`src/observer.rs` — the `LoopObserver` trait

Read-only spectators of engine events: one required method (name), every event optional.

Key items

• LoopObserver — 18 callbacks, all defaulting to no-op: run start/end, turn start/end, response, text/thinking deltas, tool call received/pre/post, stream success/failure, compaction, fallback, model switched, loop/convergence detected, reset.
• ObserverHost — register (append; duplicate registration = duplicate events), fan-out in registration order, panic isolation (a panicking observer is logged and skipped), reset_all, len/is_empty.

Behavior notes

• Observers cannot influence control flow — for that, hooks.
• The host’s dispatch is catch_unwind-wrapped: one bad observer never takes the run down (and never silences the others).
• Delta callbacks run on the stream-ingestion path — keep them light; buffer and render elsewhere.

Deep dive: Observers. Event payloads: context.rs.