The rebuild dedup dropped any preserved pendingTools component whose toolCallId
had a persisted toolResult. A background task's initial async.state=="running"
result is persisted while EventController#handleToolExecutionEnd deliberately
keeps its component in pendingTools so a later tool_execution_update/_end can
settle it. Dropping that still-live handle stranded those updates on the running
snapshot. Only terminal results are now owned by the replay; running async
handles stay preserved. Added a regression covering the running-task case.