ADR 0113: Persist the New Task empty slot immediately and deduplicate it by message count

• Status: Accepted
• Date: 2026-08-21
• Supersedes: ADR 0084 / D220
• Related: D088 · D093 · D305 · E2E-011b · E2E-011d · E2E-011e · E2E-011g
• Amended by: ADR 0154 (first-frame empty reveal; reuse without a blocking list refresh)

Context

ADR 0084 deferred session creation until the first prompt. That removed abandoned rows, but it also made the New Task action invisible in the sidebar and removed the scoped empty-session reuse behavior. The product now requires a real, immediately visible empty session while preserving one empty slot per project or temporary sidebar group.

Titles cannot define emptiness because users may rename an empty session and the first message can produce a title independently. The host already stores the current transcript ordinal in sessions.last_seq, which is the current message count after append and rewrite operations.

Decision

When New Task is invoked for a project or the path-less Temporary group:

1. Sort that group's non-archived sessions by updatedAt descending.
2. If the most recent session is empty (messageCount = 0 and the renderer has no live rows, running turn, or submitted draft), select it and reveal its empty transcript on the first frame. Selecting the already active row is a no-op.
3. Otherwise reveal the empty home on the first frame, create a real empty session through session.create, and insert the returned summary into the sidebar. Do not block on session.list or session.get (ADR 0154).

Renderer requests for the same group are serialized. This makes rapid repeated clicks observe the first completed empty slot instead of racing multiple session.create calls. Project paths remain normalized through the existing grouping helper, and path-less sessions use the same rule rather than a separate session type.

SessionSummary.messageCount is added to the shared IPC/session contract. The Rust host derives it from sessions.last_seq; no storage migration is needed and protocol v9 remains compatible because this is an additive session-summary field. Title heuristics remain presentation-only: the sidebar renders empty rows and the reuse decision never calls isDefaultSessionTitle.

The app's startup home remains an unpersisted renderer draft so simply opening the application does not create a slot. Explicit New Task actions create or reuse the durable slot. A startup draft still materializes when a first prompt or pasted attachment needs a session.

Consequences

• New sessions are visible and selectable immediately, before the first user message.
• Repeated New Task clicks in one group are idempotent while different project groups remain independent.
• An older empty session can remain when a newer non-empty session is the group's latest; the rule intentionally considers only that latest session.
• Empty sessions persist until the user deletes or archives them.
• Protocol v9 gains one additive summary field; storage schema v11 and host ownership remain unchanged.

Alternatives considered

• Keep the unpersisted draft from ADR 0084: rejected because the action has no immediate sidebar presence and cannot provide a durable ready slot.
• Continue using a default title as the empty predicate: rejected because a manual rename changes presentation, not transcript state.
• Add a host-side special session.createOrReuse RPC: rejected because the existing renderer navigation boundary can enforce the requested grouping rule without expanding the host method catalog.