ai-agent-security — скилл для Claude Code: защита ИИ-агентов

---
name: ai-agent-security
description: Secure AI agents against prompt injection, tool abuse, and data exfiltration with defense-in-depth controls. Use when building, deploying, or hardening agentic AI systems that invoke tools, access data, or interact with production infrastructure.
license: MIT
metadata:
  author: devops-skills
  version: "2.0"
---

# AI Agent Security

Protect agentic AI systems from adversarial input, unsafe tool execution, data leakage, and privilege abuse with layered security controls.

## When to Use This Skill

Use this skill when:
- Building AI agents that invoke tools, APIs, or shell commands
- Deploying agents with access to production databases, cloud accounts, or internal services
- Hardening multi-tenant agent platforms against cross-tenant data leakage
- Adding guardrails to autonomous coding agents or SRE bots
- Designing approval workflows for high-risk agent actions
- Conducting red-team exercises against agentic systems
- Responding to incidents involving compromised or misbehaving agents

## Prerequisites

- Python 3.10+ for guardrail code examples
- Docker or Podman for sandbox execution
- OpenTelemetry collector for audit logging
- Familiarity with your agent framework (LangChain, CrewAI, Autogen, custom)
- Access to policy engine (OPA/Cedar) for permission boundaries

## Threat Model — STRIDE for AI Agents

AI agents introduce a unique threat surface. Apply STRIDE specifically to agentic components:

| Threat | Agent-Specific Example | Control |
|--------|----------------------|---------|
| **Spoofing** | Attacker crafts input that mimics a trusted internal tool response | Signed tool responses, HMAC verification |
| **Tampering** | Prompt injection modifies agent reasoning mid-chain | Input validation, prompt armoring |
| **Repudiation** | Agent takes destructive action with no audit trail | Immutable structured logging |
| **Information Disclosure** | Agent leaks PII, secrets, or internal architecture in responses | Output filtering, content classifiers |
| **Denial of Service** | Adversarial prompt causes infinite tool loops or token exhaustion | Rate limits, token budgets, circuit breakers |
| **Elevation of Privilege** | Agent escalates from read-only to write via chained tool calls | RBAC per tool, least-privilege scoping |

### Key Threat Categories

**Prompt Injection** — Untrusted content (user input, web scrapes, document contents) manipulates the agent's system prompt or reasoning chain to execute unintended actions.

**Tool Abuse** — The agent calls tools in sequences or with parameters the designer did not anticipate, achieving effects beyond its intended scope.

**Data Exfiltration** — The agent encodes sensitive data (credentials, PII, internal IPs) into its responses, tool calls, or outbound HTTP requests.

**Cross-Tenant Leakage** — In multi-tenant deployments, context from one tenant's session bleeds into another through shared memory, vector stores, or cache.

**Privilege Escalation** — The agent chains low-privilege tool calls to achieve high-privilege outcomes (e.g., read config -> extract credentials -> call admin API).

## Input Validation

Every input to an agent must be sanitized before it reaches the model or any tool. This includes user messages, tool outputs being fed back, and retrieved documents.

