Function emit_after_tool_call 

pub async fn emit_after_tool_call(
    hook_bus: &Arc<HookBus>,
    tool_name: &str,
    runtime_tool_name: Option<&str>,
    input: Value,
    output: String,
    max_tool_output: usize,
    session_id: Option<&str>,
) -> String

Emit an after_tool_call event and return the tool output to record in history — either the original output, or a Replace { output } substituted by an extension transform hook (compression, redaction, summarization). The runtime tool name is included when it differs from the API-safe name.

Fail-safe: any non-Replace result — Continue, a result rejected by the permission matrix, a crashed/timed-out handler, or any future variant — returns the original output unchanged. A misbehaving extension can never drop or corrupt a tool’s output.

Note: the event delivered to the extension carries tool_output as a size-limited preview for large outputs — a ~256 KB prefix plus a …[truncated, N total bytes] marker (see [HookEvent::after_tool_call]), matching max_tool_buffer. The final returned string is then truncated to max_tool_output (the context budget) — compress-then-truncate ordering, so a transform extension sees the full buffered output and decides what to keep before the hard cap is applied.