Vendor shared file tree + resizable picker from monorepo

[dastratakos]

Summary

Syncs the CLI's file picker and chapter detail sidebar with the monorepo file-tree overhauls that landed after the CLI was forked (~May 27). Brings the CLI up to the shared file tree architecture and the resizable panel hook.

Ports three monorepo PRs:

• #980 — extract one shared FileTree (+ FileFilterInput) rendered by both the Files-changed picker and the chapter detail sidebar. Previously the CLI's chapter sidebar used a flat FileViewRow list and the file picker had its own inlined tree reimplementation — two divergent copies, now one.
• #984 — order the collapsed picker indicators by file-tree order instead of raw API order.
• #985 — shared useResizablePanel hook + chapter-panel-constants; CollapsiblePicker gains an opt-in resize handle and the chapter side panel drops its hand-rolled drag logic.

Changes

• New: lib/use-resizable-panel.ts, components/chapter/chapter-panel-constants.ts, components/files/file-tree.tsx, components/files/file-filter-input.tsx (vendored from the monorepo, imports adapted to @/lib/*).
• Rewritten: file-picker.tsx (thin wrapper over FileTree), chapter-file-list.tsx (renders FileTree instead of a flat list), collapsible-picker.tsx (internal collapse state + shortcutKey + resize + ShortcutTooltip), chapter-side-panel.tsx (uses useResizablePanel).
• Deleted: components/chapter/file-view-row.tsx — its last consumer (the chapters index page) now renders a small local FilePathRow.
• Adaptations for the CLI: FILE_VIEWED_STATE moved into lib/diff-types; comment counts are absent so callers pass an empty map; CollapsiblePicker drops the command-board event the CLI lacks. The chapter sidebar now passes focusedFilePath so the tree highlights the active file.

Testing

• pnpm typecheck ✅
• pnpm lint ✅ (clean, no warnings)
• pnpm test ✅ 299/299
• pnpm build ✅

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Summary by cubic

Ports the monorepo’s shared file tree and resizable panel to the CLI, unifying the file picker and chapter sidebar. This removes duplicate implementations and adds filtering, resize, and consistent ordering.

• New Features

  • Shared FileTree and FileFilterInput used by the file picker and chapter sidebar; highlights the focused file and supports “viewed” toggles.
  • CollapsiblePicker gains opt-in resize via useResizablePanel, keyboard shortcut toggle, and hover preview that respects the resized width.
  • Collapsed picker indicators now follow file-tree order (not raw API order).

• Refactors

  • Chapter side panel switches to useResizablePanel and shared chapter-panel-constants; removes custom drag logic.
  • FILE_VIEWED_STATE moved to @/lib/diff-types; CLI passes an empty comment-count map; drops command-board event.
  • file-view-row.tsx removed; chapters index now renders a small local FilePathRow.

^{Written for commit f02bf49. Summary will update on new commits.}

[stage-review]

Ready to review this PR? Stage has broken it down into 8 individual chapters for you:

	Title
1	Centralize file viewed state and types
2	Implement shared resizable panel hook
3	Add shared file tree and filter components
4	Enhance CollapsiblePicker with resizing and shortcuts
5	Refactor FilePicker to use shared components
6	Update Chapter sidebar with shared architecture
7	Clean up deprecated FileViewRow component
8	Integrate updated components into main pages

_{Chapters generated by Stage for commit f02bf49 on Jun 2, 2026 4:47am UTC.}