feat: adopt active sessions across repos and worktrees

[peyton-alt]

Trail: https://entire.io/gh/entireio/cli/trails/613/adopt-active-sessions-across-repos-and-worktrees

Summary

Adds entire session adopt [session-id] --from <source-worktree> so an active agent session can be explicitly anchored into the repo/worktree where the next commit is about to happen.

This addresses the case we hit where hooks were firing correctly, but the commit happened in a repo/worktree that did not have matching local session state, so the commit had nothing to link and missed the Entire-Checkpoint trailer.

What changed

• Adds the session adopt subcommand under entire session.
• Reads source session state from the source worktree’s .git/entire-sessions store.
• Supports either an explicit session ID or a single recent active source session.
• Filters shared source stores by the requested --from worktree, using WorktreeID when available and canonical path fallback otherwise.
• Supports independent repo/worktree adoption by writing target-local session state.
• Supports same-git-common-dir linked worktree adoption by moving the shared session state to the current worktree instead of rejecting it.
• Rejects no-op adoption when source and target resolve to the same worktree.
• Validates that a preserved live transcript path is owned by the source session’s registered agent.
• Keeps the live transcript path because the transcript belongs to the continuing agent session, not necessarily the target repo.
• Seeds FilesTouched from current target repo changes so the next commit can pass the staged-file overlap check.
• Resets target-local checkpoint/transcript bookkeeping so long-running source sessions do not inherit stale checkpoint offsets, checkpoint IDs, prompt windows, or legacy transcript fields.
• Preserves cumulative turn/context metrics while anchoring the adopted prompt window at the current source turn count.
• Leaves AttachedManually false because adoption is not entire session attach.

This closes the sibling-worktree gap from #573 through an explicit agent/user command, without adding hook-time automatic matching across worktrees.

Verification

• GOCACHE=/private/tmp/entire-go-cache go test ./cmd/entire/cli -run TestSessionAdopt -count=1
• GOCACHE=/private/tmp/entire-go-cache go test ./cmd/entire/cli -run TestSessionAdopt_MovesSameStoreSessionIntoCurrentWorktree -count=1
• GOCACHE=/private/tmp/entire-go-cache go test ./cmd/entire/cli -run 'Test(SessionAdopt|PrepareCommitMsg)' -count=1
• GOCACHE=/private/tmp/entire-go-cache go test ./cmd/entire/cli -count=1
• mise run lint
• mise run check

mise run check passed locally after rebasing on current main, including lint, integration tests, Vogon canary, and roger-roger canary.

Latest commit/checkpoint:

• db9ada812c38dc67e0750d4e2633662316ffb5bf - Entire-Checkpoint: 48521e055655

Push output confirmed entire/checkpoints/v1 was already up to date on the checkpoint remote.

Caveats

This is explicit adoption, not automatic discovery. Agents or users should run it from the target repo/worktree before committing, and the source transcript path must still be readable on the same machine.

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[Copilot]

Pull request overview

This PR adds an explicit entire session adopt subcommand to copy (“adopt”) an in-progress agent session that’s currently tracked under a different repo/worktree into the current repo/worktree so the commit hooks can find local session state and reliably add an Entire-Checkpoint trailer.

Changes:

• Add entire session adopt [session-id] --from <source-worktree> command wiring under the session group.
• Implement adoption logic that locates the source worktree’s .git/entire-sessions, selects an adoptable session, and writes a target-local session state seeded with current file changes.
• Add unit tests covering cross-repo adoption, source resolution from a nested path, and PrepareCommitMsg trailer insertion after adoption.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
cmd/entire/cli/sessions.go	Adds the adopt subcommand to session help text and registers the command.
cmd/entire/cli/session_adopt.go	Implements the adopt command, source store resolution, session selection, and target-local state writing.
cmd/entire/cli/session_adopt_test.go	Adds tests for adoption behavior and hook trailer behavior after adoption.