .register(url, { scope: new URL("./", document.baseURI).pathname })
+      .catch(() => undefined);
+  });
+}

src/styles.css

@@ -0,0 +1,449 @@
+:root {
+  --toolbox-background: #f6f7fb;
+  --toolbox-surface: #fff;
+  --toolbox-surface-soft: #eff1f7;
+  --toolbox-text: #202332;
+  --toolbox-muted: #656b7d;
+  --toolbox-border: #d9dce7;
+  --toolbox-accent: #5b4ec4;
+  --toolbox-accent-hover: #493caf;
+  --toolbox-accent-soft: #ece9ff;
+  --toolbox-accent-contrast: #fff;
+  --toolbox-focus: #137d75;
+  --toolbox-danger: #b42342;
+  --mail-success: #11715c;
+  --mail-warning: #8a5508;
+}
+* {
+  box-sizing: border-box;
+}
+html {
+  min-width: 20rem;
+  min-height: 100%;
+  background: var(--toolbox-background);
+  scrollbar-gutter: stable;
+}
+body {
+  min-width: 20rem;
+  min-height: 100vh;
+  margin: 0;
+  background: var(--toolbox-background);
+  color: var(--toolbox-text);
+  font-family: Inter, ui-sans-serif, system-ui, sans-serif;
+}
+#root {
+  min-height: 100vh;
+}
+.toolbox-shell__main {
+  width: min(100%, 90rem);
+  padding: clamp(0.75rem, 1.8vw, 1.5rem);
+}
+.workbench {
+  display: grid;
+  gap: 1rem;
+}
+.workbench :where(h1, h2, h3),
+.help-dialog h2,
+.fatal h1 {
+  margin: 0;
+  color: var(--toolbox-text);
+  line-height: 1.18;
+  letter-spacing: -0.025em;
+}
+.workbench h1 {
+  font-size: clamp(1.75rem, 3vw, 2.55rem);
+}
+.workbench h2,
+.help-dialog h2 {
+  font-size: clamp(1.15rem, 2vw, 1.5rem);
+}
+.workbench h3 {
+  font-size: 0.96rem;
+}
+.workbench :where(p, ul) {
+  margin-block: 0;
+}
+.workbench :where(button, input, select, textarea),
+.help-dialog button {
+  font: inherit;
+}
+.workbench button,
+.workbench .button,
+.help-dialog button {
+  min-height: 2.55rem;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  gap: 0.4rem;
+  padding: 0.55rem 0.8rem;
+  border: 1px solid var(--toolbox-border);
+  border-radius: 0.64rem;
+  background: var(--toolbox-surface);
+  color: var(--toolbox-text);
+  font-size: 0.82rem;
+  font-weight: 720;
+  cursor: pointer;
+}
+.workbench button:hover,
+.workbench .button:hover {
+  border-color: var(--toolbox-accent);
+  background: var(--toolbox-surface-soft);
+}
+.workbench .primary-button {
+  border-color: var(--toolbox-accent);
+  background: var(--toolbox-accent);
+  color: var(--toolbox-accent-contrast);
+}
+:where(.workbench, .help-dialog)
+  :where(button, input, select, textarea):focus-visible,
+.table-scroll:focus-visible {
+  outline: 3px solid color-mix(in srgb, var(--toolbox-focus) 42%, transparent);
+  outline-offset: 2px;
+}
+.workbench :where(select, textarea) {
+  width: 100%;
+  min-width: 0;
+  padding: 0.62rem 0.7rem;
+  border: 1px solid var(--toolbox-border);
+  border-radius: 0.62rem;
+  background: var(--toolbox-surface);
+  color: var(--toolbox-text);
+  line-height: 1.4;
+}
+.workbench textarea {
+  resize: vertical;
+  font:
+    0.82rem/1.45 ui-monospace,
+    SFMono-Regular,
+    Consolas,
+    monospace;
+  tab-size: 2;
+}
+.hero,
+.panel {
+  border: 1px solid var(--toolbox-border);
+  border-radius: 0.84rem;
+  background: var(--toolbox-surface);
+  box-shadow:
+    0 1px 2px rgb(24 31 65 / 4%),
+    0 10px 30px rgb(24 31 65 / 3%);
+}
+.hero {
+  display: flex;
