Release Subtitle 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

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+@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
+
+- Added bounded SRT, WebVTT and ASS parsing, cue editing and explicit conversion.
+- Added timing shifts, stretching, frame-rate conversion and configurable
+  overlap, duration, layout and reading-speed diagnostics.
+- Added local revision comparison and browser-native playback with bounded
+  waveform extraction.
+- Added Toolbox integration, offline shell, cross-browser tests and deterministic
+  release packaging.

CONTRIBUTING.md

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+# Contributing
+
+Run `npm ci`, `npm run check`, and `npm run test:browser` before proposing a change. Keep processing local, preserve explicit limits, and include fixtures for every parser boundary.

LICENSE

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+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 +1,3 @@
+# Licences
+
+The application is GPL-3.0-or-later. Generated release artifacts include an exact runtime dependency licence inventory in `npm-runtime-licenses.txt`.

README.md

@@ -0,0 +1,45 @@
+# Subtitle Tools
+
+Edit, validate, synchronize, compare, and convert subtitle files locally in the
+browser. Subtitle Tools is an independently versioned application in the
+[add·ideas Toolbox](https://git.add-ideas.de/lotobo/toolbox-portal).
+
+## Version 0.1 scope
+
+- Bounded SRT, WebVTT, ASS and legacy SSA-compatible dialogue parsing
+- Cue timeline, direct text/timestamp editing and configurable diagnostics for
+  overlaps, order, duration, reading speed, line count and line length
+- Shift and anchor-based stretch operations, negative-time protection and
+  explicit source/target frame-rate conversion
+- SRT, WebVTT and ASS serialization with format-specific preservation where
+  possible and a visible cross-format loss warning
+- Deterministic index-aligned revision comparison
+- Immediate browser-native audio/video playback plus bounded local waveform peak
+  extraction and subtitle-start markers
+- UTF-8, UTF-16 LE/BE and ISO-8859-1 file decoding
+
+All source, media and generated output stays in the current browser. The app
+makes no external request. Validation is configurable editorial guidance, not a
+broadcast, accessibility, or legal compliance certificate. Version 0.1 does not
+perform speech recognition, automatic alignment, semantic revision matching, or
+pixel-perfect ASS rendering.
+
+## Development
+
+Requires Node.js 22 and npm 11.
+
+```sh
+npm ci
+npm run check
+npm run test:browser
+```
+
+## Release
+
+`npm run release:artifact` creates the deterministic
+`release/subtitle-tools-0.1.0.zip` and checksum sidecar.
+
+## Licence
+
+GPL-3.0-or-later. Runtime dependencies retain their own licences; see
+[THIRD_PARTY_NOTICES.md](THIRD_PARTY_NOTICES.md).

SECURITY.md

@@ -0,0 +1,3 @@
+# Security
+
+Please report vulnerabilities privately to the repository owner. Do not attach sensitive source files to public issues. Imported inputs are untrusted; parsers must remain bounded and must not execute active content or fetch external resources.

SOURCE.md

@@ -0,0 +1,7 @@
+# Corresponding source
+
+The corresponding source for Subtitle Tools 0.1.0 is available at:
+
+https://git.add-ideas.de/lotobo/subtitle-tools/src/tag/v0.1.0
+
+Build with Node.js 22, npm 11, `npm ci`, and `npm run release:artifact`.

THIRD_PARTY_NOTICES.md

@@ -0,0 +1,13 @@
+# Third-party notices
+
+Subtitle Tools 0.1.0 directly depends on these runtime packages:
+
+| Package                          | Pinned version | Declared licence |
+| -------------------------------- | -------------: | ---------------- |
+| `@add-ideas/toolbox-contract`    |          0.2.3 | Apache-2.0       |
+| `@add-ideas/toolbox-helpers`     |          0.1.0 | GPL-3.0-or-later |
+| `@add-ideas/toolbox-shell-react` |          0.2.3 | Apache-2.0       |
+| `react`                          |         19.2.8 | MIT              |
+| `react-dom`                      |         19.2.8 | MIT              |
+
+This table covers direct production dependencies, not transitive packages or development tooling. During a release build, the exact non-development dependency tree and discovered licence texts are generated from the lockfile into `LICENSES/npm-runtime-licenses.txt` and included in the release ZIP. Copyright and licence terms remain with their respective authors.

docs/ACCESSIBILITY.md

@@ -0,0 +1,10 @@
+# Accessibility
+
+The application uses labelled native controls, keyboard-reachable tabs and cue
+buttons, visible focus indicators, text alternatives for waveform content, and
+light, dark and system themes. Colour is not the only carrier for issue level.
+The cue and issue views cap rendered rows to keep navigation responsive while
+the complete bounded document remains included in validation and export.
+
+The waveform is an optional visual aid: all timing edits use numeric controls and
+do not require pointer input. Reduced-motion preferences disable transitions.

docs/ARCHITECTURE.md

@@ -0,0 +1,17 @@
+# Architecture
+
+Subtitle Tools is a relocatable React application with a framework-independent
+TypeScript subtitle model. The parser first applies byte/text and line bounds,
+then produces one normalized cue model for SRT, WebVTT and ASS. Operations return
+new documents instead of mutating parser state. Serializers are format-specific;
+cross-format export deliberately exposes its preservation boundary.
+
+Parsing and timing transformations are synchronous in v0.1 and therefore capped
+at 4,000,000 UTF-16 units, 250,000 units per physical line and 100,000 cues. The
+editor renders at most 10,000 cue rows and 2,000 issue rows, while validation and
+export still cover the complete bounded document. Revision comparison is
+index-aligned and linear rather than an unbounded semantic diff.
+
+The optional waveform component uses browser-native media decoding, keeps at
+most 2,000 peak buckets and accepts no more than 128 MiB or four decoded hours.
+It does not run a codec, speech-recognition model or network service.

docs/PRIVACY-SECURITY.md

@@ -0,0 +1,15 @@
+# Privacy and security
+
+Subtitle and media files are read only after direct selection and stay in page
+memory. No telemetry, analytics, account, upload, external font, codec, model or
+other network destination exists. The production policy uses
+`connect-src 'self'`; browser tests fail on non-local requests.
+
+Subtitle text is rendered by React as text, not interpreted as HTML. ASS override
+codes and WebVTT tags are preserved as inert source. Exports are downloads chosen
+by the user. Browser-native media playback and Web Audio decoding inherit browser
+codec support and may allocate substantial memory inside the documented bounds.
+
+Validation findings are editorial signals. They are not proof of accessibility,
+broadcast conformance, synchronization quality or legal compliance. Cross-format
+conversion can discard styles, positioning, regions, comments and metadata.

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="Edit, validate, synchronize, compare, and convert subtitles locally."
+    />
+    <link rel="icon" type="image/svg+xml" href="./favicon.svg" />
+    <link rel="manifest" href="./manifest.webmanifest" />
+    <meta name="theme-color" content="#29255f" />
+    <title>Subtitle Tools</title>
+  </head>
+  <body>
+    <div id="root"></div>
+    <script type="module" src="./src/main.tsx"></script>
+  </body>
+</html>

package.json

@@ -0,0 +1,71 @@
+{
+  "name": "subtitle-tools",
+  "version": "0.1.0",
+  "description": "Edit, validate, synchronize, compare, and convert subtitles locally in the browser.",
+  "license": "GPL-3.0-or-later",
+  "author": "Albrecht Degering",
+  "repository": {
+    "type": "git",
+    "url": "git+https://git.add-ideas.de/lotobo/subtitle-tools.git"
+  },
+  "homepage": "https://git.add-ideas.de/lotobo/subtitle-tools",
+  "bugs": {
+    "url": "https://git.add-ideas.de/lotobo/subtitle-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",
+    "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://127.0.0.1:4197", trace: "retain-on-failure" },
+  webServer: {
+    command: "npm run build && node scripts/serve-test.mjs",
+    url: "http://127.0.0.1:4197",
+    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 +1,11 @@
+# Changelog
+
+## 0.1.0 - 2026-09-01
+
+- Added bounded SRT, WebVTT and ASS parsing, cue editing and explicit conversion.
+- Added timing shifts, stretching, frame-rate conversion and configurable
+  overlap, duration, layout and reading-speed diagnostics.
+- Added local revision comparison and browser-native playback with bounded
+  waveform extraction.
+- Added Toolbox integration, offline shell, cross-browser tests and deterministic
+  release packaging.

public/CONTRIBUTING.md

@@ -0,0 +1,3 @@
+# Contributing
+
+Run `npm ci`, `npm run check`, and `npm run test:browser` before proposing a change. Keep processing local, preserve explicit limits, and include fixtures for every parser boundary.

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
+
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+software and other kinds of works.
+
+  The licenses for most software and other practical works are designed
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+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
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+                     END OF TERMS AND CONDITIONS
+
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+    (at your option) any later version.
+
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+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
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+
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+<https://www.gnu.org/licenses/why-not-lgpl.html>.

public/LICENSES/README.md

@@ -0,0 +1,3 @@
+# Licences
+
+The application is GPL-3.0-or-later. Generated release artifacts include an exact runtime dependency licence inventory in `npm-runtime-licenses.txt`.

public/README.md

@@ -0,0 +1,45 @@
+# Subtitle Tools
+
+Edit, validate, synchronize, compare, and convert subtitle files locally in the
+browser. Subtitle Tools is an independently versioned application in the
+[add·ideas Toolbox](https://git.add-ideas.de/lotobo/toolbox-portal).
+
+## Version 0.1 scope
+
+- Bounded SRT, WebVTT, ASS and legacy SSA-compatible dialogue parsing
+- Cue timeline, direct text/timestamp editing and configurable diagnostics for
+  overlaps, order, duration, reading speed, line count and line length
+- Shift and anchor-based stretch operations, negative-time protection and
+  explicit source/target frame-rate conversion
+- SRT, WebVTT and ASS serialization with format-specific preservation where
+  possible and a visible cross-format loss warning
+- Deterministic index-aligned revision comparison
+- Immediate browser-native audio/video playback plus bounded local waveform peak
+  extraction and subtitle-start markers
+- UTF-8, UTF-16 LE/BE and ISO-8859-1 file decoding
+
+All source, media and generated output stays in the current browser. The app
+makes no external request. Validation is configurable editorial guidance, not a
+broadcast, accessibility, or legal compliance certificate. Version 0.1 does not
+perform speech recognition, automatic alignment, semantic revision matching, or
+pixel-perfect ASS rendering.
+
+## Development
+
+Requires Node.js 22 and npm 11.
+
+```sh
+npm ci
+npm run check
+npm run test:browser
+```
+
+## Release
+
+`npm run release:artifact` creates the deterministic
+`release/subtitle-tools-0.1.0.zip` and checksum sidecar.
+
+## Licence
+
+GPL-3.0-or-later. Runtime dependencies retain their own licences; see
+[THIRD_PARTY_NOTICES.md](THIRD_PARTY_NOTICES.md).

public/SECURITY.md

@@ -0,0 +1,3 @@
+# Security
+
+Please report vulnerabilities privately to the repository owner. Do not attach sensitive source files to public issues. Imported inputs are untrusted; parsers must remain bounded and must not execute active content or fetch external resources.

