# `CMDCMemoryPg.CheckpointBackend`
[🔗](https://github.com/tupleyun/cmdc_memory_pg/blob/v0.1.0/lib/cmdc_memory_pg/checkpoint_backend.ex#L1)

PostgreSQL 实现 `CMDC.Checkpoint.Backend` behaviour。

## 序列化策略

`CMDC.Checkpoint.Snapshot` struct 通过 `:erlang.term_to_binary(snap, [:compressed])`
写入 `cmdc_checkpoints.snapshot` bytea 字段，**避免 jsonb 对 atom / Message
struct / 嵌套 plugin_states 等不规则数据的序列化痛点**。

## 与 `CheckpointBackend.ETS` 一致性

本模块复用 cmdc 主库 `CMDC.Checkpoint.Backend.ETS` 同套 behaviour 契约,
上游测试 suite 可一字不改替换 backend 跑通。

## 接 Cloak

encryption at rest 留给集成方在 backend wrapper 层处理:

    defmodule MyApp.EncryptedCheckpointBackend do
      @behaviour CMDC.Checkpoint.Backend

      @impl true
      def save(sid, snap, opts) do
        # snap.state 可能含 user_data.api_key 等敏感字段
        sanitized = CMDC.Checkpoint.Snapshot.redact(snap, &MyApp.Vault.encrypt/1)
        CMDCMemoryPg.CheckpointBackend.save(sid, sanitized, opts)
      end

      @impl true
      def load(sid, opts) do
        case CMDCMemoryPg.CheckpointBackend.load(sid, opts) do
          {:ok, snap} ->
            decrypted = CMDC.Checkpoint.Snapshot.redact(snap, &MyApp.Vault.decrypt/1)
            {:ok, decrypted}

          other -> other
        end
      end

      # ... list / delete 透传
    end

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*Consult [api-reference.md](api-reference.md) for complete listing*