Treat /btw as an ephemeral side conversation

Status: accepted

/btw creates one transient, multi-turn side conversation from an immutable snapshot of its parent session's effective model-visible context and request configuration. It may start while the parent is responding; the snapshot includes the active user prompt and only completed assistant and tool material, then marks the inherited active turn incomplete. Additional gptel context is materialized at invocation instead of retaining live files, buffers, overlays, or media paths. Parent and side proceed independently: later parent state is not synchronized, side turns are not merged back, and the inherited transcript is hidden from the side view. The side owns an ephemeral MevView and transient runtime request context, but no persisted session, checkpoint, input history, compaction state, workflow authority, or resumable transcript. One parent may own one non-nested side conversation, which is discarded when closed or when its parent ends.

Conversation ephemerality does not imply effect ephemerality. Inherently read-only tools and analyzer-proven read-only Bash run under the inherited sandbox and absolute denies. ApplyPatch and other mutation-capable operations cross an invocation-only approval boundary in Ask and Edits, including sides opened from Plan. Full Access bypasses ordinary asks, but not explicit denies or integrity checks; side approvals cannot create durable permission rules. Approved effects occur immediately in the shared workspace and survive side closure, while normally sanitized security and tool audit remains durable. Eval, delegation, tasks, Goals, skills, and parent workflow settlement remain unavailable, and ordinary session lifecycle hooks do not run for side turns.

Permission sources and request settings are frozen when the side is created. The side owns its permission queue and execution state, but sends only allowlisted redacted audit metadata to the durable parent telemetry stream. Mutation review warns while the parent request remains active because both conversations share the same workspace.

A durable session fork was rejected because lineage, locking, checkpoints, Rewind, and resume are contrary to an aside. A one-shot modal was rejected because follow-up questions are central to the intended use. A hard read-only boundary was rejected because read-only shell inspection and explicitly requested artifacts are useful. Installing reusable grants from an ephemeral transcript remains disallowed. Synchronization or automatic merge was rejected because concurrent histories would become timing-dependent and would contaminate the parent context.

Decision history

The original design required human one-shot approval even in Full Auto. Mode-derived authority replaced that exception: Full Access now consistently bypasses ordinary asks, and optional automatic review can settle an invocation in Ask or Edits. Ephemerality still prevents persistent grants, not the effects the user-authorized permission mode allows.