public/SOURCE.md

@@ -0,0 +1,7 @@
+# Corresponding source
+
+The corresponding source for Subtitle Tools 0.1.0 is available at:
+
+https://git.add-ideas.de/lotobo/subtitle-tools/src/tag/v0.1.0
+
+Build with Node.js 22, npm 11, `npm ci`, and `npm run release:artifact`.

public/THIRD_PARTY_NOTICES.md

@@ -0,0 +1,13 @@
+# Third-party notices
+
+Subtitle Tools 0.1.0 directly depends on these runtime packages:
+
+| Package                          | Pinned version | Declared licence |
+| -------------------------------- | -------------: | ---------------- |
+| `@add-ideas/toolbox-contract`    |          0.2.3 | Apache-2.0       |
+| `@add-ideas/toolbox-helpers`     |          0.1.0 | GPL-3.0-or-later |
+| `@add-ideas/toolbox-shell-react` |          0.2.3 | Apache-2.0       |
+| `react`                          |         19.2.8 | MIT              |
+| `react-dom`                      |         19.2.8 | MIT              |
+
+This table covers direct production dependencies, not transitive packages or development tooling. During a release build, the exact non-development dependency tree and discovered licence texts are generated from the lockfile into `LICENSES/npm-runtime-licenses.txt` and included in the release ZIP. Copyright and licence terms remain with their respective authors.

public/docs/ACCESSIBILITY.md

@@ -0,0 +1,10 @@
+# Accessibility
+
+The application uses labelled native controls, keyboard-reachable tabs and cue
+buttons, visible focus indicators, text alternatives for waveform content, and
+light, dark and system themes. Colour is not the only carrier for issue level.
+The cue and issue views cap rendered rows to keep navigation responsive while
+the complete bounded document remains included in validation and export.
+
+The waveform is an optional visual aid: all timing edits use numeric controls and
+do not require pointer input. Reduced-motion preferences disable transitions.

public/docs/ARCHITECTURE.md

@@ -0,0 +1,17 @@
+# Architecture
+
+Subtitle Tools is a relocatable React application with a framework-independent
+TypeScript subtitle model. The parser first applies byte/text and line bounds,
+then produces one normalized cue model for SRT, WebVTT and ASS. Operations return
+new documents instead of mutating parser state. Serializers are format-specific;
+cross-format export deliberately exposes its preservation boundary.
+
+Parsing and timing transformations are synchronous in v0.1 and therefore capped
+at 4,000,000 UTF-16 units, 250,000 units per physical line and 100,000 cues. The
+editor renders at most 10,000 cue rows and 2,000 issue rows, while validation and
+export still cover the complete bounded document. Revision comparison is
+index-aligned and linear rather than an unbounded semantic diff.
+
+The optional waveform component uses browser-native media decoding, keeps at
+most 2,000 peak buckets and accepts no more than 128 MiB or four decoded hours.
+It does not run a codec, speech-recognition model or network service.

public/docs/PRIVACY-SECURITY.md

@@ -0,0 +1,15 @@
+# Privacy and security
+
+Subtitle and media files are read only after direct selection and stay in page
+memory. No telemetry, analytics, account, upload, external font, codec, model or
+other network destination exists. The production policy uses
+`connect-src 'self'`; browser tests fail on non-local requests.
+
+Subtitle text is rendered by React as text, not interpreted as HTML. ASS override
+codes and WebVTT tags are preserved as inert source. Exports are downloads chosen
+by the user. Browser-native media playback and Web Audio decoding inherit browser
+codec support and may allocate substantial memory inside the documented bounds.
+
+Validation findings are editorial signals. They are not proof of accessibility,
+broadcast conformance, synchronization quality or legal compliance. Cross-format
+conversion can discard styles, positioning, regions, comments and metadata.

public/favicon.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64" role="img" aria-label="Subtitle Tools"><path fill="#5b4ec4" d="M11 4h30l12 12v44H11z"/><path fill="#fff" opacity=".28" d="M41 4v14h12"/><path fill="#fff" d="M17 31h12v5H22v7h7v5H17zm18 0h12v5h-7v7h7v5H35z"/></svg>

public/manifest.webmanifest

@@ -0,0 +1,18 @@
+{
+  "name": "Subtitle Tools",
+  "short_name": "Subtitles",
+  "description": "Edit, validate, synchronize, compare, and convert subtitles locally.",
+  "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 +1,54 @@
+const CACHE_PREFIX = "subtitle-tools-shell-";
+const CACHE_NAME = CACHE_PREFIX + "0.1.0";
+const CORE = ["./", "./manifest.webmanifest", "./favicon.svg"];
+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.subtitle-tools",
+  "name": "Subtitle Tools",
+  "version": "0.1.0",
+  "description": "Edit, validate, synchronize, compare, and convert subtitles locally.",
+  "entry": "./",
+  "icon": "./favicon.svg",
+  "categories": ["media", "text", "productivity"],
+  "tags": ["subtitles", "captions", "srt", "webvtt", "ass", "timing"],
+  "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": "Inputs stay in this browser; nothing is uploaded."
+  },
+  "source": {
+    "repository": "https://git.add-ideas.de/lotobo/subtitle-tools",
+    "license": "GPL-3.0-or-later"
+  },
+  "actions": [
+    {
+      "id": "source",
+      "label": "Source",
+      "url": "https://git.add-ideas.de/lotobo/subtitle-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.localeCompare(b.name),
+  )) {
+    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.localeCompare(b),
+)) {
+  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 +1,66 @@
+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/subtitle/";
+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);
+    response.writeHead(200, {
+      "Content-Type":
+        types.get(path.extname(file)) ?? "application/octet-stream",
+      "Cache-Control": "no-cache",
+      ...headers,
+    });
+    response.end(content);
+  } catch {
+    response.writeHead(404, { "Content-Type": "text/plain; charset=utf-8" });
+    response.end("Not found");
+  }
+});
+server.listen(4197, "127.0.0.1", () => console.log("Test server ready"));

src/App.tsx

@@ -0,0 +1,35 @@
+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" role="status">
+              Preparing Subtitle 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>Subtitle 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 +1,45 @@
+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 Subtitle Tools</h2>
+        </div>
+        <button type="button" onClick={onClose} aria-label="Close help">
+          ×
+        </button>
+      </div>
+      <p>
+        Edit, validate, synchronize, compare, and convert SRT, WebVTT, and ASS
+        subtitles locally in the browser.
+      </p>
+      <p>
+        Subtitle and optional media inputs are bounded and remain on this
+        device. Validation thresholds are guidance; cross-format conversion
+        reports its styling and metadata boundary.
+      </p>
+    </dialog>
+  );
+}

src/components/Waveform.tsx

@@ -0,0 +1,168 @@
+import { useEffect, useRef, useState } from "react";
+import type { Cue } from "../subtitle/model";
+
+interface WaveformData {
+  duration: number;
+  peaks: Float32Array;
+  url: string;
+}
+
+const MAX_AUDIO_BYTES = 128 * 1024 * 1024;
+const MAX_DURATION_SECONDS = 4 * 60 * 60;
+const PEAK_COUNT = 2_000;
+
+export function Waveform({ cues }: { cues: readonly Cue[] }) {
+  const canvas = useRef<HTMLCanvasElement>(null);
+  const audio = useRef<HTMLAudioElement>(null);
+  const [waveform, setWaveform] = useState<WaveformData>();
+  const [error, setError] = useState("");
+  const [busy, setBusy] = useState(false);
+
+  useEffect(
+    () => () => {
+      if (waveform) URL.revokeObjectURL(waveform.url);
+    },
+    [waveform],
+  );
+
+  useEffect(() => {
+    const node = canvas.current;
+    if (!node || !waveform) return;
+    const ratio = Math.max(1, Math.min(2, globalThis.devicePixelRatio || 1));
+    const width = Math.max(320, node.clientWidth);
+    const height = 180;
+    node.width = Math.floor(width * ratio);
+    node.height = Math.floor(height * ratio);
+    const context = node.getContext("2d");
+    if (!context) return;
+    context.scale(ratio, ratio);
+    const style = getComputedStyle(node);
+    context.fillStyle = style.getPropertyValue("--wave-bg") || "#f1f2f7";
+    context.fillRect(0, 0, width, height);
+    context.strokeStyle = style.getPropertyValue("--wave-line") || "#5b4ec4";
+    context.beginPath();
+    waveform.peaks.forEach((peak, index) => {
+      const x = (index / Math.max(1, waveform.peaks.length - 1)) * width;
+      context.moveTo(x, height / 2 - peak * (height / 2 - 8));
+      context.lineTo(x, height / 2 + peak * (height / 2 - 8));
+    });
+    context.stroke();
+    context.strokeStyle = style.getPropertyValue("--cue-line") || "#d3495a";
+    context.globalAlpha = 0.7;
+    for (const cue of cues) {
+      const x = (cue.startMs / 1000 / waveform.duration) * width;
+      if (x < 0 || x > width) continue;
+      context.beginPath();
+      context.moveTo(x, 0);
+      context.lineTo(x, height);
+      context.stroke();
+    }
+  }, [cues, waveform]);
+
+  const open = async (file: File | undefined) => {
+    if (!file) return;
+    if (file.size > MAX_AUDIO_BYTES) {
+      setError("Audio exceeds the 128 MiB waveform limit.");
+      return;
+    }
+    setBusy(true);
+    setError("");
+    try {
+      const AudioContextConstructor =
+        globalThis.AudioContext ??
+        (
+          globalThis as typeof globalThis & {
+            webkitAudioContext?: typeof AudioContext;
+          }
+        ).webkitAudioContext;
+      if (!AudioContextConstructor)
+        throw new Error("Web Audio is unavailable.");
+      const context = new AudioContextConstructor();
+      try {
+        const decoded = await context.decodeAudioData(await file.arrayBuffer());
+        if (
+          !Number.isFinite(decoded.duration) ||
+          decoded.duration > MAX_DURATION_SECONDS
+        )
+          throw new Error(
+            "Decoded audio exceeds the four-hour waveform limit.",
+          );
+        const channel = decoded.getChannelData(0);
+        const peaks = new Float32Array(Math.min(PEAK_COUNT, channel.length));
+        const stride = Math.max(1, Math.floor(channel.length / peaks.length));
+        for (let bucket = 0; bucket < peaks.length; bucket += 1) {
+          let peak = 0;
+          const end = Math.min(channel.length, (bucket + 1) * stride);
+          for (let index = bucket * stride; index < end; index += 1)
+            peak = Math.max(peak, Math.abs(channel[index] ?? 0));
+          peaks[bucket] = peak;
+        }
+        const url = URL.createObjectURL(file);
+        setWaveform((current) => {
+          if (current) URL.revokeObjectURL(current.url);
+          return { duration: decoded.duration, peaks, url };
+        });
+      } finally {
+        await context.close();
+      }
+    } catch (reason) {
+      setError(
+        reason instanceof Error ? reason.message : "Audio decode failed.",
+      );
+    } finally {
+      setBusy(false);
+    }
+  };
+
+  const seek = (event: React.MouseEvent<HTMLCanvasElement>) => {
+    if (!waveform || !audio.current) return;
+    const bounds = event.currentTarget.getBoundingClientRect();
+    audio.current.currentTime =
+      ((event.clientX - bounds.left) / Math.max(1, bounds.width)) *
+      waveform.duration;
+    void audio.current.play();
+  };
+
+  return (
+    <section className="waveform-workspace">
+      <div className="panel-heading">
+        <div>
+          <p className="eyebrow">Optional local media</p>
+          <h2>Waveform synchronization</h2>
+        </div>
+        <label className="file-button">
+          {busy ? "Decoding…" : "Open audio"}
+          <input
+            type="file"
+            accept="audio/*,video/*"
+            disabled={busy}
+            onChange={(event) => void open(event.target.files?.[0])}
+          />
+        </label>
+      </div>
+      <p className="muted">
+        Native playback is available immediately. Peak extraction is bounded and
+        stays in this browser; it is not speech recognition or automatic
+        alignment.
+      </p>
+      {error && (
+        <p className="error" role="alert">
+          {error}
+        </p>
+      )}
+      {waveform ? (
+        <>
+          <audio ref={audio} src={waveform.url} controls preload="metadata" />
+          <canvas
+            ref={canvas}
+            className="waveform"
+            aria-label="Audio waveform with subtitle start markers"
+            onClick={seek}
+          />
+        </>
+      ) : (
+        <p className="empty">Choose a browser-decodable audio or video file.</p>
+      )}
+    </section>
+  );
+}

