feat: Add Recall system for periodic knowledge summarization

[spoons-and-mirrors]

Summary

• Added a new Recall system alongside the existing Nudge mechanism.
• Recall injects a prompt every N messages (configurable via strategies.pruneTool.recall.frequency) asking the agent to summarize accumulated knowledge and progress.
• Implemented recallCounter in session state to track frequency independently.
• Unlike Nudge (which persists until a prune occurs), Recall triggers once at the threshold and resets, ensuring periodic prompts without repetition per message.
• Full configuration support added to lib/config.ts and lib/state.

Implementation Details

• Config: Added recall object (enabled, frequency) to PruneTool configuration.
• State: Added recallCounter to session state. It increments alongside nudgeCounter on tool usage and resets on prune actions.
• Injection: In lib/messages/prune.ts, the recall prompt is injected when the counter meets the frequency threshold. The counter is immediately reset to 0 to create a periodic interval (e.g., every 10 messages) rather than a persistent state.
• Prompts: Added lib/prompts/recall.txt with the system instruction for summarization.

[spoons-and-mirrors]

deprecated by the better extract tool approach