feat(files): hide whitespace-only changes (Advanced setting, on by default)

[pascalandr]

What changes for the user

New setting in Settings → Advanced: Hide whitespace-only changes, on by default.

Change in a file	Setting on (default)	Setting off
Only indentation, spacing or line endings (CRLF↔LF)	Hidden from the Changes list; stays unstaged	Listed as before
Real code change (with some re-indentation)	Listed; re-indented lines are not highlighted in the diff	Listed; every line is highlighted
Already staged	Always listed, so nothing is ever committed unseen	Listed

When such a file is opened with the setting off, a short note says that only whitespace, or only line endings, changed. A diff is never silently blank.

How it works

• Detection: server-side, by Git itself. When requested, the existing bounded status read adds a single git diff --numstat -z --ignore-all-space query, with no per-file processes. An unstaged tracked text file is hidden when its normal diff is non-empty but its -w diff is empty.
• Never hidden: untracked, binary, added, deleted, renamed, mode-only and conflicted changes. If detection fails, nothing is hidden.
• Visible list only: selection, range staging, drag-and-drop and counts use only the visible list, so hidden files cannot be staged by accident.
• Live toggle: changing the setting re-reads the list. A read still in flight under the old setting is discarded.
• Two rules on purpose: the list uses Git's -w, which also ignores spacing inside a line. The diff reader keeps Monaco's leading/trailing trim.

Validation

• Server tests on a real repository: whitespace-only, CRLF-only, real, binary, untracked, staged, and staged-then-re-indented files; option-keyed request sharing; a failed detection hides nothing.
• UI unit tests: staged rows kept, range staging skips hidden files, live toggle, stale reads.
• Browser: git-history.test.ts 19/19.
• Typechecks: server and UI pass.

Oversized files touched: useGitChanges.ts (~554 lines), stores/preferences.tsx (~1,589 lines) and lib/settings/behavior-registry.ts (~589 lines).

[pascalandr]

Independent gatekeeper pass 1 on ddba1ae: no P0/P1 (the notice never hid a real content change in any tested case); 1 P2 + 4 P3, merge held.

• P2 diff-whitespace.ts: line-ending-only differences (CRLF↔LF, frequent on Windows with raw worktree bytes vs Git LF) are treated as whitespace-only. Monaco never shows line endings in either mode, so the notice's advice to turn the setting off leads to a blank reader. Fix: exclude line-ending-only changes, or show a separate setting-independent note. Update the unit test and FILES_PANEL.md.
• P3 A side that is a single empty line makes Monaco's legacy algorithm report a whole-file change regardless of the trim option, yet the helper says "whitespace-only".
• P3 The trailing-blank regex is quadratic on long inner space runs (80k spaces take ~8 s on the main thread). Fix: index scans with early exit.
• P3 A leading BOM plus trailing whitespace shows 0 changes in Monaco but no notice. Fix: strip one leading .
• P3 Unused exports DIFF_WHITESPACE_MODES / DiffWhitespaceMode.

Verified: defaults for old configs, persistence, registry placement, the live toggle without a reread, the single viewer consumer, i18n and styling. UI typecheck; unit tests 3/3; git-history browser tests 19/19. Fixes and another pass follow.

[pascalandr]

Fixes for gatekeeper pass 1 pushed in 0545e07:

• P2: classifyHiddenDiffChange() separates two cases:
  • "whitespace": shows the existing notice, only while the setting is on;
  • "invisible": line endings or BOM only. Monaco never draws these, so a separate localized note always explains them.
• P3:
  • A single-empty-line side now returns null.
  • One leading BOM is stripped before comparing.
  • The quadratic regex is replaced by index scans with early exit; a 100k-space line now takes 0.6 ms (was ~2.9 s).
  • Unused exports are removed.
• Docs: FILES_PANEL.md and AGENTS.md are corrected.

Validation: UI typecheck clean; unit tests 5/5 (classifier cases and performance); git-history browser tests 19/19, including a CRLF-only file with the setting on and off.

Independent pass 2 follows.

[pascalandr]

Independent gatekeeper pass on a7c0676 (reworked list hiding): 1 P2 + 2 P3, merge held.

• P2 git-status.ts:243-247: an explicit 0 0 record in the -w numstat is treated as whitespace-only. Git lists mode changes and unmerged files as 0 0, so a chmod (update-index --chmod=+x + whitespace edit) or a pending conflict resolution got hidden. Fix: flag only paths absent from the -w output, skip unmerged entries, add server tests for both repros, and correct the docs.
• P3 The -w query and the unstaged numstat run concurrently; a real write between them can briefly hide a change. Fix: run -w after the numstat resolves.
• P3 The docs don't mention that -w also hides final-newline-only changes.

Verified OK: -z parsing (spaces, Unicode, tabs), path key alignment, binary/-diff, submodules, untracked, intent-to-add, partially staged files, commit/stage flows (hidden files are never committed), option-keyed sharing, fail-open, UI visible-list counts/selection/stale reads, i18n.
Tests: typechecks; server 6/6; UI unit 20/20; browser 19/19. Fixes and another pass follow.

[pascalandr]

Independent gatekeeper pass on 2e7c21c: ZERO FINDINGS.

Verified on throwaway repositories with Git 2.53.0.windows.2:

• Hidden (absent from the -w output): re-indents, CRLF-only, final-newline and inner-spacing changes.
• Visible: real changes; worktree mode changes listed as 0 0; staged chmods (staged row visible); conflicts resolved as "ours" or "theirs" and re-indented.
• Ordering: the -w query now runs only after the unstaged numstat resolves, and detection still fails open.
• Docs match the observed Git behaviour; UI, i18n and in-diff notes are unchanged since the previous pass.

Validation: server and UI typechecks clean; server git-status 8/8; UI unit 20/20; browser git-history 19/19.

Proceeding with the requested admin merge.