The stream ended before this tool call was complete, so it was never dispatched.
A max_tokens finish truncated the response, so every tool call in it is
unsafe to execute — a call cut off mid-arguments may mean something other
than what it appears to say.
An open text or thinking block whose content was empty or whitespace only.
An open block of a kind that cannot be built from deltas at all (image,
tool_result). Only a block-end can produce one, and none arrived.
Why a block was recorded but kept off the conversation surface.
Each reason names a decision someone would otherwise have to reconstruct from absence.