### Prompt Injection Detection

```python
import re
from dataclasses import dataclass
from enum import Enum

class RiskLevel(Enum):
    LOW = "low"
    MEDIUM = "medium"
    HIGH = "high"
    CRITICAL = "critical"

@dataclass
class ValidationResult:
    is_safe: bool
    risk_level: RiskLevel
    matched_rules: list[str]
    sanitized_input: str

INJECTION_PATTERNS = [
    (r"ignore\s+(all\s+)?(previous|prior|above)\s+(instructions|prompts|rules)", "instruction_override"),
    (r"you\s+are\s+now\s+(a|an|the)\s+", "role_hijack"),
    (r"system\s*:\s*", "system_prompt_inject"),
    (r"<\|?(system|im_start|endoftext)\|?>", "control_token_inject"),
    (r"\[INST\]|\[\/INST\]|<<SYS>>", "template_inject"),
    (r"(?:execute|run|eval)\s*\(", "code_execution_attempt"),
    (r"(?:curl|wget|nc|ncat)\s+", "network_command_inject"),
    (r"(?:rm\s+-rf|mkfs|dd\s+if=|chmod\s+777)", "destructive_command"),
    (r"(?:\/etc\/passwd|\/etc\/shadow|\.env\b|\.ssh\/)", "path_traversal"),
    (r"(?:BEGIN\s+(?:RSA|DSA|EC)\s+PRIVATE\s+KEY)", "secret_exfil_attempt"),
]

def validate_agent_input(user_input: str, max_length: int = 4096) -> ValidationResult:
    """Validate and sanitize input before passing to agent."""
    matched = []
    risk = RiskLevel.LOW

    # Length check
    if len(user_input) > max_length:
        matched.append("input_too_long")
        risk = RiskLevel.MEDIUM

    # Null byte and control character removal
    sanitized = user_input.replace("\x00", "")
    sanitized = re.sub(r"[\x01-\x08\x0b\x0c\x0e-\x1f]", "", sanitized)

    # Pattern matching
    for pattern, rule_name in INJECTION_PATTERNS:
        if re.search(pattern, sanitized, re.IGNORECASE):
            matched.append(rule_name)
            risk = RiskLevel.HIGH

    # Stacked injection detection (multiple suspicious patterns)
    if len(matched) >= 3:
        risk = RiskLevel.CRITICAL

    is_safe = risk in (RiskLevel.LOW, RiskLevel.MEDIUM)

    return ValidationResult(
        is_safe=is_safe,
        risk_level=risk,
        matched_rules=matched,
        sanitized_input=sanitized[:max_length] if is_safe else "",
    )
```

### Content Classification Middleware

Use a lightweight classifier as middleware before the agent processes any input:

```python
from functools import wraps
from typing import Callable

def input_guard(validator: Callable = validate_agent_input):
    """Decorator that guards agent entry points against unsafe input."""
    def decorator(func):
        @wraps(func)
        async def wrapper(user_input: str, *args, **kwargs):
            result = validator(user_input)

            if result.risk_level == RiskLevel.CRITICAL:
                await log_security_event(
                    event="input_blocked",
                    risk=result.risk_level.value,
                    rules=result.matched_rules,
                    input_hash=hashlib.sha256(user_input.encode()).hexdigest(),
                )
                raise InputRejectedError(
                    f"Input blocked: matched {result.matched_rules}"
                )

            if result.risk_level == RiskLevel.HIGH:
                await log_security_event(
                    event="input_flagged",
                    risk=result.risk_level.value,
                    rules=result.matched_rules,
                )
                # Allow through but flag for review
                kwargs["_security_flags"] = result.matched_rules

            return await func(result.sanitized_input, *args, **kwargs)
        return wrapper
    return decorator

# Usage
@input_guard()
async def handle_user_message(message: str, session_id: str, **kwargs):
    """Process a validated user message through the agent."""
    flags = kwargs.get("_security_flags", [])
    if flags:
        # Route to sandboxed execution path
        return await agent.run_sandboxed(message, session_id)
    return await agent.run(message, session_id)
```

## Tool Execution Sandboxing

Never let an agent execute tools directly on the host. Isolate every tool invocation inside a sandbox.

### Docker Sandbox Configuration

```yaml
# docker-compose.agent-sandbox.yml
version: "3.8"

services:
  agent-sandbox:
    image: agent-tools:latest
    read_only: true
    security_opt:
      - no-new-privileges:true
      - seccomp:seccomp-profile.json
    cap_drop:
      - ALL
    cap_add:
      - NET_BIND_SERVICE   # Only if tool needs network
    tmpfs:
      - /tmp:size=64M,noexec,nosuid
    mem_limit: 512m
    cpus: "0.5"
    pids_limit: 64
    networks:
      - sandbox-net
    environment:
      - TOOL_TIMEOUT=30
      - MAX_OUTPUT_BYTES=65536
    volumes:
      - type: bind
        source: ./tool-workspace
        target: /workspace
        read_only: false
    dns:
      - 127.0.0.1           # Block external DNS by default

networks:
  sandbox-net:
    driver: bridge
    internal: true           # No external network access
```

### gVisor Runtime for Stronger Isolation

```bash
# Install gVisor runsc runtime
curl -fsSL https://gvisor.dev/archive.key | sudo gpg --dearmor -o /usr/share/keyrings/gvisor-archive-keyring.gpg
echo "deb [signed-by=/usr/share/keyrings/gvisor-archive-keyring.gpg] https://storage.googleapis.com/gvisor/releases release main" | \
  sudo tee /etc/apt/sources.list.d/gvisor.list
sudo apt-get update && sudo apt-get install -y runsc

# Configure Docker to use gVisor
cat <<'EOF' | sudo tee /etc/docker/daemon.json
{
  "runtimes": {
    "runsc": {
      "path": "/usr/bin/runsc",
      "runtimeArgs": [
        "--network=none",
        "--directfs=false"
      ]
    }
  }
}
EOF
sudo systemctl restart docker

# Run agent sandbox with gVisor
docker run --runtime=runsc --rm \
  --read-only \
  --memory=512m \
  --cpus=0.5 \
  --pids-limit=64 \
  agent-tools:latest \
  python /tools/execute.py --tool="$TOOL_NAME" --args="$TOOL_ARGS"
```

### Tool Allowlist Enforcement

```python
from dataclasses import dataclass, field

@dataclass
class ToolPolicy:
    name: str
    allowed_args: dict[str, type]     # parameter name -> expected type
    max_calls_per_session: int = 10
    requires_approval: bool = False
    allowed_patterns: list[str] = field(default_factory=list)
    blocked_patterns: list[str] = field(default_factory=list)

TOOL_ALLOWLIST: dict[str, ToolPolicy] = {
    "read_file": ToolPolicy(
        name="read_file",
        allowed_args={"path": str},
        max_calls_per_session=20,
        allowed_patterns=[r"^/workspace/", r"^/data/public/"],
        blocked_patterns=[r"\.env$", r"\.key$", r"\.pem$", r"/etc/", r"/proc/"],
    ),
    "run_query": ToolPolicy(
        name="run_query",
        allowed_args={"sql": str, "database": str},
        max_calls_per_session=5,
        allowed_patterns=[r"^SELECT\s", r"^EXPLAIN\s"],
        blocked_patterns=[r"\bDROP\b", r"\bDELETE\b", r"\bUPDATE\b", r"\bINSERT\b", r"\bALTER\b"],
    ),
    "http_request": ToolPolicy(
        name="http_request",
        allowed_args={"url": str, "method": str},
        max_calls_per_session=10,
        requires_approval=True,
        allowed_patterns=[r"^https://api\.internal\."],
        blocked_patterns=[r"^https?://169\.254\.", r"^https?://metadata\.google\."],
    ),
    "execute_code": ToolPolicy(
        name="execute_code",
        allowed_args={"code": str, "language": str},
        max_calls_per_session=3,
        requires_approval=True,
        blocked_patterns=[r"import\s+subprocess", r"import\s+os", r"__import__", r"eval\(", r"exec\("],
    ),
}

class ToolGatekeeper:
    def __init__(self, allowlist: dict[str, ToolPolicy]):
        self.allowlist = allowlist
        self.call_counts: dict[str, int] = {}

    async def authorize(self, tool_name: str, args: dict) -> bool:
        if tool_name not in self.allowlist:
            await log_security_event(
                event="tool_denied_not_in_allowlist",
                tool=tool_name,
            )
            return False

        policy = self.allowlist[tool_name]

        # Check call count
        count = self.call_counts.get(tool_name, 0)
        if count >= policy.max_calls_per_session:
            await log_security_event(
                event="tool_denied_rate_limit",
                tool=tool_name,
                count=count,
            )
            return False

        # Validate argument types
        for arg_name, expected_type in policy.allowed_args.items():
            if arg_name in args and not isinstance(args[arg_name], expected_type):
                return False

        # Check patterns against all string arguments
        for arg_value in args.values():
            if not isinstance(arg_value, str):
                continue
            # Must match at least one allowed pattern (if any defined)
            if policy.allowed_patterns:
                if not any(re.search(p, arg_value, re.IGNORECASE) for p in policy.allowed_patterns):
                    return False
            # Must not match any blocked pattern
            if any(re.search(p, arg_value, re.IGNORECASE) for p in policy.blocked_patterns):
                await log_security_event(
                    event="tool_denied_blocked_pattern",
                    tool=tool_name,
                    arg_value_hash=hashlib.sha256(arg_value.encode()).hexdigest(),
                )
                return False

        self.call_counts[tool_name] = count + 1
        return True
```

## Permission Boundaries

Enforce least-privilege at every layer: model context, tool access, infrastructure credentials.

### RBAC Policy for Agent Tools (OPA Rego)

```rego
# policy/agent_tool_access.rego
package agent.tool_access

default allow = false

# Role definitions
roles := {
    "reader": {"read_file", "run_query", "search"},
    "writer": {"read_file", "run_query", "search", "write_file", "create_ticket"},
    "operator": {"read_file", "run_query", "search", "write_file", "create_ticket",
                  "restart_service", "scale_deployment"},
    "admin": {"read_file", "run_query", "search", "write_file", "create_ticket",
              "restart_service", "scale_deployment", "execute_code", "manage_secrets"},
}

# Allow if the agent's role includes the requested tool
allow {
    role := input.agent_role
    tool := input.tool_name
    roles[role][tool]
}

# Deny any tool call outside business hours for operator/admin roles
deny_outside_hours {
    input.agent_role == "operator"
    hour := time.clock(time.now_ns())[0]
    hour < 6
}

deny_outside_hours {
    input.agent_role == "operator"
    hour := time.clock(time.now_ns())[0]
    hour > 22
}

allow {
    not deny_outside_hours
    role := input.agent_role
    tool := input.tool_name
    roles[role][tool]
}

# High-risk tools always require human approval
requires_approval {
    high_risk := {"execute_code", "manage_secrets", "restart_service", "scale_deployment"}
    high_risk[input.tool_name]
}
```

### Querying the Policy at Runtime

```python
import httpx

OPA_URL = "http://localhost:8181/v1/data/agent/tool_access"

async def check_tool_permission(agent_role: str, tool_name: str, context: dict) -> dict:
    """Query OPA for tool access decision."""
    payload = {
        "input": {
            "agent_role": agent_role,
            "tool_name": tool_name,
            "session_id": context.get("session_id"),
            "tenant_id": context.get("tenant_id"),
        }
    }
    async with httpx.AsyncClient(timeout=2.0) as client:
        resp = await client.post(OPA_URL, json=payload)
        resp.raise_for_status()
        result = resp.json().get("result", {})
    return {
        "allowed": result.get("allow", False),
        "requires_approval": result.get("requires_approval", False),
    }
```

### Scoped Credentials with Short TTLs

```yaml
# vault-agent-policy.hcl — Vault policy for AI agent credentials
path "secret/data/agent/{{identity.entity.aliases.auth_approle.metadata.tenant_id}}/*" {
  capabilities = ["read"]
}

# Agent tokens expire in 15 minutes, cannot be renewed beyond 1 hour
path "auth/token/create" {
  capabilities = ["update"]
  allowed_parameters = {
    "ttl"       = ["15m"]
    "max_ttl"   = ["1h"]
    "policies"  = ["agent-readonly"]
    "no_parent" = ["true"]
  }
}
```

```bash
# Issue a short-lived agent credential
vault token create \
  -policy=agent-readonly \
  -ttl=15m \
  -explicit-max-ttl=1h \
  -metadata="agent_session=$SESSION_ID" \
  -metadata="tenant=$TENANT_ID" \
  -no-parent
```

## Output Filtering

Every agent response must be scanned before delivery to the user or downstream system.

### PII Detection and Redaction

```python
import re
from typing import NamedTuple

class PIIMatch(NamedTuple):
    pii_type: str
    start: int
    end: int

PII_PATTERNS = {
    "ssn": r"\b\d{3}-\d{2}-\d{4}\b",
    "credit_card": r"\b(?:\d{4}[\s-]?){3}\d{4}\b",
    "email": r"\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b",
    "phone_us": r"\b(?:\+1[\s.-]?)?\(?\d{3}\)?[\s.-]?\d{3}[\s.-]?\d{4}\b",
    "aws_key": r"\bAKIA[0-9A-Z]{16}\b",
    "private_key": r"-----BEGIN (?:RSA |EC |DSA )?PRIVATE KEY-----",
    "jwt": r"\beyJ[A-Za-z0-9_-]{10,}\.[A-Za-z0-9_-]{10,}\.[A-Za-z0-9_-]{10,}\b",
    "ipv4_internal": r"\b(?:10\.\d{1,3}\.\d{1,3}\.\d{1,3}|172\.(?:1[6-9]|2\d|3[01])\.\d{1,3}\.\d{1,3}|192\.168\.\d{1,3}\.\d{1,3})\b",
    "connection_string": r"(?:mongodb|postgres|mysql|redis):\/\/[^\s\"']+",
}

def scan_for_pii(text: str) -> list[PIIMatch]:
    """Scan text for PII and secrets."""
    matches = []
    for pii_type, pattern in PII_PATTERNS.items():
        for m in re.finditer(pattern, text, re.IGNORECASE):
            matches.append(PIIMatch(pii_type, m.start(), m.end()))
    return matches

def redact_output(text: str) -> tuple[str, list[PIIMatch]]:
    """Redact PII from agent output. Returns redacted text and match list."""
    matches = scan_for_pii(text)
    if not matches:
        return text, []

    # Sort by position descending so replacements don't shift indices
    sorted_matches = sorted(matches, key=lambda m: m.start, reverse=True)
    redacted = text
    for match in sorted_matches:
        placeholder = f"[REDACTED_{match.pii_type.upper()}]"
        redacted = redacted[:match.start] + placeholder + redacted[match.end:]

    return redacted, matches
```

### Response Validation Middleware

```python
@dataclass
class OutputPolicy:
    max_length: int = 16384
    block_on_pii: bool = True
    block_on_secrets: bool = True
    allowed_domains: list[str] = field(default_factory=lambda: [
        "docs.example.com", "api.example.com"
    ])

async def validate_agent_output(
    response: str,
    policy: OutputPolicy,
    session_id: str,
) -> str:
    """Validate and filter agent output before returning to user."""
    # Length check
    if len(response) > policy.max_length:
        response = response[:policy.max_length] + "\n\n[Output truncated]"

    # PII/secret scan
    redacted, matches = redact_output(response)
    if matches:
        secret_types = {m.pii_type for m in matches}
        await log_security_event(
            event="output_pii_detected",
            session_id=session_id,
            pii_types=list(secret_types),
            count=len(matches),
        )
        if policy.block_on_secrets and secret_types & {"aws_key", "private_key", "jwt", "connection_string"}:
            return "[Response blocked: contained credentials. This incident has been logged.]"
        if policy.block_on_pii:
            return redacted

    # URL allowlist check — block responses that contain links to unapproved domains
    urls = re.findall(r"https?://([^/\s\"']+)", response)
    for domain in urls:
        if not any(domain.endswith(allowed) for allowed in policy.allowed_domains):
            response = re.sub(
                rf"https?://{re.escape(domain)}[^\s\"']*",
                "[URL_REMOVED]",
                response,
            )

    return response
```

## Audit Logging

Every agent action must produce a structured, immutable log entry. Use OpenTelemetry for distributed tracing across agent chains.

### Structured Event Logger

```python
import json
import time
import hashlib
from datetime import datetime, timezone

class AgentAuditLogger:
    def __init__(self, service_name: str = "agent-platform"):
        self.service_name = service_name

    def log_event(self, event: dict) -> str:
        """Emit a structured audit log entry. Returns the event ID."""
        event_id = hashlib.sha256(
            f"{time.time_ns()}-{json.dumps(event, sort_keys=True)}".encode()
        ).hexdigest()[:16]

        record = {
            "event_id": event_id,
            "timestamp": datetime.now(timezone.utc).isoformat(),
            "service": self.service_name,
            **event,
        }

        # Emit as structured JSON line (ship to SIEM via Fluent Bit / Vector)
        print(json.dumps(record, default=str), flush=True)
        return event_id

    def log_tool_call(self, session_id: str, tool: str, args: dict,
                      result_status: str, duration_ms: float, agent_role: str):
        return self.log_event({
            "event_type": "tool_call",
            "session_id": session_id,
            "tool": tool,
            "args_hash": hashlib.sha256(json.dumps(args, sort_keys=True).encode()).hexdigest(),
            "result_status": result_status,
            "duration_ms": round(duration_ms, 2),
            "agent_role": agent_role,
        })

    def log_input_validation(self, session_id: str, risk_level: str,
                             matched_rules: list[str]):
        return self.log_event({
            "event_type": "input_validation",
            "session_id": session_id,
            "risk_level": risk_level,
            "matched_rules": matched_rules,
        })

    def log_output_filter(self, session_id: str, pii_types: list[str],
                          action_taken: str):
        return self.log_event({
            "event_type": "output_filter",
            "session_id": session_id,
            "pii_types_detected": pii_types,
            "action": action_taken,
        })
```

### OpenTelemetry Spans for Agent Traces

```python
from opentelemetry import trace
from opentelemetry.sdk.trace import TracerProvider
from opentelemetry.sdk.trace.export import BatchSpanProcessor
from opentelemetry.exporter.otlp.proto.grpc.trace_exporter import OTLPSpanExporter
from opentelemetry.sdk.resources import Resource

# Initialize tracer
resource = Resource.create({"service.name": "agent-platform"})
provider = TracerProvider(resource=resource)
exporter = OTLPSpanExporter(endpoint="http://otel-collector:4317", insecure=True)
provider.add_span_processor(BatchSpanProcessor(exporter))
trace.set_tracer_provider(provider)
tracer = trace.get_tracer("agent.security")

async def traced_tool_call(tool_name: str, args: dict, session_id: str):
    """Execute a tool call with full OpenTelemetry tracing."""
    with tracer.start_as_current_span(
        f"tool.{tool_name}",
        attributes={
            "agent.session_id": session_id,
            "agent.tool.name": tool_name,
            "agent.tool.args_keys": ",".join(args.keys()),
        },
    ) as span:
        try:
            result = await execute_tool(tool_name, args)
            span.set_attribute("agent.tool.status", "success")
            span.set_attribute("agent.tool.output_length", len(str(result)))
            return result
        except Exception as e:
            span.set_attribute("agent.tool.status", "error")
            span.set_attribute("agent.tool.error", str(e)[:256])
            span.record_exception(e)
            raise
```

### OpenTelemetry Collector Config

```yaml
# otel-collector-config.yaml
receivers:
  otlp:
    protocols:
      grpc:
        endpoint: 0.0.0.0:4317
      http:
        endpoint: 0.0.0.0:4318

processors:
  batch:
    timeout: 5s
    send_batch_size: 256
  attributes:
    actions:
      - key: agent.session_id
        action: upsert
      - key: agent.tool.args_raw   # Never log raw tool args
        action: delete

exporters:
  otlp/jaeger:
    endpoint: jaeger:4317
    tls:
      insecure: true
  loki:
    endpoint: http://loki:3100/loki/api/v1/push
    labels:
      resource:
        service.name: "service_name"
      attributes:
        agent.tool.name: "tool_name"
        agent.tool.status: "tool_status"

service:
  pipelines:
    traces:
      receivers: [otlp]
      processors: [batch, attributes]
      exporters: [otlp/jaeger]
    logs:
      receivers: [otlp]
      processors: [batch, attributes]
      exporters: [loki]
```

## Rate Limiting and Abuse Prevention

Prevent runaway agents and adversarial users from exhausting resources.

### Token Budget Enforcement

```python
import time
from dataclasses import dataclass, field

@dataclass
class TokenBudget:
    max_input_tokens_per_request: int = 4096
    max_output_tokens_per_request: int = 4096
    max_tokens_per_session: int = 100_000
    max_tokens_per_hour: int = 500_000
    max_tool_calls_per_session: int = 50
    max_cost_per_session_usd: float = 5.00

class BudgetEnforcer:
    def __init__(self, budget: TokenBudget):
        self.budget = budget
        self.sessions: dict[str, dict] = {}

    def _get_session(self, session_id: str) -> dict:
        if session_id not in self.sessions:
            self.sessions[session_id] = {
                "total_tokens": 0,
                "tool_calls": 0,
                "estimated_cost_usd": 0.0,
                "hourly_tokens": 0,
                "hour_start": time.time(),
            }
        return self.sessions[session_id]

    def check_budget(self, session_id: str, input_tokens: int,
                     estimated_output_tokens: int) -> tuple[bool, str]:
        """Returns (allowed, reason)."""
        s = self._get_session(session_id)

        # Reset hourly counter if needed
        if time.time() - s["hour_start"] > 3600:
            s["hourly_tokens"] = 0
            s["hour_start"] = time.time()

        if input_tokens > self.budget.max_input_tokens_per_request:
            return False, f"Input tokens {input_tokens} exceeds limit {self.budget.max_input_tokens_per_request}"

        projected = s["total_tokens"] + input_tokens + estimated_output_tokens
        if projected > self.budget.max_tokens_per_session:
            return False, "Session token budget exhausted"

        if s["hourly_tokens"] + input_tokens > self.budget.max_tokens_per_hour:
            return False, "Hourly token budget exhausted"

        if s["estimated_cost_usd"] > self.budget.max_cost_per_session_usd:
            return False, f"Session cost ${s['estimated_cost_usd']:.2f} exceeds limit"

        return True, "ok"

    def record_usage(self, session_id: str, input_tokens: int,
                     output_tokens: int, cost_usd: float):
        s = self._get_session(session_id)
        s["total_tokens"] += input_tokens + output_tokens
        s["hourly_tokens"] += input_tokens + output_tokens
        s["estimated_cost_usd"] += cost_usd

    def record_tool_call(self, session_id: str) -> tuple[bool, str]:
        s = self._get_session(session_id)
        s["tool_calls"] += 1
        if s["tool_calls"] > self.budget.max_tool_calls_per_session:
            return False, "Tool call limit exceeded"
        return True, "ok"
```

### Nginx Rate Limit Config for Agent API

```nginx
# /etc/nginx/conf.d/agent-ratelimit.conf

# Define rate limit zones
limit_req_zone $binary_remote_addr zone=agent_api:10m rate=10r/s;
limit_req_zone $http_x_tenant_id   zone=tenant_api:10m rate=30r/s;

# Connection limits
limit_conn_zone $binary_remote_addr zone=agent_conn:10m;

server {
    listen 443 ssl;
    server_name agent-api.example.com;

    location /v1/agent/chat {
        limit_req zone=agent_api burst=20 nodelay;
        limit_req zone=tenant_api burst=50 nodelay;
        limit_conn agent_conn 5;

        limit_req_status 429;
        limit_conn_status 429;

        proxy_pass http://agent-backend:8080;
        proxy_read_timeout 120s;

        # Max request body size for agent input
        client_max_body_size 64k;
    }

    location /v1/agent/tools {
        limit_req zone=agent_api burst=5 nodelay;
        limit_conn agent_conn 2;

        proxy_pass http://agent-backend:8080;
        proxy_read_timeout 30s;
        client_max_body_size 16k;
    }
}
```

## Kill Switches and Circuit Breakers

Build emergency shutoff capabilities into every agent deployment.

### Circuit Breaker Implementation

```python
import time
from enum import Enum

class CircuitState(Enum):
    CLOSED = "closed"         # Normal operation
    OPEN = "open"             # All calls blocked
    HALF_OPEN = "half_open"   # Testing recovery

class AgentCircuitBreaker:
    def __init__(
        self,
        failure_threshold: int = 5,
        recovery_timeout: int = 60,
        half_open_max_calls: int = 3,
    ):
        self.failure_threshold = failure_threshold
        self.recovery_timeout = recovery_timeout
        self.half_open_max_calls = half_open_max_calls
        self.state = CircuitState.CLOSED
        self.failure_count = 0
        self.last_failure_time = 0.0
        self.half_open_calls = 0

    def can_execute(self) -> bool:
        if self.state == CircuitState.CLOSED:
            return True
        if self.state == CircuitState.OPEN:
            if time.time() - self.last_failure_time > self.recovery_timeout:
                self.state = CircuitState.HALF_OPEN
                self.half_open_calls = 0
                return True
            return False
        if self.state == CircuitState.HALF_OPEN:
            return self.half_open_calls < self.half_open_max_calls

        return False

    def record_success(self):
        if self.state == CircuitState.HALF_OPEN:
            self.half_open_calls += 1
            if self.half_open_calls >= self.half_open_max_calls:
                self.state = CircuitState.CLOSED
                self.failure_count = 0
        self.failure_count = max(0, self.failure_count - 1)

    def record_failure(self):
        self.failure_count += 1
        self.last_failure_time = time.time()
        if self.failure_count >= self.failure_threshold:
            self.state = CircuitState.OPEN

    def force_open(self):
        """Emergency kill switch — immediately stop all agent execution."""
        self.state = CircuitState.OPEN
        self.last_failure_time = time.time() + 86400  # Block for 24 hours

    def reset(self):
        """Manual recovery after investigation."""
        self.state = CircuitState.CLOSED
        self.failure_count = 0
```

### Redis-Backed Global Kill Switch

```python
import redis

class GlobalKillSwitch:
    """Di...