+  justify-content: space-between;
+  gap: 1rem;
+  padding: clamp(1.1rem, 3vw, 2rem);
+}
+.hero p:not(.eyebrow) {
+  max-width: 55rem;
+  margin-top: 0.55rem;
+  color: var(--toolbox-muted);
+  line-height: 1.55;
+}
+.eyebrow {
+  margin: 0 0 0.3rem !important;
+  color: var(--toolbox-accent);
+  font-size: 0.68rem;
+  font-weight: 820;
+  letter-spacing: 0.115em;
+  text-transform: uppercase;
+}
+.privacy-pill,
+.count-pill {
+  flex: 0 0 auto;
+  align-self: flex-start;
+  padding: 0.38rem 0.64rem;
+  border-radius: 999px;
+  background: var(--toolbox-accent-soft);
+  color: var(--toolbox-accent);
+  font-size: 0.75rem;
+  font-weight: 780;
+}
+.panel {
+  min-width: 0;
+  padding: clamp(0.9rem, 2vw, 1.2rem);
+}
+.panel-heading {
+  display: flex;
+  align-items: flex-end;
+  justify-content: space-between;
+  gap: 1rem;
+  margin-bottom: 0.8rem;
+}
+.panel-heading p,
+.muted,
+.panel > p {
+  color: var(--toolbox-muted);
+  font-size: 0.8rem;
+  line-height: 1.5;
+}
+.file-button input {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  overflow: hidden;
+  clip: rect(0 0 0 0);
+}
+.action-row {
+  display: flex;
+  flex-wrap: wrap;
+  align-items: center;
+  gap: 0.6rem;
+  margin-top: 0.75rem;
+}
+.success,
+.error,
+.warning {
+  margin-top: 0.65rem !important;
+  padding: 0.55rem 0.65rem;
+  border-radius: 0.55rem;
+  font-size: 0.8rem;
+}
+.success {
+  color: var(--mail-success);
+  background: color-mix(in srgb, var(--mail-success) 10%, transparent);
+}
+.error {
+  color: var(--toolbox-danger);
+  background: color-mix(in srgb, var(--toolbox-danger) 10%, transparent);
+}
+.warning {
+  color: var(--mail-warning);
+  background: color-mix(in srgb, var(--mail-warning) 10%, transparent);
+}
+.tabs {
+  display: flex;
+  gap: 0.4rem;
+  overflow-x: auto;
+  padding: 0.15rem;
+}
+.tabs button[aria-pressed="true"] {
+  border-color: var(--toolbox-accent);
+  background: var(--toolbox-accent-soft);
+  color: var(--toolbox-accent);
+}
+.workspace-grid,
+.body-grid,
+.selector-grid {
+  display: grid;
+  grid-template-columns: repeat(2, minmax(0, 1fr));
+  gap: 1rem;
+}
+.selector-grid {
+  margin-bottom: 0.8rem;
+}
+.selector-grid label {
+  display: grid;
+  gap: 0.35rem;
+  color: var(--toolbox-muted);
+  font-size: 0.75rem;
+  font-weight: 700;
+}
+.part-tree,
+.part-tree ul {
+  display: grid;
+  gap: 0.35rem;
+  padding-left: 1.15rem;
+  list-style: none;
+}
+.part-tree {
+  padding-left: 0;
+}
+.part-tree li {
+  position: relative;
+  min-width: 0;
+  padding: 0.45rem 0.55rem;
+  border-left: 2px solid var(--toolbox-border);
+  background: var(--toolbox-surface-soft);
+  border-radius: 0.35rem;
+}
+.part-label {
+  overflow-wrap: anywhere;
+}
+.part-label small,
+.filename {
+  margin-left: 0.4rem;
+  color: var(--toolbox-muted);
+  font-size: 0.72rem;
+}
+.filename {
+  display: block;
+  margin: 0.25rem 0 0;
+}
+.table-scroll {
+  max-height: 31rem;
+  overflow: auto;
+  border: 1px solid var(--toolbox-border);
+  border-radius: 0.6rem;
+}
+table {
+  width: 100%;
+  border-collapse: collapse;
+  font-size: 0.78rem;
+}
+th,
+td {
+  padding: 0.55rem 0.62rem;
+  border-bottom: 1px solid var(--toolbox-border);
+  text-align: left;