src/components/Workbench.tsx

@@ -0,0 +1,684 @@
+import { useMemo, useState } from "react";
+import {
+  decodeText,
+  triggerBlobDownload,
+  type TextEncoding,
+} from "@add-ideas/toolbox-helpers";
+import {
+  DEFAULT_VALIDATION,
+  compareDocuments,
+  convertFrameRate,
+  documentSummary,
+  parseSubtitle,
+  replaceCue,
+  serializeSubtitle,
+  sortCues,
+  transformTiming,
+  validateDocument,
+  type SubtitleDocument,
+  type SubtitleFormat,
+  type ValidationOptions,
+} from "../subtitle/model";
+import { Waveform } from "./Waveform";
+
+type Tab = "source" | "cues" | "timing" | "compare" | "waveform";
+
+const EXAMPLE = `1
+00:00:01,000 --> 00:00:03,200
+Welcome to Subtitle Tools.
+
+2
+00:00:03,100 --> 00:00:05,000
+This overlap and reading speed
+are deliberately inspectable.
+`;
+
+function clock(milliseconds: number): string {
+  const sign = milliseconds < 0 ? "−" : "";
+  const value = Math.abs(Math.round(milliseconds));
+  const hours = Math.floor(value / 3_600_000);
+  const minutes = Math.floor((value % 3_600_000) / 60_000);
+  const seconds = Math.floor((value % 60_000) / 1000);
+  const fraction = value % 1000;
+  return `${sign}${String(hours).padStart(2, "0")}:${String(minutes).padStart(2, "0")}:${String(seconds).padStart(2, "0")}.${String(fraction).padStart(3, "0")}`;
+}
+
+function NumberField({
+  label,
+  value,
+  change,
+  min,
+  max,
+  step,
+}: {
+  label: string;
+  value: number;
+  change: (value: number) => void;
+  min?: number;
+  max?: number;
+  step?: number;
+}) {
+  return (
+    <label className="field">
+      <span>{label}</span>
+      <input
+        type="number"
+        value={value}
+        min={min}
+        max={max}
+        step={step}
+        onChange={(event) => change(event.target.valueAsNumber)}
+      />
+    </label>
+  );
+}
+
+export function Workbench() {
+  const [tab, setTab] = useState<Tab>("source");
+  const [source, setSource] = useState(EXAMPLE);
+  const [format, setFormat] = useState<SubtitleFormat | "auto">("auto");
+  const [encoding, setEncoding] = useState<TextEncoding>("utf-8");
+  const [document, setDocument] = useState<SubtitleDocument>(() =>
+    parseSubtitle(EXAMPLE),
+  );
+  const [selected, setSelected] = useState(0);
+  const [error, setError] = useState("");
+  const [exportFormat, setExportFormat] = useState<SubtitleFormat>("srt");
+  const [validation, setValidation] =
+    useState<ValidationOptions>(DEFAULT_VALIDATION);
+  const [shiftMs, setShiftMs] = useState(0);
+  const [scalePercent, setScalePercent] = useState(100);
+  const [anchorMs, setAnchorMs] = useState(0);
+  const [clamp, setClamp] = useState(false);
+  const [sourceFps, setSourceFps] = useState(25);
+  const [targetFps, setTargetFps] = useState(23.976);
+  const [revision, setRevision] = useState("");
+  const [revisionDocument, setRevisionDocument] = useState<SubtitleDocument>();
+  const issues = useMemo(
+    () => validateDocument(document, validation),
+    [document, validation],
+  );
+  const summary = useMemo(() => documentSummary(document), [document]);
+  const changes = useMemo(
+    () =>
+      revisionDocument ? compareDocuments(document, revisionDocument) : [],
+    [document, revisionDocument],
+  );
+  const serialized = useMemo(() => {
+    try {
+      return serializeSubtitle(document, exportFormat);
+    } catch {
+      return "";
+    }
+  }, [document, exportFormat]);
+
+  const parse = (value = source) => {
+    try {
+      const next = parseSubtitle(value, format);
+      setDocument(next);
+      setSelected(0);
+      setExportFormat(next.format);
+      setError("");
+    } catch (reason) {
+      setError(
+        reason instanceof Error ? reason.message : "Subtitle parsing failed.",
+      );
+    }
+  };
+
+  const open = async (file: File | undefined) => {
+    if (!file) return;
+    if (file.size > 8 * 1024 * 1024) {
+      setError("Subtitle file exceeds the 8 MiB byte-input limit.");
+      return;
+    }
+    try {
+      const decoded = decodeText(
+        new Uint8Array(await file.arrayBuffer()),
+        encoding,
+        false,
+      );
+      setSource(decoded);
+      const next = parseSubtitle(decoded, format);
+      setDocument(next);
+      setExportFormat(next.format);
+      setSelected(0);
+      setError("");
+    } catch (reason) {
+      setError(
+        reason instanceof Error ? reason.message : "File decoding failed.",
+      );
+    }
+  };
+
+  const applyTransform = () => {
+    try {
+      setDocument(
+        transformTiming(document, {
+          shiftMs,
+          scale: scalePercent / 100,
+          anchorMs,
+          clampToZero: clamp,
+        }),
+      );
+      setError("");
+    } catch (reason) {
+      setError(
+        reason instanceof Error ? reason.message : "Timing transform failed.",
+      );
+    }
+  };
+
+  const applyFrameRate = () => {
+    try {
+      setDocument(convertFrameRate(document, sourceFps, targetFps));
+      setError("");
+    } catch (reason) {
+      setError(
+        reason instanceof Error
+          ? reason.message
+          : "Frame-rate conversion failed.",
+      );
+    }
+  };
+
+  const download = () => {
+    try {
+      const value = serializeSubtitle(document, exportFormat);
+      triggerBlobDownload(
+        new Blob([value], { type: "text/plain;charset=utf-8" }),
+        `subtitles.${exportFormat}`,
+      );
+      setError("");
+    } catch (reason) {
+      setError(reason instanceof Error ? reason.message : "Export failed.");
+    }
+  };
+
+  const loadRevision = () => {
+    try {
+      setRevisionDocument(parseSubtitle(revision));
+      setError("");
+    } catch (reason) {
+      setError(
+        reason instanceof Error ? reason.message : "Revision parsing failed.",
+      );
+    }
+  };
+
+  const selectedCue = document.cues[selected];
+  const tabs: Array<[Tab, string]> = [
+    ["source", "Source & export"],
+    ["cues", "Cues & checks"],
+    ["timing", "Timing"],
+    ["compare", "Compare"],
+    ["waveform", "Waveform"],
+  ];
+
+  return (
+    <main className="workbench">
+      <header className="hero">
+        <div>
+          <p className="eyebrow">Local subtitle workshop</p>
+          <h1>Subtitle Tools</h1>
+          <p>
+            Inspect, edit, synchronize, validate, compare, and convert SRT,
+            WebVTT, and ASS captions without uploading media or text.
+          </p>
+        </div>
+        <span className="privacy-pill">No network requests</span>
+      </header>
+
+      <section className="summary panel" aria-label="Subtitle summary">
+        <div>
+          <span>Detected</span>
+          <strong>{summary.format.toUpperCase()}</strong>
+        </div>
+        <div>
+          <span>Cues</span>
+          <strong>{summary.cues.toLocaleString()}</strong>
+        </div>
+        <div>
+          <span>Timeline</span>
+          <strong>{clock(summary.durationMs)}</strong>
+        </div>
+        <div>
+          <span>Characters</span>
+          <strong>{summary.textCharacters.toLocaleString()}</strong>
+        </div>
+        <div>
+          <span>Issues</span>
+          <strong>{issues.length.toLocaleString()}</strong>
+        </div>
+      </section>
+
+      <nav className="tabs" role="tablist" aria-label="Subtitle workspaces">
+        {tabs.map(([value, label]) => (
+          <button
+            key={value}
+            type="button"
+            role="tab"
+            aria-selected={tab === value}
+            onClick={() => setTab(value)}
+          >
+            {label}
+          </button>
+        ))}
+      </nav>
+
+      {error && (
+        <p className="error" role="alert">
+          {error}
+        </p>
+      )}
+
+      {tab === "source" && (
+        <section className="workspace two-columns">
+          <article className="panel editor-panel">
+            <div className="panel-heading">
+              <div>
+                <p className="eyebrow">Untrusted input</p>
+                <h2>Subtitle source</h2>
+              </div>
+              <label className="file-button">
+                Open file
+                <input
+                  type="file"
+                  accept=".srt,.vtt,.ass,.ssa,text/plain,text/vtt"
+                  onChange={(event) => void open(event.target.files?.[0])}
+                />
+              </label>
+            </div>
+            <div className="form-grid">
+              <label className="field">
+                <span>Input format</span>
+                <select
+                  value={format}
+                  onChange={(event) =>
+                    setFormat(event.target.value as SubtitleFormat | "auto")
+                  }
+                >
+                  <option value="auto">Detect automatically</option>
+                  <option value="srt">SubRip (SRT)</option>
+                  <option value="vtt">WebVTT</option>
+                  <option value="ass">ASS / SSA</option>
+                </select>
+              </label>
+              <label className="field">
+                <span>File encoding</span>
+                <select
+                  value={encoding}
+                  onChange={(event) =>
+                    setEncoding(event.target.value as TextEncoding)
+                  }
+                >
+                  <option value="utf-8">UTF-8</option>
+                  <option value="utf-16le">UTF-16 LE</option>
+                  <option value="utf-16be">UTF-16 BE</option>
+                  <option value="latin1">ISO-8859-1</option>
+                </select>
+              </label>
+            </div>
+            <textarea
+              className="source-editor"
+              aria-label="Subtitle source"
+              value={source}
+              spellCheck={false}
+              onChange={(event) => setSource(event.target.value)}
+            />
+            <button className="primary" type="button" onClick={() => parse()}>
+              Parse source
+            </button>
+          </article>
+          <article className="panel editor-panel">
+            <div className="panel-heading">
+              <div>
+                <p className="eyebrow">Explicit conversion</p>
+                <h2>Export preview</h2>
+              </div>
+              <button className="primary" type="button" onClick={download}>
+                Download
+              </button>
+            </div>
+            <label className="field">
+              <span>Output format</span>
+              <select
+                value={exportFormat}
+                onChange={(event) =>
+                  setExportFormat(event.target.value as SubtitleFormat)
+                }
+              >
+                <option value="srt">SubRip (SRT)</option>
+                <option value="vtt">WebVTT</option>
+                <option value="ass">Advanced SubStation Alpha</option>
+              </select>
+            </label>
+            {exportFormat !== document.format && (
+              <p className="warning">
+                Cross-format conversion preserves cue text and timing.
+                Format-specific positioning, styles, regions, comments, and
+                metadata can be lost.
+              </p>
+            )}
+            <textarea
+              className="source-editor"
