…trion

Documents how Orchestrion's AsyncIterator kind works:
- Creates TWO channels: base + _next
- Requires TWO plugins to handle both channels
- Main plugin creates span
- Next plugin finishes span when result.done === true

This pattern is needed for async generator/iterator methods like
Pregel.stream() that return Promise<IterableReadableStream>.

Without this documentation, agents wouldn't know to:
1. Use kind: 'AsyncIterator' in the config
2. Create both plugins
3. Check result.done in asyncEnd

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>

Moved detailed AsyncIterator pattern documentation from orchestrion.md
to a dedicated async-iterator-pattern.md reference file for better
organization and emphasis.

Changes:
1. Created async-iterator-pattern.md with comprehensive AsyncIterator guide
   - When to use AsyncIterator kind
   - Two-channel pattern explanation
   - Complete two-plugin pattern with examples
   - Common mistakes and how to avoid them
   - Full LangGraph example
   - Testing strategies
   - Implementation checklist

2. Updated orchestrion.md with high-level overview and prominent link
   - Replaced 60+ line detailed section with concise summary
   - Added CRITICAL warning that AsyncIterator requires TWO plugins
   - Added REQUIRED READING directive linking to full reference
   - Updated table entry with link to reference

This ensures agents:
- See clear warning that AsyncIterator is special/complex
- Are directed to read the complete reference before implementing
- Have all implementation details in one dedicated document
- Don't miss critical requirements (two plugins, _next suffix, etc.)

Co-Authored-By: Claude Sonnet 4.5 <[email protected]>