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AGENTS.md

Instruction set for AI agents working on Draftly. CLAUDE.md is a symlink to this file — edit this one.

What Draftly is

A pluggable markdown editor and static previewer built on CodeMirror 6, published to npm as draftly. The repo is a Turborepo monorepo managed with Bun.

Two ideas carry the whole design:

  1. The document is always plain markdown text. There is no secondary document model. Richness is CodeMirror decorations layered on top, which retract when the cursor enters a construct to reveal the raw syntax.
  2. A plugin owns a markdown feature end to end — its parser extension, editor decorations, keymap, theme, and its static HTML renderer. One class, one feature, both surfaces. This is what makes editor/preview parity structural rather than aspirational.

Read artifacts/architecture/overview.md before your first substantive change.

Start every session here

Before touching any code, in this order:

  1. artifacts/memory.md — durable facts, traps that have cost time, the developer's preferences, and open questions. Non-negotiable; it exists precisely because the codebase's sharpest edges are invisible from a quick read.
  2. artifacts/tasks/index.md — what is in flight, what is blocked, what has shipped.
  3. artifacts/architecture/index.md — pick the documents relevant to your task from the "open it when" column. Do not read all of them by default.
  4. artifacts/repository-map.md — if you need to locate something.

Then load the relevant skill:

Working on Read first
Decorations, view plugins, facets, extensions, keymaps, widgets .agents/skills/codemirror/ — including references/architecture.md and references/extensions.md
turbo.json, workspaces, caching, CI, filtering .agents/skills/turborepo/ — including the topic file under references/

Both skills have references/ subdirectories with far more depth than their SKILL.md. Read the specific topic file, not just the summary.

Non-negotiable, additionally:

  • Read artifacts/architecture/plugin-table.md before any edit to plugins/table-plugin.ts. Several of its mechanisms look like accidents and are not.

Working rules

1. Ask when something is suspicious or conflicting

If the code contradicts an architecture document, a README claim, or a comment — stop and ask the developer. Do not silently pick one and "fix" the other. The document may be describing intent the code has drifted from, and that gap is information.

Six such conflicts are already logged in artifacts/memory.md. Add to that table rather than resolving unilaterally.

2. Clean architecture, strictly

  • One feature, one plugin file. Cross-plugin coupling is the thing this architecture exists to prevent.
  • editor/ never imports plugins/. Plugins are injected by the caller. Preserving this keeps the library tree-shakeable.
  • Keep pure logic pure. Text utilities, parsing, and formatting must not acquire a CodeMirror dependency. This is why the table plugin's lowest layers are testable.
  • Layer boundaries are real. Identify the layer you are editing and stay inside it.
  • ~500 LOC is the plugin ceiling. Split into a directory before exceeding it. Two files already exceed it and are tracked as debt, not precedent.

3. Modular by default

Prefer a new small module over growing an existing file. Prefer a pure function over a method that reaches into state. Prefer injecting a dependency over importing a singleton.

4. JSDoc, strictly

Every exported symbol — class, function, type, interface, constant — carries JSDoc. Follow the existing style in editor/plugin.ts and editor/draftly.ts.

/**
 * Build heading decorations by iterating the syntax tree.
 *
 * @param ctx - Decoration context with view and decoration array
 * @returns Nothing; decorations are pushed into `ctx.decorations`
 */
  • Document why, not what the code already says.
  • @param for every parameter, @returns where non-void, @example on public API.
  • Non-obvious constants get a JSDoc line explaining the choice — especially decorationPriority values.
  • Match the surrounding file's comment density. Do not add narration to code that reads clearly on its own.

5. Git history stays organised

Commit only correlated edits. Never everything at once.

  • One logical change per commit. A refactor and a bug fix are two commits, even in the same file.
  • Code and its artifact updates belong in the same commit — a doc that lands a commit later is a doc that will be forgotten.
  • Format: type(scope): Description — matching the existing history.
    • Types: feat, fix, refactor, docs, chore
    • Scopes: draftly, web, ui, or omit for repo-wide
    • Examples: feat(draftly): Emoji Plugin, fix(draftly): Ignore tailing non-table line
  • Do commit as you go. Do not stage a large change and commit it all at once.
  • Do Not branch off master unless told; do not push unless asked.
  • Add a changeset (bun changeset) for any user-facing library change.

