refactor: centralize shared render constants

[benvinegar]

Summary

• add src/core/constants.ts for shared diff, layout, scroll, watch, and theme constants
• replace repeated literals in App, DiffPane, loaders, Pierre rendering, and the vertical scrollbar with shared constants
• add explicit Pierre helper return types where they were still inferred

Testing

• bun run typecheck
• bun test

This PR description was generated by Pi using OpenAI GPT-5

[greptile-apps]

Greptile Summary

This PR is a clean refactoring that introduces src/core/constants.ts as the single source of truth for diff, layout, scroll, watch, and theme constants previously scattered as inline literals across five files. No logic is changed — every replacement is a direct 1-to-1 substitution with an identically-valued named constant.

Key changes:

• DIFF_CONTEXT_LINES = 3 replaces two hardcoded 3 literals in loaders.ts, keeping parseDiffFromFile and createTwoFilesPatch in sync
• UI_LAYOUT_CONSTANTS (6 values) replaces local const declarations inside AppShell, and introduces the previously unnamed SIDEBAR_DEFAULT_WIDTH = 34
• UI_SCROLL_CONSTANTS (4 values) replaces inline numbers in DiffPane and VerticalScrollbar; the SCROLL_RESTORE_RETRY_DELAYS_MS array is now readonly [0, 16, 48] (due to as const) — ReadonlyArray.map() is fully supported so there is no type or runtime issue
• THEME_CONSTANTS.RESERVED_PIERRE_TOKEN_COLORS replaces the identical as const object in pierre.ts; the key-lookup type inference in normalizeHighlightedColor is unaffected
• Explicit return types were added to six previously-inferred helper functions in pierre.ts

Confidence Score: 5/5

Safe to merge — purely mechanical constant extraction with no behavior changes

Every replacement is a 1-to-1 substitution of an identical value; TypeScript types are preserved (including as const narrowing and ReadonlyArray.map() compatibility); no P0 or P1 findings

No files require special attention

Important Files Changed

Filename	Overview
src/core/constants.ts	New file centralizing diff, layout, scroll, watch, and theme constants — values are correct and groupings are logical
src/core/loaders.ts	Replaces two hardcoded 3 literals with DIFF_CONTEXT_LINES; both call-sites (parseDiffFromFile and createTwoFilesPatch) remain consistent
src/ui/App.tsx	Five local layout constants replaced with UI_LAYOUT_CONSTANTS destructuring; SIDEBAR_DEFAULT_WIDTH (34) and WATCH_POLL_INTERVAL_MS (250) added and values match originals
src/ui/components/panes/DiffPane.tsx	Replaces three inline scroll constants with UI_SCROLL_CONSTANTS; SCROLL_RESTORE_RETRY_DELAYS_MS is readonly [0,16,48] from as const, and ReadonlyArray.map() is valid — no runtime or type issue
src/ui/components/scrollbar/VerticalScrollbar.tsx	Module-level HIDE_DELAY_MS now sourced from UI_SCROLL_CONSTANTS.SCROLLBAR_HIDE_DELAY_MS; value (2000 ms) unchanged
src/ui/diff/pierre.ts	Four magic literals replaced with named constants; Highlighter type alias and explicit return types added for normalizeHighlightedColor, flattenHighlightedLine, makeSplitCell, makeStackCell, prepareHighlighter, and queueHighlightedDiff

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    C[src/core/constants.ts]

    C -->|DIFF_CONTEXT_LINES| L[src/core/loaders.ts]
    C -->|UI_LAYOUT_CONSTANTS\nWATCH_POLL_INTERVAL_MS| A[src/ui/App.tsx]
    C -->|UI_SCROLL_CONSTANTS| D[src/ui/components/panes/DiffPane.tsx]
    C -->|UI_SCROLL_CONSTANTS| V[src/ui/components/scrollbar/VerticalScrollbar.tsx]
    C -->|DEFAULT_TAB_SIZE\nHIGHLIGHTER_PREFERRED\nTHEME_CONSTANTS\nTOKENIZE_MAX_LINE_LENGTH| P[src/ui/diff/pierre.ts]

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