+              aria-label="Export preview"
+              readOnly
+              value={serialized}
+            />
+          </article>
+        </section>
+      )}
+
+      {tab === "cues" && (
+        <section className="workspace cue-layout">
+          <article className="panel cue-list">
+            <div className="panel-heading">
+              <div>
+                <p className="eyebrow">Timeline</p>
+                <h2>Cues</h2>
+              </div>
+              <button
+                type="button"
+                onClick={() => setDocument(sortCues(document))}
+              >
+                Sort by start
+              </button>
+            </div>
+            <ol>
+              {document.cues.slice(0, 10_000).map((cue, index) => (
+                <li key={`${cue.sourceLine}-${index}`}>
+                  <button
+                    type="button"
+                    className={selected === index ? "selected" : ""}
+                    onClick={() => setSelected(index)}
+                  >
+                    <span>{index + 1}</span>
+                    <time>
+                      {clock(cue.startMs)} → {clock(cue.endMs)}
+                    </time>
+                    <strong>
+                      {cue.text.replaceAll("\n", " ").slice(0, 90) || "(empty)"}
+                    </strong>
+                  </button>
+                </li>
+              ))}
+            </ol>
+            {document.cues.length > 10_000 && (
+              <p className="warning">
+                The editor lists the first 10,000 cues; validation and export
+                include all cues.
+              </p>
+            )}
+          </article>
+          <div className="cue-side">
+            <article className="panel">
+              <div className="panel-heading">
+                <div>
+                  <p className="eyebrow">Selected cue</p>
+                  <h2>Edit</h2>
+                </div>
+              </div>
+              {selectedCue ? (
+                <>
+                  <div className="form-grid">
+                    <NumberField
+                      label="Start (ms)"
+                      value={selectedCue.startMs}
+                      min={0}
+                      change={(value) =>
+                        setDocument(
+                          replaceCue(document, selected, { startMs: value }),
+                        )
+                      }
+                    />
+                    <NumberField
+                      label="End (ms)"
+                      value={selectedCue.endMs}
+                      min={0}
+                      change={(value) =>
+                        setDocument(
+                          replaceCue(document, selected, { endMs: value }),
+                        )
+                      }
+                    />
+                  </div>
+                  <label className="field">
+                    <span>Text</span>
+                    <textarea
+                      value={selectedCue.text}
+                      onChange={(event) =>
+                        setDocument(
+                          replaceCue(document, selected, {
+                            text: event.target.value,
+                          }),
+                        )
+                      }
+                    />
+                  </label>
+                </>
+              ) : (
+                <p className="empty">No cue selected.</p>
+              )}
+            </article>
+            <article className="panel issues">
+              <div className="panel-heading">
+                <div>
+                  <p className="eyebrow">Rules</p>
+                  <h2>Validation</h2>
+                </div>
+              </div>
+              <div className="thresholds">
+                <NumberField
+                  label="Max characters/s"
+                  value={validation.maxCharactersPerSecond}
+                  min={1}
+                  max={200}
+                  change={(value) =>
+                    setValidation({
+                      ...validation,
+                      maxCharactersPerSecond: value,
+                    })
+                  }
+                />
+                <NumberField
+                  label="Max line length"
+                  value={validation.maxLineLength}
+                  min={1}
+                  max={1000}
+                  change={(value) =>
+                    setValidation({ ...validation, maxLineLength: value })
+                  }
+                />
+                <NumberField
+                  label="Max lines"
+                  value={validation.maxLines}
+                  min={1}
+                  max={100}
+                  change={(value) =>
+                    setValidation({ ...validation, maxLines: value })
+                  }
+                />
+              </div>
+              {issues.length ? (
+                <ul>
+                  {issues.slice(0, 2_000).map((issue, index) => (
+                    <li
+                      key={`${issue.code}-${issue.cue ?? 0}-${index}`}
+                      className={issue.level}
+                    >
+                      <code>{issue.code}</code>{" "}
+                      {issue.cue ? `Cue ${issue.cue}: ` : ""}
+                      {issue.message}
+                    </li>
+                  ))}
+                </ul>
+              ) : (
+                <p className="success">
+                  No issues under the current thresholds.
+                </p>
+              )}
+            </article>
+          </div>
+        </section>
+      )}
+
+      {tab === "timing" && (
+        <section className="workspace two-columns">
+          <article className="panel">
+            <div className="panel-heading">
+              <div>
+                <p className="eyebrow">Affine transform</p>
+                <h2>Shift and stretch</h2>
+              </div>
+            </div>
+            <div className="form-grid">
+              <NumberField
+                label="Shift (ms)"
+                value={shiftMs}
+                step={1}
+                change={setShiftMs}
+              />
+              <NumberField
+                label="Scale (%)"
+                value={scalePercent}
+                min={0.001}
+                max={10_000}
+                step={0.001}
+                change={setScalePercent}
+              />
+              <NumberField
+                label="Anchor (ms)"
+                value={anchorMs}
+                min={0}
+                step={1}
+                change={setAnchorMs}
+              />
+            </div>
+            <label className="check">
+              <input
+                type="checkbox"
+                checked={clamp}
+                onChange={(event) => setClamp(event.target.checked)}
+              />
+              Move the entire result forward if it would become negative
+            </label>
+            <button className="primary" type="button" onClick={applyTransform}>
+              Apply timing transform
+            </button>
+          </article>
+          <article className="panel">
+            <div className="panel-heading">
+              <div>
+                <p className="eyebrow">Frame interpretation</p>
+                <h2>Frame-rate conversion</h2>
+              </div>
+            </div>
+            <p className="muted">
+              Scales timestamps by source FPS ÷ target FPS. It does not inspect
+              media or snap individual cues to frames.
+            </p>
+            <div className="form-grid">
+              <NumberField
+                label="Source FPS"
+                value={sourceFps}
+                min={0.001}
+                max={1000}
+                step={0.001}
+                change={setSourceFps}
+              />
+              <NumberField
+                label="Target FPS"
+                value={targetFps}
+                min={0.001}
+                max={1000}
+                step={0.001}
+                change={setTargetFps}
+              />
+            </div>
+            <button className="primary" type="button" onClick={applyFrameRate}>
+              Convert frame rate
+            </button>
+          </article>
+        </section>
+      )}
+
+      {tab === "compare" && (
+        <section className="workspace two-columns">
+          <article className="panel editor-panel">
+            <div className="panel-heading">
+              <div>
+                <p className="eyebrow">Second revision</p>
+                <h2>Compare input</h2>
+              </div>
+            </div>
+            <textarea
+              className="source-editor"
+              aria-label="Revision subtitle source"
+              value={revision}
+              onChange={(event) => setRevision(event.target.value)}
+              placeholder="Paste SRT, WebVTT, or ASS…"
+            />
+            <button className="primary" type="button" onClick={loadRevision}>
+              Parse and compare
+            </button>
+          </article>
+          <article className="panel revision-results">
+            <div className="panel-heading">
+              <div>
+                <p className="eyebrow">Index-aligned revision</p>
+                <h2>{changes.length} changes</h2>
+              </div>
+            </div>
+            <p className="muted">
+              v0.1 compares cue positions deterministically. Insertions can
+              shift later matches; no semantic alignment is claimed.
+            </p>
+            {revisionDocument ? (
+              changes.length ? (
+                <ol>
+                  {changes.slice(0, 5_000).map((change) => (
+                    <li key={`${change.kind}-${change.index}`}>
+                      <strong>
+                        Cue {change.index + 1}: {change.kind}
+                      </strong>
+                      <span>
+                        {change.before
+                          ? `${clock(change.before.startMs)} ${change.before.text.slice(0, 80)}`
+                          : "—"}
+                      </span>
+                      <span>
+                        {change.after
+                          ? `${clock(change.after.startMs)} ${change.after.text.slice(0, 80)}`
+                          : "—"}
+                      </span>
+                    </li>
+                  ))}
+                </ol>
+              ) : (
+                <p className="success">No index-aligned changes.</p>
+              )
+            ) : (
+              <p className="empty">Paste and parse a second revision.</p>
+            )}
+          </article>
+        </section>
+      )}
+
+      {tab === "waveform" && (
+        <section className="panel">
+          <Waveform cues={document.cues} />
+        </section>
+      )}
+
+      <section className="panel boundary">
+        <p>
+          Parsing and media decoding stay local. Validation is configurable
+          guidance, not a broadcaster, accessibility, or legal compliance
+          verdict. ASS round trips retain parsed dialogue fields; cross-format
+          exports explicitly discard unsupported styling.
+        </p>
+      </section>
+    </main>
+  );
+}

