Sign off PR 5 and give PR 6 a whitespace-toggle consumer

The interactive pass on PR 5 found nothing to fix; refining the behaviour
of a few special cases can wait until the remaining PRs are written.

Toggling "ignore whitespace" re-renders the diff just like a context-size
change or a renderer switch does, so it belongs in PR 6 as a third
consumer. It is the first one whose anchor can vanish along with its hunk
or its whole file, which invalidates the candidate walk's reason for
stopping at the first change line; the walk goes unbounded instead, so the
restore lands on the nearest surviving line wherever in the diff that is.
And once staging happens in the main view, master's refusal to ignore
whitespace while staging no longer catches it - parked as an open question
for PR 7.

focused-main-view-production-plan.md

@@ -155,7 +155,7 @@ succession (§2.3); 10–11 any time after their dependencies.
 | 3 | Rename the "pagers" config to "diff renderers" — **DONE: landed on master as #5870** | — | rename + migration |
 | 4 | Support diff renderers that emit OSC 1717 diff line metadata | 2, 3 | infra + protocol |
 | 5 | Select, navigate and edit diff lines in the focused main view (copy moved to PR 7) | 2 (4 for renderers) | feature |
-| 6 | Keep your position in the diff when changing context size or switching diff renderers | 1, 2, 5 | feature |
+| 6 | Keep your position in the diff when changing context size, ignoring whitespace, or switching diff renderers | 1, 2, 5 | feature |
 | 7 | Stage, unstage and discard changes directly from the focused main view | 4, 5, 6 | feature |
 | 8 | Build custom patches directly from a commit's diff view | 7 | feature |
 | 9 | Replace the staging and patch-building panels with the focused main view | 7, 8 | removal + migration |
@@ -976,15 +976,21 @@ binding had to take its new shape *inside* its own commit, because resolving
 the replay conflict there would otherwise have re-introduced the locals the
 keybinding fixup had just removed.
 
-The §6 interactive pass is owed: selection feel under delta with
-`narrowSelectionHighlight`, hunk-on-click, drag (including the autoscroll), and
-repeated `n` across files under a metadata-emitting delta.
+#### Interactive sign-off (2026-08-15) — approved
 
-### PR 6 — Keep your position in the diff when changing context size or switching diff renderers
+The §6 pass is done and everything behaves as expected: selection feel under
+delta, hunk-on-click, drag including the autoscroll, and repeated `n` across
+files under a metadata-emitting delta. A few special cases may deserve a
+refinement of their exact behaviour later; the user's call is that getting the
+later PRs written matters more, so none of them is being touched now.
 
-The `RenderRestore` mechanism plus its two standalone consumers. After this
-PR: `{`/`}` (context size) and `|`/`\` (renderer cycle) keep your scroll
-position and selection instead of jumping to the top.
+### PR 6 — Keep your position in the diff when changing context size, ignoring whitespace, or switching diff renderers
+
+The `RenderRestore` mechanism plus its three standalone consumers. After this
+PR: `{`/`}` (context size), `ctrl+w` (ignore whitespace) and `|`/`\` (renderer
+cycle) keep your scroll position and selection instead of jumping to the top.
+(Title drafted with the third consumer added 2026-08-15; §9.5 — the user
+finalizes the wording at PR-open time — may well shorten it.)
 
 Commits:
 
