feat: add Yjs-based rich markdown file type to yjsfs

[K-Mistele]

PR Description

Ticket | Artifacts | Task

What problems was I solving

This PR enables AI agents to collaboratively edit rich markdown documents using TipTap/Yjs. Previously, agents could only work with plain text files via string-based edits. Now agents can:

• Edit rich text documents with proper structural awareness (headings, lists, code blocks, etc.)
• Make semantic edits using a sandboxed QuickJS runtime that mutates the Yjs document directly
• Collaborate with humans in real-time via Durable Streams with proper presence/cursor isolation

Success is measured by: agents successfully editing rich artifacts without corrupting document structure, and multiple TipTap editors syncing correctly via one Yjs document.

What user-facing changes did I ship

• packages/yjs-rich-markdown - New package for rich markdown artifacts with TipTap/Yjs bindings
• packages/quickjs-exec - Sandboxed QuickJS execution with console capture for agent-generated code
• examples/yjs-rich-markdown-demo - TanStack Router demo app for testing collaboration and presence
• CLI agent for rich markdown editing (bun run --cwd packages/yjs-rich-markdown agent)

How I implemented it

Core Package: packages/yjs-rich-markdown

• src/artifact-store.ts - Path-keyed artifact registry backed by Y.Map<ArtifactMetadata> in one Y.Doc
• src/yxml-proxy.ts - YXmlProxyBindings providing a DSL for agents to navigate and mutate YXml trees (root, children, get, append, prepend, insertBefore, insertAfter, insertText, deleteText, splitText, wrapTextRange, wrap, remove, setAttribute, etc.)
• src/yxml-proxy-prompt.ts - YXML_PROXY_AGENT_PROMPT with console.log diagnostic guidance and the full bindings DSL contract
• src/markdown.ts - Markdown bridge via TipTap's MarkdownManager for readArtifactMarkdown/writeArtifactMarkdown
• src/tiptap-bindings.ts - TipTap collaboration binding helpers for both fragment and field modes

Agent Tools

• src/tools/codemode-yxml-editor.ts - QuickJS code-mode edit tool returning captured console output and execution result
• src/tools/edit-rich-markdown.ts - EditTool interface implementation delegating to apply sub-agent
• src/agents/yxml-fragment-editor.ts - Apply sub-agent receiving Markdown edit intent plus current XML snapshot

CLI Agent

• src/cli/rich-markdown-agent.ts - Full CLI agent with list_artifacts, read_artifact, write_artifact, edit, and inspect_artifact tools, connects to Durable Streams, supports --interactive, --prompt, --verbose, --stream flags

QuickJS Sandbox: packages/quickjs-exec

• src/index.ts - QuickJsSyncExec and QuickJsAsyncExec with runWithConsole API, structured error capture via QuickJsExecutionError with code frame rendering

Demo App: examples/yjs-rich-markdown-demo

• TanStack Router React app with routes: /, /single, /compare, /same-doc, /awareness
• Local Durable Streams server at server/index.ts
• TipTap v3 (3.22.5) with collaboration extensions

Deviations from the plan

Implemented as planned

• Console capture via runWithConsole with globalThis.__quickjsConsoleLogs pattern
• YXmlProxyBindings full binding set matching the DSL specification
• YXML_PROXY_AGENT_PROMPT with diagnostic guidance
• Apply sub-agent architecture with QuickJS code-mode tool
• RichMarkdownArtifactStore path-keyed registry
• Markdown bridge via MarkdownManager
• CLI agent with full tool set
• Demo app with TanStack Router
• yjs-fs kept unaware of rich artifacts per design decision

Deviations/surprises

• QuickJsRunWithConsoleResult is a discriminated union: Plan specified { value, console } but implementation uses { ok: true, value, console } | { ok: false, error, console } - an improvement that bakes in structured error capture
• Errors return structured result instead of rethrowing: Callers get { ok: false, error, console } instead of thrown exceptions
• QuickJsExecutionError with code frame added: Not in plan; adds source code context rendering for debugging generated code failures
• TipTap v3 used instead of v2: Upgraded to 3.22.5 for @tiptap/markdown support
• Demo uses @tiptap/extension-collaboration-caret: The TipTap v3 rename of @tiptap/extension-collaboration-cursor

Additions not in plan

• QuickJsExecutionError class with codeFrame source context rendering
• readArtifact for raw XML output (supports inspect_artifact tool)
• test/yxml-proxy-prompt-examples.test.ts - validates prompt examples are executable
• test/yxml-invalid-structures.test.ts - documents lossy Markdown serialization
• done and i_am_stuck tools in apply sub-agent
• awaitSubAgent integration for streaming sub-agent output

Items planned but not implemented

• Phases 8-11 (comment mark anchoring, durable comment threads, yjs-fs integration direction) - deferred
• /comments demo route - not created
• Durable Streams connected integration tests - require live server infrastructure
• awareness-scope.test.ts, durable-streams-sync.test.ts - test files not created (functionality verified via demo app)

How to verify it

Manual Testing

# Set up worktree
git worktree add -b rich-markdown ~/wt/agentlayer/rich-markdown origin/rich-markdown
cd ~/wt/agentlayer/rich-markdown
bun install

# Run demo app
cd examples/yjs-rich-markdown-demo
bun run dev
# Open http://localhost:5173 in browser
# Test routes: /, /single, /compare, /same-doc, /awareness

• Create/edit artifacts in demo app
• Open multiple browser tabs and verify real-time sync
• Verify cursor presence isolation across different artifacts
• Test markdown export panel

CLI Agent Testing

cd packages/yjs-rich-markdown
export ANTHROPIC_API_KEY=your_key
bun run agent --interactive

• Use list_artifacts to see artifacts
• Use read_artifact to read content
• Use edit to make semantic edits
• Verify edits sync to demo app

Automated Tests

bun run typecheck
bun run test

Description for the changelog

Add Yjs-based rich markdown file type with TipTap collaboration, sandboxed QuickJS agent editing via YXml proxy bindings, and CLI agent for rich artifact management.