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 +1,546 @@
+:root {
+  font-family:
+    Inter,
+    ui-sans-serif,
+    system-ui,
+    -apple-system,
+    BlinkMacSystemFont,
+    "Segoe UI",
+    sans-serif;
+  color: #242233;
+  background: #f3f4f8;
+  font-synthesis: none;
+  --surface: #fff;
+  --surface-muted: #f4f3fa;
+  --line: #d8d6e5;
+  --ink-muted: #66637a;
+  --accent: #5b4ec4;
+  --accent-dark: #4336a4;
+  --danger: #a5263d;
+  --warning: #8a5700;
+  --success: #187148;
+  --wave-bg: #eeedf7;
+  --wave-line: #5b4ec4;
+  --cue-line: #ce3d59;
+}
+
+:root[data-toolbox-theme="dark"] {
+  color: #f0eff8;
+  background: #15141b;
+  --surface: #211f29;
+  --surface-muted: #2a2735;
+  --line: #454153;
+  --ink-muted: #b9b5c8;
+  --accent: #a99cff;
+  --accent-dark: #c0b7ff;
+  --danger: #ff91a2;
+  --warning: #ffd078;
+  --success: #78d7a9;
+  --wave-bg: #292634;
+  --wave-line: #aa9cff;
+  --cue-line: #ff8195;
+}
+
+@media (prefers-color-scheme: dark) {
+  :root:not([data-toolbox-theme="light"]) {
+    color: #f0eff8;
+    background: #15141b;
+    --surface: #211f29;
+    --surface-muted: #2a2735;
+    --line: #454153;
+    --ink-muted: #b9b5c8;
+    --accent: #a99cff;
+    --accent-dark: #c0b7ff;
+    --danger: #ff91a2;
+    --warning: #ffd078;
+    --success: #78d7a9;
+    --wave-bg: #292634;
+    --wave-line: #aa9cff;
+    --cue-line: #ff8195;
+  }
+}
+
+* {
+  box-sizing: border-box;
+}
+
+body {
+  margin: 0;
+  min-width: 320px;
+  min-height: 100vh;
+  background: inherit;
+  color: inherit;
+}
+
+button,
+input,
+select,
+textarea {
+  color: inherit;
+  font: inherit;
+}
+
+button,
+.file-button,
+input,
+select,
+textarea {
+  border: 1px solid var(--line);
+  border-radius: 0.72rem;
+  background: var(--surface);
+}
+
+button,
+.file-button {
+  min-height: 2.6rem;
+  padding: 0.58rem 0.9rem;
+  cursor: pointer;
+  font-weight: 700;
+}
+
+button:hover,
+.file-button:hover {
+  border-color: var(--accent);
+}
+
+button:focus-visible,
+input:focus-visible,
+select:focus-visible,
+textarea:focus-visible,
+.file-button:focus-within {
+  outline: 3px solid color-mix(in srgb, var(--accent) 35%, transparent);
+  outline-offset: 2px;
+}
+
+.primary {
+  border-color: var(--accent);
+  background: var(--accent);
+  color: #fff;
+}
+
+:root[data-toolbox-theme="dark"] .primary {
+  color: #17131f;
+}
+
+.workbench {
+  width: min(100%, 90rem);
+  margin: 0 auto;
+  padding: 1.4rem clamp(0.75rem, 2.5vw, 2rem) 3rem;
+}
+
+.hero,
+.panel-heading,
+.summary,
+.tabs,
+.form-grid,
+.two-columns,
+.cue-layout {
+  display: flex;
+}
+
+.hero {
+  align-items: flex-start;
+  justify-content: space-between;
+  gap: 1.2rem;
+  margin-bottom: 1rem;
+}
+
+h1,
+h2,
+p {
+  margin-top: 0;
+}
+
+h1 {
+  margin-bottom: 0.35rem;
+  font-size: clamp(1.8rem, 4vw, 3rem);
+}
+
+h2 {
+  margin-bottom: 0;
+  font-size: 1.15rem;
+}
+
+.hero > div > p:last-child {
+  max-width: 48rem;
+  margin-bottom: 0;
+  color: var(--ink-muted);
+}
+
+.eyebrow {
+  margin-bottom: 0.28rem;
+  color: var(--accent-dark);
+  font-size: 0.74rem;
+  font-weight: 800;
+  letter-spacing: 0.09em;
+  text-transform: uppercase;
+}
+
+.privacy-pill {
+  flex: none;
+  border: 1px solid color-mix(in srgb, var(--success) 50%, var(--line));
+  border-radius: 999px;
+  padding: 0.5rem 0.75rem;
+  color: var(--success);
+  font-size: 0.82rem;
+  font-weight: 800;
+}
+
+.panel {
+  border: 1px solid var(--line);
+  border-radius: 1rem;
+  background: var(--surface);
+  box-shadow: 0 0.45rem 1.4rem color-mix(in srgb, #151126 7%, transparent);
+  padding: 1rem;
+}
+
+.summary {
+  flex-wrap: wrap;
+  gap: 0.7rem;
+  margin-bottom: 0.8rem;
+}
+
+.summary > div {
+  flex: 1 1 9rem;
+  border-right: 1px solid var(--line);
+  padding: 0.15rem 0.8rem;
+}
+
+.summary > div:last-child {
+  border-right: 0;
+}
+
+.summary span,
+.summary strong {
+  display: block;
+}
+
+.summary span {
+  color: var(--ink-muted);
+  font-size: 0.76rem;
+  text-transform: uppercase;
+}
+
+.summary strong {
+  margin-top: 0.2rem;
+  font-variant-numeric: tabular-nums;
+}
+
+.tabs {
+  gap: 0.35rem;
+  overflow-x: auto;
+  margin-bottom: 0.8rem;
+  padding: 0.2rem 0;
+}
+
+.tabs button {
+  white-space: nowrap;
+}
+
+.tabs button[aria-selected="true"] {
+  border-color: var(--accent);
+  background: var(--surface-muted);
+  color: var(--accent-dark);
+}
+
+.workspace {
+  margin-bottom: 0.8rem;
+}
+
+.two-columns,
+.cue-layout {
+  align-items: stretch;
+  gap: 0.8rem;
+}
+
+.two-columns > *,
+.cue-layout > * {
+  min-width: 0;
+  flex: 1 1 0;
+}
+
+.panel-heading {
+  align-items: center;
+  justify-content: space-between;
+  gap: 0.8rem;
+  margin-bottom: 0.8rem;
+}
+
+.file-button {
+  position: relative;
+  display: inline-flex;
+  align-items: center;
+}
+
+.file-button input {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  overflow: hidden;
+  clip: rect(0 0 0 0);
+}
+
+.form-grid {
+  flex-wrap: wrap;
+  gap: 0.65rem;
+  margin-bottom: 0.7rem;
+}
+
+.field {
+  display: grid;
+  flex: 1 1 11rem;
+  gap: 0.28rem;
+  min-width: 0;
+  color: var(--ink-muted);
+  font-size: 0.82rem;
+  font-weight: 700;
+}
+
+.field input,
+.field select,
+.field textarea {
+  width: 100%;
+  min-height: 2.6rem;
+  padding: 0.55rem 0.65rem;
+  color: inherit;
+  font-weight: 500;
+}
+
+.field textarea,
+.source-editor {
+  resize: vertical;
+}
+
+.source-editor {
+  width: 100%;
+  min-height: 25rem;
+  margin-bottom: 0.65rem;
+  padding: 0.8rem;
+  font-family: ui-monospace, SFMono-Regular, Consolas, monospace;
+  font-size: 0.84rem;
+  line-height: 1.5;
+  tab-size: 2;
+}
+
+.warning,
+.error,
+.success,
+.muted,
+.empty {
+  font-size: 0.9rem;
+}
+
+.warning {
+  color: var(--warning);
+}
+
+.error {
+  border: 1px solid color-mix(in srgb, var(--danger) 45%, var(--line));
+  border-radius: 0.75rem;
+  background: color-mix(in srgb, var(--danger) 8%, var(--surface));
+  padding: 0.7rem;
+  color: var(--danger);
+}
+
+.success {
+  color: var(--success);
+}
+
+.muted,
+.empty {
+  color: var(--ink-muted);
+}
+
+.check {
+  display: flex;
+  align-items: flex-start;
+  gap: 0.5rem;
+  margin: 0.5rem 0 0.8rem;
+  color: var(--ink-muted);
+  font-size: 0.9rem;
+}
+
+.check input {
+  margin-top: 0.2rem;
+}
+
+.cue-list {
+  max-height: 52rem;
+  overflow: auto;
+}
+
+.cue-list ol,
+.issues ul,
+.revision-results ol {
+  margin: 0;
+  padding: 0;
+  list-style: none;
+}
+
+.cue-list li + li,
+.issues li + li,
+.revision-results li + li {
+  margin-top: 0.4rem;
+}
+
+.cue-list li button {
+  display: grid;
+  grid-template-columns: 3rem 1fr;
+  width: 100%;
+  text-align: left;
+}
+
+.cue-list li button.selected {
+  border-color: var(--accent);
+  background: var(--surface-muted);
+}
+
+.cue-list time {
+  font-variant-numeric: tabular-nums;
+  color: var(--ink-muted);
+}
+
+.cue-list strong {
+  grid-column: 2;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.cue-side {
+  display: grid;
+  align-content: start;
+  gap: 0.8rem;
+}
+
+.thresholds {
+  display: grid;
+  grid-template-columns: repeat(3, minmax(0, 1fr));
+  gap: 0.45rem;
+}
+
+.issues ul {
+  max-height: 24rem;
+  overflow: auto;
+  margin-top: 0.8rem;
+}
+
+.issues li {
+  border-left: 3px solid var(--warning);
+  padding: 0.35rem 0.55rem;
+  color: var(--ink-muted);
+  font-size: 0.84rem;
+}
+
+.issues li.error {
+  border: 0;
+  border-left: 3px solid var(--danger);
+  border-radius: 0;
+  background: transparent;
+  padding: 0.35rem 0.55rem;
+}
+
+.revision-results ol {
+  max-height: 36rem;
+  overflow: auto;
+}
+
+.revision-results li {
+  display: grid;
+  gap: 0.25rem;
+  border: 1px solid var(--line);
+  border-radius: 0.7rem;
+  padding: 0.55rem;
+}
+
+.revision-results span {
+  overflow-wrap: anywhere;
+  color: var(--ink-muted);
+  font-size: 0.82rem;
+}
+
+.waveform-workspace audio,
+.waveform {
+  display: block;
+  width: 100%;
+}
+
+.waveform-workspace audio {
+  margin-bottom: 0.7rem;
+}
+
+.waveform {
+  height: 180px;
+  border: 1px solid var(--line);
+  border-radius: 0.75rem;
+  cursor: crosshair;
+}
+
+.boundary {
+  color: var(--ink-muted);
+}
+
+.boundary p {
+  margin: 0;
+}
+
+.loading,
+.fatal {
+  width: min(100%, 90rem);
+  margin: 2rem auto;
+  padding: 1rem;
+}
+
+.help-dialog {
+  width: min(36rem, calc(100vw - 2rem));
+  border: 1px solid var(--line);
+  border-radius: 1rem;
+  background: var(--surface);
+  color: inherit;
+  padding: 1rem;
+}
+
+.help-dialog::backdrop {
+  background: rgb(16 14 25 / 55%);
+}
+
+.dialog-heading {
+  display: flex;
+  align-items: flex-start;
+  justify-content: space-between;
+  gap: 1rem;
+}
+
+@media (max-width: 800px) {
+  .hero,
+  .two-columns,
+  .cue-layout {
+    flex-direction: column;
+  }
+
+  .privacy-pill {
+    align-self: flex-start;
+  }
+
+  .two-columns > *,
+  .cue-layout > * {
+    width: 100%;
+  }
+
+  .thresholds {
+    grid-template-columns: 1fr;
+  }
+
+  .source-editor {
+    min-height: 18rem;
+  }
+}
+
+@media (prefers-reduced-motion: reduce) {
+  *,
+  *::before,
+  *::after {
+    scroll-behavior: auto !important;
+    transition: none !important;
+  }
+}