@@ -1031,13 +1037,54 @@ Commits:
    wrong-line "preserved by raw line number" cases (N§18.2); graceful no-op
    fallback for unresolvable renderers. e2e: `diff/cycle_diff_renderers`
    (renamed by #5870) keeps passing. Ref: a21c5841a.
-6. **Preserve the selection's far end too** — `selectionFarEndIdentity`
+6. **Preserve position when toggling "ignore whitespace"** (`ctrl+w`) — added
+   to the plan 2026-08-15 at the user's suggestion; **no prototype reference**,
+   the prototype never touched this path. The call itself is the same one-liner
+   as commits 4 and 5, in `ToggleWhitespaceAction.Call` before it re-renders
+   (it re-renders through `Context().CurrentSide().HandleFocus`, which walks
+   down to the side panel, so the same call covers a focused main view too).
+   What is new is the **fallback**, because ignoring whitespace can remove the
+   anchor line, its whole hunk, or its whole file from the diff:
+   - **The stop-at-the-first-change-line rule in `nearbyDiffLines` is invalid
+     here.** It exists because a change line always survives a `-U` change —
+     which is exactly the assumption ignoring whitespace breaks. So the
+     candidate list has to grow.
+   - **Decided with the user 2026-08-15: candidates run outward from the anchor
+     over the whole rendering, nearest first, unbounded** — across hunk and
+     file boundaries — and the restore lands on the first one the new diff
+     still contains. When the anchor's file was whitespace-only you therefore
+     land on the nearest surviving line of a neighbouring file, which is still
+     where you were in the diff. If nothing survives at all (every change was
+     whitespace), no restore: the view renders from the top, and PR 5's
+     visibility rules already hide the selection once there are no change lines
+     left.
+   - Whether the unbounded list *replaces* the short one for commits 4 and 5
+     too is an implementation call. It has the same ordering, so it only
+     lengthens the list — but a candidate list the size of the buffer makes
+     `findResolvedDiffLine`-per-candidate O(n²); invert it (index the new rows
+     once, then walk the candidates) before sharing it.
+   - Direction is asymmetric: turning ignoring **off** only adds lines and the
+     anchor practically always survives (a whitespace-only change shown as a
+     context line under ignoring keeps its line number, and `SamePatchLine`
+     compares `(line, isDeletion)`, so context↔addition still matches). Turning
+     it **on** is the case the fallback is for; a whitespace-only *deletion* is
+     the one identity with nothing to match in the new diff, and falls to a
+     neighbour.
+   - e2e: a main-view companion to `diff/ignore_whitespace` — position kept
+     when the anchor survives, nearest-survivor landing when its hunk is
+     whitespace-only, and the empty-diff case.
+7. **Preserve the selection's far end too** — `selectionFarEndIdentity`
    restored via `SetRangeSelectStart`; collapses to the cursor line when the
    far end didn't survive. Ref: 0412046c4, N§21.32(4).
 
 Known limitation (keep, document in PR): `NormalSecondary` is not preserved
 (N§16.1, N§18.3).
 
+Interaction to keep in mind (not this PR's job): master refuses `ctrl+w` in the
+staging and patch-building contexts, because a patch built from a
+whitespace-ignoring diff doesn't apply. Once staging happens in the main view
+the refusal no longer catches it — see §9.10.
+
 ### PR 7 — Stage, unstage and discard changes directly from the focused main view
 
