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export class DynamoAgentState {
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  private docClient: DynamoDBDocumentClient;
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  // Lưu session với version-wins conflict resolution
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  async saveSession(session: AgentSession): Promise<void> {
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    await this.docClient.send(new PutCommand({
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      TableName: "agent-sessions",
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      Item: {
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        pk: `session#${session.sessionId}`, sk: "meta",
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        data: { conversation: session.conversation.slice(-50), state: session.state },
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        version: session.version,
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        ttl: Math.floor(Date.now()/1000) + 3600,
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      },
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      // Chỉ ghi nếu version mới hơn
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      ConditionExpression: "attribute_not_exists(version) OR version < :v",
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      ExpressionAttributeValues: { ":v": session.version },
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    }));
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  }
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  // Load session với strong consistency
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  async loadSession(sessionId: string): Promise<AgentSession | null> {
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    const result = await this.docClient.send(new GetCommand({
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      TableName: "agent-sessions",
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      Key: { pk: `session#${sessionId}`, sk: "meta" },
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      ConsistentRead: true,
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    }));
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    return result.Item ? this.hydrate(sessionId, result.Item) : null;
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  }
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  // Append message — không rewrite cả conversation
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  async appendMessage(sessionId: string, msg: Message): Promise<void> {
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    await this.docClient.send(new PutCommand({
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      TableName: "agent-sessions",
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      Item: {
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        pk: `session#${sessionId}`,
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        sk: `msg#${String(msg.timestamp).padStart(14, "0")}`,
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        role: msg.role, content: msg.content, timestamp: msg.timestamp, ttl: Math.floor(Date.now()/1000) + 3600,
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      },
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    }));
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  }
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  // Tool cache
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  async cacheToolResult(tool: string, params: any, result: any, ttlMs: number): Promise<void> {
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    await this.docClient.send(new PutCommand({
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      TableName: "agent-tool-cache",
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      Item: { pk: `tool#${tool}#${this.hash(params)}`, result, cachedAt: Date.now(), hitCount: 0, ttl: Math.floor((Date.now()+ttlMs)/1000) },
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    }));
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  }
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  private hash(params: any): string {
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    return require("crypto").createHash("sha256").update(JSON.stringify(params)).digest("hex").slice(0, 16);
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  }
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}