src/subtitle/model.ts

@@ -0,0 +1,700 @@
+export type SubtitleFormat = "srt" | "vtt" | "ass";
+
+export interface Cue {
+  id: string;
+  startMs: number;
+  endMs: number;
+  text: string;
+  settings?: string;
+  assFields?: Record<string, string>;
+  sourceLine: number;
+}
+
+export interface SubtitleDocument {
+  format: SubtitleFormat;
+  cues: Cue[];
+  preamble: string[];
+  assFormat?: string[];
+  warnings: string[];
+}
+
+export interface CueIssue {
+  level: "error" | "warning" | "info";
+  code: string;
+  cue?: number;
+  message: string;
+}
+
+export interface ValidationOptions {
+  maxCharactersPerSecond: number;
+  maxLineLength: number;
+  maxLines: number;
+  minimumDurationMs: number;
+  maximumDurationMs: number;
+}
+
+export const DEFAULT_VALIDATION: ValidationOptions = {
+  maxCharactersPerSecond: 20,
+  maxLineLength: 42,
+  maxLines: 2,
+  minimumDurationMs: 500,
+  maximumDurationMs: 7_000,
+};
+
+const MAX_SOURCE_UNITS = 4_000_000;
+const MAX_CUES = 100_000;
+const MAX_LINE_UNITS = 250_000;
+
+function normalizeSource(source: string): string {
+  if (source.length > MAX_SOURCE_UNITS)
+    throw new Error("Subtitle source exceeds 4,000,000 UTF-16 units.");
+  const normalized = source.replaceAll("\r\n", "\n").replaceAll("\r", "\n");
+  if (normalized.split("\n").some((line) => line.length > MAX_LINE_UNITS))
+    throw new Error("A subtitle line exceeds 250,000 UTF-16 units.");
+  return normalized.replace(/^\uFEFF/u, "");
+}
+
+export function detectFormat(source: string): SubtitleFormat {
+  const head = source.replace(/^\uFEFF/u, "").slice(0, 16_384);
+  if (/^WEBVTT(?:[ \t]|$)/mu.test(head)) return "vtt";
+  if (/^\s*\[(?:Script Info|Events|V4\+? Styles)\]/imu.test(head)) return "ass";
+  return "srt";
+}
+
+function parseTimestamp(value: string, format: "srt" | "vtt"): number {
+  const match = /^(?:(\d{1,6}):)?(\d{2}):(\d{2})[,.](\d{3})$/u.exec(
+    value.trim(),
+  );
+  if (!match)
+    throw new Error(`Invalid ${format.toUpperCase()} timestamp: ${value}`);
+  const hours = Number(match[1] ?? 0);
+  const minutes = Number(match[2]);
+  const seconds = Number(match[3]);
+  const milliseconds = Number(match[4]);
+  if (minutes > 59 || seconds > 59)
+    throw new Error(`Timestamp component is outside its range: ${value}`);
+  const result = ((hours * 60 + minutes) * 60 + seconds) * 1000 + milliseconds;
+  if (!Number.isSafeInteger(result)) throw new Error("Timestamp is too large.");
+  return result;
+}
+
+function parseAssTimestamp(value: string): number {
+  const match = /^(\d{1,6}):(\d{2}):(\d{2})[.](\d{1,3})$/u.exec(value.trim());
+  if (!match) throw new Error(`Invalid ASS timestamp: ${value}`);
+  const hours = Number(match[1]);
+  const minutes = Number(match[2]);
+  const seconds = Number(match[3]);
+  const fraction = Number(match[4]!.padEnd(3, "0"));
+  if (minutes > 59 || seconds > 59)
+    throw new Error(`Timestamp component is outside its range: ${value}`);
+  const result = ((hours * 60 + minutes) * 60 + seconds) * 1000 + fraction;
+  if (!Number.isSafeInteger(result)) throw new Error("Timestamp is too large.");
+  return result;
+}
+
+function splitBlocks(source: string): Array<{ text: string; line: number }> {
+  const blocks: Array<{ text: string; line: number }> = [];
+  const lines = source.split("\n");
+  let start = 0;
+  for (let index = 0; index <= lines.length; index += 1) {
+    if (index < lines.length && lines[index]!.trim() !== "") continue;
+    if (index > start) {
+      const text = lines.slice(start, index).join("\n");
+      if (text.trim()) blocks.push({ text, line: start + 1 });
+    }
+    start = index + 1;
+  }
+  return blocks;
+}
+
+function parseSrt(source: string): SubtitleDocument {
+  const cues: Cue[] = [];
+  const warnings: string[] = [];
+  for (const block of splitBlocks(source)) {
+    const lines = block.text.split("\n");
+    let timingIndex = 0;
+    let id = "";
+    if (!lines[0]!.includes("-->")) {
+      id = lines[0]!.trim();
+      timingIndex = 1;
+    }
+    const timing = /^(\S+)\s*-->\s*(\S+)(?:\s+(.*))?$/u.exec(
+      lines[timingIndex] ?? "",
+    );
+    if (!timing) {
+      warnings.push(
+        `Ignored block at line ${block.line}: no valid timing line.`,
+      );
+      continue;
+    }
+    try {
+      cues.push({
+        id: id || String(cues.length + 1),
+        startMs: parseTimestamp(timing[1]!, "srt"),
+        endMs: parseTimestamp(timing[2]!, "srt"),
+        text: lines.slice(timingIndex + 1).join("\n"),
+        settings: timing[3]?.trim() || undefined,
+        sourceLine: block.line,
+      });
+    } catch (reason) {
+      warnings.push(
+        `Ignored block at line ${block.line}: ${reason instanceof Error ? reason.message : "invalid timing"}`,
+      );
+    }
+    if (cues.length > MAX_CUES)
+      throw new Error("Subtitle exceeds 100,000 cues.");
+  }
+  return { format: "srt", cues, preamble: [], warnings };
+}
+
+function parseVtt(source: string): SubtitleDocument {
+  const blocks = splitBlocks(source);
+  const first = blocks.shift();
+  if (!first || !/^WEBVTT(?:[ \t]|$)/u.test(first.text))
+    throw new Error("WebVTT must begin with WEBVTT.");
+  const cues: Cue[] = [];
+  const preamble = first.text.split("\n").slice(1);
+  const warnings: string[] = [];
+  for (const block of blocks) {
+    const lines = block.text.split("\n");
+    if (/^(?:NOTE|STYLE|REGION)(?:[ \t]|$)/u.test(lines[0]!)) {
+      preamble.push("", block.text);
+      continue;
+    }
+    const timingIndex = lines[0]!.includes("-->") ? 0 : 1;
+    const timing = /^(\S+)\s*-->\s*(\S+)(?:\s+(.*))?$/u.exec(
+      lines[timingIndex] ?? "",
+    );
+    if (!timing) {
+      warnings.push(
+        `Ignored block at line ${block.line}: no valid timing line.`,
+      );
+      continue;
+    }
+    try {
+      cues.push({
+        id: timingIndex === 1 ? lines[0]!.trim() : String(cues.length + 1),
+        startMs: parseTimestamp(timing[1]!, "vtt"),
+        endMs: parseTimestamp(timing[2]!, "vtt"),
+        text: lines.slice(timingIndex + 1).join("\n"),
+        settings: timing[3]?.trim() || undefined,
+        sourceLine: block.line,
+      });
+    } catch (reason) {
+      warnings.push(
+        `Ignored block at line ${block.line}: ${reason instanceof Error ? reason.message : "invalid timing"}`,
+      );
+    }
+    if (cues.length > MAX_CUES)
+      throw new Error("Subtitle exceeds 100,000 cues.");
+  }
+  return { format: "vtt", cues, preamble, warnings };
+}
+
+function splitLimited(value: string, count: number): string[] {
+  const result: string[] = [];
+  let start = 0;
+  for (let index = 1; index < count; index += 1) {
+    const comma = value.indexOf(",", start);
+    if (comma < 0) break;
+    result.push(value.slice(start, comma));
+    start = comma + 1;
+  }
+  result.push(value.slice(start));
+  return result;
+}
+
+const DEFAULT_ASS_FORMAT = [
+  "Layer",
+  "Start",
+  "End",
+  "Style",
+  "Name",
+  "MarginL",
+  "MarginR",
+  "MarginV",
+  "Effect",
+  "Text",
+];
+
+function parseAss(source: string): SubtitleDocument {
+  const lines = source.split("\n");
+  const cues: Cue[] = [];
+  const preamble: string[] = [];
+  const warnings: string[] = [];
+  let section = "";
+  let format = [...DEFAULT_ASS_FORMAT];
+  for (let index = 0; index < lines.length; index += 1) {
+    const line = lines[index]!;
+    const sectionMatch = /^\s*\[([^\]]+)\]\s*$/u.exec(line);
+    if (sectionMatch) section = sectionMatch[1]!.toLowerCase();
+    if (section === "events" && /^Format\s*:/iu.test(line)) {
+      format = line
+        .replace(/^Format\s*:/iu, "")
+        .split(",")
+        .map((field) => field.trim())
+        .filter(Boolean);
+      if (!format.some((field) => field.toLowerCase() === "text"))
+        warnings.push(`Events Format at line ${index + 1} has no Text field.`);
+      preamble.push(line);
+      continue;
+    }
+    const dialogue =
+      section === "events" ? /^Dialogue\s*:\s*(.*)$/iu.exec(line) : null;
+    if (!dialogue) {
+      preamble.push(line);
+      continue;
+    }
+    const values = splitLimited(dialogue[1]!, format.length);
+    if (values.length !== format.length) {
+      warnings.push(
+        `Ignored Dialogue at line ${index + 1}: field count mismatch.`,
+      );
+      continue;
+    }
+    const fields = Object.fromEntries(
+      format.map((field, fieldIndex) => [
+        field.toLowerCase(),
+        values[fieldIndex] ?? "",
+      ]),
+    );
+    try {
+      cues.push({
+        id: String(cues.length + 1),
+        startMs: parseAssTimestamp(fields.start ?? ""),
+        endMs: parseAssTimestamp(fields.end ?? ""),
+        text: (fields.text ?? "")
+          .replaceAll("\\N", "\n")
+          .replaceAll("\\n", "\n"),
+        assFields: fields,
+        sourceLine: index + 1,
+      });
+    } catch (reason) {
+      warnings.push(
+        `Ignored Dialogue at line ${index + 1}: ${reason instanceof Error ? reason.message : "invalid timing"}`,
+      );
+    }
+    if (cues.length > MAX_CUES)
+      throw new Error("Subtitle exceeds 100,000 cues.");
+  }
+  return { format: "ass", cues, preamble, assFormat: format, warnings };
+}
+
+export function parseSubtitle(
+  source: string,
+  requested: SubtitleFormat | "auto" = "auto",
+): SubtitleDocument {
+  const normalized = normalizeSource(source);
+  const format = requested === "auto" ? detectFormat(normalized) : requested;
+  const document =
+    format === "vtt"
+      ? parseVtt(normalized)
+      : format === "ass"
+        ? parseAss(normalized)
+        : parseSrt(normalized);
+  if (!document.cues.length)
+    document.warnings.push("No valid subtitle cues were found.");
+  return document;
+}
+
+function plainText(value: string): string {
+  return value
+    .replace(/<[^>]*>/gu, "")
+    .replace(/\{\\[^}]*\}/gu, "")
+    .replaceAll(/\s+/gu, " ")
+    .trim();
+}
+
+export function charactersPerSecond(cue: Cue): number {
+  const duration = cue.endMs - cue.startMs;
+  return duration > 0
+    ? (plainText(cue.text).length * 1000) / duration
+    : Infinity;
+}
+
+export function validateDocument(
+  document: SubtitleDocument,
+  options: ValidationOptions = DEFAULT_VALIDATION,
+): CueIssue[] {
+  const numbers = Object.values(options);
+  if (numbers.some((value) => !Number.isFinite(value) || value < 0))
+    throw new Error(
+      "Validation thresholds must be finite non-negative numbers.",
+    );
+  const issues: CueIssue[] = document.warnings.map((message) => ({
+    level: "warning",
+    code: "parse-warning",
+    message,
+  }));
+  document.cues.forEach((cue, index) => {
+    const cueNumber = index + 1;
+    const duration = cue.endMs - cue.startMs;
+    if (cue.startMs < 0)
+      issues.push({
+        level: "error",
+        code: "negative-time",
+        cue: cueNumber,
+        message: "Start time is negative.",
+      });
+    if (duration <= 0)
+      issues.push({
+        level: "error",
+        code: "invalid-duration",
+        cue: cueNumber,
+        message: "End time must be after start time.",
+      });
+    else {
+      if (duration < options.minimumDurationMs)
+        issues.push({
+          level: "warning",
+          code: "short-duration",
+          cue: cueNumber,
+          message: `Duration ${duration} ms is below ${options.minimumDurationMs} ms.`,
+        });
+      if (duration > options.maximumDurationMs)