6. Keep artifacts current

After you… Update
Learn something non-obvious, or get corrected artifacts/memory.md
Start, advance, or finish work artifacts/tasks/ + its index
Change structure, contracts, or mechanisms the relevant artifacts/architecture/*.md
Add or move a directory artifacts/repository-map.md

Update the front-matter Last verified line and commit hash when you revise a document.

Write to memory what a future agent could not cheaply re-derive: constraints, "why" decisions, dead ends, developer preferences. Do not write what the code or git history already says.

7. Verify before claiming done

There is no test suite (tracked as T-001). Verification is manual:

bun dev                                      # playground with hot-reloaded library
cd packages/draftly && bun run typecheck     # tsc --noEmit
bun run lint                                 # biome check — read-only, fails on errors
bun run check:fix                            # biome check --write — lint fixes + format

Lint and format are Biome, not ESLint/Prettier. lineWidth is 120. Shared presets live in packages/biome-config; each workspace's biome.json extends base plus its framework layer. Suppress with // biome-ignore lint/<group>/<rule>: <reason> — the reason is mandatory, and the comment goes above the line the diagnostic anchors to.

For a library change, work through the 8-step playground checklist in artifacts/architecture/web-playground.md. The short version: check the editor pane, the preview pane, the HTML pane, and the CSS pane; toggle your plugin off; toggle dark/light.

Report honestly. If you could not verify something, say so.

Traps that have already cost time

The full list is in artifacts/memory.md. The ones that bite most:

  • requiredNodes is the preview dispatch key. A plugin with renderToHTML() but an empty requiredNodes is silently dead in preview. First thing to check when something renders in the editor but not the preview.
  • Never walk the tree unbounded in buildDecorations. Use ctx.iterateVisible; syntaxTree(view.state).iterate costs O(document) on every keystroke and every cursor move. Fixed library-wide in C-016; the two TablePlugin facet computations are the only deliberate exceptions.
  • buildDecorations errors are swallowed only while the tree is still parsing. Genuine errors are reported via DraftlyConfig.onPluginError or a dev-only console.error, deduplicated per plugin and message. If a decoration does not appear and nothing was logged, nothing threw — the bug is in the logic.
  • Decoration.replace must never span a newline. Clamp to line.to. Canonical example: heading-plugin.ts:104.
  • Release view-scoped state in onViewDestroy. A plugin instance outlives the view that used it; EditorView has no public "destroyed" flag, so guard in-flight async work with a WeakSet as table-plugin.ts does. onUnregister is deprecated and never called.
  • Build plugins with createEssentialPlugins() / createAllPlugins(), one set per editor. Sharing one set across two editors makes them overwrite each other's config and cancel each other's table normalization (C-026). The old shared-singleton essentialPlugins / allPlugins arrays were removed in C-028.
  • Never import a heavy plugin from the plugins barrel. MermaidPlugin, MathPlugin and EmojiPlugin live at draftly/plugins/{mermaid,math,emoji}, and createAllPlugins() lives at draftly/plugins/all. tsup concatenates everything reachable from an entry point into one chunk, and a chunk's top-level import mermaid runs whenever any binding in it is used — so one barrel re-export puts 5.3 MB back on every consumer (C-027). Adding a plugin with a heavy dependency means adding an entry point, not a barrel line.
  • A widget's eq() must compare content only. Comparing from/to means it is never reused; use resolveWidgetRange() when a handler needs the range.
  • Never dispatch a transaction from buildDecorations or update(). Use the schedule* deferred pattern from table-plugin.ts, and annotate self-dispatches.
  • ThemeEnum.AUTO does not detect the system theme. It applies the default layer only.
  • sanitize() is a no-op on the server. DOMPurify needs a DOM; sanitize: true gives no SSR protection.
  • ctx.sanitize() does nothing useful for an attribute value. It parses an HTML fragment; a bare string is not one, so it comes back unchanged — quotes included. Escape attributes with escapeHtml; sanitize only real fragments.
  • wrapperClass must match between preview() and generateCSS(), or output is unstyled.
  • Bun only. pnpm install or npm install creates a conflicting lockfile.
  • CodeMirror packages stay external/peer. Two copies of @codemirror/state breaks facet identity.
  • Bump VERSION in apps/web/app/playground/page.tsx after editing seed markdown in app/data/md/, or returning users keep the cached copy.

