pi-tilldone: 400 error at long context — orphaned tool_result after context truncation (Sonnet 4.6)

[coskunarif]

Bug

pi-tilldone extension crashes with a 400 invalid_request_error at long conversations (~message 182) when using claude-sonnet-4-6.

Error

Error: Connection error.

Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.182.content.0: unexpected `tool_use_id` found in `tool_result` blocks: toolu_01LgY35a93nhAdnmSvZA8a9C. Each `tool_result` block must have a corresponding `tool_use` block in the previous message."},"request_id":"req_011CYWa6adk52dCS45D9XZDb"}

Root Cause

When conversation history gets long, pi's context window management prunes a tool_use message from history but keeps the corresponding tool_result block. Claude's API then rejects the request because it finds an orphaned tool_result (toolu_01LgY35a93nhAdnmSvZA8a9C) with no matching tool_use in the preceding message.

Steps to Reproduce

1. Use pi with pi-tilldone extension enabled
2. Model: claude-sonnet-4-6
3. Run a long agentic session (hits around message 182 in context)
4. Extension crashes with the 400 above

Environment

• pi-coding-agent (latest as of Feb 2026)
• Extension: pi-tilldone.ts
• Model: claude-sonnet-4-6
• Failure point: messages.182.content.0

Expected Behavior

Context truncation should prune tool_use + its corresponding tool_result together, or strip orphaned tool_result blocks before sending to the API.

Suggested Fix

Before sending message history to the API, validate that every tool_result block has a matching tool_use block in the preceding message. Remove any tool_result blocks that are orphaned due to context truncation.