+  vertical-align: top;
+  overflow-wrap: anywhere;
+}
+thead th {
+  position: sticky;
+  top: 0;
+  background: var(--toolbox-surface-soft);
+}
+tbody th {
+  width: 9rem;
+  color: var(--toolbox-muted);
+}
+.comparison-summary {
+  margin-bottom: 0.8rem !important;
+  color: var(--mail-warning);
+  font-weight: 700;
+}
+.body-grid > div {
+  min-width: 0;
+}
+.body-preview,
+.diff-preview,
+.report-preview,
+iframe {
+  width: 100%;
+  min-height: 21rem;
+  max-height: 36rem;
+  margin: 0.45rem 0 0;
+  overflow: auto;
+  border: 1px solid var(--toolbox-border);
+  border-radius: 0.6rem;
+  background: var(--toolbox-surface-soft);
+  color: var(--toolbox-text);
+  padding: 0.75rem;
+  white-space: pre-wrap;
+  overflow-wrap: anywhere;
+  font:
+    0.78rem/1.45 ui-monospace,
+    SFMono-Regular,
+    Consolas,
+    monospace;
+}
+iframe {
+  padding: 0;
+  background: #fff;
+}
+.diff-added {
+  color: #11715c;
+  background: color-mix(in srgb, #11715c 11%, transparent);
+}
+.diff-removed {
+  color: var(--toolbox-danger);
+  background: color-mix(in srgb, var(--toolbox-danger) 10%, transparent);
+}
+.cards,
+.diagnostic-list {
+  display: grid;
+  gap: 0.6rem;
+  padding: 0;
+  list-style: none;
+}
+.cards li {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 0.8rem;
+  padding: 0.7rem;
+  border: 1px solid var(--toolbox-border);
+  border-radius: 0.65rem;
+}
+.cards p,
+.diagnostic-list p {
+  margin-top: 0.25rem;
+  color: var(--toolbox-muted);
+  font-size: 0.76rem;
+  overflow-wrap: anywhere;
+}
+.diagnostic-list li {
+  display: grid;
+  grid-template-columns: 9rem minmax(0, 1fr);
+  gap: 0.3rem 0.7rem;
+  padding: 0.65rem;
+  border-left: 3px solid var(--mail-success);
+  background: var(--toolbox-surface-soft);
+}
+.diagnostic-list li.warning {
+  border-left-color: var(--mail-warning);
+}
+.diagnostic-list code {
+  color: var(--toolbox-muted);
+  font-size: 0.7rem;
+}
+.diagnostic-list p {
+  grid-column: 2;
+}
+.empty {
+  padding: 1rem;
+  text-align: center;
+}
+.report-preview {
+  min-height: 12rem;
+}
+.loading,
+.fatal {
+  width: min(100% - 2rem, 60rem);
+  margin: 2rem auto;
+  padding: 1rem;
+}
+.help-dialog {
+  width: min(38rem, calc(100% - 2rem));
+  border: 1px solid var(--toolbox-border);
+  border-radius: 0.9rem;
+  background: var(--toolbox-surface);
+  color: var(--toolbox-text);
+}
+.help-dialog::backdrop {
+  background: rgb(20 24 45 / 55%);
+}
+.dialog-heading {
+  display: flex;
+  align-items: start;
+  justify-content: space-between;
+  gap: 1rem;
+}
+.help-dialog p {
+  line-height: 1.55;
+}
+@media (max-width: 52rem) {
+  .workspace-grid,
+  .body-grid {
+    grid-template-columns: 1fr;
+  }
+}
+@media (max-width: 40rem) {
+  .hero,
+  .panel-heading,
+  .cards li {
+    flex-direction: column;
+    align-items: flex-start;
+  }
+  .selector-grid {
+    grid-template-columns: 1fr;
+  }
+  .cards button {
+    width: 100%;
+  }
+  .diagnostic-list li {
+    grid-template-columns: 1fr;
+  }
+  .diagnostic-list p {
+    grid-column: 1;
+  }
+}
+@media (prefers-reduced-motion: reduce) {
+  *,
+  *::before,
+  *::after {
+    transition-duration: 0.01ms !important;
+    animation-duration: 0.01ms !important;
+  }
+}

