ADR 0186: Summarize First-Turn Session Titles with a Main-Owned One-Shot

• Status: Accepted
• Date: 2026-09-08

Context

A first prompt currently needs an immediate sidebar label, but a raw truncated prompt is noisy and can obscure the task's topic. The title summary must use the same provider/model as the session without moving model execution into the renderer or changing host-owned session storage.

Decision

Keep the normalized first-prompt fallback synchronous from the renderer's point of view. After the initial turn emits agent_end, the renderer calls the allowlisted session/summarizeTitle IPC. Electron validates the session and prompt, resolves the session's effective provider/model, and invokes the agent-runtime summarizeSessionTitle one-shot with thinking disabled. The runtime sanitizes the response and an empty or failed completion leaves the fallback unchanged. The renderer persists a valid result through the existing session.rename path.

Renderer-local session metadata persists manualTitle. The automatic path also refuses to run for a persisted title that is neither a recognized default nor the deterministic first-prompt fallback. This protects manual titles made before the marker existed and prevents a completed summary from being replaced on a later renderer restart. No host RPC or storage schema version changes.

Consequences

• New sessions get immediate, readable fallback labels and a concise background summary when the configured provider succeeds.
• Manual titles remain authoritative across renderer restart.
• Provider failures cannot block or fail the conversation turn.
• The title-summary IPC is main-owned and cannot expose provider credentials or model execution to the renderer.

Alternatives considered

• Run the one-shot in the renderer: rejected because provider resolution and credentials belong to Electron main and the sidecar.
• Wait for the summary before submitting the prompt: rejected because it adds visible latency to every first turn.
• Add a host schema column for title origin: deferred; persisted renderer metadata plus the title/fallback guard covers existing and new sessions without a storage migration.