Architecture Overview

Sentinel is built as a multi-agent pipeline where each agent is a Cloudflare Durable Object communicating through Queues.

System Diagram

┌─────────────────────────────────────────────────────────────────────────┐
│                         Cloudflare Workers                              │
│                                                                         │
│  ┌──────────────┐    ┌──────────────┐    ┌──────────────┐              │
│  │ Orchestrator  │    │  Workers AI   │    │  AI Gateway   │              │
│  │  (Hono API)  │    │  (Inference)  │    │  (Routing)    │              │
│  └──────────────┘    └──────────────┘    └──────────────┘              │
│                                                                         │
│  ┌─────────────────────── Agent Pipeline ───────────────────────────┐  │
│  │                                                                   │  │
│  │  LogTailer ──→ TestGen ──→ CodeTriage ──→ FixAgent ──→ GitHub PR │  │
│  │     │              │            │              │                   │  │
│  │     ▼              ▼            ▼              ▼                   │  │
│  │  [errors-     [triage-     [fix-ready]    [completed]             │  │
│  │   detected]    ready]                                             │  │
│  │                                                                   │  │
│  └───────────────────────────────────────────────────────────────────┘  │
│                                                                         │
│  ┌──────────┐  ┌──────────┐  ┌──────────┐  ┌──────────┐              │
│  │    D1    │  │    R2    │  │  Queues  │  │ Sandbox  │              │
│  │ (SQLite) │  │ (Blobs)  │  │ (5 + DLQ)│  │(Container)│              │
│  └──────────┘  └──────────┘  └──────────┘  └──────────┘              │
└─────────────────────────────────────────────────────────────────────────┘

Design Principles

Agents SDK Over Raw Durable Objects

Sentinel uses the Cloudflare Agents SDK rather than raw Durable Objects. The SDK provides:

• this.schedule() — schedule future work (polling intervals, retries)
• this.sql — embedded SQLite for fast agent-local state
• this.setState() — reactive state management
• AgentWorkflow — durable multi-step execution with exactly-once step semantics

Dual Storage Model

Storage	Purpose	Latency
Agent SQLite (this.sql)	Hot operational state (fingerprint cache, polling cursors)	Sub-millisecond
D1	System of record (incidents, audit trail, configs)	~5ms
R2	Binary artifacts (test cases, patches, PR descriptions)	~10ms

The LogTailer maintains a fingerprint cache in agent-local SQLite for sub-millisecond dedup lookups. Authoritative records go to D1 for cross-agent queries.

Queue-Per-Stage

Each pipeline stage has its own queue with tuned batch sizes:

• Detection (batch_size: 10) — high throughput error ingestion
• Triage (batch_size: 5) — moderate throughput for LLM analysis
• Fix (batch_size: 1) — serialized to prevent concurrent repo modifications
• Completion (batch_size: 10) — logging and status updates

All queues (except completed) have a dead-letter queue (sentinel-dlq) for failed messages.

Sandbox Isolation

All untrusted code execution happens in Cloudflare Sandbox containers:

• Cloned Git repositories
• AI-generated test cases
• AI-generated code fixes
• Linting and regression checks

The Worker process never executes user code directly.

Technology Stack

Concern	Choice
Runtime	Bun
Language	TypeScript 5.9+ (strict, ESM)
Agent framework	Cloudflare Agents SDK
Sandbox	@cloudflare/sandbox
HTTP API	Hono
Validation	Zod
LLM	Workers AI + AI Gateway
Database	D1
Object storage	R2
Messaging	Queues
IDs	ULID (lexicographically sortable)