ADR 0084: Defer new-task session creation until the first message

• Status: Accepted
• Date: 2026-08-14
• Related: D220 · D088 · D093 · E2E-011b · E2E-011d

Context

Clicking New Task created a session immediately, so the sidebar history gained a default-titled 新建任务 / "New task" row even when the user never typed a message. A reuse rule (D088/D093) kept at most one empty draft per project or temporary scope, but the first empty row still appeared and remained visible until the user sent a prompt that renamed it. Empty draft sessions also left rows on disk in the host database.

Decision

New Task opens an unpersisted draft instead of creating a session:

• newSession() resets the renderer to the home empty state (keeping the requested project scope) and no longer calls session.create nor reuses a legacy empty draft. activeSessionId stays unset, which the renderer already supports as its initial and project-switching state.
• The first message (sendPrompt) or pasted files (which must attach to a session) materialize the draft through a shared materializeDraftSession helper that creates the session, applies any retained toolbar configuration, and commits the same navigation/run state the eager path used.
• Composer and top-bar model toolbar choices made on the draft are retained in a new draftConfiguration store slice and applied at materialization time instead of materializing a session on a toolbar-only interaction.
• The sidebar history filter now drops sessions whose title is still a default untitled value, hiding legacy empty drafts and any accidentally empty session as a defense in depth.

Consequences

• The sidebar history only records tasks that actually carry input; abandoned New Task drafts leave no row and no persisted session.
• No new empty sessions accumulate in the host database; legacy empty drafts remain on disk but are hidden from history.
• The renderer store, Composer, and Sidebar change; protocol v9, host RPC, and storage schema v11 are untouched, so older renderers remain compatible.

Alternatives considered

• Keep eager creation and only hide empty drafts in the sidebar: smaller change, but leaves invisible sessions on disk and keeps the reuse machinery alive for rows the user should never see.
• Create the session on the first draft keystroke: would still create rows for messages that are never sent, which is what the request asks to avoid.