Common tasks

Add a plugin

  1. Read artifacts/architecture/plugin-system.md.
  2. Create packages/draftly/src/plugins/<feature>-plugin.ts.
  3. Extend DecorationPlugin (or DraftlyPlugin if render-only). Set name, version, decorationPriority (pick within an existing band), and requiredNodes. A higher decorationPriority wins on both surfaces — it layers on top in the editor and is consulted first in preview. Two plugins on one node at equal priority warn in dev.
  4. Hoist Decoration instances to module scope — allocating per keystroke is a real cost. Walk the tree with ctx.iterateVisible, never syntaxTree(view.state).iterate — the context carries the viewport bounds, and an unbounded walk costs O(document) on every cursor movement.
  5. In renderToHTML, read class names off the decoration specs (someDecoration.spec.class) rather than retyping them. This is the mechanism that enforces parity.
  6. Guard every hiding decoration with ctx.selectionOverlapsRange(from, to).
  7. A widget's eq() compares content, never from/to — positions shift on any edit above it, so the widget would be rebuilt every keystroke. Resolve the range at event time with resolveWidgetRange() from draftly/lib.
  8. Escape attribute values, sanitize fragments, and run URLs through safeUrl(). ctx.sanitize() is for a blob of HTML that stays markup; anything going into a quoted attribute or rendered as text gets escapeHtml from draftly/lib. Apply safeUrl() on both surfaces, not just preview.
  9. Do not hold view-scoped state on the plugin. Anything derived from a specific EditorView — a pending timer, a scheduled microtask's target, the view itself — keys off the view (a WeakMap or a StateField) or is released in onViewDestroy. One instance belongs to one editor, and a retained view retains its whole document. _config/_context are the sanctioned exception: written once at composition time.
  10. Put the theme at the bottom of the file via createTheme().
  11. Register in plugins/index.ts — named export and the createEssentialPlugins() factory. If the plugin pulls a heavy third-party dependency, it goes in its own entry point instead (src/plugins/<name>.ts, plus tsup.config.ts and the exports map) and is added to createAllPlugins() in plugins/all.ts — never to the barrel.
  12. Add a row to artifacts/architecture/plugins-catalog.md.
  13. Extend apps/web/app/data/md/walkthrough.ts and bump VERSION.
  14. Verify both surfaces in the playground.

Change the editor core

Only for feature-agnostic changes — the test is whether two unrelated plugins would both want it. Read artifacts/architecture/editor-core.md first. Anything markdown-feature-specific is a plugin, not core.

Change static output

Usually a plugin's renderToHTML(). Read artifacts/architecture/preview-pipeline.md before touching preview/, especially syntax-theme.ts, which depends on undocumented CodeMirror internals.

Boundaries

  • Do commit as you go. Do not stage a large change and commit it all at once.
  • Do not push, publish, or release unless asked.
  • Do not change the public API surface without flagging it — draftly is published and consumers depend on it.
  • Do not add a runtime dependency to packages/draftly without asking; bundle size is a design constraint (it is why the heavy plugins sit behind their own entry points).
  • Do not move CodeMirror packages out of peer/external.
  • Do not put library features in apps/web. The playground is a consumer, exactly like an external user's app. Shared helpers belong in packages/draftly/src/lib/.
  • Do not resolve a conflict between docs and code on your own — ask.