ADR 0154: Reveal the New Task empty destination before host IO

• Status: Accepted
• Date: 2026-09-05
• Deciders: PI-Desktop core
• Related: D252, D305, ADR 0113, ADR 0137, E2E-011a, E2E-011d, E2E-011g

Context

ADR 0113 made New Task persist a durable empty session (or reuse the group's latest empty row). The renderer implemented that by awaiting session.list, then session.create, then another session.list, then session.get before changing the visible transcript. During that chain the previous conversation stayed on screen: a cold-switch rule (ADR 0137) is correct for opening an existing session, but for a brand-new empty destination it felt like the click did nothing, then the chat jumped.

session.list was there so a first message sent moments earlier would not be mistaken for an empty slot while messageCount was still 0. The renderer already knows that case: the session is running, has live rows, or has a submitted composer draft.

Decision

1. First-frame empty reveal. Creating a session clears the previous transcript and retained panes synchronously, before session.create. The empty home composer is the destination. Reusing an empty slot commits an empty transcript on the same frame rather than waiting for session.get.
2. Reuse without a list refresh. New Task decides from the in-memory session list plus renderer signals (runningSessions, live/cached rows, submitted drafts). Host messageCount remains the durable empty predicate; the in-memory signals only prevent treating a just-started turn as empty.
3. Commit from session.create. The created summary is inserted into the sidebar list the way a fork child is. There is no follow-up session.list or session.get for a new empty session: its transcript is known to be empty. A superseded navigation still records the row.
4. One in-flight create per group. Send and paste wait for the same-scope New Task promise instead of materializing a second session. Keystrokes typed on the empty home during create move onto the new session id.

Protocol, storage, and host RPC are unchanged. session.create remains the source of the durable id.

Consequences

• New Task no longer leaves the previous conversation on screen.
• Rapid New Task clicks and first-message races stay serialized per group.
• An empty reuse still revalidates through selectSession after the empty pane is already visible.
• Spec 04-ux/09-interaction-patterns.md §1.6, 04-ux/08-component-spec.md §11, E2E-011a / E2E-011d / E2E-011g; D305 amends D252's refresh-then-select timing, not the reuse rule.

Alternatives considered

• Client-generated session ids on session.create: first-frame id without a home-draft interval, but an additive protocol field and remapping if an older host ignores it.
• Keep the previous pane with a progress track: that is the cold-switch rule for existing transcripts and is the hitch this request removes.