feat(editor): add Document Outline and configurable Copy TOC

[ThisIs-Developer]

Adds a resizable Document Outline for navigating Markdown and copying a table of contents without leaving Editor, Preview, or Split mode.

• Place toolbar controls immediately after Emoji in the order Emoji | Find & Replace | Full Screen | Document Outline, using the bundled book-text icon and existing button styles.
• Show an automatically updated H1–H6 tree with parent chevrons, hierarchy lines, Collapse/Expand All, wrapping titles, active-section highlighting, and section navigation.
• Add Copy TOC and a compact settings drawer. Default to H2–H4; allow H1–H6 limits, bulleted or hierarchical numbered links, plain text, optional normalization of skipped levels, and a collapsible details wrapper. Disabled copy and an empty-range message handle documents without matching headings.
• Generate the TOC from the current Markdown AST, independently of preview completion or collapsed branches. Exclude YAML metadata and code examples; preserve plain heading text. Use GitHub-compatible Unicode slugs and assign duplicate suffixes across all headings before filtering. Share heading IDs with the main preview and worker, so pasted links reach the correct section.
• Reuse Find & Replace header, field, and button styles. Keep text-only header titles and matching 340px defaults; share the File Sidebar resize controls for both panels. Header buttons highlight only on hover or while pressed.
• Include translations, offline/desktop assets, dependency licenses, inline API/slug documentation, and updated README, changelog, and wiki.

The pure generator is in src/document-toc.mjs; npm run build:toc creates the committed browser/worker bundle. Symbol-only headings use the documented heading fallback; raw HTML heading blocks are outside the AST-generated TOC. Existing headings named “Table of Contents” are included when they fall within the selected depth range.

Validation:

• npm run test:unit: 22 tests covering nesting, depth, formatting/entities, code and front matter, collisions and per-document reset, output modes, Unicode/emoji, skipped levels, wrappers, empty input, and shared preview anchors.
• 56 distinct Chromium checks passed across Copy TOC, Document Outline, formatting regressions, and rich-content suites, including focused reruns. Coverage includes Editor/Preview/Split at desktop, tablet, mobile, and narrow widths; long H1–H6 headings; worker rendering; keyboard controls; neutral focus styling; and translated settings.
• npm run build and git diff --check passed; desktop resources regenerated.
• The supplied example document produced 14 default TOC entries from 15 headings. Emoji leading-hyphen behavior was checked against GitHub-rendered outlines; source references are in the unit tests.
  On screens up to 767px, Document Outline uses width: calc(80% - 24px) to leave more of the document visible. This CSS-only adjustment was not tested, as requested; the validation above covers the preceding implementation.

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Project	Deployment	Actions	Updated
markdown-viwer	Ready	Preview	Sep 27, 2026 9:46am UTC

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