src/test/setup.ts

@@ -0,0 +1,8 @@
+import "@testing-library/jest-dom/vitest";
+import { afterEach } from "vitest";
+import { cleanup } from "@testing-library/react";
+
+afterEach(() => {
+  cleanup();
+  localStorage.clear();
+});

src/toolbox/manifest.source.json

@@ -0,0 +1,41 @@
+{
+  "$schema": "https://git.add-ideas.de/lotobo/toolbox-sdk/raw/branch/main/schemas/toolbox-app.v1.schema.json",
+  "schemaVersion": 1,
+  "id": "de.add-ideas.mail-tools",
+  "name": "Mail Tools",
+  "version": "0.1.0",
+  "description": "Inspect and redact email messages locally.",
+  "entry": "./",
+  "icon": "./favicon.svg",
+  "categories": ["documents", "developer", "privacy"],
+  "tags": ["email", "eml", "mime", "headers", "attachments"],
+  "integration": {
+    "contextVersion": 1,
+    "launchModes": ["navigate", "new-tab"],
+    "embedding": "unsupported"
+  },
+  "requirements": {
+    "secureContext": false,
+    "workers": false,
+    "indexedDb": false,
+    "crossOriginIsolated": false,
+    "topLevelContext": false
+  },
+  "privacy": {
+    "processing": "local",
+    "fileUploads": true,
+    "telemetry": false,
+    "label": "Messages stay in this browser; remote content is never loaded."
+  },
+  "source": {
+    "repository": "https://git.add-ideas.de/lotobo/mail-tools",
+    "license": "GPL-3.0-or-later"
+  },
+  "actions": [
+    {
+      "id": "source",
+      "label": "Source",
+      "url": "https://git.add-ideas.de/lotobo/mail-tools"
+    }
+  ]
+}

src/toolbox/manifest.ts

@@ -0,0 +1,4 @@
+import { defineToolboxApp, parseToolboxApp } from "@add-ideas/toolbox-contract";
+import source from "./manifest.source.json";
+
+export const manifest = defineToolboxApp(parseToolboxApp(source));

src/version.ts

@@ -0,0 +1 @@
+export const APP_VERSION = "0.1.0";

