400 provider error on session resume with open tool calls

Bug Description

When resuming a Kimi Code session where the last turn has open (unresponded) tool calls, the LLM provider fails with a 400 [provider.api_error] stating:

an assistant message with 'tool_calls' must be followed by tool messages responding to each 'tool_call_id'.

This happens because the new user prompt/steer is appended to the history after the open tool calls, preventing trimTrailingOpenToolExchange from cleaning them since they are no longer "trailing" at the very end of the history. Additionally, the new user prompt gets deferred if pendingToolResultIds is not cleared from the aborted turn.

Solution

We resolved this by:

1. Clearing pendingToolResultIds at the start and end of turn boundaries (TurnFlow.runOneTurn).
2. Clearing pendingToolResultIds after replaying session records during resume (Agent.resume).
3. Reverting the step.end cleanup to correctly preserve system reminder deferral during active tool execution.

The commit with the fix on the fork is:
https://github.com/thecannabisapp/kimi-code/commit/0291e891f0d304add982598e6bcba992dd27042e

Start with packages/agent-core/src/agent/turn/index.ts and packages/agent-core/src/agent/index.ts, then compare the resume and turn-boundary handling with commit 0291e891f0d304add982598e6bcba992dd27042e. Reproduce a resumed session with open tool calls and a new prompt; done means the provider no longer returns the 400 error and the prompt is not deferred.