feat(git-diff): persist diff view mode and line wrap across reloads

[danielbachhuber]

Human comments

From https://discord.com/channels/1522478522332090528/1545179385194356856/1545395969603014657

What was wrong

Both git-diff toolbar preferences were component state, so they reset on remount and reload. Display mode also expired explicit choices during panel resizing, breakpoint changes, and panel closes; the 760px rule then overrode the choice.

What changed

Added device-local localStorage preferences for git-diff display mode (bb.thread.gitDiff.displayMode) and line overflow mode (bb.thread.gitDiff.lineOverflowMode) in apps/app/src/lib/git-diff-view-preferences.ts. apps/app/src/components/secondary-panel/git-diff/useResponsiveGitDiffPanelDisplay.ts now uses the stored display preference and exports a pure resolver; apps/app/src/components/secondary-panel/ThreadSecondaryPanel.tsx persists the wrap toggle and passes the resize handler through directly.

A stored display-mode preference overrides the 760px responsive rule at every panel width. The rule supplies the default only when no preference is stored. On a compact viewport, display mode is session-only, defaults to unified, and is never persisted, so mobile never overwrites the desktop preference.

Decisions

• Persist these preferences with Jotai atomWithStorage in localStorage, not AppSettings or PUT /settings/general: they are device-local view preferences and do not need server or CLI access.
• Apply persistent display-mode preferences only outside a compact viewport. Compact mode uses session state so a desktop split preference does not carry onto a phone-width drawer and a mobile choice does not overwrite the desktop preference.
• Use the existing useIsCompactViewport() signal (max-width: 767px) rather than a new breakpoint or panel-width proxy; tests use CompactViewportOverrideProvider.
• Keep the compact toggle functional: unified is its default, not a restriction, and an explicit compact split choice is honored for the session.
• Honor an explicit display choice at every panel width. The 760px breakpoint remains the fallback only for an unset preference, accepting that stored split can be cramped below that width.
• Remove the old expiry behavior instead of combining it with persistence, because resizing across 760px would otherwise discard the stored choice.
• Store display mode as nullable so an unset value remains distinguishable from a user choosing unified, preserving the responsive default for users who have not chosen.
• Delete handleSecondaryPanelResizeStart, whose only purpose and caller supported expiry-on-resize.
• Reuse createNullableLocalStorageEnumStorage and createLocalStorageEnumStorage from lib/browser-storage.ts; the preferences are string unions, so createBooleanPreferenceAtom does not apply.
• Use the existing bb.<area>.<name> storage-key convention and read storage on first render with { getOnInit: true }, matching the app's other atomWithStorage usage and avoiding a default-state flash.
• Extract resolveGitDiffDisplayMode({ isCompactViewport, compactDisplayMode, displayModePreference, isWideEnoughForSplit }) as a pure exported function so its combinations can be tested without rendering.

Implementation and scope

useResponsiveGitDiffPanelDisplay.ts replaces its in-memory display state and tracking refs with the compact-viewport signal, stored preference, compact session state, and an isWideEnoughForSplit: boolean | null state. It removes the resize-start handler, explicit-choice refs, breakpoint-crossing logic, and panel-close reset effect, all of which existed to expire the choice. The split breakpoint remains GIT_DIFF_SPLIT_VIEW_MIN_WIDTH_PX (760px).

useResponsiveGitDiffPanelDisplay.test.tsx adds 13 tests covering responsive fallback, preference precedence at every width, remount restoration, invalid storage values, compact defaults and toggles, compact non-persistence, preservation of an existing stored preference, and resolver combinations.

The collapse-all chevron is intentionally not persisted. Its default is derived per diff from file count and delete status, rather than from a user choice, so persisting it would conflict with that per-diff behavior. FilePreview.tsx and markdown-preview.tsx retain their independent unpersisted wrap toggles; sharing a preference is a separate product decision. There is also no settings-panel UI for these preferences.

Outside compact mode, there is no UI to return display mode to an unset responsive state: choosing unified on a wide panel remains a preference until storage is cleared. The compact session choice survives viewport changes within the same hook instance, which is intended but untested. Storage's subscribe implementation provides cross-tab sync, which the new tests do not exercise. Because localStorage is per origin, preferences do not carry between the packaged app and a checkout's dev app on a different port.

How you verified

• pnpm exec vitest run --config vitest.config.ts useResponsiveGitDiffPanelDisplay (13 tests passed)
• pnpm exec vitest run --config vitest.config.ts secondary-panel (37 files and 352 tests passed)
• pnpm exec tsc --noEmit (exited 0 with no output)
• pnpm exec oxlint src (exited 0; 184 warnings are the pre-existing baseline, and neither changed file appears in the output)

No manual reload check was performed in a running app; the automated remount-and-restore tests cover the persistence path, and reviewers should toggle both controls and reload within a single app instance.

AGENT GENERATED