src/vite-env.d.ts

@@ -0,0 +1 @@
+/// <reference types="vite/client" />

tests/browser/app.spec.ts

@@ -0,0 +1,134 @@
+import { expect, test, type Page } from "@playwright/test";
+import { Buffer } from "node:buffer";
+import { readFile } from "node:fs/promises";
+
+const ORIGIN = "http://127.0.0.1:4195";
+async function watchLocalOnly(page: Page) {
+  const external: string[] = [];
+  await page.route("**/*", async (route) => {
+    const url = new URL(route.request().url());
+    if (url.origin !== ORIGIN) {
+      external.push(url.href);
+      await route.abort();
+    } else await route.continue();
+  });
+  return external;
+}
+function errors(page: Page) {
+  const values: string[] = [];
+  page.on("pageerror", (error) => values.push(error.message));
+  page.on("console", (message) => {
+    if (message.type() === "error") values.push(message.text());
+  });
+  return values;
+}
+
+test("runs from a nested path and keeps HTML preview local and inert", async ({
+  page,
+}) => {
+  await page.setViewportSize({ width: 1800, height: 1000 });
+  const external = await watchLocalOnly(page);
+  const failures = errors(page);
+  await page.goto("/deep/nested/mail/");
+  await expect(page.getByRole("heading", { name: "Mail Tools" })).toBeVisible();
+  await expect(page.getByText(/Parsed 5 MIME parts/iu)).toBeVisible();
+  await page.getByRole("button", { name: "Bodies" }).click();
+  await page.getByLabel("Left body part").selectOption("1.2");
+  const frame = page.frameLocator(
+    'iframe[title="Sanitized HTML message body"]',
+  );
+  await expect(frame.getByText("Hello review team.")).toBeVisible();
+  expect(await page.locator("iframe").getAttribute("sandbox")).toBe("");
+  expect(await page.locator("iframe").getAttribute("srcdoc")).not.toContain(
+    "tracker.invalid",
+  );
+  expect(external).toEqual([]);
+  expect(
+    failures.filter(
+      (message) =>
+        !message.includes(
+          "Blocked script execution in 'about:srcdoc' because the document's frame is sandboxed",
+        ),
+    ),
+  ).toEqual([]);
+  expect(
+    await page
+      .locator(".toolbox-shell__main")
+      .evaluate((node) => getComputedStyle(node).width),
+  ).toBe("1440px");
+});
+
+test("opens an EML and downloads decoded attachment bytes", async ({
+  page,
+}) => {
+  await page.goto("/deep/nested/mail/");
+  const source =
+    "From: Test <test@example.test>\r\nDate: Tue, 01 Sep 2026 10:00:00 +0000\r\nContent-Type: multipart/mixed; boundary=x\r\n\r\n--x\r\nContent-Type: application/octet-stream\r\nContent-Disposition: attachment; filename=proof.bin\r\nContent-Transfer-Encoding: base64\r\n\r\nAAEC/w==\r\n--x--";
+  await page.getByTestId("mail-file-input").setInputFiles({
+    name: "fixture.eml",
+    mimeType: "message/rfc822",
+    buffer: Buffer.from(source),
+  });
+  await expect(page.getByText(/Parsed 2 MIME parts/iu)).toBeVisible();
+  await page.getByRole("button", { name: "Attachments" }).click();
+  await expect(page.getByText("proof.bin", { exact: true })).toBeVisible();
+  const pending = page.waitForEvent("download");
+  await page.getByRole("button", { name: "Download" }).click();
+  const download = await pending;
+  expect(download.suggestedFilename()).toBe("proof.bin");
+  const saved = await download.path();
+  expect(saved).not.toBeNull();
+  expect(await readFile(saved!)).toEqual(Buffer.from([0, 1, 2, 255]));
+});
+
+test("retains the last model and creates canonical and redacted exports", async ({
+  page,
+}) => {
+  await page.goto("/deep/nested/mail/");
+  await page.getByLabel("EML source").fill("not a header");
+  await page.getByRole("button", { name: "Inspect message" }).click();
+  await expect(page.getByRole("alert")).toContainText("last successful");
+  await page.getByRole("button", { name: "Export" }).click();
+  for (const [button, filename] of [
+    ["Download canonical EML", "canonical.eml"],
+    ["Download redacted EML", "redacted.eml"],
+    ["Download report", "redaction-report.json"],
+  ] as const) {
+    const pending = page.waitForEvent("download");
+    await page.getByRole("button", { name: button }).click();
+    expect((await pending).suggestedFilename()).toBe(filename);
+  }
+});
+
+test("integrates help, dark theme, PWA identity and hardened headers", async ({
+  page,
+  request,
+}) => {
+  await page.goto("/deep/nested/mail/");
+  await page.getByRole("button", { name: "Help" }).click();
+  await expect(
+    page.getByRole("dialog", { name: "About Mail Tools" }),
+  ).toContainText("opaque sandbox");
+  await page.keyboard.press("Escape");
+  await page.getByRole("button", { name: "Personalize" }).click();
+  await page.getByRole("button", { name: "Dark" }).click();
+  await expect(page.locator(".toolbox-shell").first()).toHaveAttribute(
+    "data-toolbox-theme",
+    "dark",
+  );
+  const registration = await page.evaluate(async () =>
+    Boolean(await navigator.serviceWorker.ready),
+  );
+  expect(registration).toBe(true);
+  const index = await request.get("/deep/nested/mail/");
+  expect(index.headers()["content-security-policy"]).toContain(
+    "connect-src 'self'",
+  );
+  expect(await index.text()).not.toMatch(/\b(?:src|href)=["']\//u);
+  const manifest = await request.get("/deep/nested/mail/toolbox-app.json");
+  await expect(manifest.json()).resolves.toMatchObject({
+    id: "de.add-ideas.mail-tools",
+    version: "0.1.0",
+    privacy: { processing: "local", telemetry: false },
+  });
+});

