Amazon Bedrock Prompt Management: Versioned System Prompts for Coding Agents

// ❌ Persona buried in infra
new lambda.Function(this, "Gateway", {
  environment: {
    SYSTEM_PROMPT: "You are a ruthless coding agent. Delete freely...", // nightmare
  },
});

// ✅ Runtime resolves alias → immutable version text
const PROMPT_ALIAS_ARN =
  "arn:aws:bedrock:us-east-1:123456789012:prompt/ABCDE:prod";

import boto3

br = boto3.client("bedrock-agent")

# Create prompt (API names vary slightly by SDK version — use current CreatePrompt)
prompt = br.create_prompt(
    name="coding-agent-system",
    description="System persona for multi-turn coding agents",
    variants=[
        {
            "name": "default",
            "templateType": "TEXT",
            "templateConfiguration": {
                "text": {
                    "text": (
                        "You are CheatCoders Agent for tenant {{tenant_id}}. "
                        "Prefer minimal diffs. Never run destructive git commands "
                        "unless tool policy allows. Current repo: {{repo_name}}."
                    ),
                    "inputVariables": [
                        {"name": "tenant_id"},
                        {"name": "repo_name"},
                    ],
                }
            },
            "modelId": "anthropic.claude-sonnet-4-20250514-v1:0",
        }
    ],
)

# Create a version, then alias "prod" → that version (via CreatePromptVersion / CreatePromptAlias)

// ✅ Get prompt content at runtime (bedrock-agent-runtime or agent GetPrompt)
import {
  BedrockAgentClient,
  GetPromptCommand,
} from "@aws-sdk/client-bedrock-agent";

const agent = new BedrockAgentClient({});

export async function loadSystemPrompt(aliasArn: string) {
  // Resolve alias ARN or promptId + version
  const out = await agent.send(
    new GetPromptCommand({
      promptIdentifier: aliasArn, // prompt id or ARN per API
    })
  );
  // Extract text template from variants[0]
  return out;
}

import {
  BedrockRuntimeClient,
  ConverseCommand,
} from "@aws-sdk/client-bedrock-runtime";

const runtime = new BedrockRuntimeClient({});

export async function planTurn(opts: {
  tenantId: string;
  repoName: string;
  messages: { role: "user" | "assistant"; content: { text: string }[] }[];
  tools: any[];
}) {
  const systemText = await renderPromptAlias("coding-agent-system", "prod", {
    tenant_id: opts.tenantId,
    repo_name: opts.repoName,
  });

  // ✅ Optional: ApplyGuardrail on the rendered system + user turns
  const resp = await runtime.send(
    new ConverseCommand({
      modelId: "anthropic.claude-sonnet-4-20250514-v1:0",
      system: [{ text: systemText }],
      messages: opts.messages,
      toolConfig: { tools: opts.tools },
    })
  );
  return resp;
}

# ❌ Concatenating unaudited fragments from DynamoDB + env + hardcode
system = os.environ["SYSTEM_PROMPT"] + extra_from_ddb + "DEBUG MODE ON"

// ✅ Alias selection from AppConfig — prompt body still in Prompt Management
const alias = flags.prompt_alias === "canary" ? "canary" : "prod";
const systemText = await renderPromptAlias("coding-agent-system", alias, vars);

// ✅ Fail closed on render errors
function render(template: string, vars: Record<string, string>) {
  return template.replace(/\{\{(\w+)\}\}/g, (_, k) => {
    if (!(k in vars)) throw new Error(`missing prompt var ${k}`); // ✅
    return vars[k];
  });
}

// ❌ Silent empty substitution — agent runs with blank tenant policy
template.replace(/\{\{(\w+)\}\}/g, (_, k) => vars[k] ?? "");

# ✅ Compose managed prompt + small tenant overlay
base = render_prompt_alias("coding-agent-system", "prod", {
    "tenant_id": tenant,
    "repo_name": repo,
    "policy_tier": tier,
})
overlay = ddb.get_item(...).get("persona_overlay", "")
if len(overlay) > 2000:
    raise ValueError("overlay too large")  # ✅ bound cost + injection surface
system = base + "\n\nTenant policy:\n" + overlay

// ❌ Forking entire prompt text per tenant in Prompt Management
// operational nightmare — prefer variables + thin overlays