 The headline PR. After it: in the files panel's focused main view, `space`
@@ -1377,8 +1424,8 @@ user pass before merge:
 |---|---|
 | 1 | ✅ **APPROVED 2026-08-09.** Slow-render matrix (N§11/§13): flick commits/files scrolled down; 10 s auto-refresh (`refreshInterval: 3`) — no content/scrollbar flicker; **also re-test at normal speed** (N§20.5). Found PR 1 deviations 8 and 9, both fixed; a repo with dirty submodules is the case that exposes a slow same-content re-render |
 | 4 | ✅ **APPROVED 2026-08-09.** Patched delta/difftastic/diff-so-fancy emit + render cleanly; handshake swallowed (no phantom line) |
-| 5 | **OWED** (implemented 2026-08-10). Selection feel under delta (narrowSelectionHighlight); hunk-on-click; drag; nav under metadata delta incl. repeated `n` across files |
-| 6 | `{`/`}` and renderer-cycle scrolled down: no top-jump, offset preserved, both anchor cases; ext-diff route (difftastic) |
+| 5 | ✅ **APPROVED 2026-08-15.** Selection feel under delta; hunk-on-click; drag incl. autoscroll; nav under metadata delta incl. repeated `n` across files. Some special cases are candidates for a later refinement; deliberately not pursued now |
+| 6 | `{`/`}`, `ctrl+w` and renderer-cycle scrolled down: no top-jump, offset preserved, both anchor cases; ext-diff route (difftastic); ignoring whitespace where it removes the anchor's hunk, and where it empties the diff |
 | 7 | Full staging matrix under no-renderer / patched delta (unified + SxS) / difftastic; cross-pane focus-follow; raw fallback feel under stock delta / diff-so-fancy-without-metadata; binary-file focus stability (N§21.30 repro) |
 | 8 | Gutter under delta/no-renderer/difftastic; whole-commit path on LocalCommits (canRebase menu); secondary pane preview per renderer; **secondary-pane removal under difftastic specifically** (the prototype's known-broken case: reordered `d`/`a` records, collapsed modification rows, a/b record-path leak) and under delta |
 | 10 | Ghostty, iTerm2, VS Code |
@@ -1490,6 +1537,20 @@ The remaining rows are agreed as keep/defer:
    the raw fallback?~~ Resolved 2026-08-07: probe them like any other
    renderer, since git announces itself for exactly the formats it
    describes. See PR 7 commit 10.
+10. **PRs 7/9: what does `ctrl+w` do in a main view you can stage from?**
+    (Raised 2026-08-15 while planning PR 6's whitespace consumer.) Master
+    refuses ignoring whitespace in the staging and patch-building contexts —
+    `ToggleWhitespaceAction` matches on those three context keys and answers
+    `IgnoreWhitespaceNotSupportedHere` — because a patch built from a
+    whitespace-ignoring diff doesn't apply. In the focused main view the
+    current context is `Normal`, so the refusal doesn't catch it, and once
+    PR 7 binds `space` there the toggle silently becomes a way to build a
+    broken patch. Options: refuse it when the panel beneath is
+    `Staging`/`PatchBuilding` (master's rule, expressed in the new
+    classifier); or allow it and disable the acting keys while it's on; or
+    treat it like a non-conforming renderer and stage from the raw diff.
+    Decide in PR 7; PR 9 must in any case delete the now-dead context-key
+    list.
 
 ## 10. Progress
 
@@ -1510,8 +1571,9 @@ The remaining rows are agreed as keep/defer:
       `select-diff-lines-in-main-view` (9 commits, all checks green, every
       commit builds/tests/lints clean on its own), stacked on
       `support-osc-1717-diff-metadata`. Jump-to-file menu skipped and copy
-      moved to PR 7 (see its deviations). §6 sign-off **owed**
-- [ ] PR 6 — position preserve
+      moved to PR 7 (see its deviations). §6 sign-off **approved 2026-08-15**
+- [ ] PR 6 — position preserve — branch `keep-diff-position-on-rerender`,
+      stacked on `select-diff-lines-in-main-view`
 - [ ] PR 7 — staging from the main view
 - [ ] PR 8 — custom patches from the main view
 - [ ] PR 9 — panel removal
@@ -1523,6 +1585,19 @@ deviations from this plan inline, dated.)
 
 Log:
 
+- **2026-08-15:** **PR 5 signed off** — the interactive pass found nothing to
+  fix; a few special cases might get their behaviour refined later, but the
+  user's call is to write the remaining PRs first. **PR 6 gains a third
+  consumer**, at the user's suggestion: preserving position when toggling
+  "ignore whitespace" (new commit 6, between the renderer-cycle and far-end
+  commits). It is the first consumer whose anchor can disappear along with its
+  hunk or file, so the candidate walk drops the stop-at-the-first-change-line
+  rule and runs **unbounded, nearest first** — decided with the user out of
+  three options (the alternatives confined it to the anchor's file, landing at
+  the top of the diff or on the nearest file header when the whole file went
+  whitespace-only). Also raised there and parked as §9.10: with staging in the
+  main view, master's refusal to ignore whitespace in a staging context no
+  longer catches it.
 - **2026-08-10:** **PR 5 implemented** (9 commits, green; §6 sign-off owed).
   Two of the plan's ten commits aren't in it, both by decision with the user:
   the **jump-to-file menu is skipped** (UX undecided) and **copy moves to