Stream formatter: presentation, not protocol

StreamFormatter processes text chunks for display. It is a replaceable presentation strategy; it does not change the semantics of tool authorization or model inference.

Built-in choices

• PassThroughFormatter: the default, forwards the received text.
• StandardStreamFormatter: recognizes configured tool-call tags and think markers, and emits labelled display text such as [Thinking]: and [Content]:.

Enable the standard formatter with:

let agent = Agent::make(engine_config).await?
    .with_standard_formatting();

The standard implementation maintains a bounded internal buffer (default 8192 bytes). Overflow clears the formatter's buffer and logs an error. That is a local buffer guard, not an end-to-end proof that all streaming workloads are memory bounded.

Write a formatter

use ambi::types::StreamFormatter;

struct Plain;

impl StreamFormatter for Plain {
    fn push(&mut self, chunk: &str) -> String {
        chunk.to_string()
    }
    fn flush(&mut self) -> String {
        String::new()
    }
}

let agent = Agent::make(engine_config).await?
    .with_stream_formatter(|| Box::new(Plain));

The API takes a factory closure so each streaming request gets a fresh formatter instance. Its two required methods are push(&mut self, &str) -> String and flush(&mut self) -> String.

Text formatting is useful for human-readable streams; do not parse it as a structured tool/audit event transport. For the incoming tool format, see Tool Parser; for output semantics, see Streaming.