ADR 0175: Explain quiet active turns with live agent activity status

• Status: Accepted
• Date: 2026-09-07

Context

The transcript already shows a compact Working… row before the first model or tool event and inline rows for concrete thinking and tool activity. A provider request can still spend a long interval before its first event, and a bounded retry backoff or parent-side delegated-task wait can contain no transcript row. During those intervals the only visible signal was the Stop button and a generic local timer. Users could not tell whether the turn was waiting normally, retrying, or waiting on delegated work (Issue #56).

Decision

Extend the existing normalized status event with an optional runtime-owned AgentActivity value:

1. starting covers the initial prompt handoff.
2. waiting-model starts when a provider request is issued and lasts until the first assistant event.
3. retrying covers an abortable provider backoff and carries the attempt number and calculated delay when available.
4. waiting-subagents covers parent-side convergence on delegated work and carries the number of running targets.

The sidecar emits these phases from the same boundaries that own provider requests, retry delays, and delegation waits. It clears the phase when assistant output starts or the turn reaches a terminal event. The renderer stores the latest status per session and renders a compact, localized inline row with a monotonic phase timer. The row is not a second progress card, does not claim a completion percentage, and does not change Stop or abort semantics.

Consequences

• A quiet active turn explains its current runtime-owned wait without adding decorative or duplicate progress chrome.
• Retry lifecycle remains silent in the transcript, while the retry backoff becomes observable and remains cancellable.
• Session switching remains isolated because status is keyed by session id and is cleared with terminal events and session deletion.
• The status is intentionally coarse: provider internals and subagent child events remain out of the renderer protocol unless they explain one of these user-visible waits.

Alternatives

Keep the generic Working row for every wait

Rejected because it does not distinguish a normal provider wait from a retry or delegation wait, which was the ambiguity reported in Issue #56.

Add a permanent multi-step progress card

Rejected because agent turns do not have a reliable total-step or percentage model, and the existing active-turn contract keeps the lower transcript surface inline and compact.

Emit raw provider or child-agent events

Rejected because it would expose unstable implementation details and create a larger protocol surface than the user needs. The runtime-owned phases provide the smallest useful explanation.

References

• docs/spec/03-runtime/01-ipc-protocol.md
• docs/spec/03-runtime/02-agent-runtime.md
• docs/spec/04-ux/09-interaction-patterns.md
• docs/spec/06-delivery/04-e2e-test-plan.md (E2E-008c, E2E-094)
• GitHub Issue #56