refactor(desktop): split sidebar/index.tsx god file into focused modules

[OutThisLife]

Summary

Second in the apps/desktop god-file split series. Breaks the 1,963-line src/app/chat/sidebar/index.tsx into the directory's existing sibling-module convention. index.tsx now holds only the ChatSidebar component: 1,963 → 1,416 lines.

Changes

• order.ts — adds the pure reorder helpers orderByIds, reconcileOrderIds, sameIds alongside the existing ones (+ unit tests in order.test.ts)
• reorderable-list.tsx (new) — the generic ReorderableList + useSortableBindings DnD primitive (and its Y-only auto-scroll constant)
• section-states.tsx (new) — SidebarSessionSkeletons, SidebarBlankState, SidebarPinnedEmptyState
• sessions-section.tsx (new) — SidebarSectionHeader, the large SidebarSessionsSection renderer, and the Sortable* row wrappers

Notes

• Pure restructuring — no behavior change. Code moved verbatim; only imports/exports adjusted.
• Module boundaries are acyclic: order / reorderable-list / section-states are leaves; sessions-section depends on them + the existing projects / session-row / virtual-session-list; index.tsx composes everything.
• ChatSidebar is exported unchanged; its single consumer's import path is untouched.

Test plan

• npm run typecheck (desktop) — passes
• eslint on all changed/added files — clean
• vitest run for order.test.ts (existing + new helper tests) — 10 pass
• Smoke-test the sidebar: recents/pinned/messaging/cron sections, project overview drill-in, drag-to-reorder, virtualized long list, search results, blank/empty states

Note: a whole-tree npm run lint reports 4 pre-existing errors in unrelated files on main; none are touched here.

[tonydwb]

Code Review Summary\n\nVerdict: LGTM\n\nSecond in the desktop god-file split series. sidebar/index.tsx reduced from 1,963 to 1,416 lines. 6-file change with clean module boundaries and 10 unit tests for order helpers.\n\n### Looks Good\n- Pure restructuring with no behavior change\n- Acyclic module dependencies\n- Comprehensive test coverage for the reorder helpers\n---\nReviewed by Hermes Agent

[tonydwb]

Code Review: LGTM

Splits the sidebar index.tsx god file into focused modules: ReorderableList, orderByIds, reconcileOrderIds, sameIds moved to order.ts; SidebarSectionHeader, SidebarSessionSkeletons, SidebarBlankState, SidebarPinnedEmptyState moved to section-states.ts; SidebarSessionsSection moved to sessions-section.ts. This is a classic god-file reduction -- the parent component is now a clean orchestrator. File count (6) and additions (608) are well within scope for a structural refactor.

Verdict: LGTM -- clean decomposition of a god file.