feat: workspace subgroups — data model + migration + store

[knkenko]

Summary

• Replace Workspace.layout with subgroups: SubgroupConfig[] + activeSubgroupId — each subgroup owns an independent layout tree while panes stay flat at workspace level
• Add transparent migration in store.init() that wraps existing layout into a single-element subgroups array and persists on first load
• Refactor all store actions (splitPane, closePane, movePaneToWorkspace, swapPanes, movePaneToPosition, updateNodeSizes) to operate within subgroups via findSubgroupForPane / getActiveSubgroup helpers
• Add new actions: addSubgroup (creates solo pane group), setActiveSubgroup (switches group + focuses first pane), cycleSubgroup (wrapping +1/-1 navigation)
• Update PaneArea to render only the active subgroup's layout tree
• Update sidebar pane click to switch active subgroup when clicking a pane in a different group
• Update SettingsPanel layout preset handling to operate on active subgroup
• Update useKeyboardShortcuts pane navigation to span all subgroups

Test plan

• Existing workspaces migrate cleanly on startup (single subgroup, no layout regression)
• Split pane works within a subgroup
• Close pane removes empty subgroups and switches active
• addSubgroup creates a new solo pane group and switches to it
• cycleSubgroup wraps around at boundaries
• Clicking a pane in sidebar switches to its subgroup
• Duplicate workspace deep-clones all subgroups correctly
• Move pane to workspace creates solo subgroup in destination
• Layout preset change applies to active subgroup only

🤖 Generated with Claude Code

[knkenko]

Automated Review — Findings

Summary: 8 files reviewed, 9 agents ran (code quality, security, silent failures, simplification, DRY/reuse, comments, type design, TypeScript, efficiency)

Must Fix (4 items)

• workspace-pane-actions.ts:591-600 — [6 agents] movePaneToPosition cross-subgroup data corruption: doesn't enforce same-subgroup constraint, duplicates pane into target subgroup
• layout-tree.ts:319 — [6 agents] getActiveSubgroup crashes on empty subgroups array via subgroups[0]! non-null assertion
• index.ts:250 — [2 agents] Migration truthiness check if (ws.subgroups) allows empty arrays to skip migration → crash
• workspace-pane-actions.ts:399-405 — [1 agent] closePane kills PTY before state update; ghost pane if subgroup lookup fails

Suggestions (11 items)

• workspace-pane-actions.ts:406-422,476-491 — Extract duplicated "remove pane from subgroup" helper (~15 lines copy-pasted)
• workspace-pane-actions.ts:385,419,489,617,709 — Extract updateSubgroupLayout() helper (5+ identical map expressions)
• Sidebar.tsx:155-168 — Use useStore.getState() in handlePaneClick instead of closing over workspaces
• layout-tree.ts:324-328 — findSubgroupForPane is O(N*M); short-circuit tree walk
• index.ts:265-267 — Batch migration saves into Promise.all; use console.error
• workspace-pane-actions.ts:559-565 — swapPanes cross-subgroup produces corrupted state; add validation
• workspace-pane-actions.ts:365,593 — Add console.error for silent return null in splitPane/movePaneToPosition
• workspace-pane-actions.ts:766 — cycleSubgroup doesn't handle findIndex -1 (stale activeSubgroupId)
• index.ts:250-268 — Migration as unknown as fragile; add typed interface or runtime check
• index.ts + workspace-pane-actions.ts — Extract makeSingleSubgroup(layout) factory (3x boilerplate)
• layout-tree.ts + workspace-pane-actions.ts — Export makePaneConfig for reuse in splitPane/addSubgroup

Nitpicks (5 items)

• index.ts:78-84,101-104 — JSDoc stale: references singular "layout tree", should mention subgroups
• SettingsPanel.tsx:183 — activeSg abbreviation inconsistent; use activeSubgroup
• workspace-pane-actions.ts:80 — Redundant as const in customLayout
• types.ts:225-228 — SubgroupConfig.id could use branded type
• workspace-pane-actions.ts:238 — duplicateWorkspace silently corrects stale activeSubgroupId

Review ran: code quality, security, silent failures, simplification, DRY/reuse, comments, type design, TypeScript, efficiency

[knkenko]

Review Fixes Applied

Fixed (20/20 items from 9 agents):

Must Fix:

• layout-tree.ts:315-323 — [type-design] getActiveSubgroup now throws explicit error on empty subgroups instead of returning undefined
• workspace-pane-actions.ts — [security] Migration validates subgroups with Array.isArray + length check; added LegacyWorkspace interface for type-safe migration
• workspace-pane-actions.ts:closePane — [silent-failure] Deferred killPtys after state update to prevent ghost pane references
• workspace-pane-actions.ts:movePaneToPosition — [code-reviewer] Added explicit same-subgroup validation to prevent cross-subgroup data corruption

Suggestions:

• layout-tree.ts — [dry-reuse] Extracted makePaneConfig helper, eliminating 15 duplicate pane config constructions across createLayoutFromPreset, splitPane, addSubgroup
• layout-tree.ts — [dry-reuse] Extracted updateSubgroupLayout, removePaneFromSubgroup, makeSingleSubgroup helpers — consolidated duplicate subgroup manipulation from 5+ call sites
• workspace-pane-actions.ts — [code-simplifier] Removed redundant as const in customLayout
• workspace-pane-actions.ts:swapPanes — [code-reviewer] Added same-subgroup validation using findSubgroupForPane for both panes
• workspace-pane-actions.ts:cycleSubgroup — [silent-failure] Added idx === -1 guard with console.error for corrupted activeSubgroupId
• workspace-pane-actions.ts:duplicateWorkspace — [efficiency] Added logging for stale activeSubgroupId fallback
• layout-tree.ts:findSubgroupForPane — [efficiency] Replaced O(N*M) getPaneIdsInOrder + includes with short-circuit treeContainsPane
• index.ts — [typescript-pro] Migration uses Promise.all for batched persistence instead of sequential awaits
• workspace-pane-actions.ts — [comment-analyzer] Updated JSDoc for swapPanes, movePaneToPosition, updateNodeSizes, movePaneToWorkspace to reflect subgroup semantics

Nitpicks:

• workspace-pane-actions.ts — [code-reviewer] Added console.error for invariant violations in splitPane, closePane (was silent no-op)
• layout-tree.ts — [comment-analyzer] Added JSDoc for all new helper functions
• index.ts — [comment-analyzer] Updated StoreState JSDoc for swapPanes, movePaneToPosition, movePaneToWorkspace
• Various — [typescript-pro] Replaced non-null assertions with optional chaining + early returns in setActiveSubgroup, cycleSubgroup

Skipped:

• None — all 20 findings addressed

All changes in commit 5ed84b3