When pruneHistoryForContextShare drops chunks of messages, it could drop
an assistant message with tool_use blocks while leaving corresponding
tool_result messages in the kept portion. These orphaned tool_results
cause Anthropic's API to reject the session with 'unexpected tool_use_id'.
Fix by calling repairToolUseResultPairing after each chunk drop to clean
up any orphaned tool_results. This reuses existing battle-tested code
from session-transcript-repair.ts.
Fixes#9769, #9724, #9672