feat: add @objectql/protocol-sync package for server-side sync protocol

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

packages/protocols/sync/package.json

@@ -0,0 +1,27 @@
+{
+  "name": "@objectql/protocol-sync",
+  "version": "4.2.0",
+  "description": "Server-side sync protocol for ObjectQL - delta computation, change tracking, and conflict resolution",
+  "type": "module",
+  "main": "./dist/index.js",
+  "types": "./dist/index.d.ts",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "default": "./dist/index.js"
+    }
+  },
+  "scripts": {
+    "build": "tsc",
+    "test": "vitest run"
+  },
+  "dependencies": {
+    "@objectql/types": "workspace:*"
+  },
+  "devDependencies": {
+    "typescript": "^5.3.3",
+    "vitest": "^1.0.4"
+  },
+  "keywords": ["objectql", "objectstack", "sync", "protocol", "offline", "plugin"],
+  "license": "MIT"
+}

packages/protocols/sync/src/change-log.ts

@@ -0,0 +1,85 @@
+/**
+ * ObjectQL Sync Protocol — Server-side Change Log
+ * Copyright (c) 2026-present ObjectStack Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import type { SyncServerChange, MutationOperation } from '@objectql/types';
+
+/**
+ * A checkpoint-indexed entry in the server change log.
+ */
+export interface ChangeLogEntry extends SyncServerChange {
+  /** Monotonic checkpoint sequence */
+  readonly checkpointSeq: number;
+}
+
+/**
+ * Server-side append-only change log.
+ * Records all mutations for delta computation during sync.
+ */
+export class ChangeLog {
+  private readonly entries: ChangeLogEntry[] = [];
+  private seq = 0;
+  private readonly retentionMs: number;
+
+  constructor(retentionDays = 30) {
+    this.retentionMs = retentionDays * 24 * 60 * 60 * 1000;
+  }
+
+  /** Record a change in the log */
+  record(change: {
+    objectName: string;
+    recordId: string | number;
+    operation: MutationOperation;
+    data?: Record<string, unknown>;
+    serverVersion: number;
+  }): ChangeLogEntry {
+    this.seq += 1;
+    const entry: ChangeLogEntry = {
+      objectName: change.objectName,
+      recordId: change.recordId,
+      operation: change.operation,
+      data: change.data,
+      serverVersion: change.serverVersion,
+      timestamp: new Date().toISOString(),
+      checkpointSeq: this.seq,
+    };
+    this.entries.push(entry);
+    return entry;
+  }
+
+  /** Get changes since a checkpoint (exclusive) */
+  getChangesSince(checkpoint: string | null): readonly ChangeLogEntry[] {
+    if (checkpoint === null) {
+      return [...this.entries];
+    }
+    const seq = parseInt(checkpoint, 10);
+    if (isNaN(seq)) return [...this.entries];
+    return this.entries.filter(e => e.checkpointSeq > seq);
+  }
+
+  /** Get current checkpoint string */
+  getCurrentCheckpoint(): string {
+    return String(this.seq);
+  }
+
+  /** Prune old entries based on retention policy */
+  prune(): number {
+    const cutoff = Date.now() - this.retentionMs;
+    const before = this.entries.length;
+    for (let i = this.entries.length - 1; i >= 0; i--) {
+      if (new Date(this.entries[i].timestamp).getTime() < cutoff) {
+        this.entries.splice(i, 1);
+      }
+    }
+    return before - this.entries.length;
+  }
+
+  /** Get total entries */
+  get size(): number {
+    return this.entries.length;
+  }
+}