kandev/docs/decisions/2026-08-17-separate-task-activity-from-summary-freshness.md

ADR-2026-08-17-separate-task-activity-from-summary-freshness: Separate Task Activity From Summary Freshness

Status: accepted Date: 2026-08-17 Area: backend, frontend, protocol

Context

Task sidebar rows currently use TaskStatusSummary.updated_at as their visible time and saved-view sort value. That field records when any projected status changed. A pull-request poll can therefore make many idle tasks look recently active even when no user opened them and no agent ran.

Users need both concepts. Projection freshness is useful for status diagnostics, while task activity is useful for finding recent work.

Decision

Kandev will keep TaskStatusSummary.updated_at as transport and projection freshness. It will add semantic field last_activity_at to the same bounded, rebuildable summary.

last_activity_at is the latest durable time from these sources:

• task creation or a persisted task mutation
• a user-authored prompt, including a prompt that enters the queue
• an agent turn start or completion

The timestamp does not advance for task focus, session subscription, Git or pull-request polling, queue bookkeeping, status-summary repair, or session metadata maintenance. Live projection uses source timestamps and applies a monotonic maximum. Rebuilds batch the same durable task, message, and turn sources and preserve a newer stored value.

The saved-view wire key is lastActivityAt. The existing updatedAt key keeps its behavior, so stored views remain compatible and users can choose either meaning.

This decision extends ADR-2026-08-01-separate-task-summary-session-stream-traffic. Task-list consumers continue to use the bounded task summary and do not load background session streams.

Consequences

Idle tasks stay stable when background provider status changes. Desktop and mobile saved views can sort by meaningful work without opening task sessions.

The backend needs a batched activity query and more bounded projector inputs. Turn milestones prevent per-chunk agent output from producing task-list update traffic. A running turn becomes recent when it starts and advances again when it completes.

Older summaries need a one-time semantic repair. During partial rollout, the frontend falls back to the task update or creation time when last_activity_at is absent.

Alternatives Considered

• Reuse summary updated_at. Rejected because provider and Git status changes are not user or agent activity.
• Use only tasks.updated_at. Rejected because prompts and agent turns do not always mutate the task row.
• Derive activity in each browser. Rejected because background session history is not loaded and task switchers must not subscribe to it.
• Write every activity to the task row. Rejected because message and turn domains gain extra task writes and mix activity with task edits.