tests/components/workbench.test.tsx

@@ -0,0 +1,37 @@
+import { render, screen } from "@testing-library/react";
+import userEvent from "@testing-library/user-event";
+import { describe, expect, it } from "vitest";
+import { Workbench } from "../../src/components/Workbench";
+
+describe("Mail workbench", () => {
+  it("shows parsed structure and retains it after an invalid edit", async () => {
+    const user = userEvent.setup();
+    render(<Workbench />);
+    expect(
+      screen.getByRole("heading", { name: "Mail Tools" }),
+    ).toBeInTheDocument();
+    expect(screen.getByText(/Parsed 5 MIME parts/iu)).toBeInTheDocument();
+    await user.clear(screen.getByLabelText("EML source"));
+    await user.type(screen.getByLabelText("EML source"), "bad header");
+    await user.click(screen.getByRole("button", { name: "Inspect message" }));
+    expect(screen.getByRole("alert")).toHaveTextContent(/last successful/iu);
+    expect(
+      screen.getAllByText("multipart/mixed", { exact: false }),
+    ).not.toHaveLength(0);
+  });
+
+  it("moves through body, attachment and diagnostic views", async () => {
+    const user = userEvent.setup();
+    render(<Workbench />);
+    await user.click(screen.getByRole("button", { name: "Bodies" }));
+    expect(
+      screen.getByRole("heading", { name: "Body-part comparison" }),
+    ).toBeInTheDocument();
+    await user.click(screen.getByRole("button", { name: "Attachments" }));
+    expect(screen.getByText("notes.txt", { exact: true })).toBeInTheDocument();
+    await user.click(screen.getByRole("button", { name: "Diagnostics" }));
+    expect(
+      screen.getByText(/Authentication-Results claims/iu),
+    ).toBeInTheDocument();
+  });
+});

