AI Adapters: Features and problems discovered while prototyping - #5547

Exactly what the title says.

UPDATE: Last moment contract changes and features

• access: 'read' | 'write' | 'agent' replaced with kind: 'query' | 'action' | 'agent' (clear intent)
• The core engine now supports turn suspension. This was a real blocker. Some tools require user input or some kind of acknowledgment - it became quickly clear that not offering that core feature leads to awful hacks (tools internal blocking via timeout and long Promises). Tools can now throw aiInput that suspends the turn. Resume is possible - the caller is responsible for passing the transcript and resume as usual. The implementation was tested with a prototype.
• The change above is deliberate contradiction to the original rule "core doesn't know about flows/transcripts/etc, keep it dead simple". A minimal knowledge is required so that callers have freedom to implement any feature they'd need.