Unified streaming event surfaced to a :stream consumer of Dsxir.Predictor.Predict.

Predict translates each Dsxir.LM.StreamChunk into one of these and, when listen: names output fields, injects :field_delta events carrying marker-stripped field content. A single sink therefore sees the whole stream; a UI answer-box filters to :field_delta for its field while a raw-output view consumes :token. The :type tag selects the payload:

• :token — data is the raw text delta straight from the model (markers and all); the unfiltered firehose.
• :field_delta — data is a fragment of a listened output field's value, markers stripped; field names the field. Only emitted for fields named in listen:.
• :reasoning — data is a reasoning-text fragment.
• :tool_call — data is %{id, name, arguments_delta}.
• :usage — data is a %Dsxir.Cost{}.
• :done — terminal success; data is the final accumulator (often nil).
• :error — terminal failure; data is a Dsxir.Errors.LM.*.

field is nil for every type except :field_delta.