docs(security): add guardrails documentation with @sentinelseed/moltbot

Add comprehensive documentation for integrating security guardrails
using the @sentinelseed/moltbot package:

- Input validation for prompt injection protection
- Tool call validation for dangerous command blocking
- Output validation for credential leak prevention
- Hook integration examples
- Configuration options

docs/security/guardrails.md

@@ -0,0 +1,92 @@
+---
+title: Guardrails
+summary: Input/output validation and tool call security with @sentinelseed/moltbot.
+permalink: /security/guardrails/
+---
+
+# Guardrails
+
+The [@sentinelseed/moltbot](https://www.npmjs.com/package/@sentinelseed/moltbot) package provides security guardrails for Moltbot, including prompt injection detection, tool call validation, and credential leak prevention.
+
+```bash
+npm install @sentinelseed/moltbot
+```
+
+## Usage
+
+The package exposes three main functions: `validateInput`, `validateToolCall`, and `validateOutput`. Each returns a result object with a `blocked` boolean and, when blocked, a `reason` string explaining why.
+
+**Input validation** checks user messages before they reach the agent. It detects prompt injection attempts, jailbreak patterns, and encoded payloads (base64, hex).
+
+```ts
+import { validateInput } from '@sentinelseed/moltbot';
+
+const result = await validateInput(userMessage);
+if (result.blocked) {
+  // handle blocked input
+}
+```
+
+**Tool call validation** inspects tool invocations before execution. It blocks dangerous shell commands (rm -rf, format), SQL injection patterns, path traversal attempts, and command injection via shell metacharacters.
+
+```ts
+import { validateToolCall } from '@sentinelseed/moltbot';
+
+const result = await validateToolCall({
+  name: 'shell',
+  arguments: { command: 'rm -rf /' }
+});
+```
+
+**Output validation** scans agent responses for leaked credentials. It catches API keys (OpenAI, GitHub, AWS), passwords, private keys (SSH, PGP), and tokens (JWT, bearer).
+
+```ts
+import { validateOutput } from '@sentinelseed/moltbot';
+
+const result = await validateOutput(aiResponse);
+```
+
+## Hook integration
+
+The recommended approach is to wire validation into Moltbot's hook system. The example below validates both incoming messages and tool calls before they execute.
+
+```ts
+// hooks/sentinel-guard/handler.ts
+import { validateInput, validateToolCall } from '@sentinelseed/moltbot';
+
+export default {
+  'message:before': async (ctx) => {
+    const result = await validateInput(ctx.message.text);
+    if (result.blocked) {
+      return { abort: true, reason: result.reason };
+    }
+  },
+
+  'tool:before': async (ctx) => {
+    const result = await validateToolCall(ctx.tool);
+    if (result.blocked) {
+      return { abort: true, reason: result.reason };
+    }
+  }
+};
+```
+
+## Configuration
+
+You can customize validation behavior by creating a `sentinel.config.ts` in your workspace. The config accepts custom patterns for dangerous commands and credentials.
+
+```ts
+import { defineConfig } from '@sentinelseed/moltbot';
+
+export default defineConfig({
+  blockDangerousCommands: true,
+  dangerousPatterns: [/rm\s+-rf/, /DROP\s+TABLE/i],
+  credentialPatterns: [/sk-[a-zA-Z0-9]{48}/, /ghp_[a-zA-Z0-9]{36}/],
+});
+```
+
+All validation runs locally without external API calls. Typical latency is 2-5ms per validation call.
+
+## Links
+
+See the [npm package](https://www.npmjs.com/package/@sentinelseed/moltbot) for installation details, the [source repository](https://github.com/sentinel-seed/sentinel) for implementation, and the [Sentinel documentation](https://sentinelseed.dev/docs/moltbot) for additional examples.