tests/core/mime.test.ts

@@ -0,0 +1,94 @@
+import { describe, expect, it } from "vitest";
+import {
+  attachments,
+  decodeHeaderValue,
+  parseHeaders,
+  parseMessage,
+  walkParts,
+} from "../../src/core/mime";
+
+const MULTIPART = `From: =?UTF-8?Q?Ada_=E2=9C=93?= <ada@example.test>\r
+Subject: folded\r
+ value\r
+MIME-Version: 1.0\r
+Content-Type: multipart/mixed; boundary="b"\r
+\r
+--b\r
+Content-Type: text/plain; charset=utf-8\r
+Content-Transfer-Encoding: quoted-printable\r
+\r
+hello=20world\r
+--b\r
+Content-Type: application/octet-stream\r
+Content-Disposition: attachment; filename*=UTF-8''report%20one.txt\r
+Content-Transfer-Encoding: base64\r
+\r
+YWJj\r
+--b--`;
+
+describe("MIME parser", () => {
+  it("unfolds fields and decodes RFC 2047 words", () => {
+    const headers = parseHeaders(
+      "Subject: =?UTF-8?Q?Hello_=E2=9C=93?=\r\n\tworld",
+    );
+    expect(headers[0]?.value).toBe("Hello ✓ world");
+    expect(decodeHeaderValue("=?ISO-8859-1?Q?Andr=E9?=")).toBe("André");
+    expect(decodeHeaderValue("=?UTF-8?Q?joined?=   =?UTF-8?Q?_words?=")).toBe(
+      "joined words",
+    );
+  });
+
+  it("builds nested parts and decodes transfer encodings", () => {
+    const parsed = parseMessage(MULTIPART);
+    expect(walkParts(parsed.root).map((part) => part.mediaType)).toEqual([
+      "multipart/mixed",
+      "text/plain",
+      "application/octet-stream",
+    ]);
+    expect(parsed.root.children[0]?.text).toBe("hello world");
+    expect([...parsed.root.children[1]!.bytes]).toEqual([97, 98, 99]);
+    expect(attachments(parsed.root)[0]).toMatchObject({
+      filename: "report one.txt",
+      size: 3,
+    });
+  });
+
+  it("parses nested message/rfc822 entities", () => {
+    const parsed = parseMessage(
+      "From: a@example.test\nContent-Type: message/rfc822\n\nFrom: b@example.test\nContent-Type: text/plain\n\nnested",
+    );
+    expect(parsed.root.children[0]?.text).toBe("nested");
+  });
+
+  it("decodes and exposes transferred message attachments", () => {
+    const nested = btoa(
+      "From: b@example.test\r\nContent-Type: text/plain\r\n\r\nnested",
+    );
+    const parsed = parseMessage(
+      `From: a@example.test\nContent-Type: message/rfc822; name="forwarded.eml"\nContent-Disposition: attachment; filename="forwarded.eml"\nContent-Transfer-Encoding: base64\n\n${nested}`,
+    );
+    expect(parsed.root.children[0]?.text).toBe("nested");
+    expect(attachments(parsed.root)[0]).toMatchObject({
+      filename: "forwarded.eml",
+    });
+    expect(attachments(parsed.root)[0]?.size).toBeGreaterThan(0);
+  });
+
+  it("fails closed for malformed and excessive structures", () => {
+    expect(() => parseMessage("Bad header\n\nbody")).toThrow(
+      /malformed header/iu,
+    );
+    expect(() =>
+      parseMessage("Content-Type: multipart/mixed; boundary=x\n\nnone"),
+    ).toThrow(/boundary/iu);
+    expect(() =>
+      parseMessage("From: a@example.test\n\n12345", {
+        maxChars: 4,
+        maxHeaders: 2,
+        maxParts: 2,
+        maxDepth: 2,
+        maxDecodedBytes: 8,
+      }),
+    ).toThrow(/limit/iu);
+  });
+});

tests/core/security-export.test.ts

@@ -0,0 +1,60 @@
+import { describe, expect, it } from "vitest";
+import { compareBodies } from "../../src/core/compare";
+import { diagnoseMessage } from "../../src/core/diagnostics";
+import { canonicalMessage, redactMessage } from "../../src/core/export";
+import { parseMessage } from "../../src/core/mime";
+import { sanitizeMailHtml } from "../../src/core/sanitize";
+
+describe("inert rendering and output", () => {
+  it("removes active and remote HTML while embedding a deny-all policy", () => {
+    const output = sanitizeMailHtml(
+      '<script>alert(1)</script><a href="https://bad.test">link</a><img src="https://bad.test/pixel"><p style="background:url(https://bad.test)">safe</p>',
+    );
+    expect(output).toContain("default-src 'none'");
+    expect(output).toContain("safe");
+    expect(output).not.toMatch(
+      /bad\.test|script|href=|src=|style="background/iu,
+    );
+  });
+
+  it("produces a bounded line comparison", () => {
+    expect(compareBodies("a\nb", "a\nc")).toMatchObject({
+      added: 1,
+      removed: 1,
+      equal: false,
+    });
+    expect(compareBodies("a\nb", "a\nb")).toMatchObject({ equal: true });
+    expect(compareBodies("a\nb\nc", "d\ne\nf", 2).truncated).toBe(true);
+  });
+
+  it("labels authentication fields as claims", () => {
+    const parsed = parseMessage(
+      "From: Ada <ada@example.test>\nDate: Tue, 01 Sep 2026 10:00:00 +0000\nAuthentication-Results: mx.test; spf=pass; dkim=fail\nDKIM-Signature: v=1; d=example.test; s=mail; a=rsa-sha256\n\nbody",
+    );
+    const diagnostics = diagnoseMessage(parsed);
+    expect(
+      diagnostics.some(
+        (item) => item.code === "auth.claim" && /spf, dkim/u.test(item.summary),
+      ),
+    ).toBe(true);
+    expect(
+      diagnostics.find((item) => item.code === "dkim.signature")?.detail,
+    ).toMatch(/not cryptographically verified/iu);
+  });
+
+  it("normalizes canonical output and reports focused redaction", () => {
+    const parsed = parseMessage(
+      "From: a@example.test\nReceived: from private.example\nAuthentication-Results: mx; spf=pass\nSubject: hello\n\nline1\nline2",
+    );
+    expect(canonicalMessage(parsed)).toContain(
+      "From: a@example.test\r\nReceived:",
+    );
+    const redacted = redactMessage(parsed);
+    expect(redacted.output).not.toMatch(/Received|Authentication-Results/iu);
+    expect(redacted.output).toContain("Subject: hello\r\n\r\nline1\r\nline2");
+    expect(JSON.parse(redacted.report)).toMatchObject({
+      operation: "mail-header-redaction",
+      retainedHeaderCount: 2,
+    });
+  });
+});

