README.md

dsh-editor (alpha.14)

A CodeMirror 6 tab type for the pack's right bar (dsh-rightbar) that opens text files editable. It registers the id dsh-editor and the kind editor through the bar's own tab-type registry, with its body and chip title in the keyed sidebar.right.pane.tab / sidebar.right.pane.tab.title seats and a guide entry at order: 20 for the "+" control. It is text-only (strict UTF-8, binary refused), starts blank documents, and writes through authenticated Node routes because remote.workspaceFiles exposes no mutation operation.

What it adds

• Text files open editable. patterns: ['dsh-resource://file/**'] in the extension band, which outranks every shipped viewer, with a canOpen that vetoes what a text editor has nothing to add to (.html, images, PDF, office/archive/media, binary) and paths outside the session workspace, including the session-less absolute/… form.
• Markdown is claimed too (.md, .markdown, .mdown). The toolbar's Preview button reads the shipped document preview's kind out of the tab registry (never hardcoded) and calls ctx.get('sidebarRight').openResource(address, { kind, replaceTab }), so Edit ⇄ Preview is one tab on the same file. It is refused while the document has unsaved edits, because the preview reads from disk.
• "+" → Editor opens a blank document. Save (or Ctrl/Cmd+S) asks for the file name with its extension through the shared dsh-modal modals service and creates it in the conversation's workspace folder; the parent folder must already exist and a taken name answers 409 EXISTS inside the dialog.
• Saving is optimistic and atomic. The panel PUTs the whole document with the mtime/size it opened with, and a file that moved on disk offers Reload / Save anyway rather than a silent clobber. Unsaved work is lost on tab close or restart.
• The language map. Every extension is mapped in languageExtensionFor and every lookup goes through a guard, so an engine older than the bundle opens the document unhighlighted rather than killing the tab. Lezer factories (function shape) via engineLanguage cover javascript (js/mjs/cjs/jsx/ts/tsx), json (json/jsonc), markdown (md/markdown/mdown), python (py/pyw), html (html/htm/xhtml), css and yaml (yaml/yml). CM5-style StreamParser objects (found by their token(), via engineStreamMode) cover shell (sh/bash/zsh/ksh/dash), powerShell (ps1/psm1/psd1), batch (bat/cmd, from the pack's own vendor/batch-mode.js), rust (rs) and toml (toml) from the vendored @codemirror/legacy-modes. Each returns null plus one console warning naming the missing factory and the rebuild command, so languageExtensionFor has no direct CM.<name>(...) call.
• The palette follows the app's theme: oneDark only while the app is dark, a token-driven transparent light layer otherwise, switched live through a CodeMirror Compartment reconfigured off ctx.get('theme') / theme/change, with body[data-ds-dark-theme] as the fallback. Both theme services are resolved lazily.
• The rendered Markdown body is shadowed. The keyed sidebar.right.tab.document slot is registered at priority: -10 (lowest renders), so only the page body is this package's while the shipped preview keeps its chrome; uninstalling brings the shipped body back. That body carries an Edit pill back to the editor and undoes what the preview's plain-text scrollport imposes (white-space:pre and the mono stack).
• Authored HTML is rendered, and images resolve (alpha.14). The shipped Markdown primitive draws raw HTML as literal text and only resolves an image when it is handed a pathImages vocabulary, so a README with a centred badge row, a <table>, <details> or ![shot](docs/shot.png) showed its own markup and broken pictures. The shadow body now parses block-level HTML itself and rebuilds it as React elements over an allowlist — nothing becomes an HTML string, so there is no innerHTML to poison and no attribute spelling that can smuggle an onerror= through: <script>, <style>, <iframe>, <object>, <embed>, form controls and SVG are dropped with their contents, every on* attribute is refused, a javascript: URL is refused, and an unknown structural tag loses the tag but keeps its children. Images resolve through the harness's authenticated /api/file?path= route, against the document's own absolute path (read off the resource, the same way the shipped body does), for a Markdown image and for an <img src> inside authored HTML alike; an absolute http(s) image is left exactly as written, and a source the route cannot vouch for degrades to its alt text. A fenced code block is never split, so an example's <div> still renders as code.

How it plugs in

Route	What it does
GET /api/dsh-editor/file?session=<id>&path=<rel>	read one text file (strict UTF-8, no NUL, ≤ 2 MiB; HEAD answers headers and no body)
PUT /api/dsh-editor/file	save {session, path, text, expected?: {mtimeMs, size}} - atomic temp+rename, 409 when the file moved on disk
PUT /api/dsh-editor/file with {create: true}	create a file: the parent must exist inside the workspace and is realpath-checked, the target must not exist - 409 EXISTS, create-exclusive
GET /api/dsh-editor/vendor?v=<bundle version>	the vendored CodeMirror 6 classic bundle (window.DSHEditorCM), fetched lazily on first open

The workspace root is resolved host-side (live session header first, session persistence second, typed NO_WORKSPACE otherwise) from the session id the tab's address already carries, dsh-resource://file/session/<sessionId>/<path>; the client never names a root. The engine request is version-qualified, and the route answers cache-control: no-cache over a content-hash ETag, re-stating the artifact per request, so a rebuild needs no restart.

Limits

• Text only: strict UTF-8, no NUL, ≤ 2 MiB read and save.
• No folder browser and no binary editing; canOpen refuses any address outside a session workspace.
• Create-on-save, never overwrite: a create is create-exclusive.
• Unsaved work is lost on tab close or restart.
• The HTML allowlist draws block-level authored markup: a line that starts with an allowed tag opens an HTML run, so <kbd> in the middle of a prose sentence is still the shipped renderer's literal text. An unclosed block with no closing line anywhere below it stays Markdown rather than swallowing every section after it.
• A container holds Markdown and HTML alike: <div align="center"> on its own line, a blank line, then # Title draws the title as an h1 inside the div, which is what GitHub does (CommonMark ends an HTML block at the blank line, and the browser nests what follows in the element still open). Only one element left open, closed on a line of its own, becomes a container; anything else - several elements open at once, a dropped tag like <svg>, no closing line - keeps the conservative fallback and renders as literal Markdown.

Verify

node scripts/checks/check-client-bundles.mjs
node scripts/checks/check-node-routes.mjs

check-client-bundles.mjs drives the browser half through a real React runtime: the registration and guide order, the seats, the shadowed document body, the language-map guard, the Preview hand-off, the authored-HTML splitter (fenced examples excluded, an unclosed block left as Markdown, a div holding a heading drawn as a container), the allowlist (a <script> dropped with its contents, onerror and javascript: refused, no HTML string injected) and the image resolver (a relative destination rewritten to /api/file?path=, an http one left alone, an unresolvable one left as alt text). It also renders this repository's own README header and asserts that the title reaches the Markdown renderer as a heading inside the centred div, because that is the first thing a reader sees in the pane. check-node-routes.mjs drives the routes against a scratch workspace.

Install

The launcher (scripts\setup\install.bat / ./scripts/setup/install.sh) auto-discovers the package as a standard dsh.bundle, and the uninstall twins do the same. It is a live link in the web profile, so code edits need a restart of npx @deepseek-ai/dsh web plus a hard refresh.