> ## Documentation Index
> Fetch the complete documentation index at: https://uip-f4b0bbe5.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Concepts

> The architecture in 90 seconds.

## The 13-step request lifecycle

1. Parse request body.
2. Per-IP global rate limit (pre-auth).
3. Authenticate (API key or JWT).
4. Per-tenant rate limit.
5. PII scan.
6. Prompt-injection scan (parallel with 5).
7. Policy resolution → `ALLOW` / `REDACT` / `BLOCK` / `ESCALATE`.
8. Enforce.
9. Forward to LLM (Groq, Gemini, Mistral, Ollama).
10. Response compliance check.
11. Write HMAC-signed, hash-chained audit row.
12. Nightly Merkle anchor (S3 Object Lock).
13. Deliver response with `X-AGCMS-Interaction-ID`.

## Multi-tenancy

Postgres row-level security partitions every table by `tenant_id`. The gateway
sets `current_setting('app.current_tenant')` on each connection. There is no
shared global query path that bypasses RLS — including the audit log.

## The audit chain

Each row's HMAC-SHA256 signature is computed over `(payload || previous_log_hash)`,
and the row's `previous_log_hash` equals the prior row's signature. Per-tenant
sequence numbers are assigned via a Postgres advisory lock so rows are
contiguous within a tenant. Every night a per-tenant Merkle tree is built over
the day's signatures; the root is signed with a separate anchor key and pushed
to an S3 Object-Lock bucket in Compliance mode (default 7-year retention).

## Why this design wins compliance reviews

1. Truncation, reordering, or row substitution breaks the chain.
2. Substituting a Merkle root requires bypassing S3 Object Lock.
3. The bundle exporter ships a self-contained `verify.py` — auditors never
   need AGCMS credentials to validate integrity.