feat: URL imports via into.md - @https://example.com syntax

Summary

Extend the existing file import syntax (@./path.md) to support URL imports that automatically convert web pages to markdown using into.md.

Proposed Syntax

# In your agent file body:
@https://docs.example.com/api-reference

# Or with tilde-style for saved bookmarks:
@~/bookmarks/react-docs.url

How It Would Work

1. Detect URLs in @ imports (pattern: @https?://...)
2. Fetch the URL through into.md API to get clean markdown
3. Inline the result just like local file imports
4. Support recursive imports if the converted markdown contains more @ references

Use Cases

• Documentation as Context: @https://react.dev/reference/react/useState to give the agent API docs
• Research Tasks: Import blog posts, articles, or technical specs directly
• Dynamic Agents: Agent files that always have fresh documentation context

Implementation Notes

• Add URL pattern matching in src/imports.ts
• Create into.md API client (likely just fetch to their endpoint)
• Consider caching fetched URLs to avoid repeated API calls
• Error handling for offline/unreachable URLs

Questions for Discussion

• Should we cache converted pages? If so, for how long?
• Rate limiting considerations for into.md API?
• Should this be opt-in via a flag or enabled by default?

Related

This is part of exploring into.md integration opportunities.

Start in src/imports.ts and compare the existing @./path.md handling with the proposed URL and ~/bookmarks/react-docs.url forms. Resolve the caching, rate-limiting, opt-in, and error-handling questions before implementation. Done means URL content is converted through into.md, inlined like local imports, and recursive imports continue to work.