fix(editor): preserve U+00A0 non-breaking space (#3037) (#7585)

* fix(editor): preserve U+00A0 non-breaking space (#3037)

Non-breaking spaces were silently normalized to regular spaces at every
ingestion point, so typed/pasted/imported nbsps never reached the
changeset and users could not glue words against line-wrap in French or
other languages that require nbsp typography.

Removed the four strip sites that replaced U+00A0 with U+0020:
  - src/node/db/Pad.ts cleanText
  - src/static/js/contentcollector.ts textify
  - src/static/js/ace2_inner.ts textify
  - src/static/js/ace2_inner.ts importText raw-text guard

Updated both processSpaces functions (domline and ExportHtml) to tokenize
U+00A0 as a separate unit, emit it verbatim as  , and treat it as
content (not whitespace) for the run-collapse bookkeeping so adjacent
regular-space runs aren't miscounted.

Added backend round-trip tests for spliceText and setText, and extended
the cleanText case table. Updated the existing contentcollector and
importexport specs whose expectations encoded the previous buggy
behavior; they now assert genuine nbsp preservation.

Verified manually in Firefox: clipboard U+00A0 → paste → pad → getText
returns c2 a0; getHTML emits `100 km`.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(contentcollector): collapse display-artifact nbsp runs on DOM read-back

processSpaces is a lossy one-way display transform: leading/trailing
spaces and all-but-the-last of a run get rendered as &nbsp; so HTML
doesn't collapse them. When incorporateUserChanges reads text back from
the DOM, those display-artifact nbsps were being stored in the changeset
model instead of being normalized back to plain spaces.

This broke handleReturnIndentation, whose /^ *(?:)/ regex only matches
ASCII spaces: auto-indent after `foo:\n` produced 4 spaces instead of
the expected prev-indent (2) + THE_TAB (4) = 6, because the previous
line's model had nbsps where it used to have spaces.

Fix: in contentcollector.textify, collapse any [  ]+ run back to
plain spaces UNLESS the run is pure U+00A0 AND strictly interior to
word chars. That preserves user-intended typographic nbsps like
"100 km" while undoing the one-way display transform.

Updated 7 contentcollector tests and 7 importexport tests whose
assertions needed to reflect the new rule (boundary/mixed runs collapse;
pure-interior nbsp runs preserve).

Fixes the Playwright regression in indentation.spec.ts:117 that the
previous commit introduced.

* fix(contentcollector): canonicalize nbsp runs at line assembly, not per text node

Addresses Qodo code review feedback on PR #7585.

## Bug fix — nbsp lost at DOM text-node boundary

The previous approach ran the "collapse display-artifact nbsp" rule inside
textify(), which is called per individual DOM TEXT_NODE. A user-intended
nbsp sitting at a text-node boundary (e.g., <span>100</span><span>&nbsp;km
</span>) was incorrectly seen as non-interior (before === '' for the second
text node) and normalized back to a regular space.

Fix: move the canonicalization out of textify() and run it on each
fully assembled line string inside cc.finish(). The rule remains:

    [  ]+ run  ->  plain spaces
                   UNLESS pure U+00A0 AND strictly interior to non-ws chars

It is length-preserving, so attribute offsets and line lengths are
unaffected.

Added a regression test (contentcollector.spec.ts) for the cross-span
case.

## Docs concern

Reverted the type-only addition of spliceText to PadType. spliceText
is an existing Pad runtime method; the backend test now uses a cast
(`(pad as any).spliceText`) so the PR does not expand the declared
public type surface, avoiding a separate documentation requirement.

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/node/db/Pad.ts

@@ -51,8 +51,7 @@ type PadSettings = {
  */
 exports.cleanText = (txt:string): string => txt.replace(/\r\n/g, '\n')
     .replace(/\r/g, '\n')
-    .replace(/\t/g, '        ')
-    .replace(/\xa0/g, ' ');
+    .replace(/\t/g, '        ');
 
 class Pad {
   private db: Database;

src/node/utils/ExportHtml.ts

@@ -537,13 +537,16 @@ const _processSpaces = (s: string) => {
   const doesWrap = true;
   if (s.indexOf('<') < 0 && !doesWrap) {
     // short-cut
-    return s.replace(/ /g, '&nbsp;');
+    return s.replace(/[ \u00a0]/g, '&nbsp;');
   }
-  const parts = [];
-  s.replace(/<[^>]*>?| |[^ <]+/g, (m) => {
+  const parts: string[] = [];
+  s.replace(/<[^>]*>?|[ \u00a0]|[^ \u00a0<]+/g, (m) => {
     parts.push(m);
     return m
   });
+  // U+00A0 is content for run-bookkeeping - it terminates a space run
+  // just like a word character would, so runs of regular spaces adjacent
+  // to a nbsp are not miscounted as one long run (issue #3037).
   if (doesWrap) {
     let endOfLine = true;
     let beforeSpace = false;
@@ -578,6 +581,9 @@ const _processSpaces = (s: string) => {
       }
     }
   }
+  for (let i = 0; i < parts.length; i++) {
+    if (parts[i] === '\u00a0') parts[i] = '&nbsp;';
+  }
   return parts.join('');
 };