tsconfig.app.json

@@ -0,0 +1,27 @@
+{
+  "compilerOptions": {
+    "tsBuildInfoFile": "./node_modules/.tmp/tsconfig.app.tsbuildinfo",
+    "target": "ES2023",
+    "lib": ["ES2023", "DOM", "DOM.Iterable"],
+    "module": "ESNext",
+    "types": ["vite/client", "node"],
+    "allowArbitraryExtensions": true,
+    "skipLibCheck": true,
+    "moduleResolution": "Bundler",
+    "allowImportingTsExtensions": true,
+    "verbatimModuleSyntax": true,
+    "moduleDetection": "force",
+    "noEmit": true,
+    "jsx": "react-jsx",
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "erasableSyntaxOnly": true,
+    "noFallthroughCasesInSwitch": true,
+    "strict": true,
+    "noUncheckedIndexedAccess": true,
+    "useDefineForClassFields": true,
+    "resolveJsonModule": true,
+    "isolatedModules": true
+  },
+  "include": ["src", "tests"]
+}

tsconfig.json

@@ -0,0 +1,11 @@
+{
+  "files": [],
+  "references": [
+    {
+      "path": "./tsconfig.app.json"
+    },
+    {
+      "path": "./tsconfig.node.json"
+    }
+  ]
+}

tsconfig.node.json

@@ -0,0 +1,24 @@
+{
+  "compilerOptions": {
+    "tsBuildInfoFile": "./node_modules/.tmp/tsconfig.node.tsbuildinfo",
+    "target": "ES2023",
+    "lib": ["ES2023"],
+    "module": "ESNext",
+    "types": ["node"],
+    "skipLibCheck": true,
+    "moduleResolution": "Bundler",
+    "allowImportingTsExtensions": true,
+    "verbatimModuleSyntax": true,
+    "moduleDetection": "force",
+    "noEmit": true,
+    "strict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true
+  },
+  "include": [
+    "vite.config.ts",
+    "playwright.config.ts",
+    "eslint.config.mjs",
+    "scripts/**/*.mjs"
+  ]
+}

vite.config.ts

@@ -0,0 +1,16 @@
+/// <reference types="vitest/config" />
+import { defineConfig } from "vite";
+import react from "@vitejs/plugin-react";
+
+export default defineConfig({
+  base: "./",
+  plugins: [react()],
+  test: {
+    environment: "jsdom",
+    setupFiles: "./src/test/setup.ts",
+    css: true,
+    maxWorkers: 2,
+    restoreMocks: true,
+    exclude: ["tests/browser/**", "node_modules/**", "dist/**"],
+  },
+});