+        issues.push({
+          level: "warning",
+          code: "long-duration",
+          cue: cueNumber,
+          message: `Duration ${duration} ms exceeds ${options.maximumDurationMs} ms.`,
+        });
+      const cps = charactersPerSecond(cue);
+      if (cps > options.maxCharactersPerSecond)
+        issues.push({
+          level: "warning",
+          code: "reading-speed",
+          cue: cueNumber,
+          message: `${cps.toFixed(1)} characters/s exceeds ${options.maxCharactersPerSecond}.`,
+        });
+    }
+    const lines = cue.text.split("\n");
+    if (!plainText(cue.text))
+      issues.push({
+        level: "warning",
+        code: "empty",
+        cue: cueNumber,
+        message: "Cue has no visible text.",
+      });
+    if (lines.length > options.maxLines)
+      issues.push({
+        level: "warning",
+        code: "line-count",
+        cue: cueNumber,
+        message: `${lines.length} lines exceed ${options.maxLines}.`,
+      });
+    let longest = 0;
+    for (const line of lines)
+      longest = Math.max(longest, [...plainText(line)].length);
+    if (longest > options.maxLineLength)
+      issues.push({
+        level: "warning",
+        code: "line-length",
+        cue: cueNumber,
+        message: `Longest line (${longest}) exceeds ${options.maxLineLength} characters.`,
+      });
+    if (index > 0) {
+      const previous = document.cues[index - 1]!;
+      if (cue.startMs < previous.startMs)
+        issues.push({
+          level: "warning",
+          code: "order",
+          cue: cueNumber,
+          message: "Cue starts before the preceding source cue.",
+        });
+      if (cue.startMs < previous.endMs)
+        issues.push({
+          level: "warning",
+          code: "overlap",
+          cue: cueNumber,
+          message: `Overlaps the preceding cue by ${previous.endMs - cue.startMs} ms.`,
+        });
+    }
+  });
+  return issues;
+}
+
+function cloneDocument(
+  document: SubtitleDocument,
+  cues: Cue[],
+): SubtitleDocument {
+  return {
+    ...document,
+    cues,
+    preamble: [...document.preamble],
+    assFormat: document.assFormat ? [...document.assFormat] : undefined,
+    warnings: [...document.warnings],
+  };
+}
+
+export interface TimingTransform {
+  shiftMs?: number;
+  scale?: number;
+  anchorMs?: number;
+  clampToZero?: boolean;
+}
+
+export function transformTiming(
+  document: SubtitleDocument,
+  transform: TimingTransform,
+): SubtitleDocument {
+  const shift = transform.shiftMs ?? 0;
+  const scale = transform.scale ?? 1;
+  const anchor = transform.anchorMs ?? 0;
+  if (
+    ![shift, scale, anchor].every(Number.isFinite) ||
+    scale <= 0 ||
+    scale > 100
+  )
+    throw new Error(
+      "Timing transform requires finite values and scale in (0, 100].",
+    );
+  const converted = document.cues.map((cue) => ({
+    ...cue,
+    assFields: cue.assFields ? { ...cue.assFields } : undefined,
+    startMs: Math.round(anchor + (cue.startMs - anchor) * scale + shift),
+    endMs: Math.round(anchor + (cue.endMs - anchor) * scale + shift),
+  }));
+  let minimum = 0;
+  for (const cue of converted) minimum = Math.min(minimum, cue.startMs);
+  if (minimum < 0 && !transform.clampToZero)
+    throw new Error("Timing transform would create negative timestamps.");
+  if (minimum < 0)
+    for (const cue of converted) {
+      cue.startMs -= minimum;
+      cue.endMs -= minimum;
+    }
+  return cloneDocument(document, converted);
+}
+
+export function convertFrameRate(
+  document: SubtitleDocument,
+  sourceFramesPerSecond: number,
+  targetFramesPerSecond: number,
+): SubtitleDocument {
+  if (
+    !Number.isFinite(sourceFramesPerSecond) ||
+    !Number.isFinite(targetFramesPerSecond) ||
+    sourceFramesPerSecond <= 0 ||
+    targetFramesPerSecond <= 0 ||
+    sourceFramesPerSecond > 1000 ||
+    targetFramesPerSecond > 1000
+  )
+    throw new Error("Frame rates must be finite values in (0, 1000].");
+  return transformTiming(document, {
+    scale: sourceFramesPerSecond / targetFramesPerSecond,
+    anchorMs: 0,
+  });
+}
+
+export function sortCues(document: SubtitleDocument): SubtitleDocument {
+  return cloneDocument(
+    document,
+    [...document.cues]
+      .map((cue) => ({
+        ...cue,
+        assFields: cue.assFields ? { ...cue.assFields } : undefined,
+      }))
+      .sort(
+        (left, right) =>
+          left.startMs - right.startMs || left.endMs - right.endMs,
+      ),
+  );
+}
+
+export function replaceCue(
+  document: SubtitleDocument,
+  index: number,
+  changes: Partial<Pick<Cue, "startMs" | "endMs" | "text">>,
+): SubtitleDocument {
+  if (
+    !Number.isSafeInteger(index) ||
+    index < 0 ||
+    index >= document.cues.length
+  )
+    throw new Error("Cue index is outside the document.");
+  const cues = document.cues.map((cue, cueIndex) =>
+    cueIndex === index ? { ...cue, ...changes } : cue,
+  );
+  return cloneDocument(document, cues);
+}
+
+function formatTimestamp(milliseconds: number, separator: "," | "."): string {
+  if (!Number.isSafeInteger(milliseconds) || milliseconds < 0)
+    throw new Error("Cannot serialize a negative or unsafe timestamp.");
+  const hours = Math.floor(milliseconds / 3_600_000);
+  const minutes = Math.floor((milliseconds % 3_600_000) / 60_000);
+  const seconds = Math.floor((milliseconds % 60_000) / 1000);
+  const fraction = milliseconds % 1000;
+  return `${String(hours).padStart(2, "0")}:${String(minutes).padStart(2, "0")}:${String(seconds).padStart(2, "0")}${separator}${String(fraction).padStart(3, "0")}`;
+}
+
+function formatAssTimestamp(milliseconds: number): string {
+  if (!Number.isSafeInteger(milliseconds) || milliseconds < 0)
+    throw new Error("Cannot serialize a negative or unsafe timestamp.");
+  const centiseconds = Math.round(milliseconds / 10);
+  const hours = Math.floor(centiseconds / 360_000);
+  const minutes = Math.floor((centiseconds % 360_000) / 6_000);
+  const seconds = Math.floor((centiseconds % 6_000) / 100);
+  const fraction = centiseconds % 100;
+  return `${hours}:${String(minutes).padStart(2, "0")}:${String(seconds).padStart(2, "0")}.${String(fraction).padStart(2, "0")}`;
+}
+
+function serializeSrt(document: SubtitleDocument): string {
+  return `${document.cues
+    .map(
+      (cue, index) =>
+        `${index + 1}\n${formatTimestamp(cue.startMs, ",")} --> ${formatTimestamp(cue.endMs, ",")}${cue.settings ? ` ${cue.settings}` : ""}\n${cue.text}`,
+    )
+    .join("\n\n")}\n`;
+}
+
+function serializeVtt(document: SubtitleDocument): string {
+  const preamble =
+    document.format === "vtt" && document.preamble.join("\n").trim()
+      ? `${document.preamble.join("\n").trim()}\n\n`
+      : "";
+  const body = document.cues
+    .map(
+      (cue) =>
+        `${cue.id ? `${cue.id}\n` : ""}${formatTimestamp(cue.startMs, ".")} --> ${formatTimestamp(cue.endMs, ".")}${cue.settings ? ` ${cue.settings}` : ""}\n${cue.text}`,
+    )
+    .join("\n\n");
+  return `WEBVTT\n\n${preamble}${body}\n`;
+}
+
+function minimalAssPreamble(): string[] {
+  return [
+    "[Script Info]",
+    "ScriptType: v4.00+",
+    "WrapStyle: 0",
+    "ScaledBorderAndShadow: yes",
+    "",
+    "[V4+ Styles]",
+    "Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding",
+    "Style: Default,Arial,42,&H00FFFFFF,&H000000FF,&H00000000,&H64000000,0,0,0,0,100,100,0,0,1,2,0,2,40,40,30,1",
+    "",
+    "[Events]",
+    `Format: ${DEFAULT_ASS_FORMAT.join(", ")}`,
+  ];
+}
+
+function serializeAss(document: SubtitleDocument): string {
+  const format =
+    document.format === "ass" && document.assFormat?.length
+      ? document.assFormat
+      : DEFAULT_ASS_FORMAT;
+  const preamble =
+    document.format === "ass" ? [...document.preamble] : minimalAssPreamble();
+  let eventsIndex = preamble.findIndex((line) =>
+    /^\s*\[Events\]\s*$/iu.test(line),
+  );
+  if (eventsIndex < 0) {
+    preamble.push("", "[Events]");
+    eventsIndex = preamble.length - 1;
+  }
+  const nextSectionIndex = preamble.findIndex(
+    (line, index) => index > eventsIndex && /^\s*\[[^\]]+\]\s*$/u.test(line),
+  );
+  const eventsEnd = nextSectionIndex < 0 ? preamble.length : nextSectionIndex;
+  const hasEventsFormat = preamble
+    .slice(eventsIndex + 1, eventsEnd)
+    .some((line) => /^\s*Format\s*:/iu.test(line));
+  if (!hasEventsFormat)
+    preamble.splice(eventsIndex + 1, 0, `Format: ${format.join(", ")}`);
+  const dialogue = document.cues.map((cue) => {
+    const values = format.map((field) => {
+      const key = field.toLowerCase();
+      if (key === "start") return formatAssTimestamp(cue.startMs);
+      if (key === "end") return formatAssTimestamp(cue.endMs);
+      if (key === "text") return cue.text.replaceAll("\n", "\\N");
+      return (
+        cue.assFields?.[key] ??
+        {
+          layer: "0",
+          style: "Default",
+          name: "",
+          marginl: "0",
+          marginr: "0",
+          marginv: "0",
+          effect: "",
+        }[key] ??
+        ""
+      );
+    });
+    return `Dialogue: ${values.join(",")}`;
+  });
+  return `${preamble.join("\n").replace(/\n+$/u, "")}\n${dialogue.join("\n")}\n`;
+}
+
+export function serializeSubtitle(
+  document: SubtitleDocument,
+  format: SubtitleFormat,
+): string {
+  if (document.cues.length > MAX_CUES)
+    throw new Error("Subtitle exceeds 100,000 cues.");
+  return format === "vtt"
+    ? serializeVtt(document)
+    : format === "ass"
+      ? serializeAss(document)
+      : serializeSrt(document);
+}
+
+export interface RevisionChange {
+  kind: "added" | "removed" | "timing" | "text" | "timing-and-text";
+  index: number;
+  before?: Cue;
+  after?: Cue;
+}
+
+export function compareDocuments(
+  before: SubtitleDocument,
+  after: SubtitleDocument,
+): RevisionChange[] {
+  if (before.cues.length + after.cues.length > 100_000)
+    throw new Error("Revision comparison is limited to 100,000 combined cues.");
+  const changes: RevisionChange[] = [];
+  const count = Math.max(before.cues.length, after.cues.length);
+  for (let index = 0; index < count; index += 1) {
+    const left = before.cues[index];
+    const right = after.cues[index];
+    if (!left && right) changes.push({ kind: "added", index, after: right });
+    else if (left && !right)
+      changes.push({ kind: "removed", index, before: left });
+    else if (left && right) {
+      const timing =
+        left.startMs !== right.startMs || left.endMs !== right.endMs;
+      const text = left.text !== right.text;
+      if (timing || text)
+        changes.push({
+          kind: timing && text ? "timing-and-text" : timing ? "timing" : "text",
+          index,
+          before: left,
+          after: right,
+        });
+    }
+  }
+  return changes;
+}
+
+export function documentSummary(document: SubtitleDocument) {
+  let first = 0;
+  let last = 0;
+  let textCharacters = 0;
+  if (document.cues.length) {
+    first = document.cues[0]!.startMs;
+    last = document.cues[0]!.endMs;
+    for (const cue of document.cues) {
+      first = Math.min(first, cue.startMs);
+      last = Math.max(last, cue.endMs);
+      textCharacters += plainText(cue.text).length;
+    }
+  }
+  return {
+    format: document.format,
+    cues: document.cues.length,
+    firstMs: first,
+    lastMs: last,
+    durationMs: Math.max(0, last - first),
+    textCharacters,
+  };
+}

