## ADDED Requirements

### Requirement: Core concepts guide exists at docs/developers/concepts.md
The system SHALL provide a concepts guide at `docs/developers/concepts.md` that explains the AgentIdP model in plain English with no assumed prior knowledge of AGNTCY or OAuth 2.0.

#### Scenario: Developer understands what AgentIdP is
- **WHEN** a developer reads the concepts guide
- **THEN** they SHALL be able to explain in one sentence what SentryAgent.ai AgentIdP does and why they need it

### Requirement: Concepts guide explains what an AI agent identity is
The guide SHALL explain in plain English what it means to give an AI agent an identity — how it differs from a human user account and why agents need their own identity model.

#### Scenario: Agent identity vs human identity distinction is clear
- **WHEN** the developer reads the agent identity section
- **THEN** they SHALL understand that agents are non-human, machine-operated identities that need persistent, auditable credentials — not session-based logins

### Requirement: Concepts guide explains the AGNTCY alignment
The guide SHALL explain what AGNTCY is (Linux Foundation standard), why SentryAgent.ai aligns to it, and what benefit that gives the developer — without requiring the developer to read the AGNTCY specification.

#### Scenario: Developer understands AGNTCY without external reading
- **WHEN** the developer reads the AGNTCY section
- **THEN** they SHALL understand that AGNTCY-aligned agent IDs are interoperable across the AI agent ecosystem, and that SentryAgent.ai implements this for free

### Requirement: Concepts guide explains the agent lifecycle
The guide SHALL explain the four lifecycle states of an agent (active, suspended, decommissioned) and what each state means for credential and token behaviour.

#### Scenario: Developer understands what happens when an agent is decommissioned
- **WHEN** the developer reads the lifecycle section
- **THEN** they SHALL understand that decommissioning is irreversible, all credentials are revoked, and no new tokens can be issued

### Requirement: Concepts guide explains OAuth 2.0 Client Credentials in plain English
The guide SHALL explain the Client Credentials grant in plain English — no RFC references, no formal OAuth jargon — focused on how agents use it to authenticate.

#### Scenario: Developer understands client_id and client_secret without prior OAuth knowledge
- **WHEN** the developer reads the OAuth section
- **THEN** they SHALL understand that client_id identifies the agent and client_secret proves it — analogous to a username and password for machines

### Requirement: Concepts guide explains the free-tier limits
The guide SHALL document all free-tier limits (100 agents, 10,000 tokens/month, 100 req/min, 90-day audit retention) in a clear table.

#### Scenario: Developer knows the limits before hitting them
- **WHEN** the developer reads the free-tier section
- **THEN** they SHALL see a table with all four limits and a note on what happens when each is exceeded
