fix(editor): prevent XSS in details summary previews

[bobleer]

Summary

Fix XSS in the Markdown editor’s source-backed details summary preview. Sanitize descendants before unwrapping unsupported HTML elements, reject foreign namespaces, and validate link/image protocols using browser URL parsing and explicit allowlists. Without a DOM, return escaped text instead of raw HTML.

Type and Areas

Type: Bug fix (security)

Areas: Web UI / Markdown editor, browser regression tests

Motivation / Impact

The previous traversal could retain event handlers inside an unsupported wrapper. Its URL prefix check also missed control characters normalized by the browser. These paths could execute document-controlled JavaScript when rendering or interacting with a details summary, including live source-block edits.

The fix preserves supported formatting, links, image metadata, and original Markdown bytes. Regression coverage exercises both initial document loading and live editing; the initial parser and source-backed preview use different paths.

Verification

• Focused editor/Markdown unit and DOM suite: 151 passed, including 39 new sanitizer cases:

pnpm --dir src/web-ui run test:run src/tools/editor/meditor/utils/sanitizeDetailsSummaryHtml.test.ts src/tools/editor/components/MarkdownEditor.test.tsx src/tools/editor/meditor/components/MEditor.test.tsx src/tools/editor/meditor/utils/tiptapMarkdown.test.ts src/tools/editor/meditor/utils/embeddedSource.test.ts src/tools/editor/meditor/utils/markdownFrontmatter.test.ts src/tools/editor/meditor/components/Preview.test.tsx src/tools/editor/meditor/utils/loadLocalImages.test.ts src/infrastructure/markdown/rehypeSourceRange.test.ts src/infrastructure/markdown/MarkdownRenderer.test.tsx

• pnpm run check:web: passed.
• pnpm --dir src/web-ui exec tsc --noEmit: passed on the final implementation.
• pnpm --dir src/web-ui exec vitest run src/tools/editor/meditor/utils/sanitizeDetailsSummaryHtml.test.ts: 39 passed after the final traversal adjustment.
• pnpm --dir tests/e2e exec wdio run ./config/wdio.markdown-browser.ts: the 10 existing browser cases passed. After correcting the new test fixture and interaction steps, pnpm --dir tests/e2e exec wdio run ./config/wdio.markdown-browser.ts --mochaOpts.grep 'sanitizes loaded' passed the new security case, including no script execution and exact save/source round-trip preservation.
• Browser verification used Node 24 and Chrome 152; local Node 26 failed to create a WebDriver session. The incomplete local driver cache was repaired before the successful runs.
• Focused sanitizer ESLint and git diff --check: passed.

Reviewer Notes

AI-assisted implementation; testing level: focused automated unit/DOM and real-browser verification. No native Tauri, live SSH workspace, Remote Connect, Peer Device Mode, or Detached Dispatch execution was tested. Relative and supported host/workspace URLs are covered as sanitizer inputs; that is not live remote-transport coverage.

No server configuration, dependency versions, persisted schemas, or user-facing strings change. No migration is required.

Checklist

• This PR is focused and does not include secrets, temporary prompts, generated scratch files, or unrelated artifacts.
• Relevant verification is recorded above, or skipped checks are explained.
• User-facing strings, docs, and locales are updated where applicable (no changes required).