orca/docs/split-groups-rollout-pr1.md

Split Groups PR 1: Model Foundations

This branch lands the behavior-neutral tab-group model groundwork.

Scope:

• add persisted tab-group layout state
• add active-group persistence and hydration
• add group-aware unified-tab helpers in the store
• connect editor/open-file flows to the unified tab-group model

What Is Actually Hooked Up In This PR:

• the store persists groupsByWorktree, layoutByWorktree, and activeGroupIdByWorktree
• workspace session save/hydration includes tab-group layouts
• editor actions create and activate unified tabs through the group model
• the visible workspace renderer is still the legacy single-surface path

What Is Not Hooked Up Yet:

• Terminal.tsx does not render split groups
• no split-group UI components are mounted
• no PTY lifecycle changes land here
• no worktree activation fallback changes land here

Non-goals:

• no split-group UI rollout
• no terminal PTY lifecycle changes
• no worktree activation changes