fix(git-sync): review #4404 batch — sanitize-title echo, per-space gate, move-echo, merge-agreement, fence-aware conflict scan, e2e asserts

Addresses reviewer comment #4404 (critical + blocking):

- Critical #2: renamePage skips the echo where the incoming title equals
  sanitizeTitle(current title) — a Docmost title with FS-hostile chars (: / " |,
  newlines, double-space, >120) was pulled to a sanitized stem then written back,
  permanently corrupting the real title. (datasource)
- Blocking #3: runOnce enforces per-space settings.gitSync.enabled (the event
  path bypassed opt-in; any edited space would git-init + export). (orchestrator)
- Blocking #6: movePage no-ops the position-less same-parent echo that clobbered
  the user's chosen sibling order. (datasource)
- Blocking #9: hasConflictMarkers is fence-aware — '<<<<<<< HEAD' inside a code
  block (git-tutorial page) no longer trips the all-or-nothing gate that froze
  the whole space's refs. (push.ts)
- Blocking #11: three-way tryMergeRegion short-circuits when live==target (diff3
  agreement) instead of logging a false 'same-block conflict resolved to git' —
  the echo noise that masked real data-loss signals. (three-way-merge)
- Blocking #12/#13: e2e-advanced — drop the delete-cap block (no such feature;
  failed with a scary '(data loss!)'); non-member assert now expects 404 (existence
  not leaked), not 403.

Verified on stand: sanitized-title rename preserves DB title (vault file
sanitized); non-enabled space creates no vault; fenced conflict markers ingest
without jamming; build clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/git-sync/src/engine/push.ts

@@ -1159,15 +1159,47 @@ export function isPageFile(path: string): boolean {
  * `|||||||` and `=======`): the base text is neither side's current content, so
  * keeping it would inject obsolete lines AND leak a raw `|||||||` marker.
  */
-const CONFLICT_BEGIN_RE = /^<{7}/m;
-const CONFLICT_END_RE = /^>{7}/m;
 const CONFLICT_BEGIN_LINE_RE = /^<{7}/;
 const CONFLICT_BASE_LINE_RE = /^\|{7}/;
 const CONFLICT_SEP_LINE_RE = /^={7}/;
 const CONFLICT_END_LINE_RE = /^>{7}/;
 
+// A code-fence open/close line (``` or ~~~), matching markdown-to-prosemirror's
+// CODE_FENCE_RE. Used to make conflict-marker detection fence-aware.
+const CONFLICT_CODE_FENCE_RE = /^(\s*)(`{3,}|~{3,})/;
+
 export function hasConflictMarkers(body: string): boolean {
-  return CONFLICT_BEGIN_RE.test(body) && CONFLICT_END_RE.test(body);
+  // Fence-aware scan (review #9). A page documenting git (a ```-fenced block that
+  // literally contains `<<<<<<< HEAD` ... `>>>>>>>`) must NOT be flagged as a
+  // conflict: with autoMergeConflicts OFF the all-or-nothing gate would then jam
+  // the ENTIRE space's refs forever, re-failing the batch every cycle. Only count
+  // begin/end marker lines that live OUTSIDE a fenced code block.
+  let inFence = false;
+  let fenceMarker = "";
+  let sawBegin = false;
+  for (const line of body.split("\n")) {
+    const fence = line.match(CONFLICT_CODE_FENCE_RE);
+    if (inFence) {
+      // Close on a fence line of the same marker char, length >= the opener.
+      if (
+        fence &&
+        fence[2][0] === fenceMarker[0] &&
+        fence[2].length >= fenceMarker.length
+      ) {
+        inFence = false;
+        fenceMarker = "";
+      }
+      continue; // everything inside a fence is inert
+    }
+    if (fence) {
+      inFence = true;
+      fenceMarker = fence[2];
+      continue;
+    }
+    if (CONFLICT_BEGIN_LINE_RE.test(line)) sawBegin = true;
+    else if (sawBegin && CONFLICT_END_LINE_RE.test(line)) return true;
+  }
+  return false;
 }
 
 function stripConflictMarkers(body: string): string {