Analysis Summary
Clawdbot implements comprehensive history and tool result pruning using the pi-coding-agent SDK. Here's what they built:
1. Context Pruning Extension (pi-extensions/context-pruning/)
A pi-coding-agent extension that hooks into the context event to prune tool results before they're sent to the LLM.
Two modes:
Key settings:
keepLastAssistants: 3 - protects the last 3 assistant turns from any pruning- Tools can be allow/deny listed via glob patterns
- Skips tool results containing images (hard to partially prune safely)
- Never prunes anything before the first user message (protects bootstrap context files like SOUL.md, USER.md)
2. History Turn Limiting (pi-embedded-runner/history.ts)
Limits conversation history to the last N user turns for long-running DM sessions. Configurable per-provider and per-user via dmHistoryLimit.
3. Session Tool Result Guard (session-tool-result-guard.ts)
Monkey-patches SessionManager.appendMessage to:
- Track pending tool calls and synthesize missing tool results if the agent crashes mid-execution
- Strip
<final> tags from assistant text before persistence
- Support optional
transformToolResultForPersistence hook for pre-persist transformations
4. Compaction Safeguard Extension (pi-extensions/compaction-safeguard.ts)
Hooks into session_before_compact to generate summaries when the SDK's built-in compaction triggers:
- Chunks large message histories that exceed the context window
- Tracks and includes tool failures in summaries
- Appends file operation lists (read files, modified files) to summaries
- Falls back gracefully if summarization fails
Integration Point
All this is wired into the embedded pi runner via buildEmbeddedExtensionPaths() which registers these as SDK extensions:
The pruning uses char-based estimates (4 chars/token) rather than precise token counting for performance.
