Worktree session owns plan execution

Status: accepted

Current decision

An approved plan implemented in a worktree is a Worktree Fork of the planning session at the reply that proposed it. The fork carries the planning conversation, receives its own byte-identical accepted-plan artifact and a retry record for the equivalent Here handoff, and runs every context (Current, Fresh, Summary) and execution (Direct, Goal) exactly as Here does. Its view replaces the planning view in the same windows, and the planning session, saved with only its approval archive, is closed. Execution stays attached to the session that changes files, and the user keeps the conversation that led to the plan.

For a shared planning session, the fork gets its own room before the source closes. Connected guests receive fresh continuation links at their existing authority tier and an explicit room-ended explanation with an Open action. Existing bearers never retarget to the fork. Sharing failure is visible but does not block native handoff. Unshared sessions do not start sharing.

Selected model, effort, and permission mode belong to the one Direct request or the durable Goal's implementation policy, not to session defaults, which the fork copies from the planning session. The selected Goal budget sets the Goal slot only, never a new-Goal default. Standalone Plan has no verification-pending state.

The source retry record advances through durable steps: fork point, branch and directory reservation before Git mutation, the fork's published save path, then the installed fork record. A retry reopens the recorded or uniquely discoverable fork instead of forking again, recognizes an installed plan by its hash, and clears the source record only after the fork owns its own, so one session owns the implementation at every point.

Direct retries reuse the accepted policy. Goal construction persists it before clearing source recovery, so active Goal turns and resume retain the selection. New ordinary chat with an inactive Goal uses the baseline. Model resolution is exact, with no silent baseline fallback. Implementation children inherit the request's permission-mode override under live shared rules and hard denies; their model workloads remain independent. Summary and unrelated requests do not acquire implementation settings. See ADR 0067 for policy ownership and the strict Goal record.

Decision history

The first Worktree Fork handoff preserved native conversational continuity but ended a browser's room as a killed buffer, without an explanation or a route to the implementation. Explicit same-tier continuation replaces that abrupt end; fresh room credentials retain the session-bound bearer contract in ADR 0099. Worktree acceptance is also available to browser owners through a host-validated branch input, while full-link guests retain feedback but cannot accept Worktree.

The worktree session was originally a clean session created beside the source, which kept the retry record and a separate target-preparation step. Context Current was refused there, Fresh received a setup stub, and Summary was generated from the source without compaction, then rewritten to repository-relative paths and inserted into the target. In use, accepting a plan opened a new buffer that lacked the whole planning conversation, and the planning conversation simply ended: the user had to find the new buffer and could not continue the discussion there. Worktree Fork, added later (mevedel-session-fork-create), already copies a conversation into a linked worktree with retargeted paths and restored session-edited files, so the clean-session path, its target-only recovery, the worktree-only summary and the target Goal reservation were removed in favour of forking. Consequences: the worktree now includes files the session itself edited, restored by the fork; and accepting refuses while the session cannot fork (pending input, a request, live executions, active agent turns or an active Goal) instead of failing afterwards.

The earlier handoff applied the selected implementation settings to the target session itself. Here execution therefore overwrote ordinary source-session settings, while Worktree execution replaced the target's baseline. It also changed the target's new-Goal budget default. Request/Goal ownership replaces those mutations because approval authorizes implementation, not a lasting change to ordinary chat policy. A snapshot/restore alternative was rejected: restoring old settings after execution would overwrite concurrent user changes. The existing inherited preset and worktree setup context remain part of target preparation, not an implementation-policy promotion.