ADR 0011: Progress event architecture

Context

Network bytes, batch completion, retries, failures, cancellation, terminals, and notebooks need one truthful model without coupling rendering to business logic.

Decision

Emit typed immutable events through a reporter protocol with callback, terminal, and null adapters.

Alternatives

Printing in transport and callback-only byte counters were considered.

Consequences

Applications can render or record progress consistently across sync and async paths.

Rejected shortcuts

Invented percentages for unknown lengths and retry-silent progress are rejected.

Operational implications

Known transfers reach exactly 100%; batches count completed items and cancellation is explicit.