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.subtitle-tools",
+  "name": "Subtitle Tools",
+  "version": "0.1.0",
+  "description": "Edit, validate, synchronize, compare, and convert subtitles locally.",
+  "entry": "./",
+  "icon": "./favicon.svg",
+  "categories": ["media", "text", "productivity"],
+  "tags": ["subtitles", "captions", "srt", "webvtt", "ass", "timing"],
+  "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": "Inputs stay in this browser; nothing is uploaded."
+  },
+  "source": {
+    "repository": "https://git.add-ideas.de/lotobo/subtitle-tools",
+    "license": "GPL-3.0-or-later"
+  },
+  "actions": [
+    {
+      "id": "source",
+      "label": "Source",
+      "url": "https://git.add-ideas.de/lotobo/subtitle-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 +1,79 @@
+import { expect, test, type Page } from "@playwright/test";
+
+const ORIGIN = "http://127.0.0.1:4197";
+async function localOnly(page: Page) {
+  const external: string[] = [];
+  await page.route("**/*", async (route) => {
+    const url = new URL(route.request().url());
+    if (
+      (url.protocol === "http:" || url.protocol === "https:") &&
+      url.origin !== ORIGIN
+    ) {
+      external.push(url.href);
+      await route.abort();
+    } else await route.continue();
+  });
+  return external;
+}
+
+test("runs from a nested path without external requests", async ({ page }) => {
+  const errors: string[] = [];
+  page.on("pageerror", (error) => errors.push(error.message));
+  page.on("console", (message) => {
+    if (message.type() === "error") errors.push(message.text());
+  });
+  const external = await localOnly(page);
+  await page.goto("/deep/nested/subtitle/");
+  await expect(
+    page.getByRole("heading", { name: "Subtitle Tools" }),
+  ).toBeVisible();
+  await expect(page.getByText("No network requests")).toBeVisible();
+  expect(external).toEqual([]);
+  expect(errors).toEqual([]);
+});
+
+test("parses, validates, edits and converts the example", async ({ page }) => {
+  const external = await localOnly(page);
+  await page.goto("/deep/nested/subtitle/");
+  await expect(page.getByText("SRT", { exact: true })).toBeVisible();
+  await page.getByRole("tab", { name: "Cues & checks" }).click();
+  await expect(page.getByText("overlap", { exact: true })).toBeVisible();
+  await page.getByLabel("Text").fill("Edited locally");
+  await page.getByRole("tab", { name: "Source & export" }).click();
+  await page.getByLabel("Output format").selectOption("vtt");
+  await expect(page.getByLabel("Export preview")).toHaveValue(/WEBVTT/u);
+  await expect(page.getByLabel("Export preview")).toHaveValue(
+    /Edited locally/u,
+  );
+  expect(external).toEqual([]);
+});
+
+test("applies a bounded timing shift", async ({ page }) => {
+  await page.goto("/deep/nested/subtitle/");
+  await page.getByRole("tab", { name: "Timing" }).click();
+  await page.getByLabel("Shift (ms)").fill("500");
+  await page.getByRole("button", { name: "Apply timing transform" }).click();
+  await page.getByRole("tab", { name: "Cues & checks" }).click();
+  await expect(page.getByText(/00:00:01\.500/u).first()).toBeVisible();
+});
+
+test("serves release identity and hardened local-only headers", async ({
+  request,
+}) => {
+  const index = await request.get("/deep/nested/subtitle/");
+  expect(index.ok()).toBe(true);
+  expect(index.headers()["content-security-policy"]).toContain(
+    "connect-src 'self'",
+  );
+  expect(index.headers()["content-security-policy"]).not.toMatch(
+    /connect-src[^;]*https?:/u,
+  );
+  expect(await index.text()).not.toMatch(/\b(?:src|href)=["']\//u);
+  const manifest = await request.get("/deep/nested/subtitle/toolbox-app.json");
+  await expect(manifest.json()).resolves.toMatchObject({
+    id: "de.add-ideas.subtitle-tools",
+    version: "0.1.0",
+    entry: "./",
+    privacy: { processing: "local", telemetry: false },
+  });
+});

tests/components/app.test.tsx

@@ -0,0 +1,18 @@
+import { render, screen } from "@testing-library/react";
+import { describe, expect, it, vi } from "vitest";
+import { App } from "../../src/App";
+
+describe("Subtitle Tools", () => {
+  it("renders the local workbench and standard shell", async () => {
+    vi.stubGlobal(
+      "fetch",
+      vi.fn(async () => new Response("Not found", { status: 404 })),
+    );
+    render(<App />);
+    expect(
+      await screen.findByRole("heading", { name: "Subtitle Tools" }),
+    ).toBeVisible();
+    expect(await screen.findByText("No network requests")).toBeVisible();
+    expect(screen.getByRole("tab", { name: "Timing" })).toBeVisible();
+  });
+});

tests/subtitle/model.test.ts

@@ -0,0 +1,97 @@
+import { describe, expect, it } from "vitest";
+import {
+  compareDocuments,
+  convertFrameRate,
+  parseSubtitle,
+  serializeSubtitle,
+  transformTiming,
+  validateDocument,
+} from "../../src/subtitle/model";
+
+const SRT = `1\r\n00:00:01,000 --> 00:00:02,500\r\nHello world\r\n\r\n2\r\n00:00:02,400 --> 00:00:04,000\r\nSecond cue\r\n`;
+
+describe("subtitle model", () => {
+  it("parses SRT and reports overlap", () => {
+    const document = parseSubtitle(SRT);
+    expect(document.format).toBe("srt");
+    expect(document.cues).toHaveLength(2);
+    expect(document.cues[0]).toMatchObject({
+      startMs: 1000,
+      endMs: 2500,
+      text: "Hello world",
+    });
+    expect(
+      validateDocument(document).some((issue) => issue.code === "overlap"),
+    ).toBe(true);
+  });
+
+  it("round-trips WebVTT identifiers, settings and notes", () => {
+    const source = `WEBVTT - sample\n\nNOTE inert note\nline two\n\nc1\n00:00:01.000 --> 00:00:02.000 align:start\n<v Ada>Hello</v>\n`;
+    const document = parseSubtitle(source);
+    expect(document).toMatchObject({ format: "vtt" });
+    expect(document.cues[0]).toMatchObject({
+      id: "c1",
+      settings: "align:start",
+    });
+    const serialized = serializeSubtitle(document, "vtt");
+    expect(serialized).toContain("NOTE inert note");
+    expect(serialized).toContain("align:start");
+    expect(parseSubtitle(serialized).cues[0]?.text).toBe("<v Ada>Hello</v>");
+  });
+
+  it("parses ASS dialogue fields containing commas and preserves styles", () => {
+    const source = `[Script Info]\nScriptType: v4.00+\n\n[V4+ Styles]\nFormat: Name, Fontname\nStyle: Loud,Arial\n\n[Events]\nFormat: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text\nDialogue: 0,0:00:01.00,0:00:03.25,Loud,Ada,0,0,0,,Hello, world\\Nagain\n`;
+    const document = parseSubtitle(source);
+    expect(document.format).toBe("ass");
+    expect(document.cues[0]).toMatchObject({
+      startMs: 1000,
+      endMs: 3250,
+      text: "Hello, world\nagain",
+    });
+    const serialized = serializeSubtitle(document, "ass");
+    expect(serialized).toContain("Dialogue: 0,0:00:01.00,0:00:03.25,Loud");
+    expect(serialized).toContain("Hello, world\\Nagain");
+  });
+
+  it("writes an Events format even when only a style format was supplied", () => {
+    const source = `[Script Info]\nScriptType: v4.00+\n\n[V4+ Styles]\nFormat: Name, Fontname\nStyle: Default,Arial\n\n[Events]\nDialogue: 0,0:00:01.00,0:00:02.00,Default,,0,0,0,,Hello\n`;
+    const serialized = serializeSubtitle(parseSubtitle(source), "ass");
+    expect(serialized).toMatch(
+      /\[Events\]\nFormat: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text/u,
+    );
+    expect(parseSubtitle(serialized).cues).toHaveLength(1);
+  });
+
+  it("converts formats and timing without silently creating negatives", () => {
+    const document = parseSubtitle(SRT);
+    expect(() => transformTiming(document, { shiftMs: -2000 })).toThrow(
+      /negative/u,
+    );
+    const clamped = transformTiming(document, {
+      shiftMs: -2000,
+      clampToZero: true,
+    });
+    expect(clamped.cues[0]?.startMs).toBe(0);
+    const converted = convertFrameRate(document, 25, 50);
+    expect(converted.cues[0]).toMatchObject({ startMs: 500, endMs: 1250 });
+    expect(serializeSubtitle(converted, "vtt")).toMatch(/^WEBVTT/u);
+  });
+
+  it("compares revisions deterministically", () => {
+    const before = parseSubtitle(SRT);
+    const after = parseSubtitle(SRT.replace("Hello world", "Hello again"));
+    expect(compareDocuments(before, after)).toMatchObject([
+      { index: 0, kind: "text" },
+    ]);
+  });
+
+  it("rejects pathological input bounds", () => {
+    expect(() => parseSubtitle("x".repeat(4_000_001))).toThrow(/4,000,000/u);
+    expect(() =>
+      parseSubtitle(`1\n00:61:00,000 --> 00:61:01,000\nBad`),
+    ).not.toThrow();
+    expect(
+      parseSubtitle(`1\n00:61:00,000 --> 00:61:01,000\nBad`).cues,
+    ).toHaveLength(0);
+  });
+});

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"],
+    "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/**"],
+  },
+});