L5 - Persona

The Persona layer (L5) defines the agent’s identity, behavioral contract, and operational constraints. It serves as the agent’s “constitution” - immutable rules that govern its behavior.

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Overview

A Persona is a cryptographically signed document that defines who the agent is, what it can do, and how it should behave. It cannot be changed at runtime and must be validated before the agent starts.

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Core Concepts

Identity

Unique identifier and role definition

Constraints

Allowed/denied capabilities and operational limits

Personality

Tone, verbosity, and behavioral traits

Immutability

Cannot be changed without agent restart

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Persona Definition

Complete Schema

{
  "id": "persona-uuid",
  "name": "Customer Support Assistant",
  "role": "customer_support",
  "version": "1.0.0",
  "created_at": "2026-01-15T12:00:00Z",
  "constraints": {
    "allowed_capabilities": ["*"],
    "denied_capabilities": [
      "database:write",
      "filesystem:write",
      "dangerous_action"
    ],
    "max_reasoning_depth": 5,
    "max_memory_mb": 512,
    "require_confirmation": [
      "send_email",
      "delete_*",
      "charge_payment"
    ],
    "rate_limits": {
      "requests_per_minute": 100,
      "tokens_per_hour": 100000
    }
  },
  "personality": {
    "tone": "professional",
    "verbosity": "concise",
    "language": "en-US",
    "formality": "formal"
  },
  "metadata": {
    "organization": "Acme Corp",
    "department": "Customer Service",
    "owner": "support-team@acme.com"
  },
  "signature": {
    "algorithm": "ed25519",
    "public_key": "...",
    "signature": "...",
    "signed_at": "2026-01-15T12:00:00Z"
  }
}

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Key Requirements

Identity & Versioning

Requirement	Description
Unique ID	Each persona must have a unique identifier
Version	Semantic versioning for compatibility tracking
Role	Descriptive role defining agent’s purpose

Constraints

Requirement	Description
Capability Control	Explicitly allow/deny capabilities
Depth Limits	Maximum reasoning iterations to prevent loops
Resource Limits	Memory, compute, and network quotas
Confirmation Requirements	High-risk actions requiring approval

Immutability & Security

Requirement	Description
Runtime Immutable	Cannot be changed while agent is running
Validated at Startup	Must pass validation before agent starts
Cryptographic Signature	Should be signed for authenticity
Enforced by L6	Orchestration layer enforces constraints

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Capability Constraints

Wildcard Allow with Denials

{
  "allowed_capabilities": ["*"],
  "denied_capabilities": [
    "database:write",
    "filesystem:delete",
    "network:write:*external*"
  ]
}

Explicit Allowlist

{
  "allowed_capabilities": [
    "web_search",
    "send_email",
    "database:read",
    "calculate"
  ],
  "denied_capabilities": []
}

Pattern Matching

{
  "allowed_capabilities": [
    "database:read:*",
    "api:get:*",
    "file:read:/safe/*"
  ],
  "denied_capabilities": [
    "database:write:*",
    "api:post:*",
    "file:*:/system/*"
  ]
}

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Confirmation Requirements

Configuration

{
  "require_confirmation": [
    "send_email",
    "delete_*",
    "charge_*",
    "publish_*",
    "modify_production_*"
  ],
  "confirmation_timeout_seconds": 300
}

Confirmation Flow

{
  "pending_action": {
    "action_id": "uuid",
    "capability": "send_email",
    "parameters": {
      "to": "user@example.com",
      "subject": "Important Notice",
      "body": "..."
    },
    "reason": "Requires confirmation per persona constraints",
    "expires_at": "2026-01-15T12:05:00Z"
  }
}

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Personality Traits

Tone Options

Tone	Description	Example
Professional	Formal and business-like	”I would be happy to assist you with…”
Friendly	Warm and approachable	”Hey! I’d love to help you with…”
Technical	Precise and detailed	”Executing query: SELECT * FROM…”
Casual	Relaxed and informal	”Sure thing! Let me grab that for you…”

Verbosity Levels

Level	Description	Response Length
Concise	Brief, to-the-point	1-2 sentences
Moderate	Balanced explanation	2-4 sentences
Detailed	Comprehensive	4+ sentences
Verbose	Exhaustive	Full paragraphs

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Cryptographic Signature

Signing Process

# Generate keypair
openssl genpkey -algorithm ed25519 -out private.pem
openssl pkey -in private.pem -pubout -out public.pem

# Sign persona
openssl dgst -sha256 -sign private.pem -out persona.sig persona.json

# Embed signature
jq --arg sig "$(base64 persona.sig)" '.signature.signature = $sig' persona.json

Verification

{
  "signature": {
    "algorithm": "ed25519",
    "public_key": "MCowBQYDK2VwAyEA...",
    "signature": "base64-encoded-signature",
    "signed_at": "2026-01-15T12:00:00Z",
    "issuer": "Acme Corp PKI"
  }
}

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Validation at Startup

Validation Checklist

• ✅ Schema validation (all required fields present)
• ✅ Signature verification (if signed)
• ✅ Version compatibility check
• ✅ Capability constraints are valid
• ✅ No conflicts in allowed/denied lists
• ✅ Resource limits are reasonable

Validation Failure

{
  "validation_error": {
    "code": "invalid_persona",
    "message": "Persona signature verification failed",
    "details": {
      "field": "signature",
      "reason": "Public key does not match signature"
    }
  }
}

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Enforcement by L6

Orchestration Check

{
  "request": {
    "agent_id": "agent-uuid",
    "capability": "database:write",
    "parameters": {...}
  },
  "persona_check": {
    "allowed": false,
    "reason": "Capability 'database:write' is in denied list",
    "action": "reject_request"
  }
}

Override Attempt Log

{
  "event": "persona_violation",
  "timestamp": "2026-01-15T12:00:00Z",
  "agent_id": "agent-uuid",
  "attempted_action": "database:write",
  "persona_constraint": "denied_capabilities",
  "outcome": "blocked",
  "severity": "high"
}

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Best Practices

1. Sign Your Personas: Use cryptographic signatures for production
2. Principle of Least Privilege: Only grant necessary capabilities
3. Version Your Personas: Track changes with semantic versioning
4. Test Constraints: Verify constraints work as intended
5. Document Personality: Clearly define expected behavior
6. Require Confirmation: Flag dangerous actions
7. Set Resource Limits: Prevent runaway agents
8. Audit Persona Changes: Log all persona modifications

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Common Persona Types

Assistant

Helpful, conversational, low-risk capabilities

Analyzer

Read-only, data analysis, reporting

Executor

Task automation, write capabilities, supervised

Guardian

Security monitoring, read-only, alerting

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Related Layers

• L4 - Reasoning: Must respect Persona constraints
• L6 - Orchestration: Enforces Persona constraints
• Specification: Full requirements for L5 Persona
• Security: Persona security requirements

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