fix: buffer operations in Stale/StaleWithBuffer instead of throwing (#6342)

When 5+ users edit concurrently, revision gaps trigger the Stale state
which throws 'Ignored server-side change.' on incoming operations. This
causes document divergence, silent data corruption, and eventually
force-resets that discard local edits.

Changes:
- Stale/StaleWithBuffer.applyServer: buffer incoming operations instead
  of throwing, apply them sequentially after missing ops arrive
- Stale.applyClient: carry pendingOps to StaleWithBuffer on transition
- editor-socketio-server: retry-based force-reset (3 failures) instead
  of immediate nuclear reset on any OT error
- hex2rgb: defensive null checks for old non-hex color records

Signed-off-by: bxff <51504045+bxff@users.noreply.github.com>

lib/ot/editor-socketio-server.js

@@ -51,14 +51,23 @@ EditorSocketIOServer.prototype.addClient = function (socket) {
                 self.onOperation(socket, revision, operation, selection);
                 if (typeof self.operationCallback === 'function')
                     self.operationCallback(socket, operation);
+                socket._opRetries = 0;
             } catch (err) {
+                logger.error("Operation error from client " + socket.id + ": " + err.message);
+                if (!socket._opRetries) socket._opRetries = 0;
+                socket._opRetries++;
                 setTimeout(function() {
                     var docOut = {
                         str: self.document,
                         revision: self.operations.length,
-                        clients: self.users,
-                        force: true
+                        clients: self.users
                     };
+                    // Only force-reset after 3 consecutive failures as a last resort.
+                    // Without force:true, the client will use its Stale recovery to resync.
+                    if (socket._opRetries >= 3) {
+                        docOut.force = true;
+                        socket._opRetries = 0;
+                    }
                     socket.emit('doc